Ultralong Single‐Ended Random Fiber Laser and Sensor

Random fiber laser (RFL) utilizing stimulated Raman scattering and distributed random Rayleigh backscattering in fiber as optical gain and feedback mechanisms, respectively, has been developed rapidly in the past decade. Here, it is found, for the first time, that the combination of a high-order pump and new transmission fiberthat has lower transmission loss, Rayleigh backscattering coefficient, and Raman gain coefficient than standard single-mode fibercan break the length limits of both random fiber lasing and sensing. With a higher-order pump and ultralow loss fiber (ULLF), the position of maximum intracavity lasing power can be shifted toward the far end of the fiber span resulting in more remote pump power for the erbium-doped fiber (EDF) inserted in the fiber span, which plays a dominant role of cavity length extension in RFL. A 200 km ultralong single-ended RFL and sensor are experimentally demonstrated, which are the longest single-ended RFL and sensor with functional remote reflectors reported to date. It is believed that the proposed combination of high-order random lasing and ULLF with EDF can become a general method to extend the working distance of various fiber sensing systems for safety monitoring of ultralong infrastructures, such as power transmission lines and oil/gas pipelines.