Patent Points to Corvis Secrets

Speculation about the technology being used in Corvis Corp.'s all-optical switch reached fever pitch last week after Light Reading published a story suggesting that some new developments from Iolon Inc., a startup, might provide a clue (see Corvis's Secret Sauce?)

A much more likely candidate has now emerged. Corvis, it turns out, filed a patent some time ago -- International Publication Number WO 00/05832 -- which spells out a switch architecture based on research originally carried out at Imperial College in London. Although Corvis itself declines to say whether its switch is based on this patent, other sources close to Corvis and Imperial College say that it definitely is.

Corvis is reckoned to have developed the only all-optical switch that's anywhere close to deployment. It's known to be a 6-by-6 port switch, and Corvis has made a big thing out of saying that it's built from standard components -- the reliability of which has been proven in practice.

That description exactly fits the switch architecture cited in the patent. Essentially, it's built around 36 fiber amplifiers that allow light to pass when they're powered up and block light at other times. Each input port is connected to a splitter that divides the light among six of these amplifiers. At the other end of the amplifiers, the reverse happens. The light is collected by six further splitters and steered to the output ports.

The upshot is a relatively small, clunky, all-optical switch made from standard components -- rather a lot of components, which raises question marks regarding cost and reliability, according to some experts.

It's also worth noting that Corvis's all-optical switch is unlikely to deliver all-optical networks in practice. In order to use bandwidth efficiently, the wavelength of some streams of light pulses would need to be changed. Right now, the only way of accomplishing this is to shunt them out of the switch, convert them into electrical signals, retransmit them at the new wavelength, and then shunt them back into the switch for the next leg of their journey.

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