Ringing a microscopic light switch.

The idea of manipulating photons instead of electrons in microscopic circuits has long appealed to researchers interested in speeding up optical communications and information processing.

Recent advances in the miniaturization of lasers have provided one of the key building blocks of photonic integrated circuits. Now, researchers have fabricated another essential component of such a system--a tiny switch that call channel photons from one path to another.

It's the smallest optical switch yet produced, says electrical engineer Seng-Tiong Ho of Northwestern University in Evanston, Ill. Ho and his coworkers describe their device in a paper accepted for publication in Optics Letters.

Called a microcavity resonator, the device consists of a ring or disk made from layered gallium arsenide and aluminum gallium arsenide. When light of just the right wavelength travels down a narrow waveguide (in effect, a wire for photons) close to the resonator, it leaks into the resonator, where it circulates. The circulating light, in turn, channels into another, nearby waveguide. Light at other wavelengths stays in its original path.

Ho and his colleagues have already constructed a photonic wire laser, in which a microscopic tube squeezes confined photons into a laser beam (SN: 6/10/95, p. 367). By combining resonators with lasers on a chip, researchers can manipulate light to handle communication over optical fibers. Eventually, such components could serve as the basis for an optical computer.