The most well studied of all systems in quantum optics are those that produce laser action. The basic ideas of the laser have given rise to a number of laser-like offspring, including the laser with saturable absorber and the laser with injected signal. In this dissertation our attention is to be directed to another member of this family, namely optical bistability (OB). Under certain circumstances, OB is studied when a beam of light is injected into a ring cavity filled with a homogeneously broadened medium of two-level atoms. In this phenomenon we simply have two stationary values for the transmitted light intensity corresponding to the same incident intensity, so that the medium appears as either transparent or absorbent. The aim of this dissertation is the study of the behavior of the present system in order to show the effect of the system parameters on OB. For this reason we apply the semiclassical treatment where the system can be described by the Coupled Maxwell-Bloch (CMB) equations. Optical tristability (OT), in which we have three stationary values for the transmitted light intensity rather than two, can be obtained when two different sorts of atom exist in the cavity.
