Exceeding 50% slope efficiency DBR fiber laser based on a Yb-doped crystal-derived silica fiber with high gain per unit length.

We fabricated a Yb-doped yttrium aluminium garnet (Yb:YAG) crystal-derived silica fiber (YCDSF) using an assembly consisting of a YAG crystal rod and silica tube on a CO laser-heated drawing tower. The fiber has