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The steady-state nonlinear behavior in a ring cavity based on a Λ-type atomic model is investigated. It is shown that, due to the existence of strong spontaneously generated coherence, optical bistability still can be realized even if both coherent fields in resonance with the medium. Moreover, the appearance or disappearance of bistability can be controlled by adjusting the relative phase between the two coherent fields. When the probe field is not resonant, it is found that the threshold intensity for producing bistability is very sensitive to the relative phase, and bistability and multistablity can transform mutually by adjusting the relative phases. [Copyright &y& Elsevier]

The effect of spontaneously generated coherence (SGC) on the pump–probe response of a nearly degenerate Λ system is investigated by taking into account the dephasing of the low-frequency coherence. It is found, in the case of small dephasing, that instead of electromagnetically induced transparency (EIT) at resonance, electromagnetically induced absorption (EIA) can occur due to the effect of SGC. We also study the effect of relative phase between the two applied fields and find that EIA and EIT can transform mutually by adjusting the relative phase. [Copyright &y& Elsevier]

Abstract: We investigate the steady-state optical bistability behavior in a three-level Λ-type atomic system closed by a microwave field under the condition that the applied fields are in resonance with corresponding atomic transitions. It is shown that the bistable hysteresis cycles can be controlled by both the amplitude and the phase of the microwave field. [Copyright &y& Elsevier]