Fujitsu develops high-speed multichannel optical switch based on MEMS mirrors

EDP Weekly's IT Monitor, Oct 6, 2003

Fujitsu Network Communications Inc. has announced the development of an 80-channel optical communications switch that adopts MEMS (Micro Electro-Mechanical System) mirrors. The new MEMS device, which integrates electrical circuitry and mechanical structures, achieves a switching speed of one millisecond, the fastest of any multi-channel optical switch to date. The new switch is expected to enable the development of Dynamic OADMs essential for next-generation optical transmission networks.

Details of the technology used in this switch were presented at ECOC-IOOC 2003 (European Conference on Optical Communication/International Conference on Integrated Optics and Optical Fibre Communications), held in Rimini, Italy starting September 21.

Because of the need to efficiently transmit the massive amounts of data carried over high-speed Internet connections, there has been an increase in demand for cross-connect equipment, which is required for the effective operation of fiber-optic networks and for network interconnections. With conventional equipment, however, optical signals need to be converted to electrical signals for processing, limiting the ultimate performance that could be achieved through wave-division multiplexing or other optical multiplexing techniques. The goal, therefore, has been to develop cross-connect equipment with all-optical switching so that the optical signals need not be converted.

Fujitsu's development depends on MEMS mirrors to bounce light beams. MEMS mirrors can be tilted to deflect the beam to different points in space, resulting, in this case, in a three-dimensional optical MEMS-mirror switch. There are three key features of this technology--rapid switching, a compact optical switching fabric, and an optic power-level feedback mechanism.

Rapid switching: A notch filter (i.e., a filter that eliminates a specified narrow bandwidth frequency from a signal consisting of frequencies of a given bandwidth) in the MEMS mirror serves to suppress the mechanical resonance (a phenomenon whereby the input of an external signal at a certain frequency induces strong vibrations) that normally occurs when switching the optical signal. The notch filter eliminates just the MEMS mirror's resonant frequency from the driving electrical waveform.

Compact optical switching fabric: Fujitsu developed a folded optical switch fabric configuration whereby the input beam is reflected through a roof-type retro-reflector on its way to the output (see figure 2). Compared to flat mirrors, this configuration halves the length of the optical path, making for a more compact switch overall.

Optic power-level feedback mechanism: The tilt of the MEMS mirrors is precisely controlled thanks to a feedback loop in a built-in control function, which maintains the optical power at a fixed level. This makes it possible to compensate for variations in the power levels of each channel and also eliminates the need to have variable optical external to the switch.

The combination of these three technologies results in a switch with 1 millisecond switching speed, compact dimensions (150 x 400 x 300 mm) and optical power stability within /-0.5 dB.

Some of this research was conducted on behalf of the Telecommunications Advancement Organization of Japan under a contract for the research and development of photonic networking using optical burst switching.