Israeli startup KaiLight Photonics Ltd. (formerly ChiLight Technologies Ltd.) is preparing an all-optical wavelength converter (AOWC), which it intends to demonstrate for the first time at the upcoming Optical Fiber Communication Conference and Exhibit (OFC).

This will mark the company's first public appearance. What's more, KaiLight CEO Sagie Tsadka reckons that the demo will be one of the first, if not the first live showing of an AOWC working at 10 Gbit/s.

That claim seems a little surprising given that all-optical wavelength conversion has been around for a long time. Scientists have been studying ways of translating one wavelength to another without first turning it back into electricity since the early 1990s. On the other hand, it's only in the last few years that potential applications have seemed realistic and that venture capital has been available to commercialize all the research (see Interest Grows in Wavelength Conversion).

All-optical wavelength conversion could slash costs in carrier networks in the long term, so it's hardly surprising that there are plenty of startups in this area, including Lightbit Corp., Luxcore Networks Inc., and Optovation, Inc. to name but a few. It's not so much the existence of KaiLight's AOWC that's interesting, but the fact that it is based on a completely different approach to that of other vendors, according to Tsadka.

But pinning down exactly how KaiLight's widget works isn't easy, because the company isn't giving many clues as to what's inside the box.

AOWCs generally fall into two camps: those based on indium-phosphide Semiconductor Optical Amplifiers (SOAs) , such as the chip offered by Alcatel Optronics (Nasdaq: ALAO; Paris: CGO.PA), and those based on lithium niobate. "I guess you could say we're a new category," Tsadka says.

He does reveal that the device exploits a non-linear effect inside optical fibers. These are coupled to other (unspecified) components, and the end result is a subsystem that resembles Erbium Doped-Fiber Amplifiers (EDFAs) in size, he adds. Probably, those other components include a source laser (maybe a tunable one), to provide the new wavelength, and an amplifier, because Nonlinear Effects are only significant at high optical powers.

The upside, according to Tsadka, is that all these components are in common use in today's networks, and therefore are readily available. There's no need to develop new chips, as both other approaches must do.

A competitor, who did not wish to be named, says KaiLight's original name, Chilight, offers the biggest clue: "The name comes from the Greek character Chi, which is often used for denoting mixing operations. DFG [difference frequency generation] would be a chi-squared operation, and FWM [four wave mixing] would probably be a chi-cubed operation," says the competitor.

Kind of makes you wonder if the company changed its name to try to throw people off the scent!

FWM is tricky to explain to someone without a physics degree, but the U.K.'s National Physical Laboratory has posted a plucky attempt at it here: http://www.npl.co.uk/npl/sections/photonics/nonlinear/four_wave_mixing.html.

In short, it's a "mixing effect", creating light at new wavelengths using the power from the both the original and pump signals. This differs from a "gating effect" where the original signal is used to modulate the new wavelength, but the power for the new wavelength is supplied by a separate pump laser. SOA-based wavelength conversion uses a gating effect, while lithium niobate converters rely on a mixing effect.

Mixing effects have a big drawback, according to proponents of the gating effect: For a certain combination of input wavelength and pump wavelength, it's only possible to access a group of output wavelengths rather than the entire range.

But Tsadka claims that's not a problem in KaiLight's case. "There is a kind of dependency, but that's all taken care of in the electronics," he says. "The end result is we can convert any input wavelength into any output wavelength."

Developers of lithium niobate solutions, which, as noted, are based on a mixing effect, argue that non-linear effects in optical fiber are weak, requiring many meters of fiber to perform the same function as just a few centimeters of lithium niobate chip.

But in the end, vendors acknowledge that no one approach to AOWC is perfect, considering the early stage of the technology.

KaiLight has received $7 million total funding, from Lucent Venture Partners Inc., Ofer Brothers High-Tech Group, The Yozma Group, and Plentyum, an Israeli incubator.

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