Dispersion Battles Continue
ATLANTA -- OFC -- The last few years have seen plenty of answers for Chromatic Dispersion and Polarization Mode Dispersion (PMD), but an eight-person startup called Aelis Photonics Inc. claims to have an equalization method that can outdo them all.
Based in Israel, Aelis claims it's developing a compensation technique that eliminates a number of interference problems that affect optical networks at high speeds. Aelis says it can wipe out chromatic dispersion and PMD, as well as phase distortion and nonlinearities, all in a single chip that can handle multiple channels simultaneously.
Aelis officials don't expect the product to draw revenues until late 2004. But they used this week's OFC Conference to begin laying the groundwork, including announcing the company and adding Bell Labs veteran and Phaethon Communications founder Alan Willner to their advisory board (see Aelis Boosts Optical Reach, Speed and Aelis Photonics Adds to Board).
The company's chip, targeting 10-Gbit/s networks, is completing trials at two major OEMs and one carrier, says chairman Eran Yarkoni. What's next, though, is for Aelis to meet with potential customers to determine what form the final product should take. To that end, nearly half the company has come to Atlanta: Yarkoni, CEO Menachim Tipris, and CTO Varda Herskowits.
Aelis's technology, called ReachExtender, takes whatever signal it's handed and reconstructs a proper eye diagram. The result is that dispersion is corrected without the Aelis device having to know anything about what caused the problems. The device won't build an eye from white noise, but it can reconstruct a completely obscured eye, provided the bits aren't spread across more than 2.5 bits-worth of signaling time.
"Rather than looking to the physical basis of each and every distortion source, we are looking from the receiver's point of view. We try to give the receiver what it is designed to get," Herskowits says.
The technique works in the optical domain, meaning it can operate on parameters that electronic dispersion compensation can't, such as phase. And while companies like the late Yafo Networks developed optical methods of compensation, they haven't been able to handle higher-order PMD the way Aelis can, Herskowits says.
Aelis won't disclose details of its technology, but Herskowits says the technique is best described as "specially tailored filter architectures in conjunction with a proprietary algorithm." She adds that Aelis got its ideas from the wireless world, adapting methods that have been used in cellular communications but ignored in the optical realm.
Founded in mid-2001, Aelis numbers just eight people and has gotten by with $2 million in financing, although the company will be looking to raise more this year, says Yarkoni.
For those who consider Aelis a bit too far out, there are several other vendors demonstrating dispersion compensation at the OFC show, among them, Accumux Technologies Inc., Applied Micro Circuits Corp. (AMCC) (Nasdaq: AMCC), and Santel Networks Inc.
Accumux announced it has begun shipping the second generation of its etalon-based Light Fixer modules announced in September (see Accumux Demos Dispersion Compensator). Accumux now claims Light Fixer can control chromatic dispersion at distances of 200 km on singlemode fiber. A built-in slope compensator allows dispersion compensation of up to 2,688 ps/nm.
The distance figure is important because it's more than twice the typical 80km distance between amplifier huts. So, carriers can deploy Light Fixer to every other hut with comfortable margin to spare, says Ross Kocen, vice president of marketing.
Kocen says Accumux got the extra distance by adding more of its modular optical subassemblies into the device. The company could have tried for more than 200 km but was afraid adding too many subassemblies could rack up too much insertion loss.
A more important improvement over the first-generation Light Fixer is the size. The original "was like a cube of butter, and the feedback we got from customers is that they wanted something that would fit on a line card," Kocen says. The size may be why Accumux was a bit shy about Light Fixer at last year's OFC (see Dispersion: New Version).
Elsewhere at this year's OFC, AMCC demonstrated its electronic compensation product, which taps forward error correction (FEC) information to help rebuild data (see AMCC Demos Electronic Compensation). And Santel announced it has begun sampling the two-chip set that has had some trouble getting out of the gate (see Santel Undeterred by Chip Glitch).
— Craig Matsumoto, Senior Editor, Light Reading
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