Optics Start Up Offers High Power, Low Loss with Dispersion Compensation
By: Erik Kreifeldt
A year-old start-up hopes to win system designers and network operators over to its new dispersion compensation technique, promising reduced cost and increased functionality in fiber networks. The device contributes less loss and accommodates more power than traditional dispersion-compensating fiber and fiber Bragg gratings, the company claims.
Dubbed "spatial mode transformation," the technique uses high-efficiency transformers on both ends of a high order mode fiber to compensate for chromatic dispersion. The technique's inventor, Yochay Danziger, founded Lasercom Inc. with his colleagues in January 1998 to develop a commercial product by the end of 1999.
"They're classical optics guys," observes Fujitsu veteran Mark Barratt, Lasercomm's VP of business development. Barratt and a colleague work out of the company's headquarters in Richardson, TX, while the other 19 Lasercomm employees work at an R&D facility in Israel.
Lasercomm's fiber exhibits characteristics between that of standard singlemode fiber and multimode fiber. It compensates for dispersion with only one-sixth the length of fiber required in conventional modules, and therefore contributes less loss to the system. In a typical application, spatial mode transformation contributes only 5 dB of loss to an amplifier system, compared with 9 dB of typical dispersion compensation modules.
Operating within a given loss budget, engineers can design the extra 4 dB into another part of the system, eliminating a costly component or adding a new feature, Barratt explains. Reconfiguring an amplifier to eliminate a gain stage, for instance, would remove a device that comprises nearly half of an amplifier's cost, Barratt says.
Using high-order modes evens out the amount of dispersion across DWDM wavelengths in a fiber, allowing transmission of more channels with fewer compensation devices. A tailored dispersion slope corrects second order dispersion characteristics in signal transmission. With a 100 nm spectral correction, the device accommodates DWDM channel counts of 100 or more at 10 Gbps line rates. "Carriers can prepare their fiber for L-band utilization," Barrat says. "They really like that."
Today's dispersion compensation modules based on fiber coils are only effective across a bandwidth of 20 nm, and fiber Bragg gratings only correct 5 nm of spectrum, Barratt points out. By reducing the number of devices required, he says the Lasercomm technique simplifies the system and reduces cost.
The Lasercomm fiber's large core diameter enables a 12 dB increase in transmission power compared with singlemode fiber, Barratt continues. "We can add enough power for add/drop applications," he says, without incurring the noise that prevents the feature in today's systems. Extra transmission power can also free up designs for ring architectures and cross-connects.
More power transmits signals farther, reducing the number of amplifiers and regenerators in a network. At $100,000 or more a pop, amplifier sites and SONET regenerators are a major source of network cost, Barratt notes. He says systems designed with the Lasercom device can increase span lengths from 400 km to 600 km.
While the device's applications suit equipment vendors, Barratt expects carriers to buy the dispersion compensation modules directly and use them as a quick way to enable a network of standard singlemode fiber to handle data rate upgrades from 2.5 to 10 Gbps without changing network architecture or management.
Barratt says the spatial mode transformers will not pose manufacturing problems. Lasercom is seeking out a partner to supply fiber with its proprietary profile, he notes. Lasercom so far has lab invites from one carrier and two equipment vendors he says. The company plans to ship commercial products in November 1999.