Elimination of self-mode-locking pulses in high-power continuous-wave Yb-doped fiber lasers with external feedback.

Abstract

Sustained self-pulsing and self-mode-locking (SML) are detrimental to the performance of continuous-wave (CW) fiber lasers. We demonstrate an all-fiber method to eliminate SML pulsing by employing a low-reflectivity fiber Bragg grating (FBG) outside of a laser cavity to provide feedback. A narrow-bandwidth FBG is used to form an external cavity with the output coupler FBG, which suppresses the SML up to a certain output power level, at which point, the laser emission linewidth is still within the bandwidth of the FBG. On the other hand, a broad-bandwidth FBG forms a chirped cavity with the output coupler FBG, which can suppress the SML at a much higher power level, tested up to 50W. This method provides a simple effective all-fiber solution for suppressing self-pulsing in CW fiber lasers at high pump levels with no need to change the laser configuration.