Japanese firms push MEMS development

Research continues to focus on technologies that could yield the next optical-network building block: all-optical switches. As reported previously, micro-electromechanical systems (MEMS) show promise in this area, and several firms in the United States have launched development programs in hopes of maturing the technology first. This ambition is not exclusive to the United States, however, as two Japanese firms recently displayed their work in this field at the recent InterOpto '99 exhibition in Tokyo.

MEMS consist of tiny, movable micromachines mounted on integrated circuits. Frequently, these machines contain a mirror as a reflective element. The switch displayed by Japan Aviation Electronics Industry (Tokyo) at the show falls into this category. The device consists of a 50-micron mirror mounted on an electrostatic micro-actuator; the switch benefits from the company's film deposition and silicon etching technology, said sources at the show. The mirror raises into the incoming photon stream when called upon to switch the optical carrier to another channel. When fully developed, the device should provide larger-scale integration and lower power consumption than conventional switches, the company claims.

Company sources at the show revealed aggressive performance goals, which they said they expected to meet within a year. These specifications include

Chip size of 1 sq mm.

Power consumption of <5 mW.

Crosstalk >70 dB.

Under 5V of driving voltage.

Switching time of <5 msec.

Insertion loss of <2 dB.

Return loss <60 dB.

The company expects to target such applications as crossconnects, add/drop multiplexers, and optical measuring instruments.

Meanwhile, NTT Electronics (Ibaraki, Japan) has combined its planar lightwave circuit technology with MEMS concepts to create the Olive thermo-capillary optical switch. The design elevates the novel concept of MEMS into the realm of the exotic. The switch comprises intersecting waveguides (the company displayed a 1x8 configuration at the show), a pair of microheaters, and index matching oil in slits that cut across waveguide junctions diagonally (see Figure). To switch a beam of light, the microheaters decrease the surface tension of the oil, causing the column of oil to expand toward the lower temperature side and into the path of the light beam because of thermo-capillary force. When the oil is removed from the cross point of the waveguides, the light path is switched via total internal reflection on the slit side wall.

The Olive switch uses olive oil to regulate the direction of optical streams.

NTT Electronics describes the mechanically self-latching device as providing high optical transparency and on/off ratio. However, the company admits that the device is currently suitable only for relatively slow switching applications, as it has a typical rise time of 50 msec. The 1x8 configuration offers:

Chip size of 12 mm x 13 mm.

Crosstalk of <-50 dB.

Insertion loss of <3 dB.

Isolation >50 dB.

On/off ratio of >45 dB.

The development of optical switches using MEMS technology appears to be several years away, although Astarte Fiber Networks Inc. has teamed with MEMS-supplier Texas Instruments in hopes of speeding development. Both Lucent Technologies and AT&T Lightwave Networks Research have also publicized their research in this area. Based on the work revealed in Tokyo, it appears MEMS research is truly an international phenomenon.