为了实现偏振编码的自由空间量子密钥分发实验，研制了偏振保持的光机系统，并对该系统所采用的相位延迟传输机理及应用进行了研究，建立了偏振误码率在允许范围内的量子链路.首先，采用矩阵光学理论对偏振光的方位角、相位延迟与消光比的关系进行了介绍.接着，通过矩阵光学理论及实验验证了偏振光学系统的相位延迟线性叠加原理.然后，在相位延迟线性叠加原理的基础上，设计了一套偏振保持光学系统，并通过理论分析及实验验证了此系统具备良好的偏振保持效果.最后，将偏振保持光学系统的设计机理应用于量子通信光机系统的设计之中，并取得了良好的设计效果.实验结果表明：相位之间的相互抵消可以有效地进行偏振保持设计，最终设计的量子通信光机系统的偏振消光比优于500∶1.满足了自由空间量子通信实验中对偏振误码率的要求.

In order to realize free space quantum key distribution, an optical system with the property of retaining the polarization state is customized to reduce the quantum bit error rate, and the mechanism and application of phase shift in polarized optical system is investigated. Firstly, based on the principle of matrix optics, the relationship among azimuth angle, phase shift and extinction ratio of polarized light is presented. Then the principle of phase shift added linearly is validated in the theorem and experiments. Based on the principle of phase shift added linearly, a set of polarization keeping system is designed and validated in the theorem and experiments，and the principle is applied to design optical systems for quantum communication successfully. Experimental results indicate that the extinction ratio of polarized light of optical systems for quantum communication exceed 500:1. It can satisfy the system requirements of quantum bit error rate for quantum communication.