Controlling optical bistability in a three-level atomic system

We have experimentally studied the optical bistable behavior in an optical ring cavity filled with a collection of three-level $\ensuremath{\Lambda}$-type rubidium atoms, interacting with two collinearly propagating laser beams. The bistability so observed is very sensitive to the induced atomic coherence in this electromagnetically induced transparency system or consequently to the altered nonlinearity in the system and, thus, can easily be controlled by changing the intensity and the frequency detuning of the coupling field.