Researchers at AlliedSignal Inc. in Morristown, N.J., have found a new use for synthetic opals. In experiments, the researchers introduced carbon into the faux gemstone's lattice. Then they chemically removed the gem, leaving behind a crystalline array of spheres several hundred nanometers wide. The physical properties of these "inverse opals" could make them important in photonic crystals. Because of their three-dimensionality and regularity, they strongly diffract visible light, which the researchers capitalized on to build an optical switch. The scientists hope the switch might also work well with IR wavelengths in the future.