Papers - Ota, Yasutomo

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.

• Access to Document (DOI)

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.