Stable Single-Longitudinal-Mode Fiber Laser With Ultra-Narrow Linewidth Based on Convex-Shaped Fiber Ring and Sagnac Loop

摘要： In this investigation, a convex-shaped ?ber ring (CSFR)-based single-longitudinal-mode (SLM) erbium-doped ?ber laser (EDFL) is proposed and experimentally veri?ed. The CSFR, composed of only two optical couplers and forming a double-ring architecture, is employed to serve as a high quality mode ?lter to eliminate the dense longitudinal modes of the EDFL. The unpumped erbium-doped ?ber in the Sagnac loop is utilized to produce the ultra-narrowband auto-tracking ?lter effect as a saturable absorber to guarantee the SLM out. The experimental results show that the linewidth of the proposed EDFL is 840 Hz with a high optical signal to noise ratio of 63 dB. In addition, the stability of the EDFL with the maximum output power ?uctuation of 0.01 dB and the maximum central wavelength variation of 0.01 nm, in both the short-term and the long-term observations. Hence, we obtained a SLM EDFL with extremely high stability, ultra-narrow linewidth and high optical signal to noise ratio (OSNR).