Papers - Ota, Yasutomo

Experimental realization of wide-mode-area slow light modes in valley photonic crystal heterostructure waveguides

Zhang C., Lu G., Pholsen N., Ota Y., Iwamoto S.

Optical Materials Express 15 ( 10 ) 2447 - 2459 2025.10

Research paper (scientific journal), Joint Work, Accepted

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We experimentally realized wide-mode-area slow-light modes in valley photonic crystals (VPhCs) heterostructure waveguides. The waveguides are fabricated on a silicon slab by inserting gapless photonic graphene layers with varying widths and modifying the unit cell spacing near the domain walls. By reducing the spacing between unit cells at the domain boundaries, slow-light guided modes are achieved in VPhCs heterostructure waveguides. The presence of wide-mode-area modes is verified by observing the radiation in the light propagation of leaky guided modes above the light line. To characterize guided modes below the light line, we introduce air-slot terminations to induce out-of-plane scattering and measure intensity profiles. The results show that the mode widths are tunable for both fast-light and slow-light modes in VPhCs heterostructure waveguides by adjusting the number of photonic graphene layers. The ability to support wide-mode-area slow-light modes in VPhC heterostructures offers promising opportunities for the development of high-power, on-chip photonic integrated devices.

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Quantum-dot single-photon source based on a two-dimensional photonic crystal nanocavity transfer-printed on a Si wire waveguide

Fujita A., Pholsen N., Ji S., Kamei T., Okano M., Kakuda M., Iwamoto S., Arakawa Y., Ota Y.

Journal of Applied Physics 138 ( 10 )  2025.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00218979

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We report a quantum-dot single-photon source (QD SPS) with a two-dimensional photonic crystal (2D PhC) nanocavity hybrid-integrated on a low-loss hydrogenated amorphous silicon waveguide via transfer printing. The large bandgap effect of the 2D PhC supports efficient coupling of QD radiation into the cavity. We suppressed unwanted cavity loss due to polarization conversion in the on-glass 2D PhC by loading an additional glass thin film on top of the structure, leading to low-loss evanescent coupling from the cavity to the underlying waveguide. We observed single-photon generation from a QD in the cavity and its propagation in the waveguide by low-temperature photoluminescence measurements.

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Space-Time Optical Hopfion Crystals

Lin W., Mata-Cervera N., Ota Y., Shen Y., Iwamoto S.

Physical Review Letters 135 ( 8 )  2025.08

Research paper (scientific journal), Joint Work, Accepted

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Hopfions-higher-dimensional topological quasiparticles with sophisticated 3D knotted spin textures discovered in condensed matter and photonic systems-show promise in high-density data storage and transfer. Here, we present crystalline structures of hopfions lying in space-time constructed by spatiotemporally structured light. Practical methodologies using bichromatic structured light beams or dipole arrays to assemble 1D and higher dimensional hopfion lattices are proposed, and a technique for tailoring topological orders is elucidated. Optical hopfion crystals constitute a new platform for high-dimensional topological information transfer.

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Flatband localization in 1D moiré bilayer photonic crystals with staggered potential

Trushin S.M., Ito T., Ishii Y., Iwamoto S., Ota Y.

Optics Letters 50 ( 7 ) 2405 - 2408 2025.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

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Moiré photonic crystals exhibit a variety of exciting phenomena, including flatband localization. In bilayer moiré photonic crystals, activating flatband localization often requires precise tuning of various structural parameters, which may limit its experimental realization and applications. In this work, we discuss one-dimensional moiré bilayer photonic crystals with staggered potential introduced into each layer. Moiré patterns were formed by slightly differentiating the lattice periods of the top and bottom grating layers, which were double-periodically modulated for introducing the staggered potential. We found that the staggered potential helps in inducing flatband localization in a wider parameter space. We identified the magnitude of the staggered potential as a handy tuning parameter for the manipulation of photonic moiré bands and their wave functions. Our finding here will accelerate the nano-/microcavity formation through moiré physics.

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Slow light waveguides based on bound states in the continuum

Tanimura Y., Ishii Y., Takata K., Uemura T., Notomi M., Iwamoto S., Ota Y.

Optics Letters 50 ( 6 ) 2013 - 2016 2025.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

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The concept of bound states in the continuum (BIC) has been advancing light confinement technology in leaky environments. In this Letter, we propose and numerically demonstrate a slow light waveguide based on a BIC mode. We considered a waveguide with a polymer core loaded on a plane slab, which supports a leaky guided mode coupled to the radiation continuum in the slab. We found that periodic modulation of the polymer core along the propagation direction can result in a high group index mode with a low propagation loss due to BIC confinement. The introduction of one-dimensional photonic crystals into the BIC waveguides will largely expand its functionality and applications in integrated photonics.

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Transfer-printed nanophotonic waveguide on an erbium doped crystal towards hybrid photonic quantum devices

Okajima T., Ohta R., Sato T., Tachizaki Y., Xu X., Okamoto H., Ota Y.

Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers 64 ( 3 )  2025.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

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We report the design, fabrication and optical characterization of silicon nanophotonic waveguides on an erbium doped crystal. The silicon waveguide allows for efficient optical addressing of erbium ions embedded near the crystal surface. We employed the transfer printing method to assemble the heterogeneous photonic structure in a simple pick-and-place manner. We observed coupling of the emission from erbium ions into the waveguide in the telecommunication wavelength band. The developed methodology opens the way to functional hybrid quantum devices mediating between photons, electrons and phonons.

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Electrically tunable InAs/GaAs QD in a nanocavity with a transfer-printed ITO electrode

Pholsen N., Fujita A., Kakuda M., Arakawa Y., Ikeda K., Kobayashi N., Ota Y., Iwamoto S.

Optical Materials Express 15 ( 2 ) 290 - 298 2025.02

Research paper (scientific journal), Joint Work, Accepted

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We demonstrate the electrical tuning of InAs/GaAs quantum dots (QDs) embedded in a photonic-crystal (PhC) cavity with transparent indium tin oxide (ITO) electrodes hybridintegrated by transfer printing. The design includes spacer layers between the cavity and the electrodes to reduce absorption loss while still maintaining a significant bias field. The bottom electrode, PhC cavity, and top electrode were fabricated independently and integrated by transfer printing, and an electrical connection was made by inkjet printing, both implemented locally without affecting the entire chip. We observed the electrical tuning of QD emissions into the cavity mode and Purcell enhancement. This work paves the way for utilizing multiple hybrid-integrated QDs on the same chip.

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Telecom-Band Quantum Dots Compatible with Silicon Photonics for Photonic Quantum Applications

Katsumi R., Ota Y., Benyoucef M.

Advanced Quantum Technologies 8 ( 2 )  2025.02

Research paper (scientific journal), Joint Work, Accepted

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Silicon photonics is promising for quantum photonics applications owing to its large-scale and high-performance circuitry enabled by complementary-metal-oxide-semiconductor fabrication processes. However, there is a lack of bright single-photon sources (SPSs) capable of deterministic operation on Si platforms, which largely limits their applications. To this end, on-Si integration of high-performance solid-state quantum emitters, such as semiconductor quantum dots (QDs), is greatly desired. In particular, it is preferable to integrate SPSs emitting at telecom wavelengths for fully leveraging the power of silicon photonics, including efficient chip-to-fiber coupling. In this review, recent progress and challenges in the integration of telecom QD SPSs onto silicon photonic platforms are discussed.

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Nanocavity-based quantum-dot single-photon source on a SiN waveguide integrated by transfer printing

Pholsen N., Fujita A., Okano M., Bart N., Ludwig A., Wieck A.D., Ota Y., Iwamoto S.

Optics Express 33 ( 1 ) 252 - 262 2025.01

Research paper (scientific journal), Joint Work, Accepted

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Silicon nitride (SiN) integrated photonics is a highly promising platform for photonic quantum information processing. However, the efficient generation of single photons remains a significant challenge. Epitaxial InAs/GaAs quantum dots (QDs) embedded in wavelength-scale nanocavities offer a promising solution as single-photon sources (SPSs), but their integration with SiN has not yet been demonstrated. In this work, we employed a photonic crystal (PhC) nanobeam cavity to realize a QD SPS on a SiN waveguide. We found that the second-order mode of a period-modulated PhC nanobeam cavity is located close to the waveguide mode in the momentum space and could present a way to efficiently couple photons from the QD SPS into the waveguide. We fabricated the SiN circuitry and QD SPSs separately and integrated the SPS onto the waveguide by transfer printing. We observed Purcell enhancement by the cavity and confirmed the coupling of single photons into the waveguide.

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Magneto nanophotonics platform based on monocrystalline yttrium iron garnets

Ota Y., Gao S., Taniguchi K., Yambe T., Tanimura Y., Iwamoto S.

International Conference on Metamaterials Photonic Crystals and Plasmonics    741 - 742 2025

Research paper (international conference proceedings), Joint Work, Accepted

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Monocrystalline yttrium iron garnets (YIGs) are an outstanding material for magneto-optics. However, their application to nanophotonics has been limited due to the difficulty of fine nanopatterning. Here, we report a platform of magneto-nanophotonics based on YIG realized by the development of high-quality YIG membranes and their nanopatterning using dry etching.

Micro-transfer Printed Membrane Laser and Electroabsorption Modulator on Si waveguide Integrated with Polymer Spot-size Converter

Maeda Y., Hiraki T., Aihara T., Homma H., Fujii T., Takeda K., Sato T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Optical Fiber Communication Conference in Proceedings Optical Fiber Communication Conference Ofc 2025 and Optical Fiber Communication Conference Ofc Postdeadline Papers 2025  2025

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate micro-transfer printing for integrating multiple III-V devices with different bandgaps on Si platforms. Membrane DFB lasers and EA modulators are fabricated on Si waveguides with polymer-based spot-size converters, modulating at 128 Gbit/s-NRZ signal.

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Micro-transfer Printed Membrane Laser and Electroabsorption Modulator on Si waveguide Integrated with Polymer Spot-size Converter

Maeda Y., Hiraki T., Aihara T., Homma H., Fujii T., Takeda K., Sato T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

2025 Optical Fiber Communications Conference and Exhibition Ofc 2025 Proceedings  2025

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate micro-transfer printing for integrating multiple III-V devices with different bandgaps on Si platforms. Membrane DFB lasers and EA modulators are fabricated on Si waveguides with polymer-based spot-size converters, modulating at 128Gbit/s-NRZ signal.

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Reconfigurable synthetic dimension frequency lattices in an integrated lithium niobate ring cavity

Dinh H.X., Balčytis A., Ozawa T., Ota Y., Ren G., Baba T., Iwamoto S., Mitchell A., Nguyen T.G.

Communications Physics 7 ( 1 )  2024.12

Research paper (scientific journal), Joint Work, Accepted

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Harnessing non-spatial properties of photons as if they represent an additional independent coordinate underpins the emerging synthetic dimension approach. It enables probing of higher-dimensional physical models within low-dimensional devices, such as on a planar chip where this method is relatively nascent. We demonstrate an integrated thin-film lithium niobate ring resonator that, under dynamic modulation, simulates a tight-binding model with its discrete frequency modes representing lattice sites. Inter-mode coupling, and the simulated lattice geometry, can be reconfigured by controlling the modulating signals. Up to a quasi-3D lattice connectivity with controllable gauge potentials has been achieved by simultaneous synchronized nearest-, second- and third-nearest-neighbor coupling, and verified by acquiring synthetic band structures. Development of synthetic frequency dimension devices in the thin-film lithium niobate photonic integration platform is a key step in increasing the complexity of topological models achievable on a chip, combining efficient electro-optic mode coupling with non-linear effects for long-range mode interactions.

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On-chip optical skyrmionic beam generators

Lin W., Ota Y., Arakawa Y., Iwamoto S.

Optica 11 ( 11 ) 1588 - 1594 2024.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  23342536

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Optical skyrmion beams, which encompass a two-dimensional topology in their spatial structures, are promising candidates for ultra-dense optical communications and advanced matter manipulation. Generating such light beams using a chip-based approach will broaden their applications and promote the advancement of untapped fundamental science. Herein, we present a breakthrough in chip-based technology by experimentally demonstrating on-chip devices capable of generating optical skyrmions with tailored topological invariants. These devices, fabricated with high precision, exhibit behaviors that closely align with theoretical predictions and numerical simulations. The realization of on-chip optical skyrmion beam generators ushers a new dawn in optical and material sciences.

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Topological Laser in Anomalous Quadrupole Topological Phases

Lu G., Ota Y., Iwamoto S.

Laser and Photonics Reviews 18 ( 11 )  2024.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18638880

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Topological photonics shows considerable promise in revolutionizing photonic devices through the use of topological phases, leading to innovations like topological lasers that enhance light control. One of the recent breakthroughs is reducing the size of these systems by utilizing lower-dimensional boundary states, notably via higher-order topological phases. This paper presents the experimental demonstration of a topological laser in an anomalous quadrupole topological phase, an instance of higher-order phases. To facilitate this, a topological nanocavity with a quality factor near 6000 is engineered through a twisting operation. The topological nature of this system is validated by the calculation of nested Wannier centers and the emergency condition of corner states. The experimental observations reveal the manifestation of corner states and the achievement of single-mode pulsed laser, driven by an optical gain from multiple quantum wells at telecommunication wavelengths and a temperature of 4 K. A lasing threshold of 23 µW and a cold quality factor of 1500 are deduced through rate equation. This work gives a new potential in the application of topological principles to advance nanophotonic technologies.

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Wide-mode-area slow light waveguides in valley photonic crystal heterostructures

Zhang C., Ota Y., Iwamoto S.

Optical Materials Express 14 ( 7 ) 1756 - 1766 2024.07

Research paper (scientific journal), Joint Work, Accepted

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We designed slow-light waveguides with a wide mode area based on slab-type valley photonic crystal (VPhC) heterostructures which are composed of a graphene-like PhC sandwiched by two topologically distinct VPhCs. The group velocity of the topological guided mode hosted in a VPhC heterostructure can be slowed down by shifting the VPhC lattice toward the graphene-like PhC at the domain interfaces. Simultaneously, the mode width of the slow-light topological guided mode can be widened by increasing the size of the graphene-like PhC domain. We found that employing the graphene-like structure at the center domain is crucial for realizing a topological single-guided mode in such heterostructures. Furthermore, the impact of random fluctuations in air-hole size in the graphene-like domain was numerically investigated. Our simulation results demonstrate that the transmittance for the slow-light states can be kept high as far as the size fluctuation is small although it drops faster than that for fast-light states when the disorder level increases. The designed wide-mode-area slow-light waveguides are based on hole-based PhCs, offering novel on-chip applications of topological waveguides.

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Nonadiabatic nonlinear non-Hermitian quantized pumping

Ezawa M., Ishida N., Ota Y., Iwamoto S.

Physical Review Research 6 ( 3 )  2024.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  26431564

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We analyze a quantized pumping in a nonlinear non-Hermitian photonic system with nonadiabatic driving. The photonic system is made of a waveguide array, where the distances between adjacent waveguides are modulated. It is described by the Su-Schrieffer-Heeger model together with a saturated nonlinear gain term and a linear loss term. A topological interface state between the topological and the trivial phases is stabilized by the combination of a saturated nonlinear gain term and a linear loss term. We study the pumping of the topological interface state. We define the transfer-speed ratio ω/ω by the ratio of the pumping speed ω of the center of mass of the wave packet to the driving speed ω of the topological interface. It is quantized topologically as ω/ω=1 in the adiabatic limit. It remains to be quantized dynamically unless the driving is not too fast even in the nonadiabatic regime. On the other hand, the wave packet collapses and there is no quantized pumping when the driving is too fast. In addition, the stability against disorder is more enhanced by stronger nonlinearity.

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Design of GaAs microcavity on SiN waveguide for efficient single-photon generation by resonant excitation

Pholsen N., Ota Y., Iwamoto S.

Materials for Quantum Technology 4 ( 2 )  2024.06

Research paper (scientific journal), Joint Work, Accepted

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Silicon nitride (SiN) photonic circuits are attracting significant interest as a platform for photonic quantum information processing. Integration of deterministic single photon sources (SPSs) is required for large-scale single-photon-based quantum applications. InAs/GaAs quantum dots (QDs) have been demonstrated to be state-of-the-art deterministic SPSs under resonant excitation. However, InAs/GaAs QD SPSs integrated on chip often suffer from unwanted crosstalk from scattering of resonant excitation laser. Moreover, the mismatch in refractive indices of SiN and GaAs impedes efficient coupling of single photons into the photonic circuit. In this work, we design a GaAs photonic crystal (PhC) nanobeam cavity with an embedded QD on top of a SiN waveguide in SiO<inf>2</inf> that can suppress crosstalk from resonant excitation and realize high coupling efficiency at the same time. The crosstalk is reduced by employing a carefully designed nanobeam cavity that removes complex structures around the excitation spot. The high coupling efficiency is achieved with a weak hybridized mirror formed by proximity of GaAs PhC nanobeam and SiN waveguide that makes the cavity and helps transferring photons into the waveguide. This enables more than 90% coupling efficiency. The designed device is expected to be a bright source of indistinguishable photons.

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Micro-Transfer-Printed InP-Based Membrane Photonic Devices on Thin-Film Lithium Niobate Platform

Maeda Y., Nishi H., Diamantopoulos N.P., Fujii T., Aihara T., Yamaoka S., Hiraki T., Takeda K., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Journal of Lightwave Technology 42 ( 11 ) 4023 - 4030 2024.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  07338724

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We demonstrate a heterogeneous integration of electrically-pumped membrane lasers and semiconductor optical amplifiers (SOAs) on a thin-film lithium niobate (TFLN) platform by a micro-transfer-printing (μTP) method. Thanks to the low coupling loss (∼1.0 dB) between the InP-based membrane photonic devices and the TFLN waveguides, mW-class output power laser and low-power-consumption SOA on a TFLN platform are achieved. A 128-Gbit/s non-return-to-zero (NRZ) signal modulation is also demonstrated with a TFLN Mach-Zehnder modulator and an integrated membrane laser. These results indicate that the heterogeneous integration of membrane devices using μTP is promising for manufacturing TFLN photonic integrated circuits for optical communications and other applications.

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High-Q two-dimensional photonic crystal nanocavity on glass with an upper glass thin film

Kawata R., Fujita A., Pholsen N., Iwamoto S., Ota Y.

Optics Letters 49 ( 9 ) 2345 - 2348 2024.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

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We numerically analyze two-dimensional photonic crystal (PhC) nanocavities on glass with a thin glass film on top of the structure. We investigated a multistep heterostructure GaAs PhC nanocavity located on glass. We found that covering the structure even with a very thin glass film efficiently suppresses unwanted polarization mode conversion occurring due to the asymmetric refractive index environment around the PhC. We also uncovered that the glass-covered structure can exhibit a higher Q factor than that observed in the structure symmetrically cladded with thick glass. We point out that the mode mismatch between the PhC nanocavity and modes in the upper glass film largely contributed to the observed Q-factor enhancement. These observations were further analyzed through the comparison among different types of on-glass PhC nanocavities covered with thin glass films. We also discuss that the in-plane structure of the upper glass film is important for additionally enhancing the Q factor of the nanocavity.

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Efficient light couplers to topological slow light waveguides in valley photonic crystals

Yoshimi H., Yamaguchi T., Ishida S., Ota Y., Iwamoto S.

Optics Express 32 ( 4 ) 6382 - 6390 2024.02

Research paper (scientific journal), Joint Work, Accepted

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We numerically and experimentally demonstrate efficient light couplers between topological slow light waveguides in valley photonic crystals (VPhCs) and wire waveguides. By numerical simulations, we obtained a high coupling efficiency of −0.84 dB/coupler on average in the slow light regime of a group index n<inf>g</inf> = 10 − 30. Experimentally, we fabricated the couplers in a Si slab and measured the transmitted power of the devices. We realized a high coupling efficiency of approximately −1.2 dB/coupler in the slow light region of n<inf>g</inf> = 10 − 30, which is close to the result from the numerical simulations. These demonstrations will lay the groundwork for low-loss photonic integrated circuits using topological slow light waveguides.

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Hybrid distributed Bragg reflector laser on Si with a transfer printed InAs/GaAs quantum dot amplifier

Morais N., Fujikata J., Kwoen J., Nakamura T., Ota Y., Arakawa Y.

