基于少模光纤模分复用的量子—经典信号同传方案中,光纤内的模式耦合效应会导致信道间发生串扰,造成误码。为此,构建了少模光纤分段化链路模型,研究了光纤拼接误差导致的模式耦合强度大小,并在此基础上推导了存在模式耦合时系统的量子误码率(QBER)公式。通过比较各模式所受到的耦合强度,确定该同传方案中量子信号的最优传输模式;进一步讨论了不同纤芯轴向偏移距离、扭转角度和光纤长度对系统QBER的影响。结果表明,这三个影响链路模式耦合强弱的因素都与QBER成正相关,光纤拼接误差较小的短距离量子—经典信号模分复用同传系统可有效降低QBER。

In the quantum-classical signal simultaneous transmission scheme sharing a same few-mode fiber based on mode division multiplexing, the mode coupling effect in the optical fiber will lead to crosstalk between channels, resulting in bit error. In this paper, a segmented link model of few-mode fiber is constructed, and the magnitude of mode coupling strength due to fiber splicing error is studied, based on which the system quantum bit error rate (QBER) formula is deduced in the presence of mode coupling. By comparing the coupling strength of each mode, the optimal transmission mode of quantum signal in the scheme is determined. The effects of mismatch distance, torsion angle, and fiber length on the QBER are discussed. The results show that the three factors that affect the coupling strength of link mode are positively correlated with the QBER, and the quantum-classical signal simultaneous transmission system with small fiber splicing error in short distance can effectively reduce the QBER.