中文摘要：

空间相干光通信系统的信噪比受激光器线宽的影响很大。对比分析了两光束到达平衡探测器光敏面的时间差τd和探测器特性参数不同时,激光器线宽对外差探测输出信噪比的影响。理论分析和实验结果表明,激光器线宽展宽引起差频信号带宽增大与τd无关。当差频信号带宽增大2.673倍时,输出信噪比减小0.369 2倍,约等于1/2.673。增大探测器的内增益、响应度和响应带宽,可以减缓信噪比随激光器线宽增大而减小的速度,但内增益和响应带宽过大,相应的噪声信号也越强,反而不利于信噪比的提高。

英文摘要：

The signal-to-noise ratio （SNR） of space coherent optical communication system is greatly influenced by the laser linewidth. This paper compares and analyzes the influence of laser linewidth on the SNR of the heterodyne detection output when the time difference τd that two beams arrive at the photosensitive surface of the balanced detector and the detector characteristic parameter are different. Theoretical analysis and experiment result show that the differential frequency signal bandwidth increasing caused by laser linewidth broadening is independent withτd . When the differential frequency signal bandwidth increases by 2. 673 times, the output SNR decreases by 0. 369 2 times, which is approximately equal to 1/2. 673. Increasing the internal gain, response degree and response bandwidth of the detector can slow down the SNR decreasing speed as the laser linewidth increases; however, when the internal gain and response bandwidth are too large, corresponding noise signal is also stronger, which is not benefit to the improvement of the SNR.