KEIO RESEARCHERS INFORMATION SYSTEM

Profile 【 Display / hide 】

Profile 【 Display / hide 】

• He received his B.S. in Electronics and Electrical Engineering from Keio University, Yokohama, Japan, in March 2000, and his M.S. and Ph. Design Engineering from the same institution in September 2001 and March 2004, respectively.
  He was a research associate of the 21st Century Center of Excellence (COE) program in optical and electronic device technology for access networks at Keio University from November 2002 to March 2004. He received a Certificate for Distinguished Activity as Research Assistant at Keio Information, Electronics, and Electrical Engineering Field COE. On April 2004, he joined NTT Basic Research Laboratories, NTT Corporation, in Atsugi, Japan. On April 2010, he moved to Electronics and Electrical Engineering at Keio University, where he is currently a professor. He received Scientific American 50 Award in 2007, and the Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology, The Young Scientists’ Prize in 2010. Dr. Tanabe is a member of the Optical Society, IEEE Photonics Society, SPIE, the Japan Society of Applied Physics, the Laser Society of Japan, and the Institute of Electronics, Information, and Communication Engineers. He is currently a Senior Editor for the IEEE Journal of Selected Topics in Quantum Electronics and Associate Editor for AIP Advances (APS) and Scientific Reports (NPG). He is also serving as a conference committee member in various conferences, including the general chair for CLEO:2022, program chair for CLEO:2020 and ALPS2023, vice-program chair for ICNN, sub-committee chair for CLEO:2018/2019 and CLEO Pacific Rim 2022, the committee in Optica Congress, LEOS, ALPS, APLS, ICO-24, ICNN, WOMBAT, LSJ, and JSAP.

Profile Summary 【 Display / hide 】

Profile Summary 【 Display / hide 】

• 微小光共振器を用いて光を強く閉じ込めることによって，微小な光強度で非線形光学効果を発現させます．それによって，微弱なエネルギーで動作する光スイッチ・光メモリや光トランジスタを実現させます．また，光を究極的に閉じ込めることによる新たな光物理の可能性についても探索します．

Career 【 Display / hide 】

Career 【 Display / hide 】

• 2002.11

  -

  2004.03

  Research associate of the 21st Century Center of Excellence (COE) program in optical and electronics device technology for access network

• 2004.04

  -

  2009.03

  NTT Basic Research Laboratories, NTT Corporation

• 2009.04

  -

  2010.03

  Research Engineer, NTT Basic Research Laboratories, NTT Corporation

• 2010.04

  -

  2012.03

  Lecturer, Department of Electronics and Electrical Engineering, Keio University

• 2012.04

  -

  2018.03

  Associate Professor, Department of Electronics and Electrical Engineering, Keio University

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Academic Background 【 Display / hide 】

Academic Background 【 Display / hide 】

• 2000.03

  Keio University, Faculty of Science and Engineering, Department of Electronics and Electrical Engineering

  University, Graduated

• 2001.09

  Keio University, Graduate School, Division of Science and Engineering, School of Integrated Design Engineering

  Graduate School, Completed, Master's course

• 2004.03

  Keio University, Graduate School, Division of Science and Engineering, School of Integrated Design Engineering

  Graduate School, Completed, Doctoral course

Academic Degrees 【 Display / hide 】

Academic Degrees 【 Display / hide 】

• Ph.D., Keio University, Coursework, 2010.03

Research Areas 【 Display / hide 】

Research Areas 【 Display / hide 】

• Nanotechnology/Materials / Optical engineering and photon science (Applied Optics/Quantum Optical Engineering)

Research Keywords 【 Display / hide 】

Research Keywords 【 Display / hide 】

• フォトニックナノ構造

• フォトニック結晶

• 光回路

• 微小光共振器

• 超高速光技術

Books 【 Display / hide 】

Books 【 Display / hide 】

• On-chip frequency comb

  Tetsumoto T., Fujii S., Tanabe T., On-Chip Photonics: Principles, Technology and Applications, 2024.01

  　View Summary

  An on-chip frequency comb is a light source on a chip that generates coherent multifrequency light whose frequencies are equidistant in the optical frequency domain. It even suggests the possible realization of chip-scale devices with metrological precision in terms of time and frequency. In particular, a microresonator-based frequency comb is a novel on-chip frequency comb device that exhibits intriguing features as experimental platforms on which to explore unique nonlinear phenomena and tools for practical applications. In this chapter, we first provide an overview of conventional frequency combs and on-chip frequency combs. Then, we describe the fundamentals of microresonator-based frequency combs, their key features, and applications. Finally, we summarize the chapter by discussing various challenges and future perspectives in relation to this emerging on-chip frequency comb.

  • Access to Document (DOI)

Papers 【 Display / hide 】

Papers 【 Display / hide 】

• Broadbandwidth Edge Coupler Structure for SiN-Si Heterogeneous Integration

  Sugano R., Kokubu J., Otake R., Fujii S., Tanabe T.

