Prof. Shiyoshi Yokoyama of Kyushu University

Abstract:

Recent progress of highly efficient and high-speed electro-optic (EO) modulator technology has received intensive research attention in microwave photonics and fiber-optic networks. Among the different types of materials used in the modulator, the thin-film EO waveguide offers intrinsic advantages such as a large EO coefficient (r33>150 pm/V), traveling wave modulation, and excellent compatibility with other materials and silicon-on-insulator substrates. State-of-the-art efficient EO modulators rely on the phase modulation in various types of waveguide structures. Particularly, highlights of the polymer modulators can be impressed due to the advantages in fabrication allowed by the spin-on-preparation technique, which enables various waveguide structures on the silicon-on-insulator substrates. To date, spin-on polymer waveguide modulators have shown outstanding performance such as high data rate transmission, low-power consumption, and easy integration to other substrates. The progress makes the modulator device as one of the few possible solutions to realize over 120 Gbaud high-speed signalization. It meets the critical demand in the emerging optical interconnects for short-reach and data center networks. Despite being fast and efficient, reliability issues should be investigated, i.e., stabilities against high-temperature exposure, high-intensity optical signal, humidity exposure, and recycling thermal shock. While progress is significantly being made, careful consideration should be continued to fully address the industrial applications. The heterogeneous integration of strong EO coefficient materials such as ferroelectric epitaxial films is the alternative technique. We have recently prepared the heterogeneous thin-film LnNbO3 and silicon waveguide modulator on an insulator and showed the modulation bandwidth of 60 GHz and 200 Gbit/s PAM4 transmission with error-free signal accuracy. Based on the technique, furthermore, we are investigating the high-speed modulators using the ferroelectric films-on-insulator (FFOI), consisting of ferroelectric oxides with perovskite phase such as PZT (Pb[Zi, Ti]O3), PLZT([Pb, La][Zi, Ti]O3) and BTO (BaTiO3). The EFOI modulators provide very strong EO coefficients, thus promising the modulation with lower driving voltage, lower cost, and more compact footprint properties. In this study, we utilize the spin-on technique using precursor sol-gel solutions to obtain FFOI substrates and fabricate waveguide modulators. We measured an effective EO coefficient of around 200 pm/V and half-wave voltage length (Vp×L) product smaller than 1.0 V×cm in a Mach-Zehnder interferometer (MMI) waveguide modulator. This paper discusses state-of-the-art high-speed modulator devices in telecommunications applications and our approach from a view point of materials, fabrications and devices.

Biography:

Academic background

• 1994  Dr. in Engineering, Tokyo Institute of Technology, Japan

Professional career

• 1995 Researcher, National Institute for Information and Communication Technology, Japan
• 1999 Senior Researcher, National Institute for Information and Communication Technology., Japan
• 2006 Resarch Group Leader, National Institute for Information and Communication Technology., Japan
• 2007-present, Professor, Kyushu University, Japan

Research interests

Shiyoshi Yokoyama’s main interest is to develop photonic polymer and polymer optical device applications. One recent higllight is the electro-optic polymer modulator with efficient and high-speed signaling. He has aouthored and coauthored more than 140 papers in journals and conference proceeding. In 2005, he is awarded and commended for Science and Technology by the Minister of Education, Science and Technology. Currently he is coordinating the research projects funded by JSPS, SICORP JST, A-STEP JST, CREST JST, and NEDO.

Email:

Address:Kyushu University, 744 Motooka Nishi-ku, Fukuoka, Fukuoka, Japan, 819-0395