Optics Express 82 ( 3 ) 4295 - 4304 2024.01

Research paper (scientific journal), Joint Work, Accepted

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We demonstrate a hybrid integrated laser by transfer printing an InAs/GaAs quantum dot (QD) amplifier on a Si waveguide with distributed Bragg reflectors (DBRs). The QD waveguide amplifier of 1.6 mm long was patterned in the form of an airbridge with the help of a spin-on-glass sacrificial layer and precisely integrated on the silicon-on-insulator (SOI) waveguide by pick-and-place assembly using an elastomer stamp. Laser oscillation was observed around the wavelength of 1250 nm with a threshold current of 47 mA at room temperature and stable operation up to 80°C. Transfer printing of the long QD amplifiers will enable the development of various hybrid integrated laser devices that leverage superior properties of QDs as laser gain medium.

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Enhanced Magneto-Optical Effects in Epsilon-Near-Zero Indium Tin Oxide at Telecommunication Wavelengths

Ikeda K., Liu T., Ota Y., Kobayashi N., Iwamoto S.

Advanced Optical Materials 12 ( 2 )  2024.01

Research paper (scientific journal), Joint Work, Accepted

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Epsilon-near-zero (ENZ) materials exhibit near-zero permittivity and induce various intriguing linear and nonlinear optical phenomena. Magneto-optical (MO) effects, which are notoriously weak in the optical domain, have been predicted to be significantly enhanced in ENZ materials, which can facilitate the realization of compact nonreciprocal devices. However, to date, enhanced MO effects have been predominantly observed in effective ENZ media, which are commonly based on complex combinations of photonic nanostructures. It is difficult for these effective media to achieve isotropic ENZ responses, which severely limits their use in the development of ENZ-MO devices. Here, enhanced MO effects in pristine indium tin oxide (ITO) with ENZ properties at technologically important telecommunication wavelengths are demonstrated. MO transmission (reflection) spectroscopy of ITO films with different ENZ wavelengths reveal Faraday (Kerr) rotation peaks around the respective ENZ (EN-one) wavelengths, demonstrating that these observations are due to the intrinsic properties of the ITO materials. The demonstrated mechanism of the MO effect enhancement is universal and can be applied to various ENZ materials, including those incorporating ferromagnetic materials. Native ENZ materials with enhanced MO responses will greatly expand the opportunities for the development of novel nonreciprocal nanophotonic devices, such as on-chip optical isolators and one-way topological waveguides.

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Demonstration of Magneto-optical Microdisk Resonators Based on Yttrium Iron Garnet

Yambe T., Kitai T., Taniguchi K., Gao S., Imamura R., Kumazaki H., Fujii S., Iwamoto S., Tanabe T., Ota Y.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

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A microdisk resona tor ba sed on monocrysta lline yttrium iron ga rnet is reported. The 100-μm-dia meter microdisk in a 300-nm-thick ga rnet film a llows tight spa tia l confinement to enha nce ma gneto-optica l intera ctions. Experimenta lly, we observed a high Q of 2.1 × 10⁴.

Optical skyrmion beam generation based on integrated photonics

Iwamoto S., Lin W., Ota Y.

Jsap Optica Joint Symposia Jsap 2024 in Proceedings Jsap Optica Joint Symposia 2024 Abstracts  2024

Research paper (international conference proceedings), Joint Work, Accepted

Observation of Su-Schrieffer-Heeger Topological Model Band Structure in Integrated LNOI Coupled Ring Cavities

Dinh H.X., Balcytis A., Ozawa T., Ota Y., Baba T., Iwamoto S., Mitchell A., Nguyen T.G.

16th Pacific Rim Conference on Lasers and Electro Optics CLEO PR 2024  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We report synthetic frequency dimension Su-Schrieffer-Heeger model and its band structure observation using coupled ring cavities on an integrated photonic chip. Intra-cell and inter-cell couplings between hybridized modes are controlled using radio frequency electrooptic modulation. optic modulation.

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Observation of Su-Schrieffer-Heeger Topological Model Band Structure in Integrated LNOI Coupled Ring Cavities

Dinh H.X., Balcytis A., Ozawa T., Ota Y., Baba T., Iwamoto S., Mitchell A., Nguyen T.G.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We report synthetic frequency dimension Su-Schrieffer-Heeger model and its band structure observation using coupled ring cavities on an integrated photonic chip. Intra-cell and inter-cell couplings between hybridized modes are controlled using radio frequency electro-optic modulation.

Micro-Transfer-Printed Membrane Lasers on Si platform

Maeda Y., Aihara T., Fujii T., Hiraki T., Takeda K., Tsuchizaw T., Sugiyama H., Sato T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Proceedings of SPIE the International Society for Optical Engineering 12905 2024

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  0277786X

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We fabricate directly modulated membrane distributed-reflector lasers on a Si platform using a micro-transfer printing method. Single-mode lasing with a low threshold current of 1.2 mA and 50-Gbaud-class direct modulation are demonstrated.

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Membrane Directly Modulated Lasers on Si Using Micro-Transfer Printing Integrated with Post-Processed Polymer Waveguide

Maeda Y., Hiraki T., Aihara T., Fujii T., Takeda K., Sugiyama H., Sato T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Conference Digest IEEE International Semiconductor Laser Conference  2024

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  08999406

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We fabricate directly modulated membrane lasers by micro-transfer printing and integrate a single-mode polymer waveguide after printing. An InP inverse taper waveguide is used as a spot-size converter for the polymer waveguide. Fiber-coupled mW-class output power and 100-Gbit/s signal modulation are achieved.

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Measurement of Synthetic-Dimension Band Structures in Silicon Coupled Ring Resonators

Zhang R., Li L., Kamata M., Baba T., Ozawa T., Ota Y., Iwamoto S.

16th Pacific Rim Conference on Lasers and Electro Optics CLEO PR 2024  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We fabricated integrated silicon coupled-ring resonators and measured photonic band structures for synthetic frequency lattices with different configurations. A phase difference between two modulation signals introduced a synthetic gauge flux, resulting in asymmetric band structures.

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Measurement of Synthetic-Dimension Band Structures in Silicon Coupled Ring Resonators

Zhang R., Li L., Kamata M., Baba T., Ozawa T., Ota Y., Iwamoto S.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We fabricated integrated silicon coupled-ring resonators and measured photonic band structures for synthetic frequency lattices with different configurations. A phase difference between two modulation signals introduced a synthetic gauge flux, resulting in asymmetric band structures.

Investigation of one-dimensional moiré photonic crystal nanobeam cavities

Ito T., Ishii Y., Trushin S.M., Lu G., Iwamoto S., Ota Y.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We designed nanobeam optical cavities based on moiré photonic crystals. An exponential increase of the Q factor as high as 10⁷ with increasing moiré period was observed, while the mode volume remained small around 0.5(λ/η)³.

Flat band light localization in one dimensional moiré bilayer photonic crystals with staggered potential

Trushin S.M., Ishii Y., Ito T., Iwamoto S., Ota Y.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate that double periodic modulations improve flat band light localization in bilayer one-dimensional moiré photonic crystals. Flatter optical bands were observed even at zero interlayer distance, accelerating their experimental realization and nanophotonics applications.

Fabrication of Photonic Crystal Nanocavities based on Monocrystalline Yttrium Iron Garnet

Taniguchi K., Kitai T., Yambe T., Gao S., Iwamoto S., Ota Y.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

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We report the fabrication of air-suspended photonic crystal nanocavities based on single-crystalline yttrium iron garnet (YIG). The unprecedented high-quality photonic nanostructures based on YIG will open the novel path to magneto-nanophotonics and quantum magnonics.

Photonic Frequency Space Simulation of Tight-Binding Lattices Using Integrated LNOI Ring Resonators

Balčytis A., Dinh H., Ozawa T., Ota Y., Baba T., Iwamoto S., Mitchell A., Nguyen T.G.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We use electro-optically modulated ring cavities, integrated on thin-film lithium niobate, to model frequency dimension tight-binding lattices with versatile connectivity. Inter-mode coupling range, strength, and hopping phase are controlled via the modulating radio frequency signals.

Uncooled Operation of Directly Modulated Membrane Laser with Buried Sapphire Layer on Si Substrate

Hiraki T., Maeda Y., Fujii T., Takeda K., Aihara T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Optical Fiber Communication Conference in Proceedings Optical Fiber Communication Conference Ofc 2024  2024

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

A membrane laser with a buried sapphire layer on Si has 3-dB bandwidths of 40-25 GHz at 25-80̊C. The laser demonstrates 80-Gbit/s PAM4 operations up to 80̊C at an energy cost of 0.77 pJ/bit.

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Uncooled Operation of Directly Modulated Membrane Laser with Buried Sapphire Layer on Si Substrate

Hiraki T., Maeda Y., Fujii T., Takeda K., Aihara T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

2024 Optical Fiber Communications Conference and Exhibition Ofc 2024 Proceedings  2024

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

A membrane laser with a buried sapphire layer on Si has 3-dB bandwidths of 40-25 GHz at 25-80°C. The laser demonstrates 80-Gbit/s PAM4 operations up to 80°C at an energy cost of 0.77 pJ/bit.

Transfer-printed Si waveguides on Er:YSO crystals toward efficient quantum media conversion

Okajima T., Ohta R., Sato T., Tachizaki Y., Xu X., Okamoto H., Ota Y.

Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2024 in Proceedings 2024 Conference on Lasers and Electro Optics Pacific Rim CLEO PR  2024

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We demonstrate the transfer-printing integration of silicon waveguides on Er:YSO crystals. The versatile integration technique, together with strong optical interactions with Er ions through the confined photons, facilitates the development of efficient spin-photon converters.

Transfer Printed InP-based Membrane Laser on Sapphire-Si Bonded Substrate

Hiraki T., Maeda Y., Fujii T., Takeda K., Aihara T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

IEEE International Conference on Group IV Photonics Gfp  2024

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  19492081

　View Summary

An InP-based membrane laser is transfer-printed onto a thin sapphire on a Si substrate. Thanks to the low refractive index and high thermal conductivity of the sapphire, the fabricated laser has a 3-dB bandwidth of 26 GHz and performs 53.125-Gbit/s operations at 50 degrees Celsius.

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Photonic Frequency Space Simulation of Tight-Binding Lattices Using Integrated LNOI Ring Resonators

Balčytis A., Dinh H., Ozawa T., Ota Y., Baba T., Iwamoto S., Mitchell A., Nguyen T.G.

16th Pacific Rim Conference on Lasers and Electro Optics CLEO PR 2024  2024

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We use electro-optically modulated ring cavities, integrated on thin-film lithium niobate, to model frequency dimension tight-binding lattices with versatile connectivity. Inter-mode coupling range, strength, and hopping phase are controlled via the modulating radio frequency signals.

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Valley photonic crystal waveguides fabricated with CMOS-compatible process

Yamaguchi T., Yoshimi H., Seki M., Ohtsuka M., Yokoyama N., Ota Y., Okano M., Iwamoto S.

Japanese Journal of Applied Physics 62 ( 8 )  2023.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

　View Summary

Valley photonic crystal (VPhC) waveguides have attracted much attention because of their ability to enable robust light propagation against sharp bends. However, their demonstration using a CMOS-compatible process suitable for mass production has not yet been reported at the telecom wavelengths. Here, by tailoring the photomask to suppress the optical proximity effect, VPhC patterns comprising equilateral triangular holes were successfully fabricated using photolithography. We optically characterized the fabricated VPhC devices using microscopic optics with NIR imaging. For comparison, we also fabricated and characterized line-defect W1 PhC waveguides, in which the transmission intensities decreased at some regions within the operating bandwidth when sharp turns were introduced into the waveguide. In contrast, the developed VPhC waveguides can robustly propagate light around the C-band telecommunication wavelengths, even in the presence of sharp bends. Our results highlight the potential of VPhC waveguides as an interconnection technology in silicon topological photonic ICs.

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Faraday rotator based on a silicon photonic crystal slab on a bismuth-substituted yttrium iron garnet thin film

Gao S., Ota Y., Liu T., Tian F., Iwamoto S.

Applied Physics Express 16 ( 7 )  2023.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

　View Summary

We report the design of an ultrathin Faraday rotator consisting of a silicon photonic crystal (PhC) slab on a bismuth-substituted yttrium iron garnet (Bi:YIG) thin film. By directing light into guided modes in the Bi:YIG layer via diffraction in the PhC layer, we numerically demonstrate a Faraday rotation angle of ∼45° at a telecom wavelength with a Bi:YIG layer thickness of only ∼500 nm. This structure permits a high light transmittance of about 70%, enabled by electromagnetically induced transparency. The proposed design only requires nanopatterning of the Si layer, providing a viable route to practical ultrathin Faraday rotators.

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Micro-Transfer-Printed Membrane Distributed Reflector Lasers on Si Waveguide Modulated with 50-Gbit/s NRZ Signal

Maeda Y., Aihara T., Fujii T., Hiraki T., Takeda K., Tsuchizawa T., Sugiyama H., Sato T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Journal of Lightwave Technology 41 ( 12 ) 3866 - 3873 2023.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  07338724

　View Summary

In this work, we fabricate directly modulated membrane distributed reflector (DR) lasers on a Si waveguide by utilizing micro-transfer printing method. Micro-transfer printing enables low-loss coupling between the lasers and the silicon photonics circuit, and since it is a back-end process, we can test the lasers prior to integration. A membrane laser is as thick as the Si waveguides, which makes optical coupling between the two quite easy. In addition, membrane lasers with a lateral p-i-n diode structure have low capacitance and a large optical confinement factor, which means they can achieve a low threshold current and high-speed modulation operation with low energy consumption. The fabricated membrane DR laser integrated with a 220-nm-thick Si waveguide exhibits a low threshold current of 1.2 mA and single-mode operation at 1535 nm with a side-mode suppression ratio (SMSR) of about 40 dB at the bias current of 14 mA. It also achieves the E-O bandwidth of over 25 GHz and 50-Gbit/s non-return-to-zero (NRZ) signal modulation with an extinction ratio of 2.5 dB.

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Optimizing the optical and magneto-optical response of all-dielectric metasurfaces with tilted side walls

Gao S., Ota Y., Tian F., Liu T., Iwamoto S.

Optics Express 31 ( 9 ) 13672 - 13682 2023.04

Research paper (scientific journal), Joint Work, Accepted

　View Summary

All-dielectric metasurfaces based on ferrimagnetic iron garnets are a promising platform for realizing ultra-compact magneto-optical (MO) devices with low loss. However, ferrimagnetic iron garnets are notorious for being intractable on fine nanopatterning, hindering the faithful fabrication of designed nanostructures. In this regard, it is important to assess the influence of fabrication imperfections on the performance of MO metasurfaces. Here, we investigate the optical properties of a MO metasurface with structural imperfections. As the most typical fabrication error, we studied the impact of the tilted side walls of cylindrical garnet disks that constitute the metasurfaces. We found that tilting the side walls drastically degrades the MO response and light transmittance of the device. Nevertheless, it was also found that the performance can be recovered by optimizing the refractive index of the material covering the upper half of the nanodisks.

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Supersymmetric non-Hermitian topological interface laser

Ezawa M., Ishida N., Ota Y., Iwamoto S.

Physical Review B 107 ( 8 )  2023.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

　View Summary

We investigate laser emission at the interface of the topological and trivial phases in one dimension. The system is described by a generalized Su-Schrieffer-Heeger model with site-dependent hopping parameters involving the interface width parameter where gain (loss) is introduced only to the A (B) sites of the bipartite lattice. The topological interface state is described by the Jackiw-Rebbi state with a pure imaginary energy, reflecting the non-Hermiticity of the system. It feels only the gain effect since it is strictly localized at the A sites. The Jackiw-Rebbi state exists for any value of the interface width. We, thus, obtain a large area single-mode laser by making the interface width wide enough. We also find a series of analytic solutions of excited states based on supersymmetry (SUSY) quantum mechanics where the A and B sites of the bipartite lattice form SUSY partners. Furthermore, we study the system containing loss and gain with saturation by extending the Jackiw-Rebbi mode to a nonlinear theory.

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CMOS-compatible integration of telecom band InAs/InP quantum-dot single-photon sources on a Si chip using transfer printing

Katsumi R., Ota Y., Tajiri T., Iwamoto S., Ranbir K., Reithmaier J.P., Benyoucef M., Arakawa Y.

Applied Physics Express 16 ( 1 )  2023.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

　View Summary

We report the hybrid integration of a telecom band InAs/InP quantum-dot (QD) single-photon source on a CMOS-processed Si photonics chip using transfer printing. The integration technique allows for the assembly of photonic components in a pick-and-place operation and therefore can introduce them on Si photonics chips after completing the entire CMOS-compatible fabrication processes. We demonstrate telecom single-photon generation from an InAs/InP QD integrated on Si and its coupling into a waveguide. We also demonstrate the integration of a QD on a fiber-pigtailed Si chip and single-photon output through the optical fiber, showing a novel pathway for modularizing solid-state quantum light sources.

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Exploiting Photonic Topology in Semiconductor Nanophotonics

Iwamoto S., Ota Y.

Jsap Optica Joint Symposia in Proceedings Jsap Optica Joint Symposia 2023 Abstracts Jsap 2023  2023

Research paper (international conference proceedings), Joint Work, Accepted

Realization of large magneto-optical effect by diagonal permittivity change in epsilon-near-zero materials

Ikeda K., Liu T., Ota Y., Iwamoto S., Kobayashi N.

2023 IEEE International Magnetic Conference Short Papers Intermag Short Papers 2023 Proceedings  2023

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

The Epsilon near-zero (ENZ) effect has been suggested as a method to enhance the magneto-optical (MO) effect; however, the enhancement of the MO effect in the ENZ materials has not been experimentally verified. Here, we measured the MO properties of ENZ materials and analyzed the correlation between the diagonal permittivity and MO effect. The Faraday effect is enhanced in the wavelengths where the real part of diagonal permittivity is almost zero and the Kerr effect is enhanced in the wavelengths where the diagonal permittivity is almost one. Our findings would lead to various potential applications, including on-chip isolators and one-way topological waveguides.

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Ultrathin magneto-optical devices based on all-dielectric metasurfaces

Ota Y., Gao S., Iwamoto S.

International Conference on Metamaterials Photonic Crystals and Plasmonics    438 - 439 2023

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

Magneto-optical (MO) devices play a key role in introducing nonreciprocity in optical systems, but tend to be bulky due to weak MO effects available in the optical regime. In this talk, we discuss our recent efforts to design of all-dielectric MO metasurfaces toward ultrathin MO devices. We found that large Faraday rotations and high light transmittance can be realized in MO metasurfaces that are much thinner than the operating wavelength.

Topological corner states in photonic bilayer square lattice with π flux

Ishida N., Ezawa M., Lu G., Lin W., Ota Y., Arakawa Y., Iwamoto S.

International Conference on Metamaterials Photonic Crystals and Plasmonics    789 - 790 2023

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We analyzed a bilayer photonic structure consisting of two topologically distinct square lattices with π flux by using a tight-binding model. In the weak interlayer coupling regime, a topological corner state exists at each corner of the finite bilayer lattice, while it disappears when the coupling strength exceeds a critical value, indicating the occurrence of a topological phase transition induced by the interlayer coupling. This phenomenon could be applicable to control light localization in bilayer photonics systems.

Synthetic frequency dimension state coupling in modulated LNOI ring cavity devices

Balčytis A., Dinh X.H., Ozawa T., Ota Y., Baba T., Iwamoto S., Mitchell A., Nguyen T.G.

2023 Conference on Lasers and Electro Optics CLEO 2023  2023

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We created a modulatorequipped thinfilm lithium niobate integrated ring resonator simulating a synthetic frequency dimension tightbinding model. It produces frequency states spaced over a 600 GHz bandwidth. Reconfigurable coupling enables simulation of disparate twodimensional interactions.

Topologically-Protected Single-Photon Sources with Topological Slow Light Photonic Crystal Waveguides

Kuruma K., Yoshimi H., Ota Y., Katsumi R., Kakuda M., Arakawa Y., Iwamoto S.

