Noticeable positive Doppler effect on optical bistability in an N-type active Raman gain atomic system

We theoretically investigate the Doppler effect on the optical bistability in an N-type active Raman gain atomic system inside an optical ring cavity. It is shown that the Doppler effect can greatly enhance the dispersion and thus create the bistable behavior or greatly increase the bistable region, which has been known as the positive Doppler effect on the optical bistability. In addition, we find that the positive Doppler effect can change the optical bistability from the hybrid dispersion-gain type to the dispersive type.