Real-time compensation of phase drift for phase-encoded quantum key distribution systems

Phase drift is an inherent problem in phase-encoded quantum key distribution (QKD) systems. The current active phase tracking and compensation solutions cannot satisfy the requirements of a system with nonlinearity in phase modulation. This paper presents a four-phase scanning method, which is based on the quantitative analysis of the quantum bit error rate (QBER) from phase drift and the performance requirements of phase compensation. By obtaining the four interference fringes and adjusting the coding matrix of the system, this method automatically calculates the accurate driving voltages for the phase modulator. The implementation and experimental tests show that the proposed method can compensate phase drift caused by environmental changes and the system’s nonlinearity, and is applicable to large-scale QKD networks.