Laser and Photonics Reviews 16 ( 8 )  2022.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18638880

　View Summary

Slow light waveguides are advantageous for implementing high-performance single-photon sources required for scalable operation of integrated quantum photonic circuits (IQPCs), though such waveguides are known to suffer from propagation loss due to backscattering. A way to overcome the drawback is to use topological photonics, in which robust waveguiding in topologically-protected optical modes has recently been demonstrated. Here, single-photon sources are reported using single quantum dots (QDs) embedded in topological slow light waveguides based on valley photonic crystals. Purcell-enhanced single-photon emission is demonstrated from a QD into a topological slow light mode with a group index over 20 and its robust propagation even under the presence of sharp bends. These results pave the way for the realization of robust and high-performance single-photon sources indispensable for IQPCs.

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Time-resolved physical spectrum in cavity quantum electrodynamics

Yamaguchi M., Lyasota A., Yuge T., Ota Y.

Physical Review Research 4 ( 2 )  2022.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  26431564

　View Summary

The time-resolved physical spectrum of luminescence is theoretically studied for a standard cavity quantum electrodynamics system. In contrast to the power spectrum for the steady state, the correlation functions up to the present time are crucial for the construction of the time-resolved spectrum, while the correlations with future quantities are inaccessible because of the causality, i.e., the future quantities cannot be measured until the future comes. We find that this causality plays a key role in understanding the time-resolved spectrum, in which the Rabi doublet can never be seen during the time of the first peak of the Rabi oscillation. Furthermore, the causality can influence the transient magnitude of the Rabi doublet in some situations. We also study the dynamics of the Fano antiresonance, where the difference from the Rabi doublet can be highlighted.

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Topological Band Gaps Enlarged in Epsilon-Near-Zero Magneto-Optical Photonic Crystals

Liu T., Kobayashi N., Ikeda K., Ota Y., Iwamoto S.

ACS Photonics 9 ( 5 ) 1621 - 1626 2022.05

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Topological photonics provides exciting and emerging opportunities for the manipulation of light. As the photonic analogue of quantum Hall edge states, chiral edge modes, arising at the interface between two photonic topological structures with different Chern numbers, hold great promise for robust transport of light against disorders and defects. However, for magneto-optical material-based topological photonic crystals, the transport performance of chiral edge modes is strongly dependent on the topological gap sizes, which are usually very narrow at optical frequencies due to the lack of magneto-optical materials with strong nonreciprocal responses. Here, we numerically demonstrated that the introduction of an epsilon-near-zero effect to magneto-optical photonic crystals could remarkably enlarge topological gap sizes due to the boosted magneto-optical response. Eigenmode calculation resul show that the boosted magneto-optical response correlates to the enhanced nonreciprocal power flows in magnetized photon crystals with an epsilon-near-zero diagonal permittivity. The enlarged topological band gap leads to the broadband and well-confine chiral edge modes propagating along the magnetized boundary between two oppositely magnetized photonic crystals. Mo importantly, such mode propagation shows strong robustness against sharp bends and large defects. In principle, our proposal for t enlargement of topological photonic band gaps could also be valid in photonic crystal slabs or even three-dimensional photon crystals. Our results not only suggest the possibility to improve the transport performance of one-way modes in magneto-optic photonic crystals but also enrich the physical understanding of the epsilon-near-zero effect-based topological photonics.

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A large-scale single-mode array laser based on a topological edge mode

Ishida N., Ota Y., Lin W., Byrnes T., Arakawa Y., Iwamoto S.

Nanophotonics 11 ( 9 ) 2169 - 2181 2022.04

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Topological lasers have been intensively investigated as a strong candidate for robust single-mode lasers. A typical topological laser employs a single-mode topological edge state, which appears deterministically in a designed topological bandgap and exhibits robustness to disorder. These properties seem to be highly attractive in pursuit of high-power lasers capable of single mode operation. In this paper, we theoretically analyze a large-scale single-mode laser based on a topological edge state. We consider a sizable array laser consisting of a few hundreds of site resonators, which support a single topological edge mode broadly distributed among the resonators. We build a basic model describing the laser using the tight binding approximation and evaluate the stability of single mode lasing based on the threshold gain difference Δα between the first-lasing edge mode and the second-lasing competing bulk mode. Our calculations demonstrate that stronger couplings between the cavities and lower losses are advantageous for achieving stable operation of the device. When assuming an average coupling of 100 cm-1 between site resonators and other realistic parameters, the threshold gain difference Δα can reach about 2 cm-1, which would be sufficient for stable single mode lasing using a conventional semiconductor laser architecture. We also consider the effects of possible disorders and long-range interactions to assess the robustness of the laser under non-ideal situations. These results lay the groundwork for developing single-mode high-power topological lasers.

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Synthetic dimension band structures on a Si CMOS photonic platform

Balčytis A., Ozawa T., Ota Y., Iwamoto S., Maeda J., Baba T.

Science Advances 8 ( 4 )  2022.01

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Synthetic dimensions, which simulate spatial coordinates using nonspatial degrees of freedom, are drawing interest in topological science and other fields for modeling higher-dimensional phenomena on simple structures. We present the first realization of a synthetic frequency dimension on a silicon ring resonator integrated photonic device fabricated using a CMOS process. We confirm that its coupled modes correspond to a one-dimensional tight-binding model through acquisition of up to 280-GHz bandwidth optical frequency comb-like spectra and by measuring synthetic band structures. Furthermore, we realized two types of gauge potentials along the frequency dimension and probed their effects through the associated band structures. An electric field analog was produced via modulation detuning, whereas effective magnetic fields were induced using synchronized nearest- and second nearest–neighbor couplings. Creation of coupled mode lattices and two effective forces on a monolithic Si CMOS device represents a key step toward wider adoption of topological principles.

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Demonstration of On-Chip Optical Skyrmionic Beam Generators

Lin W., Ota Y., Arakawa Y., Iwamoto S.

Optics Infobase Conference Papers  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We experimentally demonstrate on-chip optical skyrmionic beam generators. Skyrmionic beams with tailored skyrmion numbers were generated from single silicon mi-crorings diffracting two beams whose spin and orbital angular momenta were controlled via optical spin-orbit coupling.

Micro-transfer-printed Membrane DR Lasers on Si Waveguide Modulated with 50-Gbit/s NRZ Signal

Maeda Y., Fujii T., Aihara T., Hiraki T., Takeda K., Tsuchizawa T., Sugiyama H., Sato T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

2022 European Conference on Optical Communication ECOC 2022  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We fabricate directly modulated membrane distributed reflector lasers on a Si waveguide by using the micro-transfer printing. A low threshold current of 1.2 mA and good optical coupling between the laser output and 220-nm-thick Si waveguides are achieved. 50-Gbit/s NRZ signal modulation is also demonstrated.

Intrinsically chiral modes near exceptional points in modified H1 photonic crystal cavity modes

Fong C.F., Ota Y., Arakawa Y., Iwamoto S., Kato Y.K.

2022 Conference on Lasers and Electro Optics CLEO 2022 Proceedings  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We propose a scheme to generate intrinsically chiral modes via non-Hermitian backscattering caused by the loss-induced imaginary coupling between the two orthogonal linearly polarized dipole modes in the H1 photonic crystal cavity.

Intrinsically chiral modes near exceptional points in modified H1 photonic crystal cavity modes

Fong C.F., Ota Y., Arakawa Y., Iwamoto S., Kato Y.K.

Optics Infobase Conference Papers  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We propose a scheme to generate intrinsically chiral modes via non-Hermitian backscattering caused by the loss-induced imaginary coupling between the two orthogonal linearly polarized dipole modes in the H1 photonic crystal cavity.

High-temperature Operation of Membrane DR Lasers Integrated with Si Waveguide by Micro-transfer Printing Method

Maeda Y., Aihara T., Fujii T., Hiraki T., Takeda K., Tsuchizawa T., Sugiyama H., Sato T., Segawa T., Ota Y., Iwamoto S., Arakawa Y., Matsuo S.

Conference Digest IEEE International Semiconductor Laser Conference 2022-October 2022

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  08999406

　View Summary

We fabricate a membrane distributed-reflector lasers with a Si waveguide by using micro-transfer printing, achieving a low threshold current of 1.1-3.7 mA in a temperature range of 25-80 C and good optical coupling between the laser output and 220-nm-thick Si waveguides.

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Exceptional-point encirclement in an integrated non-Hermitian optomechanical system

Tian F., Ota Y., Iwamoto S.

2022 Conference on Lasers and Electro Optics CLEO 2022 Proceedings  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We propose and numerically demonstrate an integrated nonHermitian optomechanical system capable of exceptionalpoint encirclement in a deterministic manner. The proposed scheme opens a way for investigating nonHermitian optomechanics on chip.

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Exceptional-point encirclement in an integrated non-Hermitian optomechanical system

Tian F., Ota Y., Iwamoto S.

Optics Infobase Conference Papers  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We propose and numerically demonstrate an integrated non-Hermitian optomechanical system capable of exceptional-point encirclement in a deterministic manner. The proposed scheme opens a way for investigating non-Hermitian optomechanics on chip.

Design of an All-dielectric Magneto-optical Metasurface with Giant Faraday Effect and High Light Transmission

Gao S., Ota Y., Liu T., Iwamoto S.

Optics Infobase Conference Papers  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We design an all-dielectric metasurface exhibiting giant enhancement of magneto-optical Faraday rotation and high light transmission. A 760-times larger Faraday rotation than that in the unprocessed host material of the same thickness was numerically observed.

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Design of an All-dielectric Magneto-optical Metasurface with Giant Faraday Effect and High Light Transmission

Gao S., Ota Y., Liu T., Iwamoto S.

2022 Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2022 Proceedings  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We design an all-dielectric metasurface exhibiting giant enhancement of magneto-optical Faraday rotation and high light transmission. A 760-times larger Faraday rotation than that in the unprocessed host material of the same thickness was numerically observed.

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Design of a Quantum-Dot Single-Photon Source on a Silicon Nitride Waveguide for Efficient Photon Generation by Resonant Excitation

Pholsen N., Ota Y., Iwamoto S.

Conference Digest IEEE International Semiconductor Laser Conference 2022-October 2022

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  08999406

　View Summary

We design a quantum-dot single-photon source with a defect-based photonic crystal cavity on a SiN waveguide that subdues crosstalk from resonant excitation and has >90% coupling efficiency. It is expected to efficiently generate single photons with high purity and indistinguishability for scalable integrated quantum photonics.

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Design of a quantum-dot single-photon source on a silicon nitride waveguide for efficient and indistinguishable photon generation

Pholsen N., Ota Y., Katsumi R., Arakawa Y., Iwamoto S.

Optics Infobase Conference Papers  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We design quantum-dot single-photon sources based on a defect-based photonic crystal cavity on a SiN waveguide with >90% efficiency. The defect region secures distance between etched airholes and quantum dots, expected to improve photon indistinguishability.

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Design of a quantum-dot single-photon source on a silicon nitride waveguide for efficient and indistinguishable photon generation

Pholsen N., Ota Y., Katsumi R., Arakawa Y., Iwamoto S.

2022 Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2022 Proceedings  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We design quantum-dot single-photon sources based on a defect-based photonic crystal cavity on a SiN waveguide with >90% efficiency. The defect region secures distance between etched airholes and quantum dots, expected to improve photon indistinguishability.

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Demonstration of On-Chip Optical Skyrmionic Beam Generators

Lin W., Ota Y., Arakawa Y., Iwamoto S.

2022 Conference on Lasers and Electro Optics CLEO 2022 Proceedings  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We experimentally demonstrate on-chip optical skyrmionic beam generators. Skyrmionic beams with tailored skyrmion numbers were generated from single silicon microrings diffracting two beams whose spin and orbital angular momenta were controlled via optical spin-orbit coupling.

• Access to Document (DOI)

Semiconductor topological nanophotonics incorporating light emitters

Ota Y., Arakawa Y., Iwamoto S.

International Conference on Metamaterials Photonic Crystals and Plasmonics    412 - 413 2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

Topological photonic crystals made of compound semiconductors are a fascinating platform to develop topological nanophotonic devices with active functionalities. In this contribution, will discuss recent progress in IIIV-semiconductor topological nanophotonics incorporating optical gain media and quantum emitters. We will review several ways to realize topological nanocavities and topological slow light waveguides, both of which can significantly enhance light-matter interactions with embedded light emitters. These photonic structures enable the realization of topological nano/microlasers and quantum light sources capable of robust operation.

Topological modes observed in Si photonics SSH integrated circuit

Nakamura R., Nakama T., Balčytis A., Ozawa T., Ota Y., Iwamoto S., Ito H., Baba T.

Optics Infobase Conference Papers  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We fabricated a sophisticated Si photonic integrated circuit for investigating topological photonics SSH model. In the selective excitation and observation of SSH coupled microrings, we observed the wavefunctions of edge and bulk modes.

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Topological modes observed in Si photonics SSH integrated circuit

Nakamura R., Nakama T., Balčytis A., Ozawa T., Ota Y., Iwamoto S., Ito H., Baba T.

2022 Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2022 Proceedings  2022

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We fabricated a sophisticated Si photonic integrated circuit for investigating topological photonics SSH model. In the selective excitation and observation of SSH coupled microrings, we observed the wavefunctions of edge and bulk modes.

• Access to Document (DOI)

Chiral modes near exceptional points in symmetry broken H1 photonic crystal cavities

Fong C.F., Ota Y., Arakawa Y., Iwamoto S., Kato Y.K.

Physical Review Research 3 ( 4 )  2021.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  26431564

　View Summary

The H1 photonic crystal cavity supports two degenerate dipole modes of orthogonal linear polarization which could give rise to circularly polarized fields when driven with a π/2 phase difference. However, fabrication errors tend to break the symmetry of the cavity, which lifts the degeneracy of the modes, rendering the cavity unsuitable for supporting circular polarization. We demonstrate numerically a scheme that induces chirality in the cavity modes, thereby achieving a cavity that supports intrinsic circular polarization. By selectively modifying two air holes around the cavity, the dipole modes could interact via asymmetric coherent backscattering, which is a non-Hermitian process. With suitable air hole parameters, the cavity modes approach the exceptional point, coalescing in frequencies and linewidths as well as giving rise to significant circular polarization close to unity. The handedness of the chirality can be selected depending on the choice of the modified air holes. Our results highlight the prospect of using the H1 photonic crystal cavity for chiral light-matter coupling in applications such as valleytronics, spin-photon interfaces, and the generation of single photons with well-defined spins.

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Unidirectional output from a quantum-dot single-photon source hybrid integrated on silicon

Katsumi R., Ota Y., Tajiri T., Kakuda M., Iwamoto S., Akiyama H., Arakawa Y.

Optics Express 29 ( 23 ) 23 - 25 2021.11

Research paper (scientific journal), Joint Work, Accepted

　View Summary

We report a quantum-dot single-photon source (QD SPS) hybrid integrated on a silicon waveguide embedding a photonic crystal mirror, which reflects photons and enables efficient unidirectional output from the waveguide. The silicon waveguide is constituted of a subwavelength grating so as to maintain the high efficiency even under the presence of stacking misalignment accompanied by hybrid integration processes. Experimentally, we assembled the hybrid photonic structure by transfer printing and demonstrated single-photon generation from a QD and its unidirectional output from the waveguide. These results point out a promising approach toward scalable integration of SPSs on silicon quantum photonics platforms.

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Single photon generation in a topological slow light waveguide

Kuruma K., Yoshimi H., Ota Y., Katsumi R., Kakuda M., Loncar M., Arakawa Y., Iwamoto S.

2021 Conference on Lasers and Electro Optics CLEO 2021 Proceedings  2021.05

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report a topologically-protected single photon source in a slow light waveguide based on valley photonic crystals. Purcell-enhanced single photon generation from a quantum dot and its robust propagation in the topological waveguide are demonstrated.

Synthetic Dimension Photonics on a Si CMOS Platform

Balcytis A., Ozawa T., Ota Y., Iwamoto S., Maeda J., Baba T.

2021 Conference on Lasers and Electro Optics CLEO 2021 Proceedings  2021.05

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We present a dynamically modulated ring resonator on a Si CMOS platform, hosting a synthetic dimension lattice over 180 GHz. The frequency and time domain synthetic band structure was acquired and photonic transport phenomena were explored.

Experimental demonstration of topological slow light waveguides in valley photonic crystals

Yoshimi H., Yamaguchi T., Katsumi R., Ota Y., Arakawa Y., Iwamoto S.

Optics Express 29 ( 9 ) 13441 - 13450 2021.04

Research paper (scientific journal), Joint Work, Accepted

　View Summary

We experimentally demonstrate topological slow light waveguides in valley photonic crystals (VPhCs). We employed a bearded interface formed between two topologically-distinct VPhCs patterned in an air-bridged silicon slab. The interface supports both topological and non-topological slow light modes below the light line. By means of optical microscopy, we observed light propagation in the topological mode in the slow light regime with a group index ng over 30. Furthermore, we confirmed light transmission via the slow light mode even under the presence of sharp waveguide bends. In comparison between the topological and non-topological modes, we found that the topological mode exhibits much more efficient waveguiding than the trivial one, demonstrating topological protection in the slow light regime. This work paves the way for exploring topological slow-light devices compatible with existing photonics technologies.

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Microcavity-based generation of full Poincaré beams with arbitrary skyrmion numbers

Lin W., Ota Y., Arakawa Y., Iwamoto S.

Physical Review Research 3 ( 2 )  2021.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  26431564

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A full Poincaré (FP) beam possesses all possible optical spin states in its cross section, which constitutes an optical analog of a skyrmion. Until now FP beams have been exclusively generated using bulk optics. Here we propose a generation scheme of an FP beam based on an optical microring cavity. We position two different angular gratings along with chiral lines on a microring cavity and generate an FP beam as a superposition of two light beams with controlled spin and orbital angular momenta. We numerically show that FP beams with tailored skyrmion numbers can be generated from this device, opening a route for developing compact light sources with unique optical spin fields.

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Fabrication of valley photonic crystals with CMOS-compatible process

Yamaguchi T., Yoshimi H., Seki M., Ohtsuka M., Yokoyama N., Ota Y., Okano M., Iwamoto S.

26th Microoptics Conference Moc 2021  2021

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrated the fabrication of silicon valley photonic crystal structures with triangular air holes by using photolithography for the first time. The mask patterns we newly designed enable the formation of triangular air holes with reasonably high accuracy. This is an important step toward CMOS-compatible topological nanophotonics.

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One-side excited one-way modes in nonreciprocal waveguides

Liu T., Ota Y., Iwamoto S.

Optics Infobase Conference Papers  2021

Research paper (international conference proceedings), Joint Work, Accepted

Intrinsic circularly polarized H1 photonic crystal cavity modes near exceptional points

Fong C.F., Ota Y., Arakawa Y., Iwamoto S., Kato Y.K.

Optics Infobase Conference Papers  2021

Research paper (international conference proceedings), Joint Work, Accepted

Hybrid integrated light sources on silicon assembled by transfer printing

Ota Y., Iwamoto S., Arakawa Y.

2021 IEEE Photonics Conference IPC 2021 Proceedings  2021

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We will discuss the hybrid integration of micro/nanoscale light sources on silicon photonics circuits with transfer printing, which is based on pick-and-place assembly using a viscoelastic stamp. Various light sources including quantum-dot single-photon sources are readily and flexibly integrated on silicon with high positioning accuracy.

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Semiconductor Topological Nanophotonics

Ota Y., Arakawa Y., Iwamoto S.

Technical Digest International Electron Devices Meeting Iedm 2021-December   38.5.1 - 38.5.4 2021

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  01631918

　View Summary

We will discuss possible applications of topological photonics to photonic integrated circuit technologies. We design nanophotonic elements based on topological edge states emerging at the exteriors of bulk structures and apply them to compact semiconductor lasers and waveguides. Such topological photonic devices are known to be immune to fabrication imperfections and therefore are suitable for building robust optical circuitry. We also address the idea of topological high-power lasers that take advantage of topological edge states for robust single mode lasing.

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Two-dimensional Topological Photonic Crystals with Helical Edge States below the Light Line

Zhang C., Yoshimi H., Ota Y., Iwamoto S.

26th Microoptics Conference Moc 2021  2021

Research paper (international conference proceedings), Joint Work, Accepted

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We design semiconductor-based two-dimensional photonic crystals that can support topological helical edge states below the light line. We numerically demonstrate that the edge states can guide light robustly in the waveguide even with sharp bends. The structure will be a new platform for topological nanophotonic waveguides with no radiation loss.

