Polarization characteristics of He–Ne laser with different directions of polarized feedback

A polarizer is placed in an external feedback cavity to form polarized optical feedback. The effect of the different directions of polarized optical feedback on laser polarization characteristics (LPCs) is investigated experimentally and theoretically. The angle between the optical axis of the polarizer and the laser polarization is changed from 0° to 90°. It is found that LPCs vary greatly under different directions of polarized optical feedback. The angle range can be divided into five zones (two flipping zones, ⊥-polarization zone, bistable zone, and ∥-polarization zone) according to the different LPCs. When the angle is in the range of the ⊥-polarization zone (∥-polarization zone), the laser outputs ⊥-polarization (∥-polarization). Thus, one can choose either ⊥-polarization or ∥-polarization by properly aligning the axis of the polarizer.