  IEICE Transactions on Electronics E108C ( 11 ) 572 - 578 2025.11

  ISSN  09168524

  　View Summary

  SUMMARY We study how to optimize the coupling efficiency between silicon nitride and silicon waveguides using an edge coupler with an inverse-tapered structure, specifically targeting broad bandwidth applications. Initially, we hypothesized that mode matching alone would suffice for effective coupling. However, our results indicate that maximizing the coupling efficiency requires the simultaneous optimization of mode coupling and effective refractive-index matching. Theoretical simulations predicted a maximum coupling efficiency of 0.963, while experimental measurements yielded an efficiency of 0.588. We analyzed the wavelength dependence of our coupler, and found that the edge coupler exhibited broader bandwidth properties than a standard multilayer coupler, making it more suitable for applications across a wide wavelength range. These results indicate the potential for integrating such couplers with microresonator frequency comb systems, offering the possibility of a wide range of photonic applications.

  • Access to Document (DOI)

• Record-high-Q AMTIR-1 microresonators for mid- to long-wave infrared nonlinear photonics

  Yang L., Sugano R., Takabayashi R., Kanzawa H., Kumazaki H., Zhuang Y., Wei X., Tanabe T., Fujii S.

  Optics Letters 50 ( 21 ) 6554 - 6557 2025.11

  　View Summary

  AMTIR-1 chalcogenide glass has shown its potential for use in thermal imaging systems owing to its low refractive index, thermal resistance, and high transparency across the infrared wavelength regime. Here, we report a millimeter-scale high-Q whispering gallery mode microresonator made of AMTIR-1. The recorded Q-factor has reached 1.2×107 at 1550 nm, which is almost two orders of magnitude higher than previously reported values. We characterize the thermal properties, where low thermal conductivity plays an important role in thermal resonance tuning. We further show that AMTIR-1 resonators support anomalous dispersion as well as a low absorption coefficient near the 7 µm wavelength band, thus offering the possibility of providing suitable platforms for mid-infrared, long-wave infrared nonlinear optics, including microresonator frequency comb generation.

  • Access to Document (DOI)

• Soliton-comb-based photonic microwave filter operating in the 300 GHz band

  Tanikawa K., Imamura M., Yomoda A., Kogure S., Sugano R., Kawanishi S., Fujii S., Tanabe T.

  Photonics Research 13 ( 5 ) 1282 - 1289 2025.05

  ISSN  23279125

  　View Summary

  We present a 300 GHz photonic filter based on a soliton microcomb, addressing the increasing demand for high-frequency, low-phase-noise signals in THz-band wireless communications. Utilizing a uni-traveling-carrier photodiode (UTC-PD), our configuration enables the generation of 300 GHz waves through beat signals from adjacent longitudinal modes of the microcomb. By combining the UTC-PD with a photonic filter approach, we demonstrate that RF photonic filters with high suppression ratios are achieved in the 300 GHz band. Additionally, by mitigating the effects of higher-order dispersion, we achieve a stopband rejection exceeding 30 dB. These results underscore the potential of our photonic filter for advanced THz applications and provide a promising pathway for low-noise, high-bandwidth wireless communication systems.

  • Access to Document (DOI)

• Scalable fabrication of erbium-doped high-Q silica microtoroid resonators via sol-gel coating

  Imamura R., Fujii S., Nagashima K., Tanabe T.

  Optics Continuum 4 ( 3 ) 512 - 521 2025.03

  　View Summary

  This study explores sol-gel methods for fabricating erbium-doped silica microtoroid resonators, addressing the limitations of conventional doping techniques and enhancing device scalability. We develop a reproducible sol-gel process that yields defect-free films for photonic applications and detail common defects and troubleshooting strategies. Two fabrication methods are compared: traditional film deposition on substrates and the direct coating of prefabricated resonators. The latter enables the fabrication of larger resonator diameters (up to 450 pm) without buckling while achieving a high-g factor and a low lasing threshold of 350 pW. These erbium-doped resonators exhibit multi-mode laser oscillations at 1550 nm, revealing the sol-gel method’s potential for realizing scalable, gain-doped photonic devices.

  • Access to Document (DOI)

• Field Trial of Optical Transmission Experiment Employing a Microresonator Frequency Comb Light Source for Low-Latency, Short-Reach Optical Communication

  Tanikawa K., Fujii S., Kogure S., Tanaka S., Tasaka S., Wada K., Kawanishi S., Tanabe T.

  IEICE Transactions on Electronics E108.C ( 3 ) 146 - 152 2025.03

  ISSN  09168524

  　View Summary

  We present first-time demonstration of short-reach and low-latency optical communication within a real network, employing a microresonator frequency comb as a light source. The modulated signal is transmitted through a 9-km single-mode optical fiber installed in a metropolitan network. This demonstration paves the way for realizing low-latency massively parallel optical communication, which is the key to beyond-5G and 6G network. For a proof-of-concept experiment, we employ an MgF<inf>2</inf> crystalline microresonator with a 20-GHz free-spectral range that could be used for dense wavelength division multiplexing communication. We generated a stable soliton comb and modulated it with simple 10-Gbps intensity modulation and direct detection to achieve a small excess delay of 3.1 µs.