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Topological nanophotonics and topological lasers

Ota Y., Arakawa Y., Iwamoto S.

Optics Infobase Conference Papers  2021

Research paper (international conference proceedings), Joint Work, Accepted

Synthetic dimension photonics on a Si CMOS platform

Balčytis A., Ozawa T., Ota Y., Iwamoto S., Maeda J., Baba T.

Optics Infobase Conference Papers  2021

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We present a dynamically modulated ring resonator on a Si CMOS platform, hosting a synthetic dimension lattice over 180 GHz. The frequency and time domain synthetic band structure was acquired and photonic transport phenomena were explored.

Single photon generation in a topological slow light waveguide

Kuruma K., Yoshimi H., Ota Y., Katsumi R., Kakuda M., Loncar M., Arakawa Y., Iwamoto S.

Optics Infobase Conference Papers  2021

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report a topologically-protected single photon source in a slow light waveguide based on valley photonic crystals. Purcell-enhanced single photon generation from a quantum dot and its robust propagation in the topological waveguide are demonstrated.

Strong coupling between a single quantum dot and an L4/3 photonic crystal nanocavity

Kuruma K., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Applied Physics Express 13 ( 8 )  2020.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

　View Summary

We demonstrate strong coupling between a single quantum dot (QD) and a GaAs-based L4/3-type photonic crystal nanocavity. The L4/3 cavity supports a high theoretical Q factor (∼8 106), a small mode volume [∼0.32 (λ/n)3], and an electric field distribution with the maximum electric field lying within the host dielectric material, which facilitates strong coupling with a QD. We fabricated L4/3 cavities and observed a high Q factor over 80 000 using photoluminescence measurement. We confirmed strong coupling between a single QD and an L4/3 cavity with a Q factor of 33 000 by observing a clear anti-crossing in the spectra.

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Slow light waveguides in topological valley photonic crystals

Yoshimi H., Yamaguchi T., Ota Y., Arakawa Y., Iwamoto S.

Optics Letters 45 ( 9 ) 2648 - 2651 2020.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

　View Summary

Valley photonic crystals (VPhCs) are an attractive platform for the implementation of topologically protected optical waveguides in photonic integrated circuits (PICs). The realization of slow light modes in the topological waveguides may lead to further miniaturization and functionalization of the PICs. In this Letter, we report an approach to realize topological slow light waveguides in semiconductor-slab-based VPhCs. We show that a bearded interface of two topologically distinct VPhCs can support topological kink modes with large group indices over 100 within the topological bandgap. We numerically demonstrate robust light propagation in the topological slow light waveguide with large group indices of ∼60, even under the presence of sharp bends. Our work opens a novel route to implement topological slow light waveguides in a way compatible with current PIC technology.

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Efficient Single Photon Sources Transfer-Printed on Si with Unidirectional Light Output

Katsumi R., Ota Y., Tajiri T., Kakuda M., Iwamoto S., Akiyama H., Arakawa Y.

Conference Proceedings Lasers and Electro Optics Society Annual Meeting LEOS 2020-May 2020.05

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  10928081

　View Summary

We report efficient quantum-dot single-photon sources with unidirectional output integrated on Si by transfer printing. The device was designed to be robust against misalignment accompanied by the hybrid integration. Efficient single-photon generation was experimentally Confirmed.

Slow Light Waveguide Based on Topological Edge States in Valley Photonic Crystals

Yoshimi H., Yamaguchi T., Katsumi R., Ota Y., Arakawa Y., Iwamoto S.

Conference Proceedings Lasers and Electro Optics Society Annual Meeting LEOS 2020-May 2020.05

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  10928081

　View Summary

We demonstrate slow light waveguides using topological valley kink states. We found in-gap high-group-index modes at bearded interfaces of silicon-based valley photonic crystals, clearing the path to build topologically-protected slow light waveguides only using semiconductors.

Fabrication and optical characterization of photonic crystal nanocavities with electrodes for gate-defined quantum dots

Tajiri T., Sakai Y., Kuruma K., Ji S.M., Kiyama H., Oiwa A., Ritzmann J., Ludwig A., Wieck A.D., Ota Y., Arakawa Y., Iwamoto S.

Japanese Journal of Applied Physics 59 ( SG )  2020.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

　View Summary

Among various solid-state systems, gate-defined quantum dots (QD) with high scalability and controllability for single electron spin qubits are promising candidates to realize quantum spin-photon interface. The efficiency of the spin-photon interface is expected to be significantly enhanced by optical coupling of gate-defined QDs with photonic crystal (PhC) nanocavities. As the first step towards this optical coupling, we designed and experimentally demonstrated a PhC nanocavity with electrodes. The electrodes, which can form a single QD, were introduced on the top surfaces of two-dimensional PhC nanocavities with a position accuracy of a few tens of nanometers. Despite the electrodes, a resonant mode was confirmed for the PhC nanocavities through micro-photoluminescence spectroscopy. This work marks a crucial step towards optical coupling between gate-defined QDs and PhC nanocavities.

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Active topological photonics

Ota Y., Takata K., Ozawa T., Amo A., Jia Z., Kante B., Notomi M., Arakawa Y., Iwamoto S.

Nanophotonics 9 ( 3 ) 547 - 567 2020.03

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Topological photonics emerged as a novel route to engineer the flow of light. Topologically protected photonic edge modes, which are supported at the perimeters of topologically nontrivial insulating bulk structures, are of particular interest as they may enable low-loss optical waveguides immune to structural disorder. Very recently, there has been a sharp rise of interest in introducing gain materials into such topological photonic structures, primarily aiming at revolutionizing semiconductor lasers with the aid of physical mechanisms existing in topological physics. Examples of remarkable realizations are topological lasers with unidirectional light output under time-reversal symmetry breaking and topologically protected polariton and micro/nanocavity lasers. Moreover, the introduction of gain and loss provides a fascinating playground to explore novel topological phases, which are in close relevance to non-Hermitian and parity-time symmetric quantum physics and are, in general, difficult to access using fermionic condensed matter systems. Here, we review the cutting-edge research on active topological photonics, in which optical gain plays a pivotal role. We discuss recent realizations of topological lasers of various kinds, together with the underlying physics explaining the emergence of topological edge modes. In such demonstrations, the optical modes of the topological lasers are determined by the dielectric structures and support lasing oscillation with the help of optical gain. We also address recent research on topological photonic systems in which gain and loss, themselves, essentially influence topological properties of the bulk systems. We believe that active topological photonics provides powerful means to advance micro/nanophotonics systems for diverse applications and topological physics, itself, as well.

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In situ wavelength tuning of quantum-dot single-photon sources integrated on a CMOS-processed silicon waveguide

Katsumi R., Ota Y., Osada A., Tajiri T., Yamaguchi T., Kakuda M., Iwamoto S., Akiyama H., Arakawa Y.

Applied Physics Letters 116 ( 4 )  2020.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

　View Summary

Silicon quantum photonics provides a promising pathway to realize large-scale quantum photonic integrated circuits (QPICs) by exploiting the power of complementary-metal-oxide-semiconductor (CMOS) technology. Toward scalable operation of such silicon-based QPICs, a straightforward approach is to integrate deterministic single-photon sources (SPSs). To this end, hybrid integration of deterministic solid-state SPSs, such as those based on InAs/GaAs quantum dots (QDs), is highly promising. However, the spectral and spatial randomness inherent in the QDs poses a serious challenge for scalable implementation of multiple identical SPSs on a silicon CMOS chip. To overcome this challenge, we have been investigating a hybrid integration technique called transfer printing, which is based on a pick-and-place operation and allows for the integration of the desired QD SPSs on any locations on the silicon CMOS chips at will. Nevertheless, even in this scenario, in situ fine tuning for perfect wavelength matching among the integrated QD SPSs will be required for interfering photons from dissimilar sources. Here, we demonstrate in situ wavelength tuning of QD SPSs integrated on a CMOS silicon chip. To thermally tune the emission wavelengths of the integrated QDs, we augmented the QD SPSs with optically driven heating pads. The integration of all the necessary elements was performed using transfer printing, which largely simplified the fabrication of the three-dimensional stack of micro/nanophotonic structures. We further demonstrate in situ wavelength matching between two dissimilar QD sources integrated on the same silicon chip. Our transfer-printing-based approach will open the possibility for realizing large-scale QPICs that leverage CMOS technology.

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Recent progress in topological waveguides and nanocavities in a semiconductor photonic crystal platform [Invited]

Iwamoto S., Ota Y., Arakawa Y.

Optical Materials Express 11 ( 2 ) 319 - 337 2020

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Topological photonics provides a novel route for designing and realizing optical devices with unprecedented functionalities. Topological edge states, which are supported at the boundary of two photonic systems with different band topologies, enable robust light transport immune to structural imperfections and/or sharp bends in waveguides. Furthermore, the topological edge states are expected to revolutionize cavity-based optical devices such as lasers. Optical devices with built-in topological protection with a small footprint are fascinating as on-chip optical devices for low-loss and functional photonic integrated circuits. Semiconductor photonic crystals are promising platforms enabling the miniaturization of topological optical devices. Herein, we review the recent realizations of semiconductor topological photonic crystals. In particular, we discuss topological waveguides in valley photonic crystals, which have received increasing attention because of their simple realization. In addition, we provide recent demonstrations of topological nanocavities, which are another key component of topological nanophotonics. Progress in semiconductor topological photonic crystals will propel the use of topological photonic devices in various applications as well as deepen the understanding of topological photonic phenomena at the wavelength scale.

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Efficient single photon sources transfer-printed on Si with unidirectional light output

Katsumi R., Ota Y., Tajiri T., Kakuda M., Iwamoto S., Akiyama H., Arakawa Y.

Optics Infobase Conference Papers Part F182-CLEO-QELS 2020 2020

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report efficient quantum-dot single-photon sources with unidirectional output integrated on Si by transfer printing. The device was designed to be robust against misalignment accompanied by the hybrid integration. Efficient single-photon generation was experimentally confirmed.

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Slow light waveguide based on topological edge states in valley photonic crystals

Yoshimi H., Yamaguchi T., Katsumi R., Ota Y., Arakawa Y., Iwamoto S.

Optics Infobase Conference Papers Part F183-CLEO-SI 2020 2020

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We demonstrate slow light waveguides using topological valley kink states. We found in-gap high-group-index modes at bearded interfaces of silicon-based valley photonic crystals, clearing the path to build topologically-protected slow light waveguides only using semiconductors.

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Local tuning of transfer-printed quantum-dot single-photon sources on a CMOS silicon chip

Katsumi R., Ota Y., Osada A., Tajiri T., Yamaguchi T., Kakuda M., Iwamoto S., Akiyama H., Arakawa Y.

Moc 2019 24th Microoptics Conference    308 - 309 2019.11

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report local wavelength tuning of quantum-dot single-photon sources integrated on a CMOS silicon chip as well as in-situ spectral matching between two dissimilar sources. All the necessary heterogeneous integration processes were performed in a simple pick-and-place manner based on transfer printing, largely facilitating the fabrication of complicated device structures.

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Hybrid integration of quantum dot-nanocavity systems on silicon

Ota Y., Katsumi R., Osada A., Kakuda M., Iwamoto S., Arakawa Y.

Frontiers in Optics Proceedings Frontiers in Optics Laser Science Aps Dls  2019.09

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We discuss a transfer printing method for on-silicon hybrid integration. This technique simplifies the integration process of III-V quantum dots in nanocavities on CMOS-processed circuits, enabling single photon sources and cavity QED systems on Si.

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Photoluminescence properties as a function of growth mechanism for GaSb/GaAs quantum dots grown on Ge substrates

Zon, Thainoi S., Kiravittaya S., Tandaechanurat A., Kanjanachuchai S., Ratanathammaphan S., Panyakeow S., Ota Y., Iwamoto S., Arakawa Y.

Journal of Applied Physics 126 ( 8 )  2019.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00218979

　View Summary

In this work, we use photoluminescence (PL) spectroscopy to investigate how self-assembled GaSb/GaAs quantum dots (QDs) depend on their growth mechanism. Carrier transfer (i.e., carrier recombination in QDs and escape through the barrier layer) is investigated as a function of excitation-power- and temperature-dependent PL measurements. A drastic blueshift of the QD peak energy from 1.23 to 1.30 eV and a further shift to 1.33 eV reveal the influence of the GaSb growth rate and the growth temperature on the optical properties of these QDs. The thermal activation energy is extracted from the temperature-dependent PL by fitting the integrated PL intensity of the QD peaks to the Arrhenius relation. The QDs grown at the growth rate of 0.1 monolayers/s at 450 °C have higher thermal activation energy (109 meV) than those grown at a lower growth rate and higher QD growth temperature. The observed PL characteristics are discussed in terms of QD size, uniformity of QDs, and material intermixing occurring during QD growth on the buffer layer and capping layer.

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Spin-dependent directional emission from a quantum dot ensemble embedded in an asymmetric waveguide

Lin W., Ota Y., Iwamoto S., Arakawa Y.

Optics Letters 44 ( 15 ) 3749 - 3752 2019.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

　View Summary

In this study, we examine a photonic wire waveguide embedded with an ensemble of quantum dots (QDs) that directionally emits into the waveguide depending on the spin state of the ensemble. The directional emission is facilitated by the spin-orbit interaction of light. The waveguide has a two-step stair-like cross section and QDs are embedded only in the upper step, such that the circular polarization of emission from the spin-polarized QDs controls the direction of the radiation. We numerically verify that more than 70% of the radiation from the ensemble emitter is toward a specific direction in the waveguide. We also examine a microdisk resonator with a stair-like edge, which supports selective coupling of the QD ensemble radiation into a whispering gallery mode that rotates unidirectionally. Our study provides a foundation for spin-dependent optoelectronic devices.

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Photonic crystal nanocavity based on a topological corner state

Ota Y., Liu F., Katsumi R., Watanabe K., Wakabayashi K., Arakawa Y., Iwamoto S.

Optica 6 ( 6 ) 786 - 789 2019.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  23342536

　View Summary

Topological photonics has emerged as a novel approach to engineering the flow of light and provides unprecedented means for developing diverse photonic elements, including robust optical waveguides immune to structural imperfections. However, the development of nanoscale standing-wave cavities in topological photonics is rather slow, despite its importance when building densely integrated photonic integrated circuits. In this Letter, we report a photonic crystal nanocavity based on a topological corner state, supported at a 90-deg-angled rim of a twodimensional photonic crystal. A combination of the bulk-edge and edge-corner correspondences guarantees the presence of the higher-order topological state in a hierarchical manner. We experimentally observe a corner mode that is tightly localized in space while supporting a high Q factor over 2,000, verifying its promise as a nanocavity. These results cast new light on the way to introduce nanocavities in topological photonics platforms.

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GaAs valley photonic crystal waveguide with light-emitting InAs quantum dots

Yamaguchi T., Ota Y., Katsumi R., Watanabe K., Ishida S., Osada A., Arakawa Y., Iwamoto S.

Applied Physics Express 12 ( 6 )  2019.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

　View Summary

We report a valley photonic crystal (VPhC) waveguide in a GaAs slab with InAs quantum dots (QDs) as an internal light source exploited for the experimental characterization of the waveguide. A topological interface state formed at the interface between two topologically-distinct VPhCs is used as the waveguide mode. We demonstrate robust propagation for the near-infrared light emitted from the QDs, even with the presence of sharp bends, due to the topological protection of the guided mode. Our work will be of importance for developing robust photonic integrated circuits with small footprints, as well as for exploring active semiconductor topological photonics.

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Single Plasmon Generation in an InAs/GaAs Quantum Dot in a Transfer-Printed Plasmonic Microring Resonator

Tamada A., Ota Y., Kuruma K., Watanabe K., Iwamoto S., Arakawa Y.

ACS Photonics 6 ( 5 ) 1106 - 1110 2019.05

Research paper (scientific journal), Joint Work, Accepted

　View Summary

We report single plasmon generation with a self-assembled InAs/GaAs quantum dot embedded in a plasmonic microring resonator. The plasmonic cavity based on a GaAs microring is defined on an atomically smooth silver surface. We fabricated this structure with the help of transfer printing, which enables the pick-and-place assembly of the complicated, heterogeneous three-dimensional stack. We show that a high-order surface-plasmon-polariton transverse mode mediates efficient coupling between the InAs/GaAs quantum dots and the plasmonic cavity, paving the way for developing plasmonic quantum light sources based on the state-of-the-art solid-state quantum emitters. Experimentally, we observed Purcell-enhanced radiation from the quantum dot coupled to the plasmonic mode. We also observed a strong antibunching in the intensity correlation histogram measured for scattered photons from the plasmonic resonator, indicating single plasmon generation in the resonator. Our results are important for the development of quantum plasmonic circuits integrating high-performance single plasmon generators.

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Nanocavity Based on a Topological Corner State in a Two-Dimensional Photonic Crystal

Ota Y., Katsumi R., Watanabe K., Liu F., Wakabayashi K., Iwamoto S., Arakawa Y.

2019 Conference on Lasers and Electro Optics CLEO 2019 Proceedings  2019.05

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We demonstrate a photonic crystal nanocavity based on a topological corner state. The design exploits the hierarchical bulk-edge-corner correspondence for the two-dimensional photonic crystal, opening a deterministic route to introduce nanocavities in topological photonics platforms.

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Quantum-dot single-photon source on a CMOS-processed silicon waveguide

Katsumi R., Ota Y., Osada A., Yamaguchi T., Tajiri T., Kakuda M., Iwamoto S., Arakawa Y.

2019 Conference on Lasers and Electro Optics CLEO 2019 Proceedings  2019.05

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report a quantum-dot single-photon source integrated onto a CMOS-processed silicon waveguide. The necessary hybrid integration was done in a simple pick-and-place manner with transfer printing, thus fully maintaining the compatibility with CMOS-back-end technology.

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Three-dimensional photonic crystal simultaneously integrating a nanocavity laser and waveguides

Tajiri T., Takahashi S., Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Optica 6 ( 3 ) 296 - 299 2019.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  23342536

　View Summary

Three-dimensional (3D) integration of photonic devices is an ultimate route toward highly integrated photonic circuits. 3D photonic crystals (PCs) are a promising platform for 3D integration because of their complete photonic bandgaps (cPBGs) which enables full control of light. However, simultaneous integration of active and passive devices into a 3D PC has been hindered due to fabrication difficulties. Here, we simultaneously integrate a nanocavity laser and waveguides into a 3D PC with a cPBG at near-IR wavelengths using micromanipu-lation technology. The proposed plate-insertion stacking method allowed fabrication of 3D PCs with a large number of layers, enabling integration of the active and passive circuit components. Laser emission from the photo-excited nanocavity laser was observed from the output port of the waveguides, demonstrating successful guiding of the light from the nanocavity laser in the 3D PC. This work paves the way for 3D photonic circuits using 3D PCs with cPBGs.

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Quantum-dot single-photon source on a CMOS silicon photonic chip integrated using transfer printing

Katsumi R., Ota Y., Osada A., Yamaguchi T., Tajiri T., Kakuda M., Iwamoto S., Akiyama H., Arakawa Y.

APL Photonics 4 ( 3 )  2019.03

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Silicon photonics is a powerful platform for implementing large-scale photonic integrated circuits (PICs) because of its compatibility with mature complementary-metal-oxide-semiconductor (CMOS) technology. Exploiting silicon-based PICs for quantum photonic information processing (or the so-called silicon quantum photonics) provides a promising pathway for large-scale quantum applications. For the development of scalable silicon quantum PICs, a major challenge is integrating on-silicon quantum light sources that deterministically emit single photons. In this regard, the use of epitaxial InAs/GaAs quantum dots (QDs) is a very promising approach because of their capability of deterministic single-photon emission with high purity and indistinguishability. However, the required hybrid integration is inherently difficult and often lacks the compatibility with CMOS processes. Here, we demonstrate a QD single-photon source integrated on a glass-clad silicon photonic waveguide processed by a CMOS foundry. Hybrid integration is performed using transfer printing, which enables us to integrate heterogeneous optical components in a simple pick-and-place manner and thus assemble them after the entire CMOS process is completed. We observe single-photon emission from the integrated QD and its efficient coupling into the silicon waveguide. Our transfer-printing-based approach is fully compatible with CMOS back-end processes and thus will open the possibility for realizing large-scale quantum PICs that leverage CMOS technology.

