Optical Fibers Turn a Corner

24 July 2000 7:00 pm

Adapting a coaxial-style cable might open new doors for optical technologies.

In today's cable world, photons are fast, but electrons can turn on a dime. Now, blending the best of these two worlds, researchers have proposed a way to send light racing through cables similar to those used to transmit television signals. Such a system would preserve more information than standard optical fibers, they say, and allow the use of light signals in computer chips. But right now, the plan is still on the drawing board.

Fiberoptic cables can carry a staggering amount of phone calls and other digital information. They are also simple: just a glass fiber surrounded by a reflective coating. There's a drawback, however. Light traveling through the central fiber bounces repeatedly against this cladding, but the cladding only reflects light rays that hit it at grazing angles. That's why conventional optical fibers aren't good at bending light around sharp corners.

Coaxial cables, in contrast, can snake every which way. Electromagnetic waves--which usually carry high-frequency electronic signals for cable TV and high-speed computer links--navigate corners without a problem. A team led by theoretical physicist John Joannopoulos of the Massachusetts Institute of Technology realized that the structure of the coaxial cable--an outer shield surrounding a central core--might be adapted to better guide light signals through an optical fiber.

In this design, described in the 21 July issue of Science, a reflective core is surrounded by a nonconducting layer through which light travels. Another reflective layer forms an outer shell. The reflective layers, built of several alternating layers of tellurium and polystyrene, give off many partial reflections from each layer, allowing the coating to reflect at many different light frequencies. It's also omnidirectional, reflecting light at all angles, which allows the cable to bend light around sharp corners--necessary for integrating fiberoptics into chips, for example.

The team still has to make a working prototype of their waveguide, which physicist Neil Broderick of the University of Southampton, United Kingdom, points out will be tricky using existing technology. "But it is an extremely novel and interesting idea, certainly worth exploring a lot further," he says.

Related links
General information about optical fibers

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