Tiny and Tunable

The telecommunications industry has big plans to dramatically increase information-carrying capacity by using multiple colors of light in an optical fiber. Great idea, but its practicality depends on a laser that can be “tuned” to different wavelengths. Constance Chang-Hasnain, professor of electrical engineering at the University of California at Berkeley, may have an answer.

A laser’s color can be changed by resizing its “resonant cavity”-the space in which photons bounce back and forth before emerging as a beam. In Chang-Hasnain’s device, a small increase in voltage causes a tiny cantilever arm to lower a mirror toward the chip-shrinking the resonant cavity and shortening the wavelength. The device can now be tuned across wavelengths spanning about 30 nanometers. Chang-Hasnain aims to triple that, making possible hundreds of separate communications channels.