Study of dual-coupler fiber ring and saturable absorber-based stable single-longitudinal-mode fiber laser

A configuration of single-longitudinal-mode (SLM) erbium-doped-fiber (EDF) ring laser with high stability and narrow linewidth is proposed and experimentally demonstrated. The device is composed of a dual-coupler fiber ring (DCFR) and an unpumped EDF-based saturable absorber (SA); the DCFR serves as the mode filter and facilitates the selection of the SLM while the SA produces the ultranarrow band autotracking filter effect and guarantees the SLM out. This scheme possesses the merits of being easy to fabricate, good performance, and high stability. It is easy to manufacture without strict limitations in the length of the DCFR. The output of the SLM EDF laser presents excellent performance with a linewidth of 1.52 kHz and the optical signal-to-noise ratio of 54 dB. Moreover, the proposed EDF laser exhibits remarkably good stability: the SLM operation is observed to have been stable for 3 h; the output power fluctuation and the central wavelength variation of the laser are 0.011 dB and 0.02 nm in 1 h, respectively.