随机分布反馈光纤激光器(RDF-FL)作为一种基于分布式瑞利散射和拉曼放大效应的新型光源，具有结构简单、方向性好、传输距离长等特点，因而在光纤传感及光纤通信等领域有着广泛的应用前景。但由于形成反馈的瑞利散射较弱，其激射阈值很高。研究了两种降低光纤随机激光阈值的方法，即单边光纤布拉格光栅(FBG)线形腔法和超长环形腔法。在此基础上，从理论和实验上对随机激光的输入输出及频谱特性进行了详细分析与探讨。结果表明，单边FBG线形腔与超长环形腔结构分别将一阶随机激光阈值降低到0.8 W和1.0 W。研究有助于对随机激光机理的深入认识以及新型光纤随机激光器的设计。

Random distributed feedback fiber laser (RDF-FL) is a novel kind of light source based on distributed Rayleigh scattering and Raman amplification, which has characteristics such as simple structure, good directionality as well as long-distance transmission and shows a broad prospect in the application of optical fiber sensing and communications. However, the pump threshold is relative high just because of the weak Rayleigh scattering feedback. In this paper, two methods, half-opened cavity and ultra-long ring cavity structures, are used to reduce the threshold of the RDF-FL. On this basis, the input-output characteristics and frequency spectra of the RDF-FL are analyzed theoretically and experimentally. The results show that the first-order threshold of the RDF-FL can be reduced to 0.8 W and 1.0 W respectively. This research is helpful to further understanding the mechanism of RDF-FLs as well as the design of novel random fiber lasers.