Every time a signal runs through an erbium amplifier, however, it picks up noise-elements that were not a part of the original signal. Over long-distance backbones where a signal needs to be boosted many times, fiber-optic systems must be strung with regenerators, devices that reconstruct signals that have traveled through so many amplifiers that they have degraded. Regenerators take a light signal, convert it to an electrical signal, and then produce a new light beam.
A new technique called Raman amplification (see “Five Patents to Watch: Booster Shots,” TR May 2001) will allow a signal to be amplified without introducing noise-doing away with the need for regenerators and potentially creating a new way for engineers to increase capacity. Unlike erbium amplifiers, which only work at certain wavelengths, Raman amplification holds the promise of making even more new channels available. A new company, Xtera, of Allen, TX, is hoping to take advantage of Raman amplification to enable the long-range transmission of shorter wavelengths of light than current optical networks can support. “It’s kind of a new twist on using Raman techniques,” says Joe Oravetz, Xtera’s product manager, who unveiled the company’s first new product at the Optical Fiber Communication Conference and Exhibit in March in Anaheim, CA.
But using the shorter-wavelength band is a decidedly long-term strategy, since it will require installation of new equipment at every point in the network. “Going into a new band, you have to replace all the components,” says Vladimir Kozlov, an analyst at RHK. “You need new sources. You need new amplifiers. It could be very expensive.”
Speeding Up Bits
An alternative to adding channels is to make the data stream in each channel flow faster. Just as the modems in people’s homes have gotten faster, transmitters in the backbone have increased their ability to pump data, from 100 million bits per second a decade ago to a state-of-the-art 10 billion bits (10 gigabits) per second today.
While AT&T issued a press release announcing the first 10-gigabit-per-second coast-to-coast Internet protocol backbone in January, it’s already old news: 40-gigabit-per-second systems have already been announced by Lucent Technologies, Fujitsu and NEC for sale later this year. The engineering feats involved in advances like these are tremendous: increasing the data rate required engineers to design lasers that can reliably flash on and off 40 billion times per second, and receivers that can pick out one flash from the next, when they’re coming at that overwhelming rate.