Fig. 3

The incident mirror. In (a), the incident light A split into multiple beams, A-1 and A-2 can generate the intra-cavity resonance. b shows that the feedback light B (which is produced by incident beam A-1) split into multiple beams before coupled into the fiber collimator; c shows that the feedback light C (which is produced by incident beam A-2) split into multiple beams before coupled into the fiber collimator