Department of Electrical and Electronic Engineering, Ritsumeikan University, Japan

Biography: Koichi Takiguchi was born in Ibaraki, Japan. He received the B.S. degree in electronic engineering, and M.S. and Ph.D. degrees in electrical engineering, all from the University of Tokyo, Tokyo, Japan, in 1987, 1989, and 1992, respectively. His graduation thesis and dissertation were in a GaAs/AlGaAs distributed feedback (DFB) semiconductor laser and a resonator-type fiber-optic gyroscope (RFOG), respectively.
He joined NTT Laboratories in 1992, where he engaged in the research and development of integrated-optic (silica waveguide technology-based) functional devices including the first tunable optical chromatic dispersion compensator and optical OFDM demultiplexer. From 1998 to 1999, he stayed at University of California at Santa Barbara (UCSB), USA, as a visiting scholar, where he engaged in semiconductor-based photonic functional devices.
In 2012, he joined Department of Electrical and Electronic Engineering, Ritsumeikan University, Japan, as a professor. He is now interested in optical signal processing technology and their applications to next generation optical and THz-wireless communication, and optical and THz-wave sensing systems.
Dr. Takiguchi is a member of IEEE, OSA, the Institute of Electronics, Information, and Communication Engineers (IEICE) of Japan, and the Japan Society of Applied Physics (JSAP). He serves on an associate editor of IEEE Photonics Technology Letters (PTL).

Speech Title: Tunable optical OFDM signal demultiplexers

Abstract: Optical orthogonal frequency division multiplexing (OFDM) is attractive because of its high spectral efficiency. Optical OFDM is applicable for adaptive optical networks as well as point-to-point transmission. In these advanced networks, transmission capacity needs to be changed depending on the traffic and transmission distance. In this talk, I report our two kinds of tunable OFDM signal demultiplexers based on optical Fourier transform.

We realized an integrated-optic OFDM filter with variable characteristics [1], [2]. The filter is composed of a slab star coupler-type optical Fourier transform circuit [3] and an array of Mach-Zehnder interferometer-type tunable optical couplers. The tunable couplers are used to make an input OFDM signal divided into delay lines in the filter at arbitrary intensity ratio. The number of used delay lines corresponds to the maximum processable number of OFDM sub-carriers. As a step length difference at the delay lines determines the free spectral range of the filter, we can change the maximum channel number and the channel spacing of the filter by selecting the delay lines where lightwaves are introduced.

We also realized a tunable OFDM signal demultiplexer with time lens-based optical Fourier transform [4]. The demultiplexer is composed of a phase modulator and a tunable chromatic dispersion emulator. As the parameters of these two components can easily be tuned, the demultiplexer can process various symbol rate optical OFDM signals.

This work was partly supported by JSPS KAKENHI Grant No. 16H04369.

Keywords: optical OFDM, optical Fourier transform, tunable demultiplexer