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Strongly coupled single-quantum-dot-cavity system integrated on a CMOS-processed silicon photonic chip

Osada A., Ota Y., Katsumi R., Kakuda M., Iwamoto S., Arakawa Y.

Physical Review Applied 11 ( 2 )  2019.02

Research paper (scientific journal), Joint Work, Accepted

　View Summary

A quantum photonic integrated circuit (QPIC) is a promising tool for constructing integrated devices for quantum-technology applications. In the optical regime, silicon photonics empowered by complementary-metal-oxide-semiconductor (CMOS) technology provides optical components useful for realizing large-scale QPICs. Optical nonlinearity at the single-photon level is required for QPICs to facilitate photon-photon interaction. However, to date, realization of optical elements with deterministic (i.e., not probabilistic) single-photon nonlinearity by use of silicon-based components is challenging despite the enhancement of the functionality of QPICs based on silicon photonics. In this study, we realize a strongly coupled InAs/GaAs quantum-dot-cavity-quantum-electrodynamics system on a CMOS-processed silicon photonic chip. The heterogeneous integration of the GaAs cavity on the silicon chip is performed by transfer printing. The cavity-quantum-electrodynamics system on the CMOS photonic chip realized in this work is a promising candidate for an on-chip single-photon nonlinear element, which constitutes the fundamental component for future applications based on QPICs, such as coherent manipulation and nondestructive measurement of qubit states via a cavity, and an efficient single-photon filter and router.

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Growth-Rate-Dependent Properties of GaSb/GaAs Quantum Dots on (001) Ge Substrate by Molecular Beam Epitaxy

Zon , Phienlumlert P., Thainoi S., Kiravittaya S., Tandaechanurat A., Nuntawong N., Sopitpan S., Yordsri V., Thanachayanont C., Kanjanachuchai S., Ratanathammaphan S., Panyakeow S., Ota Y., Iwamoto S., Arakawa Y.

Physica Status Solidi A Applications and Materials Science 216 ( 1 )  2019.01

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18626300

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Tuning growth of nanostructures can provide additional routes to engineer their characteristics. In this work, the authors report on a combined growth of GaSb/GaAs quantum dots (QDs) and growth of GaAs on (001) Ge substrate. Surface decorated with GaAs anti-phase domain is the initial template to investigate the growth-rate effects on the growth of self-assembled GaSb QDs. By varying the GaSb growth rates, QD ensembles with different morphologies are formed. Perpendicular alignment of elongated GaSb QDs is observed. Cross-sectional transmission electron microscopic images show a substantial reduction of lateral QD size when it is buried in GaAs matrix. Raman scattering as well as power-dependent photoluminescence spectroscopies are performed to reveal the optical properties of the nanostructures. Type-II band alignment characteristic is confirmed.

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Hybrid integration of quantum dot-nanocavity systems on silicon

Ota Y., Katsumi R., Osada A., Kakuda M., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F144-FiO 2019 2019

Research paper (international conference proceedings), Joint Work, Accepted

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We discuss a transfer printing method for on-silicon hybrid integration. This technique simplifies the integration process of III-V quantum dots in nanocavities on CMOS-processed circuits, enabling single photon sources and cavity QED systems on Si.

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Nanocavity based on a topological corner state in a two-dimensional photonic crystal

Ota Y., Katsumi R., Watanabe K., Liu F., Wakabayashi K., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F129-CLEO_SI 2019 2019

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate a photonic crystal nanocavity based on a topological corner state. The design exploits the hierarchical bulk-edge-corner correspondence for the two-dimensional photonic crystal, opening a deterministic route to introduce nanocavities in topological photonics platforms.

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Quantum-dot single-photon source on a CMOS-processed silicon waveguide

Katsumi R., Ota Y., Osada A., Yamaguchi T., Tajiri T., Kakuda M., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F128-CLEO_QELS 2019 2019

Research paper (international conference proceedings), Joint Work, Accepted

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We report a quantum-dot single-photon source integrated onto a CMOS-processed silicon waveguide. The necessary hybrid integration was done in a simple pick-and-place manner with transfer printing, thus fully maintaining the compatibility with CMOS-back-end technology.

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Topological photonic crystal nanocavity laser

Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Communications Physics 1 ( 1 )  2018.12

Research paper (scientific journal), Joint Work, Accepted

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Topological edge states exist at the interfaces between two topologically distinct materials. The presence and number of such modes are deterministically predicted from the bulk band topologies, known as the bulk-edge correspondence. This principle is highly useful for predictably controlling optical modes in resonators made of photonic crystals (PhCs), leading to the recent demonstrations of microscale topological lasers. Meanwhile, zero-dimensional topological trapped states in the nanoscale remained unexplored, despite its importance for enhancing light–matter interactions and for wide applications including single-mode nanolasers. Here, we report a topological PhC nanocavity with a near-diffraction-limited mode volume and its application to single-mode lasing. The topological origin of the nanocavity, formed at the interface between two topologically distinct PhCs, guarantees the existence of only one mode within its photonic bandgap. The observed lasing accompanies a high spontaneous emission coupling factor stemming from the nanoscale confinement. These results encompass a way to greatly downscale topological photonics.

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Scheme for media conversion between electronic spin and photonic orbital angular momentum based on photonic nanocavity

Fong C.F., Ota Y., Iwamoto S., Arakawa Y.

Optics Express 26 ( 16 ) 21219 - 21234 2018.08

Research paper (scientific journal), Joint Work, Accepted

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Light with nonzero orbital angular momentum (OAM) or twisted light is promising for quantum communication applications such as OAM-entangled photonic qubits. Methods and devices for the conversion of the photonic OAM to photonic spin angular momentum (SAM), as well as for the photonic SAM to electronic SAM transformation are known but the direct conversion between the photonic OAM and electronic SAM is not available within a single device. Here, we propose a scheme which converts photonic OAM to electronic SAM and vice versa within a single nanophotonic device. We employed a photonic crystal nanocavity with an embedded quantum dot (QD) which confines an electron spin as a stationary qubit. The confined spin-polarized electrons could recombine with holes to give circularly polarized emission, which could drive the rotation of the nanocavity modes via the strong optical spin-orbit interaction. The rotating modes then radiate light with nonzero OAM, allowing this device to serve as a transmitter. As this can be a unitary process, the time-reversed case enables the device to function as a receiver. This scheme could be generalized to other systems with a resonator and quantum emitters such as a microdisk and defects in diamond for example. Our scheme shows the potential for realizing an (ultra)compact electronic SAM-photonic OAM interface to accommodate OAM as an additional degree of freedom for quantum information purposes.

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Lasing in a topological photonic crystal nanocavity

Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

2018 Conference on Lasers and Electro Optics CLEO 2018 Proceedings  2018.08

Research paper (international conference proceedings), Joint Work, Accepted

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We report lasing oscillation in a zero-dimensional edge state formed at the boundary of two photonic crystal nanobeams with distinct band topologies. The topological origin of the nanocavity mode ensures a single mode operation.

Quantum dot single photon sources transfer-printed on wire waveguides

Katsumi R., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

2018 Conference on Lasers and Electro Optics CLEO 2018 Proceedings  2018.08

Research paper (international conference proceedings), Joint Work, Accepted

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We report quantum dot single photon sources coupled to glass-clad wire waveguides by transfer printing, which enables the heterogeneous source integration in a simple pick-and-place manner. A high waveguide coupling efficiency >60% is experimentally demonstrated.

Quantum-dot nanolasers on Si photonic circuits

Osada A., Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

2018 Conference on Lasers and Electro Optics CLEO 2018 Proceedings  2018.08

Research paper (international conference proceedings), Joint Work, Accepted

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We report the hybrid integration of quantum dot nanolasers on silicon photonic circuits using transfer printing. The pick-and-place assembly method facilitates the integration of two nanolasers on a single CMOS-processed waveguide that supports two-wavelength output.

Two dimensional photonic crystal nanocavities with InAs/GaAs quantum dot active regions embedded by MBE regrowth

Vo Q.H., Ota Y., Watanabe K., Kageyama T., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 57 ( 8 )  2018.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

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We demonstrate two dimensional photonic crystal nanocavities embedding spatially-isolated active regions containing InAs/GaAs self-assembled quantum dots. We fabricated the GaAs-based structures by a combination of electron-beam lithography, dry/wet etching and crystal regrowth using molecular beam epitaxy. The fabricated nanocavity based on a photonic crystal double heterostructure supports a cavity mode with a high experimental quality factor over 10,000, despite the existence of a mound structure on the nanocavity formed during the regrowth. Using electromagnetic simulations, we discuss the origin of the cavity mode and a direction for further increasing the quality factor. The two dimensional photonic crystal nanocavities with buried quantum dot active regions will provide a useful platform for developing high performance nanolasers.

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Advanced photonic crystal nanocavity quantum dot lasers

Ota Y., Watanabe K., Kakuda M., Iwamoto S., Arakawa Y.

IEICE Transactions on Electronics E101C ( 7 ) 553 - 560 2018.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  09168524

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We discuss our recent progress in photonic crystal nanocavity quantum dot lasers. We show how enhanced light matter interactions in the nanocavity lead to diverse and fascinating lasing phenomena that are in general inaccessible by conventional bulky semiconductor lasers. First, we demonstrate thresholdless lasing, in which any clear kink in the output laser curve does not appear. This is a result of near unity coupling of spontaneous emission into the lasing cavity mode, enabled by the strong Purcell effect supported in the nanocavity. Then, we discuss self-frequency conversion nanolasers, in which both near infrared lasing oscillation and nonlinear optical frequency conversion to visible light are simultaneously supported in the individual nanocavity. Owing to the tight optical confinement both in time and space, a high normalized conversion efficiency over a few hundred %/W is demonstrated. We also show that the intracavity nonlinear frequency conversion can be utilized to measure the statistics of the intracavity photons. These novel phenomena will be useful for developing various nano-optoelectronic devices with advanced functionalities.

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Transfer-printed quantum-dot nanolasers on a silicon photonic circuit

Osada A., Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Applied Physics Express 11 ( 7 )  2018.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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Quantum-dot (QD) nanolasers integrated on a silicon photonic circuit are demonstrated for the first time. QD nanolasers based on one-dimensional photonic crystal nanocavities containing InAs/GaAs QDs are integrated on CMOS-processed silicon waveguides with silicon dioxide cladding. We employed transfer printing, whereby the three-dimensional stack of photonic nanostructures is assembled in a pick-and-place manner. The lasing operation and waveguide coupling of an assembled single nanolaser are confirmed through micro-photoluminescence spectroscopy. Furthermore, by repetitive transfer printing, two QD nanolasers integrated onto a single silicon waveguide are demonstrated, opening a path to the development of compact light sources potentially applicable to wavelength division multiplexing.

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Time-resolved vacuum Rabi oscillations in a quantum-dot-nanocavity system

Kuruma K., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Physical Review B 97 ( 23 )  2018.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

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We report time domain observation of vacuum Rabi oscillations in a single quantum dot strongly coupled to a nanocavity under incoherent optical carrier injection. We realize a photonic crystal nanocavity with a very high quality factor of >80000 and employ it to clearly resolve the ultrafast vacuum Rabi oscillations by simple photoluminescence-based experiments. We found that the time domain vacuum Rabi oscillations were largely modified when changing the pump wavelength and intensity, even when marginal changes were detected in the corresponding photoluminescence spectra. We analyze the measured time domain oscillations by fitting to simulation curves obtained with a cavity quantum electrodynamics model. The observed modifications of the oscillation curves were mainly induced by the change in the carrier capture and dephasing dynamics in the quantum dot, as well as the change in bare-cavity emission. This result suggests that vacuum Rabi oscillations can be utilized as a highly sensitive probe for the quantum-dot dynamics. Our work points out a powerful alternative to conventional spectral-domain measurements for a deeper understanding of the vacuum Rabi dynamics in quantum-dot-based-cavity quantum electrodynamics systems.

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Transfer-printed single-photon sources coupled to wire waveguides

Katsumi R., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Optica 5 ( 6 ) 691 - 694 2018.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  23342536

　View Summary

Photonic integrated circuits (PICs) are attractive platforms to perform large-scale quantum information processing. While highly functional PICs (e.g., silicon-based photonic circuits) and high-performance single-photon sources [SPSs, e.g., compound-semiconductor quantum dots (QDs)] have been independently demonstrated, their combination for single-photon-based applications has still been limited. This is largely due to the complexities of introducing SPSs into existing PIC platforms, which are generally realized with different materials and using distinct fabrication protocols. Here, we report a novel approach to combine SPSs and PICs prepared independently. We employ transfer printing, by which multiple desired SPSs can be integrated in a simple pick-and-place manner with a theoretical waveguide coupling efficiency >99%, fulfilling the demanding requirements of large-scale quantum applications. Experimentally, we demonstrated QD-based SPSs with high waveguide coupling efficiencies, together with the integration of two SPSs into a waveguide. Our approach will accelerate scalable fusion between modern PICs and cutting-edge quantum technologies.

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Nanowire-quantum-dot lasers on flexible membranes

Tatebayashi J., Ota Y., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Applied Physics Express 11 ( 6 )  2018.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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We demonstrate lasing in a single nanowire with quantum dots as an active medium embedded on poly(dimethylsiloxane) membranes towards application in nanowire-based flexible nanophotonic devices. Nanowire laser structures with 50 quantum dots are grown on patterned GaAs(111)B substrates and then transferred from the as-grown substrates on poly(dimethylsiloxane) transparent flexible organosilicon membranes, by means of spin-casting and curing processes. We observe lasing oscillation in the transferred single nanowire cavity with quantum dots at 1.425 eV with a threshold pump pulse fluence of ∼876 μJ/cm², which enables the realization of high-performance multifunctional NW-based flexible photonic devices.

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High-Q nanocavities in semiconductor-based three-dimensional photonic crystals

Takahashi S., Tajiri T., Watanabe K., Ota Y., Iwamoto S., Arakawa Y.

Electronics Letters 54 ( 5 ) 305 - 307 2018.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00135194

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The high-quality factors (Q-factors) of nanocavities in three-dimensional photonic crystals were experimentally demonstrated by increasing the in-plane area of the structure. Entire structures made of GaAs were fabricated by a micro-manipulation technique, and the nanocavities contained InAs self-assembled quantum dots that emitted near-infrared light. The obtained Q-factor was improved to 93,000, which is 2.4 times larger than that in a previous report of a three-dimensional photonic crystal nanocavity. Due to this large Q-factor, a lasing oscillation from this cavity mode was successfully observed.

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Large vacuum Rabi splitting between a single quantum dot and an H0 photonic crystal nanocavity

Ota Y., Takamiya D., Ohta R., Takagi H., Kumagai N., Iwamoto S., Arakawa Y.

Applied Physics Letters 112 ( 9 )  2018.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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Strong light matter interactions between semiconductor quantum dots and optical micro/nanocavities are useful resources for developing quantum information processing devices and for exploring diverse quantum optical phenomena. In pursuit of better device performances and novel physics, it is desirable to achieve a larger coupling constant between the quantum dot and the cavity while keeping the high coherence of the coupled system. In this letter, we report the observation of a large vacuum Rabi splitting of ∼328 μeV using a single InAs quantum dot embedded in a GaAs-based H0 photonic crystal nanocavity, which possesses a near-diffraction limited mode volume as well as a high experimental Q factor of ∼52 000. The resulting figure of merit of the strongly coupled systems, defined as a ratio of the coupling constant to the cavity decay rate, reaches 6.4, which is the record high value for semiconductor QD-nanocavity systems reported to date.

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Lasing in a topological photonic crystal nanocavity

Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F94-CLEO_SI 2018 2018

Research paper (international conference proceedings), Joint Work, Accepted

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We report lasing oscillation in a zero-dimensional edge state formed at the boundary of two photonic crystal nanobeams with distinct band topologies. The topological origin of the nanocavity mode ensures a single mode operation.

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Quantum dot single photon sources transfer-printed on wire waveguides

Katsumi R., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F93-CLEO_QELS 2018 2018

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report quantum dot single photon sources coupled to glass-clad wire waveguides by transfer printing, which enables the heterogeneous source integration in a simple pick-and-place manner. A high waveguide coupling efficiency > 60% is experimentally demonstrated.

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Topological confinement of light in photonic crystals

Iwamoto S., Ota Y., Arakawa Y.

Optics Infobase Conference Papers Part F125-OPJ 2018 2018

Research paper (international conference proceedings), Joint Work, Accepted

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We will discuss a topological locarized state of light realizedin a photonic crystal (PhC) nanbeam platform. By carefuly tunig the unit cell structure, we can design two topologically distinct PhC nanobeams. The bulk-edge correpondence guarantees the existence of single localized mode at the interface between them within their common bandgap. We demonstrate the lasing osscilation using the mode as a nanocavity mode.

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Quantum-dot nanolasers on Si photonic circuits

Osada A., Ota Y., Katsumi R., Watanabe K., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F94-CLEO_SI 2018 2018

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report the hybrid integration of quantum dot nanolasers on silicon photonic circuits using transfer printing. The pick-and-place assembly method facilitates the integration of two nanolasers on a single CMOS-processed waveguide that supports two-wavelength output.

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A photonic crystal nanocavity with a quantum dot active region embedded by MBE regrowth

Vo Q.H., Ota Y., Watanabe K., Kageyama T., Iwamoto S., Arakawa Y.

22nd Microoptics Conference Moc 2017 2017-November   90 - 91 2017.11

Research paper (international conference proceedings), Joint Work, Accepted

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We fabricated a two dimensional photonic crystal nanocavity embedding a spatially-isolated active region containing InAs quantum dots using crystal regrowth with molecular beam epitaxy. We observed a cavity mode with a quality factor over 10,000, despite the existence of a mound structure on top of the buried active region due to faceting during the regrowth.

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Circularly polarized vacuum field in three-dimensional chiral photonic crystals probed by quantum dot emission

Takahashi S., Ota Y., Tajiri T., Tatebayashi J., Iwamoto S., Arakawa Y.

Physical Review B 96 ( 19 )  2017.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

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The modification of a circularly polarized vacuum field in three-dimensional chiral photonic crystals was measured by spontaneous emission from quantum dots in the structures. Due to the circularly polarized eigenmodes along the helical axis in the GaAs-based mirror-asymmetric structures we studied, we observed highly circularly polarized emission from the quantum dots. Both spectroscopic and time-resolved measurements confirmed that the obtained circularly polarized light was influenced by a large difference in the photonic density of states between the orthogonal components of the circular polarization in the vacuum field.

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Time-domain observation of vacuum Rabi oscillations in a strongly coupled quantum dot-nanocavity system

Kuruma K., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

2017 Conference on Lasers and Electro Optics CLEO 2017 Proceedings 2017-January   1 - 2 2017.10

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report the time-domain observation of vacuum Rabi oscillations in a single quantum dot-photonic crystal nanocavity system under optical carrier injection. A significantly-improved cavity Q-factor facilitates the direct access to the ultrafast exciton-photon dynamics.

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Demonstration of lasing oscillation in a plasmonic microring resonator containing quantum dots fabricated by transfer printing

Tamada A., Ota Y., Kuruma K., Ho J., Watanabe K., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 56 ( 10 )  2017.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

　View Summary

We demonstrate room-temperature lasing oscillation in a plasmonic microring resonator containing InAs/GaAs self-assembled quantum dots. The resonator is composed of a GaAs microring placed on an atomically flat silver surface. Such a structure was fabricated by transfer printing, through which we can pick the dielectric microring and place it on the silver surface at will, hence maintaining a high-quality metal surface without introducing any complex fabrication process. Our result will be important in the development of nanoscale light sources in future densely integrated plasmonic circuits.

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Method for generating a photonic NOON state with quantum dots in coupled nanocavities

Kamide K., Ota Y., Iwamoto S., Arakawa Y.

Physical Review A 96 ( 1 )  2017.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699926

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We propose a method to generate path-entangled NOON-state photons from quantum dots and coupled nanocavities. In the systems we considered, cavity mode frequencies are tuned close to the biexciton two-photon resonance. Under appropriate conditions, the system can have the target NOON state in the energy eigenstate, as a consequence of destructive quantum interference. The NOON state can be generated by a resonant laser excitation. This method, first introduced for a two-photon NOON state (N=2), can be extended toward a higher NOON state (N>2) based on our recipe, which is applied to the case of N=4 as an example.

