Takakiyo Nakagami

Recent progress in optoelectric integrated circuits (OEIC's)

Recent developments in both GaAs- and InP-based opto-electronic circuits (OEICs) which incorporate both optoelectronic and electronic devices on the same semiconductor substrates will be discussed. Several key technologies required for optoelectronic integration and the present status of the technology are explained by reviewing some of OEIC transmitters and receivers that have been realized up to now. Possibilities of application of OEICs and further technological challenges to enhance the advantages of OEICs are discussed.

Compact transmitter and receiver modules with optoelectronic-integrated circuits for optical LAN's

Compact transmitter and receiver modules with monolithic optoelectronic-integrated circuits, i.e., OEICs, are demonstrated, and 400- and 800-Mbit/s transmission experiments are successfully carried out over up to 4 and 2 km, respectively, with these modules, for the first time. The design of the monolithic-integrated circuits and the compact module structure are presented. The soldering technique based on the use of YAG laser simplifies the packaging procedures, and an efficient and simple scheme for coupling between OEICs and fibers make the OEIC modules compact. Both modules are attractive for applications in high data-rate communication systems, particularly in local area networks, CATV systems, and intra-office links.

Wavelength Tunable Operation in Si Waveguide Grating That Has a Ferroelectric Liquid Crystal Cladding

We obtained the wavelength selective operation in a grating Si rib waveguide that has an ferroelectric liquid crystal (FLC) cladding. The FLC cladding gives a phase shift change for the traveling lightwave in the waveguide in accordance with the polarity of the applied voltage. We propose the wavelength selective filter using this operation and demonstrate the selective switching and the tunable operation of our fabricated device. We also report its time response and dependence on the applied voltage and propose a new operating method to achieve a continuous phase change by using the FLC layer that has binary characteristics.

Tunable Optical Filter With Cascaded Waveguide Fabry–Pérot Resonators Featuring Liquid Crystal Cladding

We developed and fabricated a tunable optical filter using Si-waveguide multiple-cavity Fabry-Pérot resonators with ferro-electric liquid crystal cladding. The proposed filter can be monolithically integrated with other Si photonics devices because no cleaved facets are required. Also, the bistable characteristic of ferro-electric liquid crystal cladding means the power consumption is low. We tested wavelength operation in the fabricated device and determined that it was able to obtain a phase shift of 0.38 π. It also had improved resonant wavelength characteristics.

Demonstration of switching operation in a symmetric Mach-Zehnder interferometer switch using Si waveguide with a ferro-electric liquid crystal cladding

We proposed and fabricated a novel optical switching device using a Si-waveguide symmetric Mach-Zehnder interferometer having a ferro-electric liquid crystal cladding. We demonstrated the wavelength switching operation with the experimental device fabricated at 1550 nm wavelength.

Si-Waveguide with Ferro-Electric Liquid Crystal Cladding for Use in Optical Switching Devices

We studied a silicon (Si) waveguide using ferro-electric liquid crystal (FLC) cladding for various applications in optical networks. The FLCs in the cladding layer change their effective refractive index corresponding to the applied voltage polarity, and give a phase shift to the traveling lightwave in the waveguides. The phase change coefficients of three-layer slab waveguides with FLC/Si/SiO 2 structure were calculated. We observed an amplitude change in the output light of an experimental modulator consisting of a Mach-Zehnder interferometer with FLC-cladding Si-rib waveguides on a silicon-on-insulator wafer, and evaluated the phase shift at a wavelength of 1550 nm. We propose optical switching devices using Si-rib waveguide Mach-Zehnder interferometers having FLC cladding. Switching of experimental devices operating at 1550 nm wavelength was demonstrated.

Ferroelectric liquid-crystal polarization-control devices with a double-layer cell structure

We analyzed the polarization-switching characteristics of a ferroelectric liquid-crystal polarization control device using a double-layer cell structure for free-space optical processing and switching systems. We theoretically derived the optimum arrangement of layered cells for 90° polarization switching. The theory shows that the optimum parameter range for the double-layer cell structure is wider than that for a single-layer cell. We verified our theory by measuring the polarization cross talk of experimental polarization control devices.

A wavelength switching operation of a Si-waveguide asymmetric Mach-Zehnder interferometer having a ferro-electric liquid crystal cladding

We proposed and fabricated a novel optical switching device using a Si-waveguide asymmetric Mach-Zehnder interferometer with a ferro-electric liquid crystal cladding. We demonstrated the wavelength switching operation with the experimental device fabricated at 1550 nm wavelength.

Tunable wavelength selective operation in grating silicon waveguide having ferroelectric liquid crystal cladding

We proposed and fabricated a wavelength selective switch with grating Si-waveguide having ferroelectric liquid crystal cladding. We demonstrated the tunable wavelength selective operation and obtained about 20dB of extinction ratio at 1530.5nm-wavelength.

Optical routing switches incorporating ferroelectric liquid crystals for use in photonic networks (Invited Paper)

Optical switching allows us to make the photonic network flexible and expandable. We have been studying two types of optical switches incorporating ferro-electric liquid crystals (FLCs). One type of them is a polarization-controlled free-space optical switch whose operation principle is based on the polarization switching by FLC cells. It has a novel integrated structure consisted with FLC polarization control devices (FLC-PCDs), thin-film beam-splitters and mirrors. The FLC-PCD with a metal mirror electrode is the key element in this switch. The design theory for the FLC-PCD to achieve an accurate 90-degree polarization switching for the oblique incident light has been developed and verified by experiments. 2x2 and 4x4 optical switches were fabricated for optical communication wavelengths of 1300 and 1550nm and their feasibility was demonstrated. The other switch type is a waveguide switch composed of an optical waveguide having FLC claddings. The FLCs in the cladding layer change their effective refractive index corresponding to the applied voltage polarity, providing the phase shift of the travelling lightwave in the waveguide. The operation principle of the switch has been confirmed by an experimental Si waveguide Mach-Zehnder interferometer (MZI) having FLC claddings.