Ibaraki University's
Graduate School of Science and Engineering (Engineering)
Department of Electrical and Electronic Engineering

Associate Professor

YOKOTA Hirohisa

  • Birth:1967


  1. Ibaraki University, Research Assocoate 1995/04/01-2003/03/31
  2. Ibaraki University, Lecturer 2003/04/01-2009/03/31
  3. Associate Professor, Ibaraki University 2009/04/01-Present

Academic background

  1. Osaka University Faculty of Engineering Communication Engineering 1990 Graduated
  2. Osaka University Graduate School, Division of Engineering Communication Engineering Doctor later 1995 Completed

Academic degrees

  1. Doctor of Engineering Osaka University

Current state of research and teaching activities

Study of optical fiber devices for optical fiber transmission sysyems
The theme of my studies are designs and fabrications of fiber devices, such as functional fibers, fiber couplers, fiber gratings, and their combinations, for optical fiber transmission systems.

Research Areas

  1. Electronic Device/Electronic Equipment

Research keywords

  1. Optoelectronics, Optical fiber, Fiber Optic communication system, Functional fiber, Optical fiber coupler, Optical fiber grating, Optical fiber sensor

Subject of research

  1. Research of optical fiber grating couplers and their applications In this research, optical fiber grating couplers that are refractive index modulated gratings are written in the tapered regions of the fused fiber couplers are designed and fabricated, and their applications are investigated.
  2. Fabrication of optical fiber couplers using carbon dioxide laser irradiation Fabrications of high performance optical fiber couplers are investigated by introducing carbon dioxide laser irradiation.
  3. Designs and fabrications of photonic crystal fiber couplers Photonic crystal fiber couplers are designed using finite difference beam propagation method and fabricated using carbon dioxide laser irradiation.
  4. Research of optical fiber transmission system using single polarization Optical fiber transmission lines using single polarization are investigated to realize high-speed optical transmission with simple and low-cost devices in transmitters and receivers.


  1. Ultrafast Opto-electronics REALIZE Science & Emgineering 2003/07/31


  1. Research paper (scientific journal) Joint Light propagation characteristics in photonic crystal fibers with α-power profiles of air hole diameter distributions and their application to fiber collimator Hirohisa Yokota, Keiichi Higuchi and Yoh Imai Japanese Journal of Applied Physics The Japan Society of Applied Physics 55/ 8S3, 08RE10 2016/07/22 10.7567/JJAP.55.08RE10 Light propagation characteristics in photonic crystal fibers (PCFs) with α-power profiles of air hole diameter distributions were theoretically investigated. It was clarified that the intensity peak of the beam propagating in the PCF with Gaussian beam excitation varied periodically with little power attenuation. It was found that the envelope of the periodic intensity variation depended on α. We theoretically demonstrated that the PCF with the α-power profile of the air hole diameter distribution could be applied to a collimator for a conventional PCF with uniform air holes in Gaussian beam excitation to reduce coupling loss, where a PCF of appropriate length with the α-power air hole diameter distribution was spliced to a conventional PCF. It was also found that the coupling efficiency was higher for a larger α.
  2. Research paper (scientific journal) Joint Fabrication of photonic crystal fiber optical attenuators with air hole diameter control using CO2 laser irradiation technique Hirohisa Yokota, Kosuke Ushiroda, Naoya Inoue, Yoh Imai, and Yutaka Sasaki Optical Fiber Technology 23, 37-41 2015/06/01
  3. Research paper (scientific journal) Joint Fabrication of polarization-maintaining photonic crystal fiber coupler with air hole state control using CO2 laser irradiation technique H. Yokota, Y. Ito, H. Kawashiri, H. Kiue, H. Tobita, Y. Imai, Y. Sasaki IEICE Transactions on Electronics E95-C/ 10, 1689-1691 2012/10/01 Polarization-maintaining photonic crystal fiber couplers (PM-PCFCs) were fabricated using a CO2 laser irradiation technique. We could control the states of air holes in the tapered region of couplers by adjusting the laser power density in the fusion and the elongation processes. It was demonstrated that the air hole remaining PM-PCFC exhibited polarization-splitting characteristics and that the air hole collapsed PM-PCFC had polarization insensitive coupling characteristics.
  4. Research paper (scientific journal) Joint Reduction of splice loss between single-mode optical fiber and high nonlinear photonic crystal fiber by air hole diameter control with CO2 laser irradiation Hirohisa Yokota, Hirotomo Yashima, Yoh Imai, Yutaka Sasaki IEICE Transaction on Electronics (Japanese Edition) J94-C/ 2, 53-56 2011/02/01 単一モード光ファイバとモードフィールド径(MFD)の小さい高非線形フォトニック結晶ファイバの接続時に生じるMFD不整合損失の低減法として,CO2レーザ照射による空孔径制御を用いることを提案し,その有効性を理論的・実験的に明らかにした.
  5. Research paper (scientific journal) Joint Demonstration of an all-optical switching operation using an optical fiber grating coupler H. Yokota, M Kobayashi, H. Mineo, N. Kagawa, H. Kanbe, Y. Sasaki Optics Communications 281/ 19, 4893–4898 2008/10/01 An optical fiber grating coupler (FGC) is a fused optical fiber coupler with a tapered region in which refractive index-modulated gratings are written. In the FGC, the light with specific wavelength satisfying the Bragg condition of the grating can be dropped to one output port and other lights are transmitted to another output port when lights with various wavelengths are launched into the input port. The FGC can operate as an all-optical switch by controlling the Bragg wavelength of the grating using a third order nonlinear optical effect caused by a control light that are launched with a signal light. In this paper, an all-optical switching operation due to a third order nonlinear optical effect in an FGC is first demonstrated for a signal light with 1.55 lm-wavelength to be changed from one port of the FGC to another one by the 720W peak of a control light from a Nd:YAG laser with 1.06 lm-wavelength. The switching efficiency obtained was 7%. It was clarified that a longer pulse length of the control light compared to the grating length is required to obtain a large Bragg wavelength shift for the switching. It was also clarified that the Bragg wavelength shift is caused by a third order nonlinear effect and a photothermal effect. A contribution of the photothermal effect was estimated. We also estimated the switching efficiency for pump power in the FGC switch.

Research presentations

  1. Oral presentation(general) CO2レーザ照射によるフォトニック結晶ファイバへの長周期グレーティング形成 第75回応用物理学会秋季学術講演会 2014/09/18
  2. Oral presentation(general) ファイバグレーティングの反射特性に対する放射線照射の影響 第75回応用物理学会秋季学術講演会 2014/09/18
  3. Oral presentation(general) ファイバ曲げを用いた偏波保持フォトニック結晶ファイバ可変光減衰器 第61回応用物理学会春季学術講演会 2014/03/17
  4. Oral presentation(general) 偏波保持ファイバブラッググレーティングの特性に対する放射線照射の影響 光ファイバ応用技術研究会 2014/02/28
  5. Oral presentation(general) 空孔径制御を用いた偏波保持フォトニック結晶ファイバ光減衰器の作製 電子情報通信学会・光ファイバ応用技術研究会 2013/01/25

Intellectual property rights

  1. Patent 光ファイバ、光ファイバケーブル及び光ファイバ接続方法 特願2015-205117 2015/10/16

Alloted class

  1. Mathematics Exercises I
  2. 電気電子工学ゼミナール
  3. Quantum Electronics
  4. Presentation for Electrical and Electronic Engineering
  5. Electrical and Electronic Engineering Experiments III

Memberships of academic societies

  1. The Institute of Electronics, Information, and Communication Engineers
  2. The Japan Society of Applied Physics
  3. The Institute of Electric and Electronics Engineers

Committee Career

  1. The Institute of Electronics, Information, and Communication Engineers 光ファイバ応用技術研究会・研究専門委員会顧問 2014/04-Present
  2. The Japan Society of Applied Physics 英文論文誌 Optical Review 編集委員 2012/05-Present
  3. The Institute of Electronics, Information, and Communication Engineers 光通信インフラの飛躍的な高度化に関する研究会(EXAT研究会)研究専門委員 2010/04-Present
  4. The Institute of Electronics, Information, and Communication Engineers 光ファイバ応用技術研究会・研究専門委員 2008/04-2014/03
  5. The Institute of Electronics, Information, and Communication Engineers 東京支部学生会顧問 2007/05-Present