MEMS Technology Propels Telecom Systems Toward An All-Optical Network

Agilent Technologies is using a hybrid process that combines CMOS with microfluidic micromachining steps. Based on the company's ink-jet printing technology, fluid-based switches are used. These consist of intersecting silica waveguides, with a trench etched diagonally at each point of intersection. Each trench contains an index-matching fluid that in the default mode allows light to be transmitted through it unimpeded. To switch the light path, bubbles are formed and removed hundreds of times per second by a thermal actuator. The bubbles reflect the light from the input waveguide to the output waveguide. This approach offers the advantage of no moving parts.

More details about switch architectures will be discussed in the second part of this report. Suffice it to say that in the micromachined mirror ap-proach, two main designs are being pursued: 2N configurations, where N input ports and N output ports require 2N controllable mirrors, and N² configurations, where N input ports and N output ports require N² controllable mirrors. It should be obvious that the former approach can be more easily scaled to larger port counts (say 1000 times 1000) than the latter approach. But the 2N approach is more difficult to control with larger port counts.

One thing is becoming increasingly clear. For any company to be successful in the optical MEMS market, it must rely on its experience in mass producing such devices cost effectively and reliably. Janusz Bryzek, a noted MEMS pioneer as well as president and CEO of Transparent Optical Inc., cautions, "The adaptation of the automotive MEMS experience is likely to improve the manufacturability and reliability of next-generation optical switches." Bryzek cites the hundreds of millions of automotive MEMS sensors presently used in an environment that's significantly harsher than the communications sector as an example where mastering the manufacturability of optical MEMS switches can be achieved.

That's one reason why Tellium has signed an agreement with Analog Devices to have the latter make MEMS micromirrors for Tellium. Analog Devices, one of the largest suppliers of automotive MEMS sensors, is leveraging its planar micromachining process in which it integrates signal-conditioning electronics on the same chip with optical micromirrors.

Thanks to its acquisition of BCO Technologies in Ireland, Analog Devices is implementing silicon-on-insulator (SOI) technology on its micromachined mirrors. The company feels confident enough about its manufacturing expertise that it supplies reference designs to any customer it works with. Customers can obtain prototype integrated versions of micromachined optical MEMS switches, complete with the signal-conditioning electronics.

Given all of the aforementioned technical challenges, there appears to be enough industry momentum and confidence that the right solutions should be achieved in the next couple of years. Will that happen? Stay tuned.