Koichi Takiguchi

Functional PLC devices

This paper reports recent advances in photonic functional devices. These devices are being developed for advanced optical networks and are fabricated by using planar lightwave circuit technology. After briefly summarizing the fabrication, properties, and progress of silica based planar lightwave circuits, this work describes lattice-form dynamic devices designed to compensate for unwanted fiber characteristics with respect to high-speed wavelength division multiplexing transmissions. These dynamic devices include adaptive chromatic dispersion, polarization-mode dispersion, and gain non-uniformity compensators. The paper then describes optical signal processing devices for communications use, namely an optical label recognition device, an optical encoder/decoder for time-spreading/wavelength-hopping code division multiple access, and a spectrum synthesis device.

Real-time wireless OFDM communication in THz-band using optical dft processing

Real-time THz-wave wireless OFDM communication, which is assisted by optical technology, is reported. A 4 × 10 Gbit/s THz-wave OFDM signal is transferred into an optical OFDM signal, and the optical OFDM signal is successfully demultiplexed into four sub-carrier channels with an integrated-optic DFT circuit.

Demultiplexing method of terahertz-wave OFDM sub-carrier channels using integrated-optic DFT circuit

I propose a real-time demultiplexing method of terahertz-wave OFDM signal, which utilizes the optical technology. The received and amplified electrical OFDM signal is transferred into an optical OFDM signal through an optical modulator. Then, the optical OFDM signal is processed with an integrated-optic DFT circuit, which is mainly composed of a slab star coupler. This optical DFT circuit is compact, and can demultiplex up to a 10 × 10 Gbaud (100 Gbaud) optical OFDM signal. I report the operating principle of the method and some preliminary experimental results.

Integrated-optic tunable chromatic dispersion compensator composed of lattice-form circuit with interleave filter

I report a lattice-form tunable optical dispersion compensator whose number of operable channels is doubled with the use of an interleave filter. In this scheme, interleaved signals are introduced into two different inputs of the lattice-form compensator and are provided with the same dispersion value based on unitary properties of the compensator transfer matrix. Thus this configuration can activate inoperable bands that account for nearly half of the total bandwidth in existing lattice-form compensators. The proposed compensator was realized by connecting the silica waveguide-based interleave filter and dispersion compensator with fibers. The dispersion of -283 to 252 ps/nm was obtained over 40 GHz bandwidth with a period of 50 GHz.

Optical OFDM signal generation using integrated-optic multiplexer based on optical IFFT

We demonstrate an integrated-optic device for multiplexing an OFDM signal based on optical IFFT. The silica waveguide-based multiplexer is composed of four inputs followed by mutually connected directional couplers, an array of delay lines, and a combiner. Four signals modulated with different sequences of data are fed into the multiplexer, and an optical OFDM signal is generated through the IFFT process directly in the optical domain. We report the configuration, operating principle, and experimental results to indicate that the multiplexer operates properly. We successfully generated 40 and 80 Gbit/s OFDM signals with the multiplexer.

Modulation format converter for mapping OOK to 4-level PAM data using balanced detection and intensity modulation

I report a simple modulation format converter of OOK to 4-level PAM data, which comprises a balanced photo-detector and an intensity modulator. Two 20 Gbit/s OOK signals were converted into a 40 Gbit/s PAM signal.

Optical XOR circuit using combined technology of photonics and electronics

I propose and demonstrate a novel and simple optical exclusive OR circuit for binary signals, which is composed of a balanced photo-detector and a Mach-Zehnder intensity modulator. Two input optical signals into the photo-detector produce an electrical signal to drive the modulator. The modulator outputs an optical exclusive OR signal of the two input optical signals. I report the configuration, operating principle, and primary experimental results using 10 Gbit/s binary signals to demonstrate that the exclusive OR circuit operates properly. The proposed simple circuit is suitable for the future hybrid integration of photonics and electronics.