Optical feedback characteristics in He-Ne dual frequency lasers

Optical feedback characteristics in He-Ne dual frequency lasers are studied systematically in different feedback power ratios with a variable attenuator. Feedback power ratios vary from 0.010 up to 0.998. Five distinct regimes of self-interference effects are found and defined as regimes I, II, III, IV and V. Accordingly, five optical feedback levels have been put forward in He-Ne dual frequency lasers. Strong mode competitions are observed in regimes III and IV. In regime V, multiple feedback effects are investigated. The basic theoretical analysis is also presented. Our results can advance the research of self-mixing interferometer and displacement sensor of He-Ne orthogonally polarized dual frequency lasers.