  • Access to Document (DOI)

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Papers, etc., Registered in KOARA 【 Display / hide 】

Papers, etc., Registered in KOARA 【 Display / hide 】

• Development of high-repetition optical pulse source by miroresonator

  Tanabe, Takasumi

  科学研究費補助金研究成果報告書 2023

• Increased performance of nanophotonic devices by utilizing structural fluctuation information with deep learning

  Tanabe, Takasumi

  科学研究費補助金研究成果報告書 2022

• Development of small light source with extended-nano space processing

  Tanabe, Takasumi

  科学研究費補助金研究成果報告書 2019

• Sensing of volatile organic compounds in breathing air by using packaged optical microcavity device

  Tanabe, Takasumi

  学事振興資金研究成果実績報告書 (慶應義塾大学)  2018

• Study on energy-saving optical frequency comb source based on an optical microcavity

  Tanabe, Takasumi

  科学研究費補助金研究成果報告書 2018

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

Research Projects of Competitive Funds, etc. 【 Display / hide 】

• Increased performance of nanophotonic devices by utilizing structural fluctuation information with deep learning

  2021.07

  -

  2023.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Challenging Research (Exploratory), Principal investigator

• Development of high-repetition optical pulse source by miroresonator

  2019.04

  -

  2024.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A) , Principal investigator

• 拡張ナノ領域プロセシングが実現させる微小光源開発

  2018.06

  -

  2020.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Challenging Research (Exploratory) , Principal investigator

• Nonlinear optics in coupled resonators

  2016.04

  -

  2018.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Challenging Exploratory Research, Principal investigator

• Study on energy-saving optical frequency comb source based on an optical microcavity

  2015.04

  -

  2019.03

  MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (A), Principal investigator

Awards 【 Display / hide 】

Awards 【 Display / hide 】

• Poster Awards

  Hiroshi Kudo, Yohei Ogawa, Takasumi Tanabe, and Atsushi Yokoo, 2012.03, International Conference on Optical and Optoelectronic Properties of Materials and Applications (ICOOPMA), Fabrication of Whispering Gallery Mode Cavities using Crystal Growth

  Type of Award： Other

• 第24回安藤博記念学術奨励賞

  TANABE Takasumi, 2011.06

  Type of Award： Award from publisher, newspaper, foundation, etc.

• 文部科学大臣表彰 若手科学者賞

  TANABE Takasumi, 2011.04

  Type of Award： Other

• The 6th Annual Scientific American 50 Award

  TANABE Takasumi, 2007.11, Scientific American, Light Manipulation

  Type of Award： Other

• 第31回レーザー学会業績賞 論文賞(オリジナル部門)

  TANABE Takasumi, 2007.05, シリコンフォトニック結晶共振器を用いた全光スイッチおよび5GHz RZ光パルス列変調

  Type of Award： Award from Japanese society, conference, symposium, etc.

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Courses Taught 【 Display / hide 】

Courses Taught 【 Display / hide 】

• SEMINAR IN ELECTRONICS AND INFORMATION ENGINEERING(2)

  2025

• SEMINAR IN ELECTRONICS AND INFORMATION ENGINEERING(1)

  2025

• RECITATION IN ELECTRONICS AND INFORMATION ENGINEERING

  2025

• PHOTONICS

  2025

• PHOTONIC NANOSTRUCTURE

  2025

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Courses Previously Taught 【 Display / hide 】

Courses Previously Taught 【 Display / hide 】

• フォトニクス

  Keio University

  2014.04

  -

  2015.03

  , 

  Autumn Semester, Lecture

• フォトニックナノ構造

  Keio University

  2014.04

  -

  2015.03

  , 

  Spring Semester, Lecture

Memberships in Academic Societies 【 Display / hide 】

Memberships in Academic Societies 【 Display / hide 】

• AIP Advances, 

  2013.04

  -

  Present

• 電子情報通信学会超高速光エレクトロニクス研究会, 

  2013.04

  -

  Present

• レーザー学会 編集委員会, 

  2011.04

  -

  Present

• 電子情報通信学会レーザ・量子エレクトロニクス, 

  2011.04

  -

  Present

• 電子情報通信学会超高速光エレクトロニクス研究会, 

  2011.04

  -

  2013.03

Committee Experiences 【 Display / hide 】

Committee Experiences 【 Display / hide 】

• 2017.04

  -

  Present

  Subcommittee Chair, CLEO:2018

• 2017.04

  -

  Present

  Associate Editor, Scientific Reports, Nature Publishing Group

• 2013.04

  -

  Present

  編集委員, AIP Advances

• 2013.04

  -

  Present

  専門委員, 電子情報通信学会超高速光エレクトロニクス研究会

• 2013.04

  -

  Present

  Accosiate Editor, AIP Advances

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