Papers - Ota, Yasutomo

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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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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

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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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