Large-region tunable optical bistability in saturable absorber-based single-frequency Brillouin fiber lasers

The optical bistability in saturable absorber-based single-frequency Brillouin fiber laser (BFL) has been experimentally investigated. A Sagnac fiber loop with unpumped erbium-doped fiber (EDF) is embedded in the BFL cavity as a saturable absorber (SA). This component serves as both an auto-tracking narrowband dynamic grating to guarantee single-longitudinal-mode (SLM) operation, and an intensity-dependent loss switch leading to the bistable behavior. The feature of the intensity-dependent loss is well verified and characterized. A bistable region is found as large as 418.8 mW in the laser with the Brillouin gain media of 50 m single mode fiber. Furthermore, the flexible tunability of bistable region can be implemented by designing the unpumped EDF length and the Brillouin gain media with a proper fiber length or fiber type.