Analysis of dispersive and absorptive bistability in a four-level system typical of organic media

Abstract

We investigate a general theory of optical bistability for a four-level system with single and triple states. Both absorptive and dispersive mechanisms are included. By solving the stable-state equation of a density matrix and using the mean-field approximation, we derive the state equation of bistability. The bistabilities with dispersion and absorption of single and triplet states, including pure dispersion and pure absorption, are numerically studied. The effects of cooperative parameters, resonant transition detuning, and cavity detuning parameters on bistable behavior are analyzed. We find that the absorption of triplet states is beneficial to dispersive bistability but is detrimental to absorptive bistability. The detuning of the resonant transition between single states is detrimental to bistability, whereas that between triplet states is beneficial to bistability. The structure of four levels with single and triplet states is a typicality of organic media. Our analysis is helpful for research into bistability devices of organic media.