Controlling the optical bistability via interacting dark-state resonances

Abstract

We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a cavity and two external coherent fields by means of a unidirectional ring cavity. We find that without interacting dark resonances and for large intensity of coupling field, the optical bistability disappears. So, the double dark resonances could significantly establish the optical bistability. Moreover, we demonstrate that the double dark resonances can dramatically reduce the threshold of optical bistability.