Polarization flipping and intensity transfer in laser with optical feedback from an external birefringence cavity

We demonstrate the influences of optical feedback from an external birefringence cavity on dynamic characteristics of output intensity and polarization in He-Ne laser. Polarization flipping accompanying with intensity transfer between two eigenstates of one laser mode is observed. The position of polarization flipping or duty cycle of two polarization states in one period of laser intensity modulation is a function of phase difference of birefringence element. The conditions of symmetrical transfer of intensity are found. The doubling frequency of intensity modulation is observed and the second order polarization flipping is shown experimentally. Experimental results are explained qualitatively, and the potential use of experiment results is also discussed.