Real-time polarization compensation system for wavelength division multiplexing in low noise fiber channel based on single photon counting feedback

The physical effects such as random birefringence of fiber optic channels due to environmental influencesmake the optical signals transmitted in them have sensitive polarization variations, which seriously affects theperformance of polarization biased code quantum key distribution systems. In this paper, a low-noise fiberchannel wavelength division multiplexing real-time polarization compensation system is presented, where singlephoton counting is used as a feedback signal. The system can acquire the fiber channel polarization changeinformation by detecting the photon counting of the conjugate reference light. In the system, the compensationalgorithm is designed to control the electric polarization controller to calibrate the polarization state of thequantum signal light under the corresponding polarization base in real time, and the stable fiber channelpolarization compensation is successfully achieved. In order to verify the effectiveness of the compensationsystem, a quantum key distribution test based on BB84 protocol with a transmission distance of 25.2 km isconducted, and stable test results of up to 8 hours are obtained in the laboratory environment and thesimulated metropolitan area network buried fiber environment, with the average quantum bit error rate being0.52% and 1.25%, respectively. The experimental results show that this system can guarantee the stableoperation of polarization-encoded quantum key distribution in the buried fiber environment in urban areas