双平衡式外差探测中的偏振混合误差理论分析

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

将双平衡式探测方法应用到激光雷达等微弱信号检测领域。首先采用矩阵光学的方法推导了数学理论模型。该数学理论模型不仅可以得出待测信号的频率、强度信息,而且还可以提取出相位和偏振态的信息,弥补了传统单元探测器的不足。分析了偏振分束棱镜等光学元件内部存在的固有缺陷对正交解调信号精度的影响,最后讨论了入射光的偏振度因子所引起的双平衡式探测系统的偏振混合误差。数值仿真结果表明:当偏振光照射在偏振分束器上时,形成的椭圆偏振度在(0,0.02)范围内,所产生的垂直正交因子为0.523。

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.