Etsu Hashimoto

Thermally Controlled Magnetization Microrelay

A novel micro-mechanical relay using a thermally controlled magnetization actuator has been developed. The actuator is actuated by heating it with integrated titanium film heaters which changes its local magnetization, thus realizing a simple structure without an electromagnetic coil. The microrelay uses installed permanent magnets to achieve self-latching. It was fabricated by nickel electroplating; its estimated generated force is about 60 /spl mu/N. The heating time needed to reduce its magnetization is less than 10 milli-seconds, so the switching speed is comparable to that of a conventional mechanical relay.

High-frequency synchronized signal generation using semiconductor lasers

Generation of high-speed optical pulses is an important technology for not only optical data transmission/processing, but also optical subcarrier transmission in wireless-access networks. Semiconductor lasers are the most promising optical pulse sources for these application fields. The typical methods of generating optical pulses with repetition frequencies of up to subterahertz from semiconductor lasers are reviewed in this paper. Synchronization of subterahertz optical pulses to an electrical clock and suppression of phase noise are essential for many applications. A few techniques that enable free-running subterahertz pulses to be synchronized to a given clock with lower frequency are also introduced. Our experimental results on the synchronization of 0.2-THz free-running pulses generated from a harmonic colliding pulse mode-locked laser using photonic down-conversion with phase-locked loop (PDC-PLL) are described. It is shown theoretically and experimentally that the clock-source-limited low-timing-jitter subterahertz pulses can be generated using PDC-PLL.

Electrically separated two-axis MEMS mirror array module for wavelength selective switches

A novel two-axis MEMS mirror array module for wavelength selective switches feature a new electrode structure that reduces electrical interference between adjacent channels. The fabricated 50-channel mirror module has good characteristics satisfying system requirements.

Low-Loss Transponder Aggregator Using Spatial and Planar Optical Circuit

We propose a compact transponder aggregator (TPA) consisting of a wavelength selective switch (WSS) array and a direction switch array. It has no intrinsic splitting loss and therefore the number of ports can exceed that of a conventional multicast switch. A waveguide-based frontend that incorporates spatial beam transformers enables us to increase the number of ports and integrate multiple WSSs in a simple optical system. The direction switch array is integrated in the frontend. We describe an 8 × 24 prototype, which is the largest port count yet achieved for a TPA with no intrinsic splitting loss.

Clock source-limited low jitter, subterahertz signal generation from mode-locked semiconductor laser controlled by phase locked loop (PLL) with photonic downconversion

Reference clock-limited low jitter of 0.14 ps, 197 GHz signal generation is successfully demonstrated from a harmonic colliding pulse mode-locked laser diode controlled by a PLL with photonic down-conversion using high order modulation side bands.

Temperature-compensated, highly accurate wavelength-tunable filters for photonicnetworks

A temperature compensation technique is proposed and demonstrated for highly accurate control of the transmission wavelength of wavelength-tunable optical bandpass filters. The technique calculates wavelength error, which is caused by transient variations of the operating temperature of filter modules, by use of the theory of thermal conduction and controls the filter with an appropriate offset according to the calculated value to maintain a constant transmission wavelength. A disk-shaped wavelength-tunable filter based on a mechanical tuning mechanism is demonstrated to confirm the validity of the technique. For the filter, the transmission wavelength is controlled to an accuracy of 0.01 nm against drastic temperature variations whose maximal change rate reaches 2.5 °C∕min in the range of 20-50 °C. A filter controlled with this technique has the potential to provide high-performance channel selectors for wavelength-division-multiplex-based photonic networks, and its feasibility is confirmed by transmission experiments at 2.5 Gbit/s.

Wavelength-scanning optical bandpass filters based on optomechatronics for optical-frequency sweepers

We propose and demonstrate a method for improving optical-frequency sweepers that uses a disk-shaped optical bandpass filter operated under the synchro-scan mode. We optimize the filter layer structure to achieve high linearity in optical-frequency tuning with the rotation angle of the disk, while maintaining a constant band-inhibition performance. We introduce an optical system that narrows the bandwidth by using an optimized beam coupler and improves the filtering performance by using a multiple-path method. The optimized filter enables a stable linear optical-frequency sweep when it is used with a motor stabilized by phase locking. The improved optical frequency sweepers can extend the sweep range to above 2 THz, while suppressing the accumulation of spontaneous emission noise.

A physical modeling and long-term measurement of tilting angle drift caused by dielectric surface charging in MEMS micromirrors

Dielectric charging of MEMS micromirrors causes tilt angle drift, which is a major reliability problem for telecom applications. In this paper, we propose a physical model of angle drift in a MEMS mirror system considering surface charge motion on dielectric oxide. Good agreement is obtained between the model calculation and experimental results, which suggest that angle drift can be predicted by the proposed model.

Autonomic control of photonic networks based on absolute wavelength management

An autonomic network control scheme is presentd for wavelength-division multiplexing based photonic networks. An aboslute wavelength control scheme using a disk-shaped wavelength tunable optical bandpass filter is presented. The wavelength reproducibility of 0.02 nm for the entire tuning range at various temperatures is promising for the automonic wavelength management. To verify the control scheme, an optical add/drop multiplexing subsystem is constructed using optical switches utilizing oil latchign interferential tension effect and wavelength-tunable devices. Its detailed operating performances are experimentally evaluated. The switching speed of less than 20 ms and extinction ratios of less than 45 dB of the switching element are allowable in practical systems. Error-free transmission performance at 10 Gbps with negligible coherent cross talk at an intersection of the switch is obtained. The optical carriers generated by a wavelength-tunable ring laser usign a disk filter, are allowable for data transmissions. These results show that the autonomic entwork contorl scheme is feasible.