MURRAY HILL, N. J. -- Scientists at Bell Labs, the research and development arm of Lucent Technologies Inc. here, announced they have built the first bidirectional semiconductor laser, a single device that does the work of two.
They expect that the experimental light source may be used to detect pollutants in the atmosphere or to increase the capacity of lightwave communications systems.
The device emits light at two widely different wavelengths, or colors, depending on the direction of electrical current flowing through it. The direction is changed by switching between negative and positive voltage applied across the device. In all other semiconductor lasers, current can flow in only one direction.
The new laser was designed by Bell Labs researcher Claire Gmachl, of the Semiconductor Physics Research Department. "It's a radically new concept," said Federico Capasso, head of the department and a member of the research team. "This is one laser that behaves as if it were two, emitting light at different wavelengths depending on whether the applied voltage is negative or positive."
The prototype laser emits light in the invisible region of the spectrum, where most gases and vapors have telltale light-absorption "fingerprints," so it could find applications in pollution detection in the atmosphere. If the wavelength of the laser pulses is varied, from being in resonance with the "fingerprint" of a gas to being out of resonance, changes in the intensity of light arriving at the detector can be used to determine the concentration of the pollutant.
It might also have applications as a communications laser if it were re-designed to emit at the shorter wavelengths used in lightwave communications. The transmission capacity of an optical link could be doubled if binary information were encoded on both streams of pulses emitted at different wavelengths in different time slots.
The lasers are grown by molecular beam epitaxy (MBE), a crystal-growth technology developed by Alfred Cho, director of the Bell Labs Semiconductor Research Lab, which involves building new materials one atomic layer at a time.
The bidirectional laser research team includes Gmachl, Alessandro Tredicucci, Deborah Sivco, Albert Hutchinson, Capasso and Cho. Their work is described in the current issue of the journal Science.