Taking a walk on the lighter side.

Materials that change their shape - moving and bending controllably after exposure to specific wavelengths of light - may make possible a new class of communication devices.

Improvements in such "photostrictive" materials, says Kenji Uchino of Pennsylvania State University in University Park, are progressing to the point where "we may soon see photo-driven relays, robots, and acoustic devices, which will a key role in the era of optical communication."

Scientists first observed the photostrictive effect 15 years ago, when they saw that light, especially in the purple region, could cause certain ceramics to change shape, though not because of thermal expansion. Subsequent research found that light energy creates an electric field in the material, causing a deformation.

Uchino and his colleagues built a "photo-driven walking device." Made of a lead-lanthanum zirconate-titanate ceramic doped with tungsten oxide, the two-legged walker creeps along a tabletop like an inchworm when the legs are irradiated alternately with light at a wavelength of 366 nanometers.

"The alternating irradiation makes the legs bend," Uchino says. "It walks by remote control without any internal circuitry."

The underlying mechanism of photostriction remains unclear, adds Uchino, though he believes it arises from "some combination of photovoltaic and piezoelectric effects."

Current versions of photostrictive materials react relatively slowly to light. Response times are speeding up, however, Uchino says.

Today's telephones translate sound into electrical signals and back again. Early in the next century, Uchino believes, photostrictive-based "photophones" may convert laser light directly into sound, giving rise to a new type of telephony.