Kailight tackles PMD mitigation
Neil Salisbury, vice president of marketing at Kailight Photonics (www.kailight.com), believes there are several reasons why 40-Gbit/sec networking has not been more readily adopted. The first is the high cost of the 40-Gbit/sec transponders themselves and the second is the need to compensate for chromatic dispersion-for which recent advances in optical duobinary technology should help, he says. But the third problem, polarization-mode dispersion (PMD), has not yet been solved, and this is where Kailight hopes to differentiate itself from its competitors.
PMD is caused by different polarizations within the signal traveling through the fiber at different speeds and arriving at different times. The net effect is a blurring or smearing of the received signal.
Kailight has developed an analog-based PMD mitigation technology, which it is integrating into its existing Tunable All-optical Signal Regenerator (TASR). “It is kind of a spin-out technology from our TASR line,” says Salisbury. While the company’s PMD mitigation technology is patent-pending, Salisbury will say that it creates an averaging effect on PMD in the network. “If your network is jumping all over the place very quickly, you are still getting the benefit [of the PMD mitigation], which you wouldn’t get if it were being done electrically,” he says. “Electrical is not fast enough.”
For his part, Salisbury is bullish on the use of analog or optical technology to compensate for dispersion. He cites a recent customer request for more than 100 psec of differential group delay (DGD) improvement at 10 Gbits/sec and more than 30 psec of improvement at 40 Gbits/sec. “Analog is the only way to get there,” he says, noting that Kailight’s 10-Gbit/sec TASR with built-in PMD mitigation achieves those specifications. “I believe we are quoting better improvement than anyone who would be doing it electronically,” he adds.