7 April 2000

Breakthrough Heralds "Infinite Bandwidth"

by Kate Melville

A team of U.S. researchers has created a device that operates at less than one volt and is capable of converting electric signals into optical transmissions at a rate of 100 gigabytes of information per second, according to a paper published in the 7 April issue of Science. At that speed, the device could potentially eliminate download time on the Internet and significantly increase the efficiency of information processing. The Science authors claim that the technology could dramatically alter fiber optic telecommunications.

The device, a type of electro-optic modulator, could also be applied to technologies like aircraft navigation and anticollision radar in cars, says Larry Dalton, University of Washington and University of Southern California chemist and co-author of the Science paper which describes the new modulator.

Modulators are the translators of the electro-optic world of communication, encoding electrical signals onto optical beams of information. Improvements in electro-optic materials have increased the speed (broadened the bandwidth) at which these modulators translate, but only at the cost of high operating voltage that limits the strength of the signal and increases its level of distortion. As the Science authors note in their paper, researchers have been on a quest for "the Holy Grail" of modulators, a device that delivers wide bandwidth but that operates with less than one volt.

As part of that quest, Dalton and his colleagues built a modulator consisting of organic molecules called chromophores embedded in a polymer matrix. Chromophores have impressive electro-optic capabilities, and for over a decade, scientists have tried to exploit these promising properties in modulator designs. But when previous researchers tried to combine chromophores into such a device, they were stymied by interactions between the electrical fields of chromophores that sapped their electro-optic efficiency.

Dalton and others overcame this obstacle with the help of some of their earlier theoretical work, which showed that changing the shape of the chromophores could minimize the clash in their electrical fields. "It gave us guidance on how to design these molecules," says Dalton. After tinkering with the chromophore structure, the research team became the first to reach the long-sought goal--a high bandwidth, polymer modulator device below one volt.

With this device, Dalton says,"We'll be able to take telephone signals, computer data, tv signals, any type of signal you can think of, put it on fiber optic, route it around the world with almost no optical signal loss, and accomplish this with infinite bandwidth. It has the potential of revolutionizing the way we all function."

Telecommunications and high-speed data processing will probably be some of the first fields to benefit from the new technology, but the modulator also acts as a natural steering device that could be "a tremendous benefit to radar and satellite communications," according to Dalton. Practical applications of this range from better navigation systems for commercial and military aircraft to "smart cars" that warn drivers about possible fender benders on the road ahead.

Along with its impressive bandwidth and efficiency, the new modulator has another feature that Dalton fears may not be as readily appreciated--ease of integration. The devices can be arranged in a variety of sophisticated, high-density packages without optical energy leaking between them or overheating. This may make them useful components in increasingly powerful computers jam-packed with heat-generating transistors.

It may also give them a leg up on their current competition--modulators made from inorganic lithium niobate crystals. Along with their higher voltage needs and smaller capacity, lithium niobate modulators generate heat and can't be integrated directly on to silicon chips. "Our device clearly demonstrates the advantages of polymer modulators compared to all competitive materials," notes Dalton.