Single-Longitudinal-Mode(Slm) Fiber Ring Laser Based On Semicircular Single Mode Fiberstructure

A single longitudinal mode (SLM) fiber ring laser based on asemicircularsingle mode fiber (SSMF) structure is proposed.In thefiber ring laser, a piece of erbium doped fiber (EDF) pumped by a 980 nm semiconductor laser diode (LD) through a wavelength division multiplexer (WDM).Afiber Bragg grating (FBG) is used as a filter. And acommercial single mode fiber (SMF)is bent into semicircular structure between a one -dimensional precision translation stage (TS) and a fixed stage (FS) to form SSMF structure.Birefringence interference in the SSMF with much bigger free spectrum range of 9.42 nm than the linewidth of FBG is very benefit for beat noise suppression because of Vernier effect. As a result,multi longitudinal mode laser, vanishing laser and SLM laser can be observed periodically by tuning theTSlittle by little. The side mode suppression ratio (SMSR) of SLM laser is 31.5 dB and the peak power is -13dBm. The system is very simple and lower cost.