Takafumi Chiba

Polarization stabilizer using liquid crystal rotatable waveplates

In standard single-mode fiber (SMF) transmission systems, a polarization stabilizer is useful for optimizing the performance of polarization dependent systems or devices. We have proposed and developed a polarization stabilizer which employs liquid crystal (LC) rotatable waveplates. It has a simple configuration, no moving parts, and endless-control characteristic. High polarization stability was confirmed under various state of polarization (SOP) fluctuations. The maximum response speed of the polarization stabilizer is about 900/spl deg//s, but this can be increased by improving the controller. We applied the polarization stabilizer to a semiconductor optical amplifier (SOA) having polarization dependence, and achieved good gain stabilization.

Novel architecture of wavelength interleaving filter with Fourier transform-based MZIs

A novel wavelength interleaving filter (interleaver) has been demonstrated with Fourier transform-based Mach Zehnder interferometers (MZIs). The interleaver works as two independent 1/spl times/2 interleavers by sharing their delay lines and couplers.

Dynamic gain equalizer using proposed adjustment procedure for thermooptic phase shifters under the influence of thermal crosstalk

A dynamic gain equalizer (DGE) is required to automatically compensate for gain variations related to fiber amplifiers. This paper proposes a DGE with thermooptic (TO) phase shifters based on a single-filtered-arm interferometer. A design procedure was newly developed for the control of the TO phase shifters, which could be used to accurately control the intended attenuation profile in one adjustment. In this procedure, the Taylor series method was used as an optimization algorithm, and thermal crosstalk was taken into account. From the point of view of thermal crosstalk, the behavior of phase shifters in an array and the effect of three-dimensional (3-D) trenches formed around the phase shifters were precisely investigated. A DGE module based on 1.5%-/spl Delta/ planar lightwave circuits and the 3-D trench structure are demonstrated. The measured spectra were found to be in good agreement with arbitrarily designed profiles under open-loop control, even when there was some thermal crosstalk between phase shifters. The results indicate that the design procedure and the estimation of the thermal crosstalk are effective for accurate control of the DGE.

Liquid crystal rotatable waveplates

We propose and demonstrate rotatable waveplates using liquid crystal for the first time which can be used for polarization control. To realize a waveplate with an arbitrary direction of birefringence, we use a vertically-aligned nematic liquid crystal cell with a lateral electric field. The orientation of the waveplate can be rotated endlessly. It was confirmed that the direction of the waveplate could be rotated endlessly at a rate of 7200/spl deg//s, which is sufficient to construct polarization controlling devices for most SMF transmission systems.

Waveguide interleaving filters

Optical Interleaving filters are attractive components in WDM systems especially narrower than 100GHz channel spacing system. Several types of interleaving filters have been proposed and realized. An interleaving filter is required to have the Box-like characteristics such as the periodic response, flat-passband, low insertion loss and low crosstalk. In addition, low chromatic dispersion (CD) is indispensable for DWDM systems. We focus on planar lightwave circuit interleaving filters. In this paper, we present interleaving filters with a tandem configuration of Fourier transform-based MZIs. The circuit using PLC technique is fabricated with high index contrast waveguides of Δ1.5%. We also have demonstrated monolithically integrated 1×4 (50-200GHz) interleaving filters and arrayed waveguide gratings(AWGs) with 200GHz-channel spacing suitable for interleaving WDM system.

High resolution dynamic gain equalizer using super-high /spl Delta/ planar lightwave circuit technology

A dynamic gain equalizer has been successfully demonstrated based on super-high-/spl Delta/ PLC with 53-channel AWGs and novel trench formation technology. Low insertion loss and well-fitted spectral response were achieved over 55-nm wavelength range.

Dynamic gain equalizer using hybrid integrated silica-based planar lightwave circuits with LiNbO/sub 3/ phase shifter array

This paper proposes a dynamic gain equalizer (DGE) using hybrid integrated silica-based planar lightwave circuits (PLCs) with a LiNbO/sub 3/ (LN) phase shifter array to achieve a DGE that offers both excellent optical performance and control of the phase shifters. The structure consists of two PLCs having arrayed-waveguide gratings (AWGs) and couplers directly attached to the LN phase shifter array at its end faces. To reduce polarization-dependent characteristics, a polarization diversity technique using a polarization beam splitter (PBS) and a circulator was employed. To reduce polarization-dependent loss (PDL) due to the reflected light at the PLC-LN interfaces, tilted waveguides from the normal direction to the interfaces were introduced, and the relation between PDL and power reflectivity was theoretically investigated. A hybrid integrated DGE using super-high-/spl Delta/ PLCs and a 25-channel electrooptic (EO) phase shifter array was demonstrated. The PDL was effectively suppressed with the introduced polarization diversity technique, and the measured spectra were in good agreement with designed profiles. These results indicate that the proposed hybrid integrated DGE offers good performance and controllability for practical applications.

Transmission wavelength shift of +36 nm observed with Ta/sub 2/O/sub 5/-SiO/sub 2/ multichannel wavelength filters consisting of three-dimensional photonic crystals

We have developed multichannel wavelength filters consisting of three-dimensional photonic crystals, which have multiple filter regions with different transmission wavelengths according to differences in the in-plane lattice constants of the crystals. In this study, we improved the design of the photonic crystal (PC) filters by making use of the photonic-bandgap edge and fabricated PC filters with a Ta/sub 2/O/sub 5/-SiO/sub 2/ material system. This improvement enabled us to obtain a transmission wavelength shift of +36 nm at 1550 nm, which agrees well with the results of finite-difference time-domain simulations. By connecting the multichannel wavelength filters to a 100-GHz-spaced 40-channel arrayed waveguide grating (AWG), we suppressed the crosstalk in the AWG from -40 dB to less than -60 dB.

Integration and Evaluation of Multichannel Photonic Crystal Wavelength Filters Consisting of Autocloned Ta2O5/SiO2 Multilayer Thin Films

We report on the fabrication of multichannel photonic crystal (PC) wavelength filters and their evaluation at wavelength division multiplexing (WDM) wavelengths. The devices utilize three-dimensional (3D) PCs consisting of Ta2O5/SiO2 multilayer thin films fabricated by the autocloning method. The 3D PCs serve as Bragg mirrors in the devices and finite-difference time-domain (FDTD) simulations of these mirrors revealed that their Bragg wavelength shifted by +19.8 nm as the in-plane lattice constant of the crystal increased from 400 nm to 800 nm. We fabricated these filters with a Ta2O5 cavity and obtained a wavelength shift of +24.0 nm.

Wavelength splitters for DWDM systems

We have demonstrated chromatic dispersion free DWDM wavelength splitters by novel configuration of monolithically integrated three identical circuits, which consist of Fourier transform-based Mach Zehnder interferometers (MZI)s.