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在以单模光纤作为量子信道,并采用光子偏振编码方式的量子密钥分发过程中,光纤的双折射效应会导致光子在光纤中传播时其偏振态发生随机变化,使安全密钥的最终成码率大幅度降低.利用两个四分之一波片和一个半波片的组合作为校正器,可以实现对任意偏振态的校正补偿.建立了一种以该类偏振校正器为执行机构的基于随机并行梯度下降控制算法的实时偏振补偿仿真控制模型,讨论了算法的随机扰动幅度、增益系数与收敛速度的关系,分析了算法对于偏振的校准能力.通过实验对算法的性能进行了验证.实验结果表明,经过一定次数的迭代后可将系统的偏振消光比校正到一个比较理想的状态.
In the process of quantum key distribution using single-mode optical fiber as the quantum channel and using the photon polarization coding method, the birefringence effect of the optical fiber causes the polarization state of the optical fiber to randomly change when propagating in the optical fiber so that the final security key The code rate is greatly reduced.Using the combination of two quarter-wave plates and one half-wave plate as the corrector, the compensation for any polarization state can be achieved.A method of using such a polarization corrector as the actuator The real-time polarization compensation simulation control model based on stochastic parallel gradient descent control algorithm is discussed, and the relationship between the random perturbation amplitude, gain coefficient and convergence speed is analyzed and the algorithm’s calibration ability is analyzed. The performance of the algorithm is verified through experiments. The experimental results show that after a certain number of iterations, the system’s polarization extinction ratio can be corrected to a more ideal state.