We use light to transmit information, using fiber optics. That's great. But it doesn't work as well as it might in confined spaces—say, on a microchip—because it's tough to control, zipping around as it does at the speed of light. That means that electronic circuits still rule, and even where optical communication links exist, the signal must be converted to and from an electrical one at each end.

A group of researchers at Lehigh University is working to change that by taming photons so that they'll behave in all-optical communication systems or even optical computers. To that end the team has sought to control light by temporarily slowing it down—or stopping it completely.

Lehigh graduate student Qiaoqiang Gan and his colleagues have designed a tiny grate, essentially a nanoscale comb whose teeth are cut to steadily increasing depths, that should be able to slow and even trap light—for a few trillionths of a second, anyway. The innovation is a step toward the useful harnessing of light waves on a chip.

Gan and his co-authors reported in the journal Physical Review Letters last summer that based on their simulations, such a graded grate structure would effectively trap light waves over a broad span in the terahertz range (frequencies measured in the trillions of cycles per second). But in a follow-up study this month in the same journal, the team wrote that the grate can be scaled down to work on higher-frequency infrared radiation and possibly even visible light (where frequencies are in the hundreds of terahertz), making it practicable for telecommunications purposes.

Capping the grate with a dielectric, or nonconductor, would provide a sort of trapdoor, allowing the wavelengths to be confined and released at will by modulating the temperature of the cap. If the structure were extended to the visible regime, Gan and his co-authors write, the comb could even trap a rainbow by arresting the wavelengths of visible light at different points along the length of the structure.

Photo of study co-authors Filbert Bartoli and Qiaoqiang Gan courtesy of Lehigh University