针对国内长距离相干光通信接收系统采用单管探测器接收微弱信号噪声大、信噪比低等缺点，设计了一种应用于相干光通信系统的平衡探测器，运用两个PIN 管分别加跨阻放大器(TIA)，经过两个180°混频魔T 进行耦合相减，消除了大部分的激光器相对强度噪声(RIN)。搭建了测试平衡探测器的相干光通信系统，使本振光和信号光进行光混频，输出眼图显示通信状态良好。通过对比双管和单管的频谱图，进一步说明相干光通信系统的噪声通过这种平衡探测器得到了降低，系统的信噪比提高了大约10 dB，从而证明了该平衡探测器运用于相干光通信系统的可行性和优越性。

Considering the shortcomings of the existing long distance coherent optical communication receiving system using single tube detectors which receives weak signals with large noise and low SNR, a balanced detector is designed for coherent optical communication system. The balanced detector uses two diodes with TIA respectively and reduces most of the laser′ s relative intensity noise after two hybrid magic Tee′ s coupling and subtraction. The coherent optical system is set up to test the performance of the balanced detector. The local-oscillator and signal laser are mixed and then the eye diagram shows that communication is in good condition. By comparing the spectrum, the results show that the noise of the coherent optical communication system is reduced by using the balance detector compared to the single tube. The signal-to-noise ratio of system is enhanced about 10 dB, which proves the balance detector′s feasibility and superiority for application in the coherent optical communication system.