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Optical/IP

Startup Prepares Secret Switch

The "steered beam" technology being used by Onix for its larger scale switch almost certainly refers to the way in which the MEMS switch fabric itself is made. In this process, chemicals are used to etch into a sandwich of silicon and insulator, in a way that leaves some parts suspended, and thus movable.

The movable parts can be in various forms. Onix has a cantilevered beam and Xros has something akin to a compass in gimbals. Electrodes are used to apply currents to these tiny parts to make them rotate, so they can bounce light off in different directions. Their position is monitored by measuring the strain in the silicon "hinges" on which the mirrors are suspended. The surfaces where the light bounces are typically covered in gold leaf to ensure maximum reflection.

This way of making MEMS is sometimes called "bulk machining" and now appears to be the preferred process for making large arrays of mirrors.

Lucent Technologies http://www.lucent.com recently said it was abandoning another way of making MEMS - "surface micro-machining" - for its optical switch developments. This uses a silicon-and-metal oxide rather than a silicon-on-insulator sandwich. Its prone to quality control problems, and the mirrors can stick, according to Scott Blackstone, founder and CEO of BCO Technologies PLC http://www-bco-technologies.com, a Belfast, Northern Ireland, manufacturer of silicon-on-insulator MEMS.

Lucent is rumored to be using BCO's technology for its LambdaRouter optical cross connect. BCO makes so-called thick film silicon-on-insulator MEMS. This means that the mirrors are on relatively thick pieces of silicon, which makes them particularly flat and stable, according to Blackstone.

A third method of making MEMS, called "high aspect ratio machining" uses milling equipment to cut deep holes in silicon. It's not often used for arrays of mirrors.

It's worth pointing out that MEMS technology has a wide range of potential applications, not just in telecom but also in other fields like biology. Also, MEMS are used for a wide range of optical devices within telecom. The three main ways of making them - bulk, surface and high-aspect - provide ways of implementing different functions. Developers of switching subsystems typically get specialist companies like BCO and Cronos Integrated Microsystems Inc. http://www.memsrus.com to make their MEMS switching fabric for them, sometimes specifying their own designs.

Cronos is the only company that can make MEMS using all three processes, according to Jesko von Windheim, its vice president of marketing and business development. It sometimes uses all three technologies in the same device. That might explain why it's now being acquired for $750 million by JDS Uniphase Corp. http://www.jdsunph.com (see JDS Uniphase Moves Into MEMS).

by Peter Heywood, international editor, Light Reading http://www.lightreading.com

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