AMSTERDAM -- ECOC 2001 -- Today startup Kamelian Ltd. became the second company to unveil a semiconductor optical amplifier (SOA) that is capable of amplifying multiple wavelengths simultaneously without crosstalk (see Kamelian Offers Optical Linear Amplifier).

SOAs, which provide amplification in a small, inexpensive package, could be as important to the future of metro networks as the erbium-doped fiber amplifier is to long-haul networks. They are based on a semiconductor laser without mirrors, allowing amplification to take place without the feedback that results in lasing action.

SOAs have been around for a long time, but have had significant limitations that have prevented wide commercial deployment. One of the main drawbacks of using SOAs in DWDM systems is that most aren't capable of handling multiple signals at the same time.

Here's why. When the optical intensity inside the device changes, because a signal needs to be modulated, for instance, the amount of gain in the device changes. If there is a second wavelength passing through the device, it "feels" those changes in gain, and so its output power wobbles in synchrony with the first signal. In other words, there is crosstalk. Fluctuations in gain also occur when channels are added and dropped in the network.

Until today, Genoa Corp. was the only company to have developed an SOA that overcame these restrictions (see Genoa Amps Up). Now Kamelian has solved the problem too, and gone one better, according to Paul May, the company's CEO.

"The difference from Genoa -- and this is quite a significant difference -- is that we can vary the gain applied to all the channels, and still operate linearly [with no crosstalk]," says May. This is useful because it allows network designers and engineers to control link loss budgets. Even EDFAs can't do this, he notes.

Should Genoa be worried? "Yes, definitely," says May. "We're moving right into their territory with this device."

Rick Gold, Genoa's CEO, sounds pretty calm, however. "I'm not too surprised to see other folks looking at single-chip solutions for amplification," he says. It's difficult for him to comment further, since Kamelian hasn't given any clues about its technology. May says it won't do so until it finishes filing the patents involved.

Gold says that what matters are the performance specifications. Although Kamelian isn't handing out spec sheets, it is demonstrating its new device here at the ECOC exhibition. This shows four wavelengths, each carrying 10-Gbit/s data, passing through the SOA. When one wavelength is dropped, power levels should remain steady. The product will be sampling early in 2002.

— Pauline Rigby, Senior Editor, Light Reading
http://www.lightreading.com