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Beefing Up Optics

The simplest solution for stiffening the backbone is simply to lay more cable. But that’s also the most expensive alternative: as much as 40 percent of the cost of a fiber-optic system goes toward purchasing rights-of-way, getting permits and putting cable in the ground. (It’s an old joke in telco companies that they’d gladly give up new technologies if someone would just show them how to dig a cheaper ditch.)

Two other ways to increase capacity avoid digging up the streets, relying instead on state-of-the-art equipment installed in the telephone offices where the fiber-optic strands terminate. Engineers can develop methods to increase the number of channels of information each fiber-optic strand can carry. Or they can develop ways to make the data travel faster along each channel.

Both approaches avoid the enormous cost of installing new lines. But each strategy is tricky, since making improvements in one area often causes problems in another. “There’s a strong trade-off between distance and capacity,” says Roe Hemenway, manager of network equipment research at Corning. “The further you go, the lower the capacity. We’re being asked to put more capacity on the fiber, go longer distances, and do it with even higher quality.”

Hemenway works in the laboratory at Corning’s Sullivan Park Research and Development Facility in upstate New York, where shelves hold rows of metal boxes, each one a laser that generates an infrared beam. The beams run through modulators and multiplexers, amplifiers and filters, traveling the same loop of fiber-optic cable over and over again to simulate distance, much like a digital race car on the information-superhighway version of a test track. At the end of the system a computer screen displays the number of errors produced during the run, and an oscilloscope shows graphically whether the signal came out sharp or blurry.

The setup allows Corning engineers to test how each component affects signal transmission, and what a change in one does to the system as a whole. This approach is critical to fiber-optic design, because whatever solution evolves to make fiber optics more efficient is likely to include a number of technologies, each of which might affect the others.

In the last six years, transmission speeds in the labs for the fastest fiber optics have quadrupled, and another fourfold increase is expected this year. The most pressing question is whether, given all the trade-offs, the current rate of improvement can be maintained. “I could give you a macho answer that we’re going to continue to improve fiber, but quite frankly, I don’t know,” says Joseph Antos, technology director for fiber development at Corning. “Every new invention [to increase capacity] gets harder and harder.”

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