为了探寻空间相干光通信中本振功率与相干探测灵敏度间的关系, 建立了本振光功率变化对相干探测灵敏度影响的数学模型, 仿真分析了不同参数状态下本振功率对相干探测灵敏度的影响。采用自研开发的高速大面积空间耦合平衡探测器搭建了相干探测灵敏度测试实验系统, 并就本振功率对探测灵敏度的影响进行了实验验证。实验结果表明: 相干探测系统中, 两光电管不可能完全匹配, 探测灵敏度始终受到本振强度噪声的影响, 在探测器环境参数一定时, 存在最佳本振光功率值使得相干探测灵敏度取最大值。在误码率为10-12、通信速率为5 Gb/s的条件下, 相干探测灵敏度测试的最大值为-40.16 dBm, 此时对应的本振光功率为9 dBm, 与理论极限值基本一致。该模型对提高相干探测系统的探测灵敏度具有指导意义。

To explore the relationship between the local oscillator power and the coherent detection sensitivity in free-space coherent optical communications, the mathematical model about the influence of the local oscillator power on the sensitivity of coherent detection was established, and the effect of local oscillator power on the sensitivity of coherent detection under different parameters was simulated. The coherent detection sensitivity testing system was set up by using the high-speed and large-area space-coupling balanced detector produced from Wuhan University, then the effect of the local oscillator power on the detection sensitivity was verified experimentally. The experimental results show that the detection sensitivity is always affected by the intensity noise of the local oscillator due to the dismatch of the two photodiodes in the coherent detection system; thus there exist an optimal local oscillator power which can realize the maximum value of coherent detection sensitivity with certain environment parameters of the detector. When the bit error rate is 10-12 and the communication rate is 5 Gbps, the maximum value of the coherent detection sensitivity in the test is -40.16 dBm and the corresponding optical power is 9 dBm. The proposed model has an guiding significance for the improvement of detection sensitivity of coherent detection systems.