Ultralong Raman fiber laser and sensor with optimized remotely optical pump amplification

Raman fiber laser utilizing stimulated Raman scattering in fiber as optical gain and point reflectors at both fiber ends as feedback is an ideal platform to realize ultralong cavity laser. Ultralong Raman fiber laser (URFL) is of great interest in study of laser physics, optical communication and laser sensing, while ultralong random Raman fiber laser sensor (RRFLS) can find important applications in the safety monitoring of ultralong infrastructures, such as long-haul oil/gas pipelines and power transmission lines, et al. In this work, the remotely optical pump amplification (ROPA) based on the combination of high-order random fiber laser pumping and erbium-doped fiber (EDF) is optimized theoretically and experimentally and then introduced into the URFL and RRFLS composed of ultralow loss fiber, for the first time. By optimizing the location and length of the EDF in the ROPA, a 400 km URFL with mode separation of 257 Hz and a 235 km RRFLS with 14.5 dB optical signal-to-noise ratio are achieved, which are the longest fiber laser and single-ended fiber sensor reported to date. In particular, the ultralong RRFLS with the optimized ROPA could well make up the insufficiency of current fiber sensors at single-ended sensing distances of longer than 200 km.