Theory analysis of polarization mixing error in dual-balanced heterodyne detection

The dual-balanced detection method was applied in weak signal detection at first time, such as the lidar fields. Firstly, theory model of the dual-balanced detection was derived with the help of the Jones matrix method. This dual-balanced detection technique offered higher signal-to-noise ratio than that of the conventional coherent detection technique, making use of power of local signal as much as possible. Moreover, the frequency, the phase, the intensity, and the polarization mode of the backscattered signal could be obtained simultaneously, which offseted the disadvantage of the conventional coherent detection method. The polarization mixing error, which was caused by leakage of the PBS, elliptical polarization, and non-orthogonaltity as a result of imperfect or misoriented laser source, wave plates and beam-splitters, was analyzed. It shows that when the polarization light is incident on polarization beam-splitter, the degree of elliptical polarization is between 0 and 0.02, and the verticality-orthogonality factor is 0.523.