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Manipulation of dynamic nuclear spin polarization in single quantum dots by photonic environment engineering

Fong C.F., Ota Y., Iwamoto S., Arakawa Y.

Physical Review B 95 ( 24 )  2017.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

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Optically induced dynamic nuclear spin polarization (DNP) in a semiconductor quantum dot (QD) requires many cycles of excitation of spin polarized carriers and carrier recombination. As such, the radiative lifetime of the exciton containing the electron becomes one of the limiting factors of DNP. In principle, changing the radiative lifetime of the exciton will affect DNP and thus the nuclear spin polarization. Here, we demonstrate the manipulation of DNP in single QDs through the engineering of the photonic environment using two-dimensional photonic crystals. We find that the achievable degree of nuclear spin polarization can be controlled through the modification of exciton radiative lifetime. Our results show the promise of achieving a higher degree of nuclear spin polarization via photonic environment engineering, with implications on spin-based quantum information processing.

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Growth of InGaAs/GaAs nanowire-quantum dots on AlGaAs/GaAs distributed Bragg reflectors for laser applications

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

Journal of Crystal Growth 468   144 - 148 2017.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00220248

　View Summary

We report the formation of GaAs nanowires (NWs) containing In<inf>0.2</inf>Ga<inf>0.8</inf>As/GaAs quantum dots (QDs) on patterned Al<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs distributed Bragg reflectors (DBRs) grown on GaAs(111)B substrates. The growth conditions of both GaAs and Al<inf>0.65</inf>Ga<inf>0.35</inf>As layers on GaAs(111)B are optimized for the growth of high-quality Al<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs DBRs with (111) orientation in order to obtain high reflectivity at the NW/DBR interface. Moderately high growth temperature and low V/III ratio can mitigate the formation of pyramidal hillocks, resulting in the formation of high-quality DBRs on GaAs(111)B substrates. Optical characterization at 7 K of single GaAs NW cavities containing 75-stacked InGaAs/GaAs NWQDs grown on patterned such Al<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs DBRs/GaAs(111)B substrates exhibits lasing oscillation at 1.43 eV with a threshold pump pulse fluence of 250 μJ/cm².

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Enhanced optical Stark shifts in a single quantum dot embedded in an H1 photonic crystal nanocavity

Takagi H., Ota Y., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Applied Physics Express 10 ( 6 )  2017.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

　View Summary

We demonstrate large optical Stark shifts in a single quantum dot embedded in a modified H1 photonic crystal nanocavity. We designed the nanocavity to simultaneously possess a high Q factor, a small mode volume, and a high coupling efficiency to the external laser field. This nanocavity enabled the observation of a large Stark shift of 70 μeV even under very weak laser irradiation. The large shift was sustained by only four intracavity photons on average, paving the way for the development of ultralow-power quantum/classical optical devices.

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Optical coupling between atomically thin black phosphorus and a two dimensional photonic crystal nanocavity

Ota Y., Moriya R., Yabuki N., Arai M., Kakuda M., Iwamoto S., Machida T., Arakawa Y.

Applied Physics Letters 110 ( 22 )  2017.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

　View Summary

Atomically thin black phosphorus (BP) is an emerging two dimensional (2D) material exhibiting bright photoluminescence in the near infrared region. Coupling its radiation to photonic nanostructures will be an important step toward the realization of 2D material based nanophotonic devices that operate efficiently in the near infrared region, which includes the technologically important optical telecommunication wavelength bands. In this letter, we demonstrate the optical coupling between atomically thin BP and a 2D photonic crystal nanocavity. We employed a home-build dry transfer apparatus for placing a thin BP flake on the surface of the nanocavity. Their optical coupling was analyzed through measuring cavity mode emission under optical carrier injection at room temperature.

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Thresholdless quantum dot nanolaser

Ota Y., Kakuda M., Watanabe K., Iwamoto S., Arakawa Y.

Optics Express 25 ( 17 ) 19981 - 19994 2017

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Thresholdless lasing is an outstanding challenge in laser science and is achievable only in devices having near unity quantum efficiency even when not lasing. Such lasers are expected to exhibit featureless linear light output curves. However, such thresholdless behavior hinders identification of the laser transition, triggering a long-lasting argument on how to identify the lasing. Here, we demonstrate thresholdless lasing in a semiconductor quantum dot nanolaser with a photonic crystal nanocavity. We employ cavity resonant excitation for enabling the thresholdless operation via focused carrier injection into high cavity field regions. Under conventional (above bandgap) excitation, the same nanolaser exhibits a typical thresholded lasing transition, thereby facilitating a systematic comparison between the thresholdless and thresholded laser transitions in the single device. Our approach enables a clear verification of the thresholdless lasing and reveals core elements for its realization using quantum dots, paving the way to the development of ultimately energy-efficient nanolasers.

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Time-domain observation of vacuum rabi oscillations in a strongly coupled quantum dot-nanocavity system

Kuruma K., Ota Y., Kakuda M., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers Part F43-CLEO_AT 2017 2017

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report the time-domain observation of vacuum Rabi oscillations in a single quantum dot-photonic crystal nanocavity system under optical carrier injection. A significantlyimproved cavity Q-factor facilitates the direct access to the ultrafast exciton-photon dynamics.

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Position dependent optical coupling between single quantum dots and photonic crystal nanocavities

Kuruma K., Ota Y., Kakuda M., Takamiya D., Iwamoto S., Arakawa Y.

Applied Physics Letters 109 ( 7 )  2016.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate precise and quick detection of the positions of quantum dots (QDs) embedded in two-dimensional photonic crystal nanocavities. We apply this technique to investigate the QD position dependence of the optical coupling between the QD and the nanocavity. We use a scanning electron microscope (SEM) operating at a low acceleration voltage to detect surface bumps induced by the QDs buried underneath. This enables QD detection with a sub-10 nm precision. We then experimentally measure the vacuum Rabi spectra to extract the optical coupling strengths (gs) between single QDs and cavities, and compare them to the values estimated by a combination of the SEM-measured QD positions and electromagnetic cavity field simulations. We found a highly linear relationship between the local cavity field intensities and the QD-cavity gs, suggesting the validity of the point dipole approximation used in the estimation of the gs. The estimation using SEM has a small standard deviation of ±6.2%, which potentially enables the high accuracy prediction of g prior to optical measurements. Our technique will play a key role for deeply understanding the interaction between QDs and photonic nanostructures and for advancing QD-based cavity quantum electrodynamics.

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Effect of metal side claddings on emission decay rates of single quantum dots embedded in a sub-wavelength semiconductor waveguide

Yamamoto T., Ota Y., Ishida S., Kumagai N., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 55 ( 8 )  2016.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

　View Summary

We experimentally investigate the emission decay rates of self-assembled single InAs quantum dots (QDs) embedded in sub-wavelength semiconductor waveguides with and without metal side claddings. Compared with as-grown single QDs, we observe a clear suppression (enhancement) in the radiative decay rates of single InAs QDs embedded in the sub-wavelength semiconductor waveguides without (with) metal cladding, respectively. The decay rate for QDs in metal-clad waveguides is >2 times faster than that in waveguides without metal. Numerical calculations using models that include the effects of structural imperfections show good agreement with the experimental results, and reveal that the most important structural imperfection is the gap between the metal and the semiconductor.

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A Nanowire-Based Plasmonic Quantum Dot Laser

Ho J., Tatebayashi J., Sergent S., Fong C.F., Ota Y., Iwamoto S., Arakawa Y.

Nano Letters 16 ( 4 ) 2845 - 2850 2016.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  15306984

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Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm² was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics.

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P-shell carrier assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field

Fong C.F., Ota Y., Harbord E., Iwamoto S., Arakawa Y.

Physical Review B 93 ( 12 )  2016.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  24699950

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Repeated injection of spin-polarized carriers in a quantum dot (QD) leads to the polarization of nuclear spins, a process known as dynamic nuclear spin polarization (DNP). Here, we report the observation of p-shell carrier assisted DNP in single QDs at zero external magnetic field. The nuclear field - measured by using the Overhauser shift of the singly charged exciton state of the QDs - continues to increase, even after the carrier population in the s-shell saturates. This is also accompanied by an abrupt increase in nuclear spin buildup time as p-shell emission overtakes that of the s shell. We attribute the observation to p-shell electrons strongly altering the nuclear spin dynamics in the QD, supported by numerical simulation results based on a rate equation model of coupling between electron and nuclear spin system. Dynamic nuclear spin polarization with p-shell carriers could open up avenues for further control to increase the degree of nuclear spin polarization in QDs.

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Effect of metal side claddings on emission decay rate of single quantum dots embedded in a subwavelength semiconductor waveguide

Yamamoto T., Ota Y., Ishida S., Kumagai N., Iwamoto S., Arakawa Y.

Moc 2015 Technical Digest of 20th Microoptics Conference  2016.02

Research paper (international conference proceedings), Joint Work, Accepted

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We measured the emission decay rates of self-assembled InAs single quantum dots (QDs) embedded in subwavelength-width semiconductor waveguides with and without Au side claddings. The Au claddings increased the decay rate of single QDs by ∼2 times, which is consistent with numerical simulations taking account of fabrication imperfection.

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Influence of the relative positions of quantum dots and nanocavities on the optical coupling strength

Kuruma K., Ota Y., Takamiya D., Kakuda M., Iwamoto S., Arakawa Y.

2015 11th Conference on Lasers and Electro Optics Pacific Rim CLEO PR 2015 3 2016.01

Research paper (international conference proceedings), Joint Work, Accepted

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We use scanning electron microscopy to precisely measure the locations of quantum dots buried in photonic crystal nanocavities. We show that well-positioned dots (at the field maximum) can exhibit vacuum Rabi splittings larger than 180μeV.

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Demonstration of a three-dimensional photonic crystal nanocavity in a 〈110〉-layered diamond structure

Tajiri T., Takahashi S., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Applied Physics Letters 107 ( 7 )  2015.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We experimentally demonstrate a three-dimensional photonic crystal (3D PC) nanocavity in a 〈110a〉-layered diamond structure with a quality factor (Q-factor) of 12800 at a wavelength of 1.1 μm. The observed Q is 1.2 times higher than that of a 3D PC nanocavity in a woodpile structure with the same in-plane size and the same number of stacked layers. This result indicates the potential importance of the 〈110a〉-layered diamond structure for getting high Q 3D PC nanocavities within a limited in-plane space.

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Circularly polarized light emission of quantum dots at the band edge of three-dimensional chiral photonic crystals

Takahashi S., Tajiri T., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2015-August 2015.08

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate highly circularly polarized emission from quantum dots in semiconductor chiral photonic crystals. The emission is influenced by the difference in density of states between the orthogonal circular polarizations at the polarization band edge.

Room-temperature lasing in GaAs nanowires embedding multi-stacked InGaAs/GaAs quantum dots

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2015-August 2015.08

Research paper (international conference proceedings), Joint Work, Accepted

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We report the demonstration of room-temperature lasing in a single GaAs nanowire embedding 50-stacked In<inf>0.22</inf>Ga<inf>0.78</inf>As/GaAs quantum dots at a lasing emission energy of 1.37 eV with a threshold pump pulse fluence of 138 μm/cm².

Single emitter vacuum Rabi splitting measured through direct free space spontaneous emission

Ota Y., Ohta R., Kumagai N., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2015-August 2015.08

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We measured the vacuum Rabi splitting of a single quantum emitter through direct free space spontaneous emission. This lays the groundwork for accessing diverse cavity quantum electrodynamics phenomena manifesting themselves only in the spontaneous emission.

Room-temperature lasing in a single nanowire with quantum dots

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

Nature Photonics 9 ( 8 ) 501 - 505 2015.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  17494885

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Semiconductor nanowire lasers are promising as ultrasmall, highly efficient coherent light emitters in the fields of nanophotonics, nano-optics and nanobiotechnology. Although there have been several demonstrations of nanowire lasers using homogeneous bulk gain materials or multi-quantum-wells/disks, it is crucial to incorporate lower-dimensional quantum nanostructures into the nanowire to achieve superior device performance in relation to threshold current, differential gain, modulation bandwidth and temperature sensitivity. The quantum dot is a useful and essential nanostructure that can meet these requirements. However, difficulties in forming stacks of quantum dots in a single nanowire hamper the realization of lasing operation. Here, we demonstrate room-temperature lasing of a single nanowire containing 50 quantum dots by properly designing the nanowire cavity and tailoring the emission energy of each dot to enhance the optical gain. Our demonstration paves the way toward ultrasmall lasers with extremely low power consumption for integrated photonic systems.

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Circularly polarized light emission of quantum dots at the band edge of three-dimensional chiral photonic crystals

Takahashi S., Tajiri T., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

CLEO QELS Fundamental Science CLEO QELS 2015  2015.05

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate highly circularly polarized emission from quantum dots in semiconductor chiral photonic crystals. The emission is influenced by the difference in density of states between the orthogonal circular polarizations at the polarization band edge. © OSA 2015.

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Room-temperature lasing in GaAs nanowires embedding multi-stacked InGaAs/GaAs quantum dots

Tatebayashi J., Kako S., Ho J., Ota Y., Iwamoto S., Arakawa Y.

CLEO Science and Innovations CLEO Si 2015  2015.05

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report the demonstration of room-temperature lasing in a single GaAs nanowire embedding 50-stacked In<inf>0.22</inf>Ga<inf>0.78</inf>As/GaAs quantum dots at a lasing emission energy of 1.37 eV with a threshold pump pulse fluence of 138 μJ/cm². ©2015 Optical Society of America.

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Single emitter vacuum Rabi splitting measured through direct free space spontaneous emission

Ota Y., Ohta R., Kumagai N., Iwamoto S., Arakawa Y.

CLEO QELS Fundamental Science CLEO QELS 2015  2015.05

Research paper (international conference proceedings), Joint Work, Accepted

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We measured the vacuum Rabi splitting of a single quantum emitter through direct free space spontaneous emission. This lays the groundwork for accessing diverse cavity quantum electrodynamics phenomena manifesting themselves only in the spontaneous emission. © OSA 2015.

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Vacuum Rabi spectra of a single quantum emitter

Ota Y., Ohta R., Kumagai N., Iwamoto S., Arakawa Y.

Physical Review Letters 114 ( 14 )  2015.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00319007

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We report the observation of the vacuum Rabi splitting of a single quantum emitter by measuring its direct spontaneous emission into free space. We use a semiconductor quantum dot inside a photonic crystal nanocavity, in conjunction with an appropriate cavity design and filtering with a polarizer and an aperture, enabling the extraction of the inherently weak emitter's signal. The emitter's vacuum Rabi spectra exhibit clear differences from those measured by detecting the cavity photon leakage. Moreover, we observe an asymmetric vacuum Rabi spectrum induced by interference between the emitter and cavity detection channels. Our observations lay the groundwork for accessing various cavity quantum electrodynamics phenomena that manifest themselves only in the emitter's direct spontaneous emission.

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Asymmetric out-of-plane power distribution in a two-dimensional photonic crystal nanocavity

Ota Y., Iwamoto S., Arakawa Y.

Optics Letters 40 ( 14 ) 3372 - 3375 2015

Research paper (scientific journal), Joint Work, Accepted,  ISSN  01469592

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Conventional air-bridge two-dimensional photonic crystal (2D-PhC) nanocavities emit light with an equal power distribution for upward and downward out-of-plane directions. Some applications, however, require concentration of the radiation in a preferred direction. In this Letter, we design a 2D-PhC nanocavity that radiates dominantly into one of the out-of-plane directions with a narrow far-field distribution. Our design is based on a conventional airbridge L3 photonic crystal nanocavity. The asymmetric out-of-plane power distribution is achieved solely by adding periodic shallow holes on the slab surface, which also function as a second-order grating for the directional beaming.

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Cavity QED in quantum dot-photonic crystal nanocavity coupled systems

Arakawa Y., Iwamoto S., Ota Y., Kamide K.

Optics Infobase Conference Papers  2014.10

Research paper (international conference proceedings), Joint Work, Accepted

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Highly uniform, multi-stacked InGaAs/GaAs quantum dots embedded in a GaAs nanowire

Tatebayashi J., Ota Y., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Applied Physics Letters 105 ( 10 )  2014.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate a highly uniform, dense stack of In<inf>0.22</inf>Ga<inf>0.78</inf>As/GaAs quantum dot (QD) structures in a single GaAs nanowire (NW). The size (and hence emission energy) of individual QD is tuned by careful control of the growth conditions based on a diffusion model of morphological evolution of NWs and optical characterization. By carefully tailoring the emission energies of individual QD, dotto-dot inhomogeneous broadening of QD stacks in a single NW can be as narrow as 9.3 meV. This method provides huge advantages over traditional QD stack using a strain-induced Stranski-Krastanow growth scheme. We show that it is possible to fabricate up to 200 uniform QDs in single GaAs NWs using this growth technique without degradation of the photoluminescence intensity.

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Circular dichroism in a three-dimensional semiconductor chiral photonic crystal

Takahashi S., Tajiri T., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Applied Physics Letters 105 ( 5 )  2014.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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Circular dichroism covering the telecommunication band is experimentally demonstrated in a semiconductor-based three-dimensional chiral photonic crystal (PhC). We design a rotationally stacked woodpile PhC structure where neighboring layers are rotated by 60° and three layers construct a single helical unit. The mirror-asymmetric PhC made from GaAs with sub-micron periodicity is fabricated by a micro-manipulation technique. Due to the large contrast of refractive indices between GaAs and air, the experimentally obtained circular dichroism extends over a wide wavelength range, with the transmittance of right-handed circularly polarized incident light being 85% and that of left-handed light being 15% at a wavelength of 1.3 μ m. The obtained results show good agreement with numerical simulations. © 2014 AIP Publishing LLC.

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Measuring the second-order coherence of a nanolaser by intracavity frequency doubling

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Physical Review A Atomic Molecular and Optical Physics 89 ( 2 )  2014.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  10502947

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We measured the second-order coherence at zero time delay, g(2)(0), of a high-Q photonic crystal nanocavity quantum dot laser below and above the lasing threshold, via detecting visible emission originated from the second harmonic generation (SHG) occurring within the laser cavity. The efficiency of the nonlinear frequency conversion process, defined by SHG intensity divided by the square of laser output intensity, is shown to be proportional to g(2)(0), and hence is used for the measurement. The obtained g(2)(0) values show good agreement with those measured by a Hanbury Brown-Twiss interferometer equipped with ultrafast superconducting single-photon detectors. © 2014 American Physical Society.

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Cavity quantum electrodynamics in quantum dot-photonic crystal nanocavity coupled system with large G/k

Iwamoto S., Ota Y., Takagi H., Takamiya D., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2014-January 2014

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report experimental progresses in cavity quantum electrodynamics using H1 and H0-type photonic crystal nanoacvities embedding single quantum dots. Strong coupling and enhanced optical Stark effect in these systems with large g/kwill be discussed.

Measurement of the second order coherence of a nanolaser through its intra-cavity second harmonic generation

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers  2014

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We measured the second order coherence of a photonic crystal nanolaser through measuring frequency doubling occurring within the laser nanocavity. This method enables investigation of the intensity noise properties even far below the lasing threshold. © 2014 OSA.

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Measurement of the second order coherence of a nanolaser through its intra-cavity second harmonic generation

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Conference on Lasers and Electro Optics Europe Technical Digest 2014-January 2014

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We measured the second order coherence of a photonic crystal nanolaser through measuring frequency doubling occurring within the laser nanocavity. This method enables investigation of the intensity noise properties even far below the lasing threshold.

Cavity quantum electrodynamics in quantum dot-photonic crystal nanocavity coupled system with large g/KΚ

Iwamoto S., Ota Y., Takagi H., Takamiya D., Arakawa Y.

Optics Infobase Conference Papers  2014

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report experimental progresses in cavity quantum electrodynamics using H1 and H0-type photonic crystal nanoacvities embedding single quantum dots. Strong coupling and enhanced optical Stark effect in these systems with large g/KΚ will be discussed. © 2014 OSA.

