Microdevice weds electronics, light fibers

Like superior delivery trucks, optical fibers weigh less, use less power, and protect their cargo—a stream of data—better than conventional transporters, in this case copper wires, do.

Because fibers can tote huge amounts of information, they increasingly command the information superhighway. If only they could ply the side streets as well. Technologists have long dreamed of bringing the fibers’ superior performance to local runs, say, between a computer’s microprocessor and memory chips on other circuit boards.

Converting electronic signals into light waves, however, requires bulky, relatively high-voltage equipment, making fibers impractical for replacing wires within a computer.

A team of West Coast scientists may have found a solution. By altering the chemical structures of dyelike molecules called chromophores (SN: 3/29/97, p. 188), the researchers have created tiny conversion devices that respond to low voltages. The team describes the electrooptic modulator chips in the April 7 Science.

Led by chemist Larry R. Dalton of the University of Washington (UW) in Seattle and the University of Southern California (USC) in Los Angeles, the inventors foresee many uses for their new components. Besides benefiting data transfer within individual computers, the devices may spur fiber-optic communications, high-speed data processing, and innovative designs for radar systems. Some companies plan to begin producing the chips within months, the researchers say.

Dalton and his colleagues “have almost single-handedly revolutionized this area” of electro-optic modulation, says James G. Grote of the Air Force Research Laboratory at Wright-Patterson Air Force Base in Ohio. His laboratory has confirmed the new materials’ capabilities. Military interest leans toward improving radar and replacing copper cables for internal communications in aircraft and ships.

Today’s electro-optic modulators, based on hefty crystals of lithium niobate, operate at 6 volts and handle frequencies up to only about 70 gigahertz (GHz). “Think about a big diamond [and] hooking it up to an electronics system,” Dalton says.

Instead, “you want a tiny chip,” he explains. Only about a micrometer wide, the new devices operate at up to 118 GHz and need less than 1 volt, making them compatible with a class of widely used, extremely fast microcircuits.

Applying a voltage to the new chromophores dramatically shifts their electron distributions, altering the speed of passing light waves, Dalton explains. To harness that effect, chemists must line up the molecules and bind them in a polymer. In the new device, a varying voltage creates an optical signal by modulating laser light passing through the film.

Previous attempts to fully align chromophores failed because of forces between the elliptically shaped molecules, says coauthor Cheng Zhang of USC. Guided by recent theoretical advances by UW chemist Bruce H. Robinson, the team added chemical subgroups that made the molecules more spherical, quelling disruptive forces. Dalton notes that no one knows if the films will last 10 years, as expected for commercial products.