Number 55 (Story #1), November 7, 1991 by Phillip F. Schewe and Ben Stein A SEMICONDUCTOR FOR LIGHT WAVES , a material in which certain photon wavelengths would be excluded---creating, in effect, a photon band gap analogous to the forbidden electron energy bands in semiconductors---is being developed by scientists at Bellcore and the Polytechnic University, Brooklyn (Physical Review Letters, 21 October 1991). Eli Yablonovitch (Bellcore, 908-758-2805) and his colleagues drilled three sets of holes into the top surface of a slab of dielectric material, creating a criss-cross, face-centered-cubic structure whose unit cell is a rhombic dodecahedron. Theorists had predicted that such a honeycomb geometry would result in the exclusion of light at certain wavelengths. Indeed, when the Bellcore scientists sent microwaves into one sample (which, because of the holes, was 78% empty) they discovered a forbidden gap. The researchers believe that by proper tailoring of the holes optical-wavelength bands can also be induced and that this will make these "photonic crystals" useful in a variety of research areas, such as atomic physics and microelectronics. (Science News, 2 Nov. 1991.)