自由空间量子密钥分发中的信号同步解决方案

针对目前自由空间量子密钥分发（QKD）中的信号同步这一难点问题，提出一种采用外置光信号来解决信号同步问题的方案——光同步方案。在发送端利用声光调制器将外置激光器的连续激光分割成周期光脉冲序列，并作为同步光信号发送给接收端。接收端采用光电倍增管接收同步光脉冲信号，生成一个与发送端严格同步的信号，以此作为接收端的时基标准来进行单光子计数。采用高频的内部时钟信号来“监视”接收到的同步信号，从而提高计数准确性。该方案具有长距离性、无线性、低复杂度等特点，已成功应用于一个基于B92协议的自由空间QKD系统中。

Solution for synchronization of signal in free-space quantum key distribution

Aiming at the difficulty in synchronization of signal in the system of Quantum Key Distribution (QKD) in free space, we proposed a method that deals with this problem with outer light signal, named light-synchronization method. In transmitter, continuous signal of an external laser is modulated into a light pulse sequence by using an acousto-optic modulator. And the light pulse sequence is sent to the receiver. The receiver incepts the light pulse signal by using a multiplier phototube, and generates synchronal signal as time base, then take count of single photon. The inner clock signal of high frequency is used for monitoring the generated synchronizing signal for enhancing precision. The scheme has the advantage of long-distance, wireless and low-complexity, and it has been applied in a Free-Space QKD system which is based on B92 protocol.