Both emitters and detectors are required for an optical transceiver. IBM previously solved the carbon chip emitter problem by injecting electrons and holes into opposite ends of a light-emitting nanotube. It now claims to have solved the carbon chip receiver problem using nanoscale p-n junctions formed by the electric fields surrounding its metal contacts in a graphene field-effect transistor. Look for carbon-based optical transcievers from IBM within five years. R.C.J.
IBM Corp. researchers have demonstrated that graphene, an atoms-thin layer of crystalline carbon, acts as a receiver of optical signals. In claiming the world's first graphene photodetector, scientists at IBM's Thomas J. Watson Research Center (Yorktown Heights, N.Y.) predicted it could operate at up to terahertz frequencies. The 40-GHz graphene photodetector demonstration matched IBM's earlier demonstration of a nanotube optical emitter, the second component needed for bi-directional carbon chip-based optical transceivers. Graphene is formed as a single atomic layer of carbon atoms that, unlike metals, have no bandgap. Optical materials ordinarily require a bandgap so that photons can be absorbed (received by detectors) or given off (transmitted by emitters).