Scintera Networks debuts compensation device

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Scintera Networks' (San Jose, CA) high-speed advanced signal processing platform (ASPP) blends analog and digital processing to provide high-speed, high-performance, blindly adaptive dispersion compensation. Implemented in standard 0.13-µm CMOS, the platform is also low-power and low-cost, say company representatives, who claim that the technology is "all about preserving the existing fiber and equipment."

The SCN3142 electronic dispersion compensation engine (EDCE)—based on Scintera's ASPP technology—addresses the problems associated with legacy multimode fiber, originally installed for FDDI applications. Such fiber works fine when implemented with 1- and 2-Gbit/sec traffic, but at 10 Gbits/sec, it is subject to differential modal dispersion, which limits the transmission distance.Th 136931

This 100-m span of 62.5-µm multimode fiber suffers from modal dispersion at 10 Gbits/sec, but the addition of the SCN3142 EDCE opens the eye and enables error-free transmission.

The SCN3142 compensates for dispersion in 850- and 1310-nm multimode fiber used in 10-Gigabit Ethernet, 10-Gbit/sec Fibre Channel, and short-reach SONET/SDH OC-192 data links, extending the usable distance of the fiber from 75–80 to 300 m. It features adaptive equalization that betters the typical requirement of milliseconds or hundreds of microseconds; Scintera's device clocks in at tens of microseconds or less.

The device is form-factor-agnostic; its small size—a 5×5-mm QFN package—enables the chip to seamlessly integrate into any of the 10-Gbit/sec transponder multisource agreements (MSAs). Its size also enables the chip to reduce both the number of components and complexity of enterprise networks by offering a viable alternative to the currently available LX4 CWDM approach standardized two years ago by the IEEE.

"Historically, serial has always won over parallel links both for optical and copper," explains Scintera president and CEO Abhijit Phanse. "There's something magical about the 300-m number because it enables over 90% of the installed base, and the only solution available today is the parallel solution, the LX4."

The legacy base in metro networks composes singlemode fiber, which is prone to equally disruptive dispersion problems at 10 Gbits/sec. Chromatic dispersion and polarization-mode dispersion can severely limit transmission distance, and the alternatives—installing dispersion compensating fiber or deploying amplifiers—are expensive.

"The huge cost of deployment includes not only equipment, but also engineering the link, the service calls," explains Steven Kubes, Scintera's vice president of marketing and sales. "You tweak something, and you have to go out there and reengineer the whole link, get it back up and running, and make sure it meets the performance requirements. It's expensive and it's hard to deploy."

The SCN5028 EDCE doubles the usable distance of singlemode fiber; it features an I2C interface for advanced channel monitoring; and like the SCN3142, it is also housed in a 32-pin, 5×5-mm small-form-factor QFN package. It too may be integrated with 300-pin transceivers and XENPAK, X2, XPAK, and XFP transponders.

While Scintera is bullish about the benefits of electrical compensation, some of its competitors are pushing optical solutions. Just how does an electronic dispersion compensation device stack up to an optical device? "You might use optical dispersion compensation for coarse-tuning and electronic for the fine-tuning," explains Tom Hausken, director of optical communications at market researcher Strategies Unlimited (Mountain View, CA). "So they are not necessarily competing with each other, but to the extent that they are, the optical people will say that that electronic stuff is just 'fudging'—'it's not really dispersion compensation,' they say, 'it's equalization.'"

Electronic dispersion compensation does not return the signal to its original state, a la optical compensation. Rather, it reconstructs or recreates the signal using equalization. "The electronic people say, 'Fine. What's wrong with that?'" notes Hausken, who asserts that he is "a real strong supporter" of electronic dispersion compensation because of the complexity and size constraints inherent in optics.

Scintera is optimistic about the timing of its products, which, it says, have been well received by "virtually all of the major transceiver- and transponder-module suppliers." One supplier, MergeOptics (Berlin), recently unveiled its serial X2 transponder, capable of 300-m transmission over legacy multimode fiber, thanks in part to the integration of the SCN3142 EDCE.

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