Number 177 (Story #1), May 3, 1994 by Phillip F. Schewe and Ben Stein A QUANTUM WIRE MICROCAVITY LASER uses quantum confinement effects in two ways. First, the active laser medium consists of arrays of quantum wires, practically one-dimensional semiconductor structures in which electron energies are greatly restricted to narrow bands. Secondly, the photons emitted by the quantum wires resonate in a microcavity (a "quantum dot" for photons) which allows only a single light mode to operate. Scientists at NTT Basic Research Labs in Japan (contact Arturo Chavez-Pirson, chavez@wave.ntt.jp) have now demonstrated such a device. They grow quantum wires in the crevices of a stepped gallium-arsenide substrate. This "fractional-layer superlattice" provides stacks of 6nm x 8nm x 1cm quantum wires. The wires emit light in all directions, but inside the microcavity (itself formed of semiconductor layers) they are forced to emit light in the direction of the end faces. The resultant laser system converts electrical energy into light with high efficiency. The light from a microcavity quantum-wire laser is highly anisotropic, unlike that from quantum-well lasers, in which the active medium consists of two-dimensional semiconductor layers. This means that laser light with an electric field parallel to the wires is much more intense than light whose electric field is perpendicular to the wires. The NTT scientists expect that this polarization property might be exploitable in switching the laser on and off at rates up to 100 GHz. (A.Chavez-Pirson et al., Applied Physics Letters, 4 April 1994.)