Narrow Linewidth Bismuth-Doped All-Fiber Ring Laser

We report a novel narrow linewidth Bismuth-doped all-fiber ring laser, operating at 1177 nm. We achieve a 10-mW output in a 4-GHz linewidth, direct from the oscillator under 7 W of pumping, delivered by an Yb-fiber laser. Mode suppression in the 50-m unidirectional ring cavity is provided by a narrowband fiber Bragg grating and two fiber integrated Fabry-Perot (FP) filters. The FP filters provide a factor of 20 mode suppression, while improving the relative intensity noise by up to 20 dB/Hz. The optical signal-to-noise ratio (OSNR) is ~60 dB.