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Full-spectrum WDM makes play for ultra long-haul space While many equipment providers in the ultra long-haul space live by the motto "Longer is better," a new technology called full-spectrum wave division multiplexing is turning the tables, touting instead that more profitable is better.

Full-spectrum WDM manipulates the optical signal in the time and frequency domains to strengthen the signal and enable it to travel farther without regeneration. By making the signal wider than standard WDM signals, full-spectrum WDM allows a signal to travel with less dispersion and less amplifi-cation. The technology uses 30 GHz of spectrum compared to the 10 GHz of spectrum used by other platforms, enabling more traffic to be carried over the network. Full-spectrum WDM also allows for bi-directional transmission over any fiber.

Although distance is key to profiting from an ultra long-haul platform, taking full advantage of unused spectrum is just as important to service providers investing in platforms, said Ilya Fishman, president and chief technology officer for OptiMight Communications."People are using a low percentage of what's available on the optical band," he said. "We're trying to enhance that [percentage] to utilize what everyone else has dropped on the ground."

OptiMight is developing an ultra long-haul platform based on full-spectrum WDM. Although the platform is still in its early stages, full-spectrum WDM could launch OptiMight into competitive waters, pitting the equipment provider against more established play-ers such as Corvis and Qtera (now part of Nortel Networks) or Ciena, which revealed intentions to move into the ultra long-haul space.

Though other equipment providers, including Kestrel Solutions and Centerpoint Broadband Technologies, already address the issue of packing more information on a wavelength, their solutions are aimed at the metro space. OptiMight hopes to distinguish itself in the ultra long-haul market, specifically amplification equipment.

OptiMight's solution doesn't need Raman amplifiers, a key ingredient in existing ultra long-haul platforms, to carry a signal over long distances; the company also uses network design models familiar to service providers. When completed and available around the third quarter of 2001, the company's solution will include transmitters, optical amplifiers and receivers.

"It's similar to the WDM equipment that carriers are used to," said Karl Ma, director of product development for OptiMight. Instead of Raman amplifiers, which OptiMight claims are too costly and time-consuming to produce, the company uses erbium-doped fiber amplifiers (EDFAs). "We use fewer and simpler parts for the least amount of pain," Ma added.

Standard components make up the non-proprietary system, which allows it to inter-operate with other elements in a carrier's network. As a result, carriers should be able to deploy the full-spectrum WDM system in the same way they deploy conventional WDM systems.

An ultra long-haul system that uses EDFAs in their existing locations in networks instead of Raman amplification could be attractive to carriers, according to a Current Analysis report."Full spectrum is an intriguing concept, using existing amps and network design rules but implementing a broader signal," according to the report. However, without an existing proven platform or customer trials, people should be skeptical, the report cautioned.

Corvis' platform, already tested by Broad-wing, Williams Communications and Qwest Communications, uses Raman amplifiers to allow the signal to be carried over long distances. The company considers the amplifiers a key to the platform's success, said Shyam Jha, vice president of marketing for Corvis.

"We believe Raman amplifiers are a better way to go for ultra long haul," he said."Even if the amplifier fails, the fiber doesn't go opaque because of the way our system modulates the intensity of the signal to take care of a single amplifier failure."

To help pack more data into the spectrum, Corvis acquired Algety Telecom in May. Algety uses soliton technology to achieve high speeds over long distances. Solitons are light wave pulses that balance fiber dispersion and non-linearity. Combined with Corvis' use of Raman amplification, the equipment provider hopes to use solitons to build 40 Gb/s capacity systems.

The demand for greater spectral efficiency is clear."The envelope is really being pushed both ways. It's not just a matter for spectral efficiency or distance," said Chris Hamilton, chief technologist for Williams."What matters is the highest bandwidth, distance and capacity. The most bang for the buck. Talk is cheap. But no vendor is able to keep up with our deployment in terms of what's available."