通过建立复合腔模型，分析了外光反馈对单纵模分布反馈式（DFB）光纤激光器稳定性的影响，研究了外光反馈引起的相干坍塌阈值特性。通过采用模式分裂表征方法和相位噪声表征方法，对DFB光纤激光器的相干坍塌现象进行了对照检测，成功测量了瑞利散射和端面反射分别引起单纵模DFB光纤激光器发生相干坍塌时工作纵模的分裂情况，证明只考虑瑞利散射时DFB光纤激光器的阈值传导光纤长度小于200 m。实验结果和理论分析相吻合，验证了采用上述两种方法检测相干坍塌的可行性，对于DFB光纤激光传感阵列的结构设计具有指导意义。

Based on the composite cavity model, the feedback-induced instabilities which may cause coherence collapse in single-longitudinal-mode distributed feedback (DFB) fiber lasers are analyzed. The coherence collapse of DFB fiber laser is detected, and the longitudinal operating mode splitting phenomena of DFB fiber laser due to Rayleigh backscattering and the facet reflection are measured simultaneously. Experiments show that the threshold of the length of the leading fiber cannot exceed 200 m, which keeps quantitative agreement with the results of simulation. The investigation proves the feasibility of the two methods for detecting coherence collapse, i.e., mode splitting method and phase noise method, and provides a guide to the design of DFB fiber laser sensor array.