在大气信道激光传输中, 大气湍流对系统性能会产生较大影响, 主要体现为降低传输速率和增加误码率。在具有信道互易性的双向激光传输链路中, 两终端光斑信号强度的变化相关, 可以在终端提取信道状态信息, 以对信道影响进行补偿, 从而提高传输速率。本文首先在弱湍流条件下, 根据Rytov近似理论推导了平面波双向传输链路接收到的光斑信号的相关系数与传输路径的关系, 并给出解析式。结果表明, 两终端接收的光斑信号的光通量具有相关性, 且相关系数与传输路径有关。进一步搭建了双向收发共轴激光传输系统, 并进行了外场试验, 试验结果不仅验证了双向大气信道激光传输链路具有互易性, 且两接收端光斑信号光强的实时变化趋势相同。本文结论对实现大气信道高速率、低误码率激光传输具有重要意义。

In atmospheric channel laser transmissions, atmospheric turbulence has a large influence on system performance, reducing its transmission rate and increasing its bit error rate. In a bidirectional free-space laser transmission link with channel reciprocity, as the change in optical signal intensity at the two terminals is correlated, the Channel State Information (CSI) can be obtained at the transmitter and used to compensate the channel influence, thus improves the transmission rate. In this paper, under weakly fluctuating conditions, according to Rytov approximation, the relationship between the correlation coefficient of the spot signal received by plane wave bidirectional transmission link and the transmission path is deduced, and its analytical expression is derived. The results show that the intensity of the optical signal at the receiving end of the bidirectional free-space laser transmission link is related to the transmission end and that the correlation coefficient is related to the location of the transmission path. A bidirectional coaxial laser transmission system is further established and an external field test is performed. The real-time change trend of the intensity of the speckle signal at both receivers is the same. Therefore, the atmospheric channel of the bidirectional free-space laser transmission link is reciprocal. The conclusion of this paper is of great significance for realizing high-rate and low bit error rate transmission in atmospheric channels.