Recent advances in single-frequency fiber lasers based on saturable absorbers

Abstract

Single-frequency fiber lasers (SFFLs) have excellent application prospects owing to their narrow linewidth, which leads to a long coherence distance and ultra-low noise. At present, the progress of next-generation optical communication, LiDAR and distributed fiber sensing has higher requirements for the linewidth and output power of SFFLs. Methods for narrowing the laser linewidth and improving the output power of SFFLs are current research hotspots. Unpumped gain fibers and low-dimensional materials have unique optoelectronic and nonlinear optical properties, which enable their wide use as saturable absorbers (SAs). Utilizing the saturable absorption effect, SAs can be used as excellent narrowband filters in SFFLs to further narrow the output linewidth and increase the output power. This review overviews the operational mechanism and techniques for measuring transient Bragg gratings (TBGs) and outlines the development of both linewidth and output power of SFFLs based on SAs, including unpumped doped fibers and low-dimensional materials. The pros and cons of SA-based SFFLs are summarized, and the future direction of these lasers is envisioned.