Fiber Helper: Minuscule controllers may open data floodgates

Speeding up the Internet and other long-distance data networks is an expensive proposition. To reach planned transmission rates of 40 billion bits per second (Gb/s)–up from today’s maximum rate of 10 Gb/s–telecommunications companies would have to install a new generation of optical cables that retain the quality of fast signals better than existing cables do.

CHEAP FIX. Smaller than a needle (right), a liquid-crystal and gold device tucked between these glass blocks tunes up signals passing through the optical fibers encased in the blocks. B. Acharya/Lucent

Now, researchers have developed a liquid-crystal gadget that sits on the end of a hair-thin optical fiber of the type currently installed underground and corrects the worst signal damage that such a fiber inflicts, says John A. Rogers of Bell Labs’ Lucent Technologies in Murray Hill, N.J.

“We’re really doing things right on the head of a pin,” says Rogers, who is moving to the University of Illinois at Urbana-Champaign.

Rogers and his colleagues focused on correcting a problem that results from light’s polarization, which is the orientation of its electromagnetic fields. In optical fibers, light pulses may widen because of differences in the speeds at which signals of different polarizations move. As multiple pulses smear, the information they represent becomes indecipherable.

The new device links two optical fibers aligned end-to-end. It consists of gold electrodes that sandwich a thin film of liquid crystal.

A voltage applied to the device’s electrodes produces an electric field of a chosen orientation that modifies polarization–for instance, by rotating it, says Ronald Pindak of Brookhaven National Laboratory in Upton, N.Y. Thanks to that modification, a standard device further along the optical channel can recompress the pulses.

Rogers, Pindak, and their colleagues at Lucent and the University of Minnesota in Minneapolis describe their invention in the Dec. 30, 2002 Applied Physics Letters. At a meeting in March, the team will present test results indicating that the gadget makes 40 Gb/s transmission speeds possible.

Other polarization controllers using solid crystals of lithium niobate work well, but they’re bulky and cost tens of thousands of dollars apiece, Rogers says. The new technology ultimately may cost much less, he adds.

Impressed by the new controller, David M. Walba of the University of Colorado in Boulder predicts that such “liquid crystal devices . . . could form the basis of the next generation of telecom-switching components.”


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