Product Profile Santel launches electronic dispersion compensator

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Santel Networks (Newark, CA) president and chief executive Stefan Braken-Guelke believes that a company's value proposition has to be "a no-brainer. You should look at the value proposition and say, 'Of course.'" Santel's value proposition is to provide twice the performance at half the price. Well, of course. In today's marketplace, that should be the goal of every vendor. But just how Santel provides this performance may help set it apart from the competition. Th 108726

A CMOS digital-controller chip and a silicon germanium signal conditioner chip compose Santel Networks' electronic dispersion compensator.

The company recently launched what it claims is the first commercially available electronic dispersion compensator (EDC) for both chromatic dispersion (CD) and polarization-mode dispersion (PMD). The two-chip set provides dispersion compensation and a clock and data recovery demultiplexing (CDR-D) function—at the same price as a high-performance CDR-D without dispersion compensation.

"What [our product] is really all about," says Braken-Guelke, "is dispersion tolerance." Santel's two-chip set increases the dispersion tolerance of an optical link, which enables the link to tolerate increased levels of CD or PMD while still performing to rated specifications. Its EDC compensates for signal distortion during transmission, thanks to the company's CleanSignal high-speed adaptive signal processing technology.

"Every channel is different; every channel has its quirks," says Braken-Guelke. "What we do is analyze each particular channel and gather statistics about it, and out of those statistics, we calculate coefficients. These coefficients are then used by our proprietary DSP algorithms to filter or clean the signal." This process occurs at a rate of 4,000 times per minute, and the system refreshes itself with a new set of coefficients at a rate of 4 kHz. "What our customers tell us is that all these changes in dispersion—in CD or PMD—happen at a rate of below 1 kHz," adds Braken-Guelke. "Since we refresh with 4 kHz, we have good bandwidth there to filter out things you would not even be able to cover with optical solutions."

The choice between electrical and optical dispersion compensation is also a no-brainer, say the folks at Santel. Their two-chip set is easily manufactured in volume—compared to optical compensators, which must be handcrafted and often require custom specification—and it fits on a line card. Optical compensators take up costly rack space.

Santel's EDC also comes out ahead in terms of insertion loss. "If you do this optically with PMD or CD [compensators], you loose anywhere between 5 dB and 6 dB [and] you have to use higher-powered lasers and more stringent components, which all adds to a more expensive network," explains Braken-Guelke

The linchpin for Santel is the cost of its device, which it claims is "free," in the sense that its customers have to purchase a CDR-D anyway, and Santel does not charge extra for it. Optical PMD compensators cost anywhere from $5,000 to $10,000 per lambda, while sub-band optical dispersion compensation modules are priced around $3,000. The Santel two-chip set costs under $500 in production quantities.

"It is very hard for optics to keep up with electronics in some domains—like processing information," contends Tom Hausken, director of optical communication components at Strategies Unlimited (Mountain View, CA). "Electronics is just a great technology, and it continues to get faster as they come up with new algorithms. It's also much cheaper than some of these optical solutions; it's hard to ignore that," he adds.

Santel faces competition on two fronts: the physical layer IC manufacturers, including Broadcom, AMCC, and Multilink, as well as optical dispersion compensation vendors like Yafo, Big Bear Networks, and Phaethon Communications. Braken-Guelke is quick to note, however, that none of these companies provides exactly what Santel offers.

The S44501/S44003 chipset provides full CDR-D functionality and is programmable for 9.95- to 12.5-Gbit/sec line rates. The chips are OIF 99.102-compliant and meet the jitter tolerance requirements of GR-1377-CORE. Engineering samples are now available, with volume production expected to begin in the first quarter of next year.

While Santel Networks does have a 40-Gbit/sec product in its portfolio, that product has been temporarily shelved; the company believes the near-term opportunity is in the metro at 10 Gbits/sec. But will Santel manage to convince its customers that the benefits of the EDC make it a no-brainer?

"It's always one thing to do something in a lab," admits Hausken. "It's another to go out and actually implement it—especially at 10 Gbits. There's no way of knowing until people play with this and find out if it really holds up."

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