Papers - Ota, Yasutomo

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 (Advanced Optical Materials)  12 ( 2 )  2024.01

Joint Work

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

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

Optics Express 32 (4), 6382-6390 (Optics Express)  32 ( 4 ) 6382 - 6390 2024

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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 ng = 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 ng = 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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Telecom‐Band Quantum Dots Compatible with Silicon Photonics for Photonic Quantum Applications

R Katsumi, Y Ota, M Benyoucef

Advanced Quantum Technologies, 2300423 (Wiley)   2024

Joint Work,  ISSN  2511-9044

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Abstract

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

Katsumi R., Ota Y., Benyoucef M.

Advanced Quantum Technologies (Advanced Quantum Technologies)   2024

Joint Work

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

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

 2024

Joint Work

Micro-transfer-printed membrane lasers on Si platform

Y Maeda, T Aihara, T Fujii, T Hiraki, K Takeda, T Tsuchizawa, H Sugiyama, ...

Novel In-Plane Semiconductor Lasers XXIII 12905, 92-95  2024

Joint Work

Micro-transfer-printed InP-based membrane photonic devices on thin-film lithium niobate platform

Y Maeda, H Nishi, NP Diamantopoulos, T Fujii, T Aihara, S Yamaoka, ...

Journal of Lightwave Technology (Journal of Lightwave Technology)   2024

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

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

Optics Express 32 (3), 4295-4304 (Optics Express)  32 ( 3 ) 4295 - 4304 2024

Joint Work

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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

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

Advanced Optical Materials 12 (2), 2301320  2024

Joint Work

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Valley photonic crystal waveguides fabricated with CMOS-compatible process

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

Japanese journal of applied physics 62 (8), 082002 (Japanese Journal of Applied Physics)  62 ( 8 )  2023

Joint Work,  ISSN  00214922

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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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Ultrathin magneto-optical devices based on all-dielectric metasurfaces

Y Ota, S Gao, S Iwamoto

International Conference on Metamaterials, Photonic Crystals and Plasmonics … (International Conference on Metamaterials, Photonic Crystals and Plasmonics)     438 - 439 2023

Joint Work

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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

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

International Conference on Metamaterials, Photonic Crystals and Plasmonics … (International Conference on Metamaterials, Photonic Crystals and Plasmonics)     789 - 790 2023

Joint Work

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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

A Balčytis, XH Dinh, T Ozawa, Y Ota, T Baba, S Iwamoto, A Mitchell, ...

2023 Conference on Lasers and Electro-Optics (CLEO), 1-2 (2023 Conference on Lasers and Electro-Optics, CLEO 2023)   2023

Joint Work

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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.

Supersymmetric non-Hermitian topological interface laser

M Ezawa, N Ishida, Y Ota, S Iwamoto

Physical Review B 107 (8), 085302 (Physical Review B)  107 ( 8 )  2023

Joint Work,  ISSN  24699950

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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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Slow light waveguide based on semiconductor valley photonic crystal

S Iwamoto, H Yoshimi, K Kuruma, R Miyazaki, Y Ota

Plasmonics: Design, Materials, Fabrication, Characterization, and …  2023

Joint Work

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

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

2023 IEEE International Magnetic Conference-Short Papers (INTERMAG Short … (2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings)   2023

Joint Work

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

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

Optics Express 31 (9), 13672-13682 (Optics Express)  31 ( 9 ) 13672 - 13682 2023

Joint Work

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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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Nonadiabatic nonlinear non-Hermitian quantized pumping

M Ezawa, N Ishida, Y Ota, S Iwamoto

arXiv preprint arXiv:2310.17987  2023

Joint Work

Micro-transfer-printed membrane distributed reflector lasers on Si waveguide modulated with 50-Gbit/s NRZ signal

Y Maeda, T Aihara, T Fujii, T Hiraki, K Takeda, T Tsuchizawa, H Sugiyama, ...

Journal of Lightwave Technology 41 (12), 3866-3873 (Journal of Lightwave Technology)  41 ( 12 ) 3866 - 3873 2023

Joint Work,  ISSN  07338724

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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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Magneto-optical material and production method therefor

S Iwamoto, Y Ota, K Ikeda, N Kobayashi

US Patent App. 18/019,317  2023

Joint Work