Optical bistability induced by quantum coherence in a negative index atomic medium

Bistability behaviors in an optical ring cavity filled with a dense V-type four-level atomic medium are theoretically investigated.It is found that the optical bistability can appear in the negative refraction frequency band,while both the bistability and multi-stability can occur in the positive refraction frequency bands.Therefore,optical bistability can be realized from conventional material to negative index material due to quantum coherence in our scheme.