Researchers Unveil All-Optical Advances

Tunable lasers may turn out have a key role to play in realizing the dream of building all-optical networks, judging by results of research projects in the U.S. and Norway.

In the U.S. project, called Hornet (Hybrid Optical Ring Network ), researchers at Stanford University have demonstrated that tunable lasers can switch traffic onto different channels of a DWDM (dense wave division multiplexing) network) on a packet-by-packet basis - half way towards creating a genuine optical router. The results are scheduled to be unveiled at next month's Optical Fiber Communication conference http://www.osa.org/mtg_conf/OFC/ in Baltimore.

In the Norwegian project , research and development staff at Telenor AS http://www.telenor.com, the country's incumbent carrier, have used a similar combination of tunable lasers and DWDM technology to build a mesh-topology net. It offers much better flexibility and reliability than conventional ring topology DWDM networks while eliminating requirements for optical cross-connects, according to Evi Zouganeli, Telenor's project manager.

Both projects make use of significant advances in tunable laser technology. The latest tunable lasers can pump out light at a large number of different wavelengths. They can also switch from one wavelength to another in an incredibly short time span -- less than 10 nanonseconds in the case of lasers from Altitun Inc. http://www.altitun.com/, according to Basil Garabet, its senior vice president of marketing and sales. "It's several orders of magnitude faster than anything electronic," he says.

Altitun's tunable lasers are being used in both the U.S. and Norwegian projects. Telenor is also using tunable lasers from Marconi Communications Co. http://www.marconi.com and NTT Communications http://ntt.com.



In the U.S. and Norwegian research projects, these new-style tunable lasers have been combined with the DWDM developments. In both cases, a test network of DWDM gear has been set up over which multiple virtual channels of light of different wavelengths have been configured, connecting different nodes together. These virtual channels are somewhat like virtual circuits in frame relay networks in that they create a logical connection between nodes but don't take up any capacity when they're not carrying traffic.