The intra-cavity phase anisotropy and the polarization flipping in HeNe laser

The effect of intra-cavity phase anisotropy on polarization flipping induced by optical feedback is experimentally and theoretically investigated. In experiments, we place a polarizer in feedback cavity to induce polarization flipping. The polarization flipping doesn't occur when the angle between polarizer axis and laser polarization approaches 45°. It is found that the larger the phase anisotropy is, the more easily the polarization flipping happens. As the intra-cavity phase anisotropy is increased, polarization flipping always occurs when the angle between polarizer axis and laser polarization is changed from 0° to 90°. This indicates that the phase anisotropy of the laser cavity contributes to the polarization flipping. It is necessary to keep certain phase anisotropy for the lasers used for polarization control.