T-shirt dye may improve telecom

By MIKE MARTIN, UPI Science Correspondent  |  April 8, 2002 at 9:18 PM
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ORLANDO, Fla., April 8 (UPI) -- A dye commonly used in psychedelic T-shirts might be the chemical key to futuristic telecommunications -- laser-charged, fiber-optic cables that deliver voice and computer signals faster and cheaper than today's comparatively sluggish phone lines, scientists said Monday.

"We make a thin, 1 micrometer polymer film with Procion Red, a dye used in tie-dye T-shirts," Virginia Tech physics professor James Heflin told United Press International at the 223rd American Chemical Society conference. "When you apply a small electrical field to this film, the electrical field changes the refractive index of the film, which allows us a way to modulate or control laser light passing through the film -- something that can be used in fiber-optic telecom systems."

Light waves travel at slightly different speeds in different media. The refractive index is a measure of this difference. Between air and glass, the refractive index is about 1.6 -- light travels 1.6 times faster in air than glass. Between air and water at room temperature, the refractive index is about 1.3 -- light travels 1.3 times as fast in air as in water.

The speed of light -- a famous constant -- is only constant in a vacuum. A material with a refractive index that changes on command -- by application of an electrical field, for instance -- can be used to control a continuous light beam.

Present-day fiber-optic devices use electrical signals to turn lasers and other light sources on and off in the process of relaying information over fiber-optic cables. Using the same electrical signal to open and close an optical door allows the same beam to remain on continuously. The process is faster and cheaper than turning the beam on and off.

A fan behind a door provides a simple analogy. Turning the fan on and off uses additional energy and takes more time than simply letting the fan run continuously and controlling its air flow by opening and closing a door.

Heflin and his team, Virginia Tech chemist Harry Gibson and chemical engineer Kevin Van Cott, envision a product that might soon find application in fiber optics and -- optical computers in the more distant future.

"The ultimate product might be a silicon substrate with this film applied on the surface," Heflin told UPI. "A continuous beam of laser light passing through the film could be modulated -- on and off, like zeroes and ones," in binary code, for instance.

"It's much faster and less expensive to control a continuous source than repeatedly turning the source off and on," Heflin said.

"Our group tried a similar project with mixed success," polymer chemist Andre Laschewsky, of Berlin's Fraunhofer Institute for Applied Polymer Research, told UPI. "It's very difficult to get the right orientation of the charged ends of the film -- nature works against getting this type of film assembled in the way we need to have it work properly."

Optimistic that his team may have overcome this difficulty, Heflin told UPI they are "about a year away" from something that will work well enough to have a potential commercial application.

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