为了提高全光纤差分吸收激光雷达的探测精度，研究近距离探测条件下使用光环形器的差分吸收激光雷达，这对提高气体探测精度具有重要的意义。分析了差分吸收激光雷达的探测精度与激光回波能量测量的关系，发现近距离条件下的气体探测精度将会受到环形器“串音”的影响，分析了不同探测高度下串音对探测精度的影响程度。结合CO2浓度探测的实例并通过仿真计算，得到了信噪比与探测相对误差随探测高度的变化曲线。结果表明，环形器中存在的“串音”会干扰激光回波信号，对探测信噪比与精度产生严重影响。该研究对设计与完善全光纤差分吸收激光雷达系统具有重要的借鉴意义。

In order to improve the detection accuracy of all-fiber differential absorption lidar (DIAL), it is very important to develop configuration of all-fiber DIAL system with circulator at close range. Relationship between detection accuracy of DIAL and laser echo energy is analyzed. At close range, crosstalk of circulator affects the detection accuracy. The influence of crosstalk on detection accuracy is analyzed at different heights. Combined with the example of CO2 concentration detection and simulation, signal to noise rate (SNR) and relative error with height are analyzed. The research shows that crosstalk can interfere with laser echo and seriously affect detection SNR and accuracy. The study has important significance on the design and improvement of all-fiber DIAL system.