A team of researchers has fabricated a micron-scale device that deforms significantly under the force of light, a technology that could form the basis for tiny light-actuated switches or filters in future optical devices.

In recent years several groups have engineered novel structures on scales so small that the force of light passing through them actually wields an appreciable force. The devices harness the so-called gradient optical force, by which a light beam can exert a push or pull in a direction transverse, or perpendicular, to the direction of the light's propagation. In a recent example, outlined in Nature last year by a team from Yale University and the University of Washington in Seattle, laser light routed through a tiny bridge-shaped resonator induced the bridge to vibrate up and down within a range of a few nanometers. (Scientific American is part of the Nature Publishing Group.)

The new approach, described in a paper published online Sunday in Nature, uses a pair of wagon wheel–shaped ring resonators, separated by a gap, to achieve much greater displacement. (The shape of the device is similar to one described in July by a group from the California Institute of Technology.) In addition, postdoctoral associate Gustavo Wiederhecker and his Cornell University Nanophotonics Group colleagues achieved static displacement—that is, they were able to bend and hold their structure in place rather than causing it to move back and forth.

"A lot of groups are starting to learn how to vibrate structures using light," says Cornell physicist Michal Lipson, a study co-author and the leader of the nanophotonics group. "But what we decided to do is instead of just vibrate, to really control the structure—to bend or move the structure—and keep it static just like that." Running low-power laser light, akin to that from a typical laser pointer, through the rings generates a tunable response—either attractive or repulsive, depending on the wavelength—that changed the size of the gap between the rings by as much as 20 nanometers. (A nanometer is one billionth of a meter.)

By modulating the intensity of the laser light, Lipson says, the gap can be opened or closed to varying widths. "You can completely control the amount of bending with the amount of incident power that you have," she says. Such controlled deformation could be used to form tiny switches driven by light rather than electricity.

Hong Tang, an assistant professor of electrical engineering at Yale who co-authored last year's nanobridge paper in Nature, sees these devices possibly forming the basis for tunable optical filters. By using a laser to induce movements that change a structure's resonance, he explains, the passage of light from another source—say, an optical communication channel—can be controlled.

Tang calls the new application of the gradient force "very innovative." He points out that the ring structure, which Lipson says is designed for both low mass and malleability, harnesses the optical force on a greater scale than the smaller vibrating beam did. "There are different field applications, and there is a trade-off," Tang says. "We pushed the limit to small, and they pushed the limit to large displacement."

"The displacement demonstrated in this device is 20 nanometers, which is really significant," Tang says. "This is really a big change for the optical force–induced displacement."