中文摘要：

单频激光器已成功应用于温度传感、测距和相干通信。为了在相对较长的光纤谐振腔中构建单频激光器，许多技术像基于光纤布拉格光栅（FBG）的模式选择器、采用分布式反馈机制的超短谐振腔以及基于饱和吸收体的模式过滤器等均取得了相关进展。从谐振腔结构的角度总结了光纤激光器单频输出的常见方法和近年来的研究进展，对其进行了对比分析，并提出相应的改进方案。

英文摘要：

Single-frequency lasers （SFL） have been successfully used in temperature sensing, ranging, and coherent communications. Many techniques, such as fiber Bragg grating based mode-discriminator, ultrashort fiber cavity with distributed feedback mechanism, and saturable absorber based mode filters, etc. , have been developed for the purpose of generating a single-frequency laser in a relatively long fiber cavity. Some common methods and the breakthrough of realizing single-frequency fiber lasers in recent years from the angle of the resonant cavity structure are summarized, and the comparative analysis and corresponding improvement are made.