Self-frequency summing in quantum dot photonic crystal nanocavity lasers

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Applied Physics Letters 103 ( 24 )  2013.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate self-frequency summing in photonic crystal nanocavity lasers with quantum dot gain. Two dipole modes and a hexapole mode, supported in the cavity, simultaneously showed lasing oscillation in the near infrared wavelength region under optical carrier injection. Meanwhile, within the same laser cavity, the internally generated three laser fields are up-converted to exhibit sharp visible emission lines via intra-cavity nonlinear frequency summing (and doubling) processes. This self-frequency summing process in active nanocavities will pave the way for developing nanoscale nonlinear optical light sources. © 2013 AIP Publishing LLC.

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Giant optical rotation in a three-dimensional semiconductor chiral photonic crystal

Takahashi S., Tandaechanurat A., Igusa R., Ota Y., Tatebayashi J., Iwamoto S., Arakawa Y.

Optics Express 21 ( 24 ) 29905 - 29913 2013.12

Research paper (scientific journal), Joint Work, Accepted

　View Summary

Optical rotation is experimentally demonstrated in a semiconductor-based three-dimensional chiral photonic crystal (PhC) at a telecommunication wavelength. We design a rotationally-stacked woodpile PhC structure, where neighboring layers are rotated by 45° and four layers construct a single helical unit. The mirror-asymmetric PhC made from GaAs with sub-micron periodicity is fabricated by a micro-manipulation technique. The linearly polarized light incident on the structure undergoes optical rotation during transmission. The obtained results show good agreement with numerical simulations. The measurement demonstrates the largest optical rotation angle as large as ~ 23° at 1.3 μm wavelength for a single helical unit. © 2013 Optical Society of America.

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Enhancement of valence band mixing in individual InAs/GaAs quantum dots by rapid thermal annealing

Harbord E., Ota Y., Igarashi Y., Shirane M., Kumagai N., Ohkouchi S., Iwamoto S., Yorozu S., Arakawa Y.

Japanese Journal of Applied Physics 52 ( 12 )  2013.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

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We measure polarization resolved photoluminescence from excitonic complexes in tens of single InAs/GaAs quantum dots (QDs) over a wide range of energies in two samples: one as-grown, the other subjected to rapid thermal annealing (RTA). Using the linear polarization of the X⁺ emission as a probe of the valence band mixing (VBM), we find that RTA enhances QD VBM, attributed to the increase in QD height. We complement our measurements with 8-band k · p calculations, which suggest the increase in height on annealing is responsible for this enhancement. © 2013 The Japan Society of Applied Physics.

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Multi-color visible light generation by self-frequency doubling in photonic crystal nanocavity quantum dot lasers

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

CLEO Science and Innovations CLEO Si 2013  2013.11

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report multi-color visible light generation from photonic crystal nanocavity lasers exhibiting broadband quantum dot gain in the near infrared. The visible emission is produced though self-frequency doubling, which efficiently occurs within the high Q nanocavities. © OSA 2013.

Growth of high-quality InAs quantum dots embedded in GaAs nanowire structures on Si substrates

Kwoen J., Watanabe K., Ota Y., Iwamoto S., Arakawa Y.

Physica Status Solidi C Current Topics in Solid State Physics 10 ( 11 ) 1496 - 1499 2013.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18626351

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We present the growth of InAs quantum dots (QD) embedded in GaAs nanowires (NW) on silicon and demonstrate clear single photon emission. Sharp excitonic emission (linewidth of 162 μeV) and the generation of single photons (g⁽²⁾(0) = 0.18) was observed by low temperature photoluminescence measurements, suggesting a high optical quality which can be attributed to the high crystal quality of the QD structure. It is believed that the crystal quality is high due to the Stranski-Krastanov (S-K) mode of the growth. This structure may open new ways for the integration of such photon emitters into future 'on-silicon' quantum optical circuits. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Large vacuum Rabi splitting in an H0 photonic crystal nanocavity-quantum dot system

Takamiya D., Ota Y., Ohta R., Takagi H., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Pacific Rim Conference on Lasers and Electro Optics CLEO Technical Digest  2013.10

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate a large vacuum Rabi splitting in an H0 photonic crystal nanocavity-quantum dot system. The nanocavity with an ultra-small mode volume enabled us to observe the largest splitting ever reported using single InAsquantum dots. © 2013 IEEE.

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Nonlinear photonics in single quantum dot-photonic crystal nanocavity couples systems

Iwamoto S., Ota Y., Takagi H., Kumagai N., Arakawa Y.

Pacific Rim Conference on Lasers and Electro Optics CLEO Technical Digest  2013.10

Research paper (international conference proceedings), Joint Work, Accepted

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We will present our recent advances on single quantum dot-photonic crystal nanocavity coupled systems. Cavity enhanced two-photon emission and large optical Stark effect with extremely low control power in these systems will be mainly discussed. © 2013 IEEE.

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Self-frequency summing in photonic crystal nanocavity quantum dot lasers

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Pacific Rim Conference on Lasers and Electro Optics CLEO Technical Digest  2013.10

Research paper (international conference proceedings), Joint Work, Accepted

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Self-frequency summing processes in photonic crystal nanocavity quantum dot lasers are observed. High quality factors and small mode volumes of the nanocavities facilitate efficient nonlinear frequency summing processes, generating a variety of visible emission lines. © 2013 IEEE.

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Nanocavity-based self-frequency conversion laser

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

Optics Express 21 ( 17 ) 19778 - 19789 2013.08

Research paper (scientific journal), Joint Work, Accepted

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Self-frequency conversion (SFC), where both laser oscillation and nonlinear frequency conversion occurs in the same laser crystal, has been used to efficiently extend the operational wavelength of lasers. Downsizing of the cavity mode volume (V) and increasing the quality factor (Q) could lead to a more efficient conversion process, mediated by enhanced n-th order nonlinearities that generally scale as (Q/V)ⁿ. Here, we demonstrate nanocavity-based SFC by utilizing photonic crystal nanocavity quantum dot lasers. The high Q and small V supported in semiconductorbased nanocavities facilitate efficient SFC to generate visible light, even with only a few photons present in the laser cavity. The combined broadband quantum dot gain and small device footprint enables the monolithic integration of 26 different-color nanolasers (spanning 493-627 nm) within a micro-scale region. These nanolasers provide a new platform for studying few-photon nonlinear optics, and for realizing full-color lasers on a single semiconductor chip. ©2013 Optical Society of America.

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Formation and optical properties of multi-stack InGaAs quantum dots embedded in GaAs nanowires by selective metalorganic chemical vapor deposition

Tatebayashi J., Ota Y., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Journal of Crystal Growth 370   299 - 302 2013.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00220248

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We report formation and optical properties of site-controlled, multi-stack InGaAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition. InGaAs/GaAs QDs are realized in GaAs NWs grown on patterned GaAs(111)B substrates in the form of InGaAs/GaAs heterostructures and identi.ed by structural analyses and photoluminescence characterization. Optical characterization at 10 K corroborates formation of high-quality, multi-stack InGaAs/GaAs QD-in-NWs up to 50-stack without degradation of PL intensities. In addition, light emission at room temperature from multi-stack InGaAs/GaAs QDs embedded in GaAs NWs is realized. These results would enable the realization of high-performance IBSCs based on site-controlled QD-in-NWs utilizing existing, well-established NW growth technologies on a GaAs platform. © 2012 Elsevier B.V. All rights reserved.

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Electro-mechanical Q factor control of photonic crystal nanobeam cavity

Ohta R., Ota Y., Takagi H., Kumagai N., Tanabe K., Ishida S., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 52 ( 4 PART 2 )  2013.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

　View Summary

We design and demonstrate a photonic crystal nanobeam cavity with a Q factor controllable by a micro-electro-mechanical system (MEMS). The cavity is evanescently coupled to an adjacent nanobeam waveguide, and its Q factor is controlled by electro-mechanically adjusting the gap distance between them. We experimentally demonstrate control of the Q factor from 2,250 to 2,750, by applying voltage from 0 to 11 V. © 2013 The Japan Society of Applied Physics.

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Multi-color visible light generation by self-frequency doubling in photonic crystal nanocavity quantum dot lasers

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

2013 Conference on Lasers and Electro Optics CLEO 2013  2013

Research paper (international conference proceedings), Joint Work, Accepted

　View Summary

We report multi-color visible light generation from photonic crystal nanocavity lasers exhibiting broadband quantum dot gain in the near infrared. The visible emission is produced though self-frequency doubling, which efficiently occurs within the high Q nanocavities. © 2013 The Optical Society.

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Formation of a single in(Ga)As/GaAs quantum dot embedded in a site-controlled GaAs nanowire by metalorganic chemical vapor deposition for application to single photon sources

Tatebayashi J., Ota Y., Karunathillake D., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Materials Research Society Symposium Proceedings 1439   115 - 119 2012.12

Research paper (international conference proceedings), Joint Work, Accepted,  ISSN  02729172

　View Summary

We report the formation and optical properties of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition for application to single photon sources. InAs/GaAs QD-in-NWs with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μe V are observed. Light emission from the single QD-in-NW shows photon antibunching which evidences single photon emission from high-quality QD-in-NWs. © 2012 Materials Research Society.

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High Q H1 photonic crystal nanocavities with efficient vertical emission

Takagi H., Ota Y., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Optics Express 20 ( 27 ) 28292 - 28300 2012.12

Research paper (scientific journal), Joint Work, Accepted

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We report on newly-designed H1-type photonic crystal (PhC) nanocavities that simultaneously exhibit high Q factors, small mode volumes, and high external coupling efficiencies (η) of light radiated above the PhC membrane. Dipole modes of the H1 PhC nanocavities, which are doubly-degenerate and orthogonally-polarized in theory, are investigated both by numerical calculations and experiments. Through modifying the sizes and positions of the air-holes near to the defect cavity, a Q factor of 62,000 is achieved, accompanied with an improved η of 0.38 (assuming an objective lens with a numerical aperture of 0.65). A further increase of η to more than 0.60 is observed at the expense of slight degradation of Q factor (down to 50,000). We further experimentally confirm the increase of both Q and η, using micro-photoluminescence measurements, and demonstrate high Q factors up to 25,000: the highest value ever reported for dipole modes in H1 PhC nanocavities. © 2012 Optical Society of America.

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Intra-cavity frequency doubling in photonic crystal nanocavity quantum dot lasers

Ota Y., Watanabe K., Iwamoto S., Arakawa Y.

2012 IEEE Photonics Conference IPC 2012    610 - 611 2012.12

Research paper (international conference proceedings), Joint Work, Accepted

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We report visible light generation via intra-cavity frequency doubling in photonic crystal nanocavity quantum dot lasers. A strong field enhancement in the nanocavity enables the efficient conversion process, even with only a few intra-cavity photons. © 2012 IEEE.

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Nanocavity-enhanced optical stark shift in a single quantum dot under extremely low excitation power

Takagi H., Ota Y., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers  2012.12

Research paper (international conference proceedings), Joint Work, Accepted

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An enhanced optical Stark shift in a single quantum dot is demonstrated using a newlydesigned H1-type photonic crystal nanocavity. A 70μeV shift is observed at 450nW; 110-times lower than excitation powers reported in the literature. © OSA 2012.

Optical properties of site-controlled InGaAs quantum dots embedded in GaAs nanowires by selective metalorganic chemical vapor deposition

Tatebayash J., Ota Y., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 51 ( 11 PART2 )  2012.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

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We report the optical properties of site-controlled InGaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) grown by selective metalorganic chemical vapor deposition (MOCVD). InGaAs/GaAs QD-in-NWs with various QD heights and In compositions are realized on patterned GaAs(111)B substrates in the form of InGaAs/GaAs heterostructures, and identified by structural analyses using scanning transmission electron microscopy, photoluminescence (PL) characterization, and numerical analyses of the band structure using a single-band effective mass approximation. Room temperature (RT) light emission is observed at 1.03 μm from InGaAs/GaAs QD-in-NWs which is indicative of the formation of high-quality InGaAs QD-in-NWs. Sharp emission peaks from exciton and biexciton of single In(Ga)As QD-in-NWs are observed by using μ-PL characterization at 10 K. © 2012 The Japan Society of Applied Physics.

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Cavity quantum electrodynamics and lasing oscillation in single quantum dot-photonic crystal nanocavity coupled systems

Arakawa Y., Iwamoto S., Nomura M., Tandaechanurat A., Ota Y.

IEEE Journal on Selected Topics in Quantum Electronics 18 ( 6 ) 1818 - 1829 2012.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  1077260X

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Our recent advances in solid-state cavity quantum electrodynamics and lasing oscillation in single quantum dot (QD)-photonic crystal (PhC) nanocavity coupled systems are discussed. These include the fabrication of high-quality 2-D PhC nanocavities $(Q 50 000)$, which enabled the generation of spontaneous two-photon emission from a single QD, and the realization of lasing oscillation with single QD gain in the strong coupling regime. Moreover, we have fabricated high-quality 3-D PhC nanocavities $(Q \sim 38 500)$, which have facilitated the realization of both lasing oscillation and the Purcell effect. Lasing oscillation in a 1-D PhC nanobeam cavity with gain produced by a few QDs has also been demonstrated. © 1995-2012 IEEE.

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High guided mode-cavity mode coupling for an efficient extraction of spontaneous emission of a single quantum dot embedded in a photonic crystal nanobeam cavity

Enderlin A., Ota Y., Ohta R., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Physical Review B Condensed Matter and Materials Physics 86 ( 7 )  2012.08

Research paper (scientific journal), Joint Work, Accepted,  ISSN  10980121

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We demonstrate efficient extraction of a single InAs quantum dot spontaneous emission through an air-suspended waveguide to which a photonic crystal nanobeam cavity is coupled. First, the quantum dot emission into the cavity mode is enhanced due to a high Purcell effect arising from a large quality factor and a small mode volume of the cavity mode. Second, the cavity photons can be efficiently transferred to the guided mode by optimizing the design of a structure that exhibits a high coupling rate between the two modes. This configuration has lead to the observation of a high extraction efficiency (79%) of the quantum dot emission through the waveguide. Moreover, as a result of the high extraction efficiency to the guided mode, the unwanted microphotoluminescence coupling to the free space modes and detected from the top surface of the sample is strongly suppressed. Indeed, we show that it exhibits a negative peak as a function of the detuning between the cavity mode energy and the quantum dot transition energy. © 2012 American Physical Society.

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Site-controlled formation of InAs/GaAs quantum-dot-in-nanowires for single photon emitters

Tatebayashi J., Ota Y., Ishida S., Nishioka M., Iwamoto S., Arakawa Y.

Applied Physics Letters 100 ( 26 )  2012.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We report the demonstration of site-controlled InAs/GaAs quantum dots (QDs) embedded in GaAs nanowires (NWs) by selective metalorganic chemical vapor deposition. InAs/GaAs quantum-dot-in-nanowires (QD-in-NWs) with various InAs thicknesses are realized on patterned GaAs(111)B substrates in the form of InAs/GaAs heterostructures and identified by structural analyses using scanning transmission electron microscopy and photoluminescence characterization. Sharp excitonic emission peaks at 10 K from single QD-in-NWs with the narrowest exciton linewidth of 87 μeV are observed. Light emission from the single QD-in-NW shows photon antibunching, along with biexciton-exciton cascaded emission process, which evidences single photon emission from high-quality QD-in-NWs. © 2012 American Institute of Physics.

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Wavelength tunable quantum dot single-photon source with a side gate

Nakaoka T., Tamura Y., Miyazawa T., Watanabe K., Ota Y., Iwamoto S., Arakawa Y.

Japanese Journal of Applied Physics 51 ( 2 PART 2 )  2012.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00214922

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We demonstrate photon antibunching from a wavelength controlled quantum dot single-photon source with a side gate. The photoluminescence peaks from the quantum dots embedded in the side-gate structure are clearly identified as a neutral exciton and a neutral biexciton by the studies of excitation-power dependence, polarization dependence, and photon correlation. The neutral exciton energy is controlled by the side gate via the quantum confined Stark effect. Measurement of the second-order autocorrelation function indicates g ⁽²⁾(0) = 0.07 at 0 V, 0.14 at 0.8 V, and 0.24 at 0.9 V. The results show g ⁽²⁾(0) are below the 0.5 limit necessary for classification as a single photon source even under applied gate voltage. We also show a biexciton-exciton cascade which can be used to create entangled photon pairs. © 2012 The Japan Society of Applied Physics.

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Nanocavity-enhanced optical Stark shift in a single quantum dot under extremely low excitation power

Takagi H., Ota Y., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

2012 Conference on Lasers and Electro Optics CLEO 2012  2012

Research paper (international conference proceedings), Joint Work, Accepted

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An enhanced optical Stark shift in a single quantum dot is demonstrated using a newly-designed H1-type photonic crystal nanocavity. A 70μeV shift is observed at 450nW; 110-times lower than excitation powers reported in the literature. © 2012 OSA.

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Spontaneous two-photon emission from a single quantum dot

Ota Y., Iwamoto S., Kumagai N., Arakawa Y.

Physical Review Letters 107 ( 23 )  2011.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00319007

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Spontaneous two-photon emission from a solid-state single quantum emitter is observed. We investigated photoluminescence from the neutral biexciton in a single semiconductor quantum dot coupled with a high Q photonic crystal nanocavity. When the cavity is resonant to the half energy of the biexciton, the strong vacuum field in the cavity inspires the biexciton to simultaneously emit two photons into the mode, resulting in clear emission enhancement of the mode. Meanwhile, the suppression of other single photon emission from the biexciton was observed, as the two-photon emission process becomes faster than the others at the resonance. © 2011 American Physical Society.

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Competing influence of an in-plane electric field on the Stark shifts in a semiconductor quantum dot

Nakaoka T., Tamura Y., Saito T., Miyazawa T., Watanabe K., Ota Y., Iwamoto S., Arakawa Y.

Applied Physics Letters 99 ( 18 )  2011.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We report on the fabrication of a side-gate structure which enables a purely lateral electric field to be applied onto a self-assembled quantum dot. The lateral field produces an unconventional M'-shaped exciton energy shift-a blueshift followed by a redshift. The unconventional energy shift is reproduced by calculation. The calculation shows that only the positively charged exciton shows the unconventional shift. The origin is attributed to the field-induced hole-concentration in the bottom-corner of the dot, which strongly enhances the repulsive direct Coulomb interaction and reduces the exciton binding energy. © 2011 American Institute of Physics.

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New method to isolate and distribute photoluminescence emissions from InAs quantum dots over a wide-wavelength range

Ohkouchi S., Kumagai N., Shirane M., Igarashi Y., Nomura M., Ota Y., Yorozu S., Iwamoto S., Arakawa Y.

Journal of Crystal Growth 323 ( 1 ) 250 - 253 2011.05

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00220248

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We propose a new method to isolate and distribute the photoluminescence emission wavelengths of InAs quantum dots (QDs) over a wide-wavelength range by the growth of the partial GaAs capping layer at low temperature and annealing processes. When the partial capping layer was grown at 485°C, the emission wavelengths of the QDs were distributed within a small range around the mean wavelength. On the other hand, when the partial capping layer was grown at a lower temperature of 423°C, the emission wavelengths of the individual QDs were isolated and distributed over a wide range. Thus fabricated QDs are effective for the QD based devices such as single photon sources. © 2010 Elsevier B.V. All rights reserved.

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Strong coupling between a photonic crystal nanobeam cavity and a single quantum dot

Ohta R., Ota Y., Nomura M., Kumagai N., Ishida S., Iwamoto S., Arakawa Y.

Applied Physics Letters 98 ( 17 )  2011.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrated the strong coupling between a one-dimensional photonic crystal nanobeam cavity and a single quantum dot (QD). Thanks to a high quality factor (∼25 000) with small mode volume [0.38× (n/λ) ³] of the nanobeam cavity, an anticrossing behavior with a vacuum Rabi splitting of 226 μeV was observed. The ratio of the QD-cavity coupling strength to the cavity decay rate, which is a figure of merit of quantum optical applications, is estimated to 2.1. This is the highest value among any QD-based cavity quantum electrodynamics systems reported so far. © 2011 American Institute of Physics.

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Effects of growth temperature of partial GaAs cap on InAs quantum dots in In-flush process for single dot spectroscopy

Kumagai N., Ohkouchi S., Shirane M., Igarashi Y., Nomura M., Ota Y., Yorozu S., Iwamoto S., Arakawa Y.

