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DWDM

Researchers Unveil All-Optical Advances

The tunable lasers sit at the periphery of the network, directing traffic onto the appropriate virtual channel by changing the wavelength of the light pulses.

In Telenor's project for instance, Channel 55 of its 100-channel DWDM network might connect nodes A, B, E and H. If traffic comes onto the network at A and needs to go to H, then a central computer system directs the tunable laser at A to convert the incoming electrical signals to light pulses of the wavelength used for Channel 55 and then shunt them onto the network. At the same time, the computer system sets the receiver at node H to pick up the light pulses from Channel 55 and convert them back in to electrical signals.

Telenor's project sets up the optical equivalent of a mesh-topology TDM (time division muliplex) backbone over which permanent or temporary circuits can be established. As noted, it eliminates the need for expensive cross-connects.

The scale of the network is limited by the number of channels supported by DWDM and by the level of protection and flexibility required, according to Zouganeli. She thinks that regional or national networks could be built using the network concept.

Zouganeli thinks that commercial roll-outs could happen quite quickly. "The only new technology is the tunable lasers. Once they are proved to be stable - and I don't think that will take long - this network can go ahead to the development stage," she says.

The University of Stanford's Hornet project is taking a bigger leap into the future, by aiming to go half way towards a genuine optical router. It works on the same principle as Telenor's scheme but shunts individual packets onto different virtual channels over a DWDM backbone, rather than setting up the equivalent of circuits. That's where the nanosecond switching speeds of the latest tunable lasers comes in handy. "We believe this technology will shape networks in the future," says a spokesman at Sprint Corp. http://www.sprint.com. which is funding the Hornet project. "But it's "applied research, not products," he warns. It could take years for the researchers' work to be commercialized.

Garabet is more optimistic, noting that it's taking less and less time for new optical technologies to move from laboratory experiments to commercial deployment. There's huge pent-up demand for all-optical developments, he adds. "Most of the carriers are quickly running out of capacity."

All the same, it's important to realize that these tunable laser developments only go half way towards the ultimate goal of routing light on a packet by packet basis. They have to sit at the edge of optical nets, taking in packets in electrical form and shunting them out as light pulses on different channels. They can't sit in the middle of an all-optical network, taking in light pulses and routing them without converting them into electrical signals.

Genuine optical routers are still science fiction (see Optical Illusions). "A breakthrough in fundamental physics would be needed, and that hasn't happened yet," says Per O Andersson, head of optical research at Ericsson Telecom AB (Stockholm, Sweden).

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