为了提高激光测速系统的探测灵敏度,设计了马赫-曾德尔环形结构的平衡探测系统。基于光学多普勒效应,阐述了激光测速系统的工作原理,系统地阐述了平衡探测的实现方法,详细推导了平衡探测系统光电流的表达式,并分析得出其相对于相干探测的优势。利用光电流推导了平衡探测系统信噪比的表达式,并分析影响信噪比的主要因素。仿真实验结果表明:在相同输入光信号的条件下,无损耗分束镜的反射率在(0.2908,0.7092)区间内,或两个探测器的光电转换系数的比值在(0.4632,1)之间时平衡探测信噪比高于相干探测的信噪比。将平衡探测应用于多普勒测速,大大增强了测速系统的灵敏度。 In order to improve the detection sensitivity of the laser speed measurement system, a balanced detection system of Mach-Zehnder ring structure is designed. Based on the optical Doppler effect, the principle of the laser speed measurement system is expounded. The realization of the balanced detection system is expatiated systematically. The expression of the photocurrent in the balanced detection system is deduced in detail and the advantage of the system is also analyzed. The expression of signal-to-noise ratio of balance detection system is deduced by photocurrent, and the main factors influencing signal-to-noise ratio are analyzed. The simulation results show that the reflectivity of the lossless beamsplitter is (0.2908,0.7092) or the ratio of the photoelectric conversion coefficients of two detectors is (0.4632,1) under the same input optical signal. Signal to noise ratio for balanced detection is higher than for signal to noise ratio for coherent detection. Applying balanced detection to Doppler velocities greatly enhances the sensitivity of the velocimetry system.