Physica Status Solidi C Current Topics in Solid State Physics 8 ( 2 ) 248 - 250 2011.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18626351

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We have investigated effects of growth temperature of partial GaAs cap (T<inf>cap</inf>) on InAs quantum dots (QDs) in indium-flush (In-flush) process with atomic force microscopy (AFM) and micro photoluminescence (μ-PL) measurements. T<inf>cap</inf> in In-flush process are varied from 385 °C to 485 °C as an experimental parameter. In order to investigate the effects of T<inf>cap</inf> on structural property of single InAs QD, shape of QD in initial capping process are characterized by AFM measurements in air at room temperature. While isotropic shape of QDs is kept in low T<inf>cap</inf> conditions below about 440 °C, in-plane anisotropy of initial shape of QDs are increased with increasing of T<inf>cap</inf> due to elongation to the [1̄0] direction. μ-PL measurements are performed at 7K for the investigation of the effects of T<inf>cap</inf> on optical property in single InAs QDs. In low T<inf>cap</inf> conditions from 410 °C to 435 °C, distinct emissions from excitonic states in single QDs are observed. In the same T<inf>cap</inf> range, the AFM result shows that isotropic shape of QDs is kept. On the other hand, in high T<inf>cap</inf> conditions above about 440 °C, indefinite peaks and broad emissions appear remarkably. Excitonic emissions which are observed in low T<inf>cap</inf> range are hardly observed in this high T<inf>cap</inf> range. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Zero-cell photonic crystal nanocavity laser with quantum dot gain

Nomura M., Ota Y., Kumagai N., Iwamoto S., Arakawa Y.

Applied Physics Letters 97 ( 19 )  2010.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate laser oscillation in a hexagonal-lattice photonic crystal nanocavity using an InGaAs quantum dot gain material by optical pumping at 5 K. The cavity comprises a defect created by shifting several air holes in a two-dimensional photonic crystal slab structure without removing any air holes to achieve both small mode volume and a high cavity quality factor. The measured cavity quality factors and estimated mode volume for the nanocavity are ∼33 000 and 0.004 μm³ [0.23 (λ<inf>0</inf> /n)³]. The laser threshold is compared between the zero-cell and L3-type nanocavity lasers, and the zero-cell nanolasers are found to have lower thresholds of about one-third of the L3-type nanolasers. This result suggests that a higher Purcell factor of the zero-cell nanolaser is reflected as a lower laser threshold. © 2010 American Institute of Physics.

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Charged and neutral biexcitonexciton cascade in a single quantum dot within a photonic bandgap

Shirane M., Igarashi Y., Ota Y., Nomura M., Kumagai N., Ohkouchi S., Kirihara A., Ishida S., Iwamoto S., Yorozu S., Arakawa Y.

Physica E Low Dimensional Systems and Nanostructures 42 ( 10 ) 2563 - 2566 2010.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13869477

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We investigate the recombination dynamics of positively charged and neutral biexcitons and excitons in a single InAs/GaAs quantum dot (QD) within a two-dimensional (2D) photonic bandgap (PBG). The 2D PBG makes the exciton lifetime four times longer and enhances photon-extraction efficiency compared to those without the PBG. Photon cross-correlation measurements demonstrate the cascade emissions of both charged and neutral biexcitonsexcitons from the same QD. In the charged case, a hole in the p-shell relaxes into the s-shell between the cascade, and the corresponding transition is confirmed based on the spin configuration. The long exciton lifetime with the PBG helps us to reveal the spin dynamics that did not clearly appear in intrinsic QDs. © 2009 Elsevier B.V. All rights reserved.

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Observation of unique photon statistics of single artificial atom laser

Nomura M., Kumagai N., Iwamoto S., Ota Y., Arakawa Y.

Physica E Low Dimensional Systems and Nanostructures 42 ( 10 ) 2489 - 2492 2010.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13869477

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We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain and its unique photon statistics. Gain tuning measurements and photon correlation measurements indicated that a single quantum dot plays a substantial role in the laser oscillation. Photon correlation measurements showed a distinct transition from anti-bunching to Poissonian via photon bunching around the threshold with the increase of the excitation power. Numerical simulations, including contributions of other light sources besides a single quantum dot, indicated that the photon bunching feature around the threshold can be enhanced by the interfusion of incoherent photons into the cavity mode. © 2009 Elsevier B.V. All rights reserved.

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Suppression of indefinite peaks in InAs/GaAs quantum dot spectrum by low temperature capping in the indium-flush method

Kumagai N., Ohkouchi S., Nakagawa S., Nomura M., Ota Y., Shirane M., Igarashi Y., Yorozu S., Iwamoto S., Arakawa Y.

Physica E Low Dimensional Systems and Nanostructures 42 ( 10 ) 2753 - 2756 2010.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  13869477

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We have investigated effects of growth temperature of thin GaAs capping layer in the initial stage of indium-flush process using atomic force microscopy and microscopic photoluminescence (μ-PL) methods. The shape of capped InAs quantum dot (QD) and its μ-PL properties are sensitive to the growth temperature of thin GaAs capping layer. In the case of the high temperature cap, the QD shape in initial capping stage is elongated along the [1 1 -0] direction, and μ-PL spectrum shows several peaks accompanied with indefinite peaks. On the other hand, the low temperature case, the QD shape is kept in isotropic and μ-PL spectrum shows distinctive emissions from excitonic states of the QD with suppressed indefinite peaks. These results indicate that the low temperature capping is effective to keep an isotropic shape of QD and suppress indefinite peaks. © 2009 Elsevier B.V. All rights reserved.

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Spin dynamics of excited trion states in a single InAs quantum dot

Igarashi Y., Shirane M., Ota Y., Nomura M., Kumagai N., Ohkouchi S., Kirihara A., Ishida S., Iwamoto S., Yorozu S., Arakawa Y.

Physical Review B Condensed Matter and Materials Physics 81 ( 24 )  2010.06

Research paper (scientific journal), Joint Work, Accepted,  ISSN  10980121

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We measure photon cross-correlation between two positively charged biexcitonic emission lines and a positively charged excitonic line for a single InAs/GaAs quantum dot (QD). Marked difference in the correlation function is observed, which originates from multiple spin configurations of intermediate states, i.e., excited positively charged exciton (trion) states. With the aid of a rate equation simulation, we evaluate the transition rate with p -shell hole-spin flip to be 0.8-1.0 GHz, which is almost comparable to the radiative decay rate of the ground charged exciton, presumably due to the spin scattering between carriers in a QD and a wetting layer and/or mixing of the excited trion states. In contrast, the relaxation rate with conserving p -shell hole-spin projection is estimated to be about one order of magnitude higher than that with hole-spin flip. © 2010 The American Physical Society.

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Laser oscillation in a strongly coupled single-quantum-dot-nanocavity system

Nomura M., Kumagai N., Iwamoto S., Ota Y., Arakawa Y.

Nature Physics 6 ( 4 ) 279 - 283 2010.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  17452473

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The strong coupling of photons and matter ¹ in semiconductor nanocavities has been a test bed for cavity quantum electrodynamics ^2,3 (QED). Vacuum Rabi oscillation ^4-8 -the coherent exchange of a single quantum between a single quantum dot (SQD) and an optical cavityand highly efficient cavity-QED lasers ^9-19 have both been reported. The coexistence of vacuum Rabi oscillation and laser oscillation seems to be contradictory, but it has recently been predicted theoretically that the strong-coupling effect could be sustained in laser oscillation ²⁰ . Here, we demonstrate the onset of lasing in the strong-coupling regime in an SQD-cavity system. A high-quality semiconductor optical nanocavity and strong SQD-field coupling enabled the onset of lasing while maintaining the fragile coherent exchange of quanta. © 2010 Macmillan Publishers Limited. All rights reserved.

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Neutralization of positively charged excitonic state in single InAs quantum dot by Si delta doping

Kumagai N., Ohkouchi S., Shirane M., Igarashi Y., Nomura M., Ota Y., Yorozu S., Iwamoto S., Arakawa Y.

Journal of Physics Conference Series 244 2010

Research paper (scientific journal), Joint Work, Accepted,  ISSN  17426588

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Positively charged excitonic state in single InAs quantum dot (QD) has been neutralized by Si delta doping and the optical properties of the fabricated samples are characterized by micro-photoluminescence measurements (μ-PL) at low temperature. An InAs QD sample having dominant emissions from positively charged excitonic states is prepared for a reference. By optimizing Si delta doping conditions, positively charged QDs are neutralized successfully and distinctive emissions from neutral exciton and biexciton from single QDs are achieved. For excessive doping condition, μ-PL spectra show optical degradation of lowering of peak intensity and broadening of peak width as doping concentration increases. © 2010 IOP Publishing Ltd.

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Investigation of the spectral triplet in strongly coupled quantum Dot-nanocavity system

Ota Y., Kumagai N., Ohkouchi S., Shirane M., Nomura M., Ishida S., Iwamoto S., Yorozu S., Arakawa Y.

Applied Physics Express 2 ( 12 )  2009.12

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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We experimentally investigated the excitation power dependence of a strongly coupled quantum dot (QD)-photonic crystal nanocavity system by photoluminescence measurements. At a low excitation power regime, we observed a vacuum Rabi doublet emission at the QD- cavity resonance condition. With increasing excitation power, in addition to the doublet, a third emission peak appeared. This observed spectral change is unexpected from conventional atomic cavity quantum electrodynamics. The observations can be attributed to featured pumping processes in the semiconductor QD-cavity system. © 2009 The Japan Society of Applied Physics.

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Photonic crystal nanocavity laser with single quantum dot gain

Nomura M., Kumagai N., Iwamoto S., Ota Y., Arakawa Y.

2009 Conference on Lasers and Electro Optics and 2009 Conference on Quantum Electronics and Laser Science Conference CLEO QELS 2009  2009.11

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate a photonic crystal nanocavity laser essentially driven by single quantum dot gain. A diluted quantum dot density (∼0.4/cavity) resulted in clear single quantum dot feature and distinct phase transition in photon correlation measurements. ©2009 IEEE.

Photonic crystal nanocavity laser with a single quantum dot gain

Nomura M., Kumagai N., Iwamoto S., Ota Y., Arakawa Y.

Optics Express 17 ( 18 ) 15975 - 15982 2009.08

Research paper (scientific journal), Joint Work, Accepted

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We demonstrate a photonic crystal nanocavity laser essentially driven by a self-assembled InAs/GaAs single quantum dot gain. The investigated nanocavities contain only 0.4 quantum dots on an average; an ultra-low density quantum dot sample (1.5 x 10⁸ cm^-2) is used so that a single quantum dot can be isolated from the surrounding quantum dots. Laser oscillation begins at a pump power of 42 nW under resonant condition, while the far-detuning conditions require ∼145 nW for lasing. This spectral detuning dependence of laser threshold indicates substantial contribution of the single quantum dot to the total gain. Moreover, photon correlation measurements show a distinct transition from anti-bunching to Poissonian via bunching with the increase of the excitation power, which is also an evidence of laser oscillation using the single quantum dot gain. © 2009 Optical Society of America.

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Vacuum Rabi splitting with a single quantum dot embedded in a H1 photonic crystal nanocavity

Ota Y., Shirane M., Nomura M., Kumagai N., Ishida S., Iwamoto S., Yorozu S., Arakawa Y.

Applied Physics Letters 94 ( 3 )  2009.02

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We report here the first observation of vacuum Rabi splitting in a single quantum dot (QD) embedded in a H1 photonic crystal nanocavity by photoluminescence measurement. The QD emission was tuned into a cavity mode by controlling the temperature. At the resonance condition, clear anticrossing with a Rabi splitting of ∼124 μeV was observed, where the cavity mode possesses the smallest mode volume V∼0.43 (λ/n)³ among strongly coupled QD-cavity systems reported to date. © 2009 American Institute of Physics.

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Photonic band-edge micro lasers with quantum dot gain

Nomura M., Iwamoto S., Tandaechanurat A., Ota Y., Kumagai N., Arakawa Y.

Optics Express 17 ( 2 ) 640 - 648 2009.01

Research paper (scientific journal), Joint Work, Accepted

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We demonstrate optically pumped continuous-wave photonic band-edge microlasers on a two-dimensional photonic crystal slab. Lasing was observed at a photonic band-edge, where the group velocity was significantly small near the K point of the band structure having a triangular lattice. Lasing was achieved by using a quantum dot gain material, which resulted in a significant decrease in the laser threshold, compared with photonic band-edge lasers using quantum well gain material. Extremely low laser thresholds of ∼80 nW at 6 K was achieved. Lasing was observed in a defect-free photonic crystal as small as ∼7 m square. © 2009 Optical Society of America.

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Photonic crystal nanocavity laser with single quantum dot gain

Nomura M., Kumagai N., Iwamoto S., Ota Y., Arakawa Y.

Optics Infobase Conference Papers  2009

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate a photonic crystal nanocavity laser essentially driven by single quantum dot gain. A diluted quantum dot density (~0.4/cavity) resulted in clear single quantum dot feature and distinct phase transition in photon correlation measurements. © 2009 OSA.

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Enhanced photon emission and absorption of single quantum dot in resonance with two modes in photonic crystal nanocavity

Ota Y., Nomura M., Kumagai N., Watanabe K., Ishida S., Iwamoto S., Arakawa Y.

Applied Physics Letters 93 ( 18 )  2008.11

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00036951

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We demonstrate simultaneous enhancement of photon emission and absorption of a single InGaAs self-assembled quantum dot (QD) in resonance with two modes in a photonic crystal nanocavity. The QD, whose ground and excited states are resonant, respectively, with the first and second lowest order cavity modes, is excited by cavity resonant excitation at the wavelength of the second order cavity mode and shows 180 times greater photon emission from the ground state than a bare QD. This large enhancement is attributed to a combination of Purcell effect, efficient photon extraction, and cavity resonant absorption enhancement. © 2008 American Institute of Physics.

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Achievement of ultra-low threshold excitation power (8 nW) in a nearly-single quantum dot nanocavity laser

Nomura M., Ota Y., Kumagai N., Iwamoto S., Arakawa Y.

2008 Conference on Quantum Electronics and Laser Science Conference on Lasers and Electro Optics CLEO QELS  2008.09

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate photonic crystal nanocavity laser with nearly-single quantum dot gain. Continuous-wave lasing was achieved at photocarrier generation rate of 5 × 10⁹/s, corresponding to several carrier injection into nearly-single quantum dot. © 2008 IEEE.

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Efficient excitation and emission of single quantum dot by simultaneous coupling to two different photonic crystal nanocavity modes

Ota Y., Nomura M., Kumagai N., Watanabe K., Ishida S., Iwamoto S., Shirane M., Kono S., Yorozu S., Arakawa Y.

2008 Conference on Quantum Electronics and Laser Science Conference on Lasers and Electro Optics CLEO QELS  2008.09

Research paper (international conference proceedings), Joint Work, Accepted

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We utilized simultaneous coupling of higher and ground states of a single QD with two different resonant modes of a PhC nanocavity for efficient excitation and emission. Enhanced emission with strongly suppressed background was demonstrated. © 2008 IEEE.

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Large vacuum rabi splitting in single self-assembled quantum dot-nanocavity system

Nomura M., Ota Y., Kumagai N., Iwamoto S., Arakawa Y.

Applied Physics Express 1 ( 7 ) 0721021 - 0721023 2008.07

Research paper (scientific journal), Joint Work, Accepted,  ISSN  18820778

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We report on the observation of the strong-coupling regime in a single InGaAs self-assembled quantum dot (QD) and photonic crystal nanocavity system. There was a strong Interaction between the QD exciton and dlscretlzed photon mode and the strong coupling was manifest in photoluminescence data, which displayed a distinct anti-crossing in temperature tuning measurements. A vacuum Rabi splitting of 180μeV was observed, which was larger than the values given in previous studies with clear exciton polariton modes. In addition, the exciton-photon coupling strength amounted to about 90μeV. A distinct energy mixing, which resulted from the reversible photon emission process of a QD, was also observed when the system formed a QD exciton polariton state. © 2008 The Japan Society of Applied Physics.

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Refraction and diffraction by a metal-dielectric multilayered structure

Kameda S., Ohta Y., Kikutal H.

Journal of the Optical Society of America A Optics and Image Science and Vision 25 ( 4 ) 903 - 910 2008.04

Research paper (scientific journal), Joint Work, Accepted,  ISSN  10847529

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An optical refraction prism consisting of metal and dielectric, subwavelength, periodic multilayered thin films has been proposed. The multilayered structure of metal and dielectric thin films has a cylindrical dispersion surface for TM polarized light. The light behaviors are very different from those of conventional glass prisms and photonic crystal superprisms. Refraction and diffraction of the light wave for the metal-dielectric multilayered prism has been investigated by numerical simulations and graphical representation based on the dispersion surface. A prism with 0.2 μm period had an angular dispersion of 0.20̊/nm for ̃0.8 μm wavelength light. The finite thick metal-dielectric multilayered structure acted as a slab waveguide. © 2008 Optical Society of America.

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Achievement of ultra-low threshold excitation power (8 nW) in a nearly-single quantum dot nanocavity laser

Nomura M., Ota Y., Kumagai N., Iwamoto S., Arakawa Y.

Optics Infobase Conference Papers  2008

Research paper (international conference proceedings), Joint Work, Accepted

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We demonstrate photonic crystal nanocavity laser with nearly-single quantum dot gain. Continuous-wave lasing was achieved at photocarrier generation rate of 5 x 109/s, corresponding to several carrier injection into nearly-single quantum dot. © 2008 OSA / CLEO/QELS 2008.

Efficient excitation and emission of single quantum dot by simultaneous coupling to two different photonic crystal nanocavity modes

Ota Y., Nomura M., Kumagai N., Watanabe K., Ishida S., Iwamoto S., Shirane M., Kono S., Yorozu S., Arakawa Y.

Optics Infobase Conference Papers  2008

Research paper (international conference proceedings), Joint Work, Accepted

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We utilized simultaneous coupling of higher and ground states of a single QD with two different resonant modes of a PhC nanocavity for efficient excitation and emission. Enhanced emission with strongly suppressed background was demonstrated. © 2008 OSA/CLEO/QELS 2008.

Fabrication and characterization of photonic crystal nanocavity with degenerated cavity modes for generating entangled photon pairs using quantum dots

Ota Y., Nomura M., Kumagai N., Watanabe K., Ishida S., Iwamoto S., Shirane M., Kono S., Yorozu S., Arakawa Y.

Pacific Rim Conference on Lasers and Electro Optics CLEO Technical Digest  2007.12

Research paper (international conference proceedings), Joint Work, Accepted

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We successfully fabricated photonic crystal nanocavities for generating entangled photon pairs using single quantum dots. The fabricated cavities have a minimum splitting between two orthogonal dipóle modes of ∼250 μeV and measured cavity Qs of ∼2,000. A maximum fidelity of 0.95 for entangled photon pairs is expected with this cavity.

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Fabrication of photonic crystal nanocavity for generating entangled photon pairs using quantum dots

Ota Y., Nomura M., Kumagai N., Watanabe K., Ishida S., Iwamoto S., Shirane M., Kono S., Yorozu S., Arakawa Y.

2007 International Nano Optelectronics Workshop Inow    226 - 227 2007.12

Research paper (international conference proceedings), Joint Work, Accepted

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We fabricated photonic crystal nanocavities which have two orthogonal dipole modes with a minimum splitting of ∼250 μeV and measured cavity Qs of -2,000. Those cavities are applicable for generating entangled photon pairs using quantum dots. © 2007 IEEE.

• Access to Document (DOI)

Fabrication and characterization of photonic crystal nanocavity with degenerated cavity modes for generating entangled photon pairs using quantum dots

Ota Y., Nomura M., Kumagai N., Watanabe K., Ishida S., Iwamoto S., Shirane M., Kono S., Yorozu S., Arakawa Y.

Optics Infobase Conference Papers  2007

Research paper (international conference proceedings), Joint Work, Accepted

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We successfully fabricated photonic crystal nanocavities for generating entangled photon pairs using single quantum dots. The fabricated cavities have a minimum splitting between two orthogonal dipole modes of-250 ieV and measured cavity Qs of-2,000. A maximum fidelity of 0.95 for entangled photon pairs is expected with this cavity. © CLEO Pacific Rim 2007.