Criteria for optical bistability in a lossy saturating Fabry-Perot

Large optical nonlinearities occur in a variety of multiple quantum-well and n-i-p-i materials in which the nonlinearity saturates and there is residual absorption. The conditions for bistability when such media are placed with a Fabry-Perot etalon are discussed. It is proved analytically that the ratio of the optically induced saturated index change to the linear loss per unit length must be larger than the wavelength divided by π. It is shown, however, that practical devices require twice this value. It is found that there is a tradeoff in cavity design between minimizing the switching intensity and minimizing the required nonlinear phase change. Finally, approximate expressions for the switching intensity versus detuning are given