Single-Longitudinal-Mode Triple-Ring Brillouin Fiber Laser With a Saturable Absorber Ring Resonator

A single-longitudinal-mode triple-ring Brillouin fiber laser (TR-BFL) with a saturable absorber ring (SAR) resonator is proposed and investigated experimentally. Triple ring is composed of a 1-km-long single-mode fiber (SMF) ring, a 100-m-long SMF ring, and an SAR with 8-m-long unpumped Erbium-doped fiber, respectively. Compared with the existing techniques, a better performance of TR-BFL can be obtained because of the 1-km-long cavity length and the triple-ring configuration with an SAR, which suppresses the weaker unwanted mode and does not require power control accurately and import additional loss. At the same time, a frequency-locking system based on Pound-Drever-Hall technology is used to reduce the external perturbations and the instability caused by 1-km-long cavity and triple-ring configuration, respectively. In the experiment, 185 linewidth-reduction ratio is obtained while still maintaining 72-dB optical signal-to-noise ratio. Meanwhile, approximately 65-Hz linewidth is measured with a delayed self-heterodyne method using a 100-km delay fiber, and 5% power fluctuation at 1-mW laser output power is observed every 1 min in 50 min.