Materials for fast switching and logic devices

Nonlinear optical properties of some materials, which are of current interest, are reviewed. Emphasis is put on GaAs-AlGaAs multiple-quantum-wells, bulk GaAs and CdS_xS_1-x-doped glasses. The use of these materials for high-speed optical logic devices is described. Optical NOR-gate operation of a GaAs-AlGaAs etalon with picosecond switch-on and off times is highlighted. Optical materials are attractive both for device applications as well as for the fundamental understanding of their optical properties. Optical characterization of nonlinear materials is a subject of extensive research efforts by several groups. Interaction of light with matter, especially at high excitationhighexcitation levels, and the subsequent many-body effects are of fundamental importance. The physics of high density exciton phenomena, dynamics of electron-electron and electron-phonon interactions in semiconductors are of particular interest. Generation of femtosecond laser pulses and application of short-pulse techniques allow direct measurements of these dynamical effects with incredible time-resolution. Optical nonlinear materials play an important role in optical devices.^{1, 2, 3}Optical signal processing and ultimately optical computing depend critically on nonlinear materials. Nonlinear optical devices need materials with rapid response times, large nonlinearity and room-temperature capability. Optical bistable devices and logic gates are essential for parallel processing, while guided wave devices are needed for serial applications.