Integrated optical devices for optical communication

Optical communication is the enabling technology for the information society today. I am involved in research of developing novel integrated optical devices for improving optical communication, as listed below.

  • I helped proposing novel simplified optical coherent receivers [1]. Coherent receivers are mandatory for large capacity communication, but currently they were complex and expensive. We proposed and demonstrated a novel dual polarization coherent receiver with drastically simplified characteristics, such as the polarization rotator splitter is no longer required, and the number of photodetectors is reduced to 5.

  • I was involved in development and evaluation of simplified integrated polarization controllers [2]. Polarization controllers are mandatory for efficient optical communication, but it was difficult to be realized as a compact device on InP platform. We proposed and demonstrated novel design methodology to greatly simplify the device fabrication.

  • I committed in the proposal and design of polarization rotator splitters that can be realized on various integrated photonics platforms [3,4]. In coherent optical communication, polarization rotator-splitter (PRS) is one of the essentially required component. However, it was difficult to realize a PRS on integrated photonics platforms like InP and multi-micron silicon, which are important for practical applications. We proposed and demonstrated PRS that can operate on such platforms by proposing and designing optimized waveguide structures, mode conversion tapers, and mode splitters.

  • I contributed in the device evaluation and research supervision for the research of surface normal coherent optical receivers. Conventional optical coherent receivers are based on waveguides, which inherently hinders the realization of 2D array of receivers, that will be mandatory for extremely large capacity optical communication with massive spatial parallelization. We enabled surface normal coherent receivers that can be naturally extended to a 2D array, by using the circular polarization as signal light and local oscillators, combining them by a polarization beam combiner, and detecting them with photodetectors after polarizers with 4 different directions. We utilized the wire grid nanometallic grating that simultaneously serve as electrode and polarizers that can be directly integrated on a high-speed photodetector, and experimentally demonstrated the concept.

光通信用集積光デバイス

光通信は昨今の情報化社会を実現可能にしている技術です。私は以下のように光通信の高度化に関する研究にも関与しています。

  • 光コヒーレント受信器の簡易化した構成の考案に携わりました[1]。光コヒーレント受信器は大容量通信には必須ですが、従来構成は複雑で高コストでした。我々は偏波回転分離器が不要、光検出器数が5個まで削減できる、など大幅に簡略化された低コストな光コヒーレント受信器を新たに提案・実証しました。

  • 簡易化した集積偏光制御器の開発・評価に貢献しました[2]。偏光制御器は光通信の高効率化には必須ですが、InP基板上において小型な素子として実現することは困難でした。我々は偏光制御器を大幅に簡略化するデバイス設計を新たに構成し、実証しました。

  • 種々の光回路基盤上で高効率に動作可能な偏波回転分離器の考案・設計に貢献しました[3,4]。コヒーレント光通信において必須の構成要素となる偏波回転分離器は、InPや厚膜シリコン等実用上重要な光集積回路技術基盤において実現が困難でしたが、我々は、最適化された導波路構造、モード変換テーパやモード分離器の設計を考案することで、それぞれの基盤上で偏波回転分離器を実証しました[3,4]。

  • 垂直入射型コヒーレント光受信器の評価や研究計画等に貢献しました[5]。従来のコヒーレント光受信器は導波路型であり、大容量光通信システムにおいて必要となる大規模空間並列化に必須の二次元アレイ化が困難でした。我々は、各円偏向に信号光と局発光を割り当て、偏波合波器を用いて合波し、4つの異なる角度を持つ偏光子を介して光の偏光成分を検出することで、コヒーレント光受信が可能となることを見出し、実証しました。金属回折格子を用いることで電極としても兼用可能な偏光子を高速動作する受光器上に直接集積でき、

[1] G. Soma, S. Ishimura, R. Tanomura, T. Fukui , M. Ito, Y. Nakano, and T. Tanemura, “Integrated dual polarization coherent receiver without polarization splitter rotator,” Optics Express, vol. 29, no. 2, pp. 1711 1721, 2021.

[2] M. Ito, K. Okawa, T. Suganuma, T. Fukui , E. Kato, T. Tanemura, and Y. Nakano, “Efficient InGaAsP MQW based polarization controller without active passive integration,” Optics Express, vol. 19, no. 7, pp. 10538 10545 , 2021.

[3] M. Ito, T. Fukui, T. Tanemura, and Y. Nakano, “Compact symmetric polarization rotator-splitter on InP,” Optics Express, vol. 30, no. 3, pp. 4179-4188, 2022.

[4] Y. Suzuki, A. Elfiqi, T. Fukui, M. Ito, T. Tanemura, and Y. Nakano, “V-groove-assisted polarization splitter-rotator on multi-micron silicon photonics,” Photonics in Switching and Computing (PSC'22), MD2-6, Toyama, Jul. 2022.

[5] G. Soma, W. Yanwachirakul, T. Miyazaki, E. Kato, B. Onodera, R. Tanomura, T. Fukui, S. Ishimura, M. Sugiyama, Y. Nakano, and T. Tanemura, “Ultra-broadband surface-normal coherent optical receiver with nanometallic polarizers,” ACS Photonics (accepted). doi: 10.1021/acsphotonics.2c00759