Optical Bistability

The replacement of electrical currents by optical beams in information processing has become feasible due to the discovery of optical bistability and related devices+. An optically bistable device is one which can exhibit two steady transmission states for the same input intensity. A fabry-Perot resonator containing a medium with a nonlinear refractive index constitutes the simplest example of such a system. As a laser light is irradiated on the cavity and increased from zero to a maximum and back to zero, the output-input characteristic can show a hysteresis cycle: the lower and upper branches (Fig. 1) are locally stable and hence the system is said to be bistable. Under suitable choice of parameters a device of this kind can function e.g. as a memory, as an optical transistor and can be used in optical logic [2,3]. From a theoretical viewpoint, optical bistability constitutes an example of a first-order phase transition in a farfrom-equilibrium system [4] . In this paper we shall concentrate on the device aspects.