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Interest Grows in Wavelength Conversion

A growing number of companies are developing all-optical wavelength converters

November 23, 2001

4 Min Read
Interest Grows in Wavelength Conversion

Optovation Inc.'s funding this week draws attention to a technology that's attracting increasing attention and investment: all-optical wavelength conversion.

Components that can translate a data signal from one wavelength to another without first having to convert it back into electricity have been under investigation since the early 1990s, with Alcatel Optronics (Nasdaq: ALAO; Paris: CGO.PA) one of the pioneers in this area. But investor and vendor interest has perked up in the last year or so. Now that other forms of all-optical technology, such as all-optical crossconnects, have started moving into the real world, there is a place where all-optical wavelength conversion could slot into the network and provide big benefits.

Companies like Optovation and Luxcore Networks Inc. started out in life as systems integrators developing all-optical packet switches. Optovation was the components house for the now defunct Roshnee Corp. (see Roshnee to Split in Two and Optovation Brings in $20M). Luxcore didn't get enough cash to complete its switch, so it decided to refocus on components (see Luxcore to Demo Optical Switch Advance and Luxcore Pulls a Switcheroo).

Both saw wavelength conversion as the answer to contention inside the switch -- when one wavelength on an input fiber needs to connect to a different wavelength on the output fiber. Of course, this can be done with standard OEO (optical-electronic-optical) transponders, but that partially defeats the purpose of making the guts of the switch all-optical in the first place.

However, both Alcatel and Luxcore now believe that the first application for wavelength conversion will come from a different quarter. "Wavelength conversion is not the only function this component can produce. It is also an all-optical regenerator," says Guy Mesquida, executive director of Alcatel Optronics. The chip sold by Alcatel can both (re)amplify and reshape the data signal (so-called 2R regeneration), he says.

Today, signal regeneration is done with OEO transponders. The problem with this is it requires a dedicated transponder for every combination of protocol, bit-rate, reach, and wavelength in the network. In a typical carrier network, there can be thousands of permutations. A spare needs to be carried for each one, and the costs soon add up.

"Storing all these replacements results in significant cost and administration penalties, including tax liabilities associated with fixed assets, inventory management, and storage space for the life of the transponder, which is typically 15 years," notes Luxcore's chairman and CEO Gerald Ramdeen.

This "sparing" argument is exactly the same one that's driving development of tunable lasers. In some ways, the all-optical wavelength converter can be thought of as a tunable transponder.

Luxcore and Optovation appear to be using similar technology inside their wavelength converters. Both say that it's based on what's called cross-phase modulation, a non-linear effect that takes place inside semiconductor optical amplifiers (SOAs) -- see beginners guide on Nonlinear Effects for more. Without going into the details of how this works, the end result is that the signal on the input wavelength is used to modulate a continuous signal supplied at a different wavelength, possibly by a tunable laser.

There are other ways of making all-optical wavelength converters, says Optovation's CEO Larry Tarof, but this approach has the advantage that the output wavelength is independent of the input wavelength. That's important if the output wavelength is going to need to change.

Luxcore is reportedly using technology developed at Stanford University, whereas Optovation actually buys indium phosphide chips from Alcatel, which it then packages. "A lot of the cost of turning this into a product relates to the packaging," says Tarof, noting that the packaging process involves three interdependent alignments with submicron tolerances.

The fact that Optovation buys chips rather than packaged products from Alcatel implies that the pair have a rather special relationship. "It's a policy we do not sell any chips," says Alcatel Optronics' Mesquida. "We only deliver chips where we have a specific partnership."

In addition to Luxcore and Optovation, there are at least two other stealth-mode startups focused on all-optical wavelength conversion: Israel's ChiLight Technologies Ltd., and Mountain View, California-based Lightbit Corp. Little is known about these other than what is revealed on their Websites. The lead investor in ChiLight is The Yozma Group. Lightbit is funded by Accel Partners and Mayfield Fund.

According to Alcatel Optronics' Mesquida, JDS Uniphase Inc. (Nasdaq: JDSU; Toronto: JDU) also has expertise in wavelength converter technology through its acquisition of Philips Optoelectronics in 1998. And any company selling SOAs, such as Kamelian Ltd. and Opto Speed SA, is also likely to be working in this field, he says. Opto Speed, which spun out of the Swiss Federal Institute of Technology, Zurich (ETHZ) could provide a route to market for wavelength converter developments that have been reported by Prof. Hans Melchior's group at ETHZ.

— Pauline Rigby, Senior Editor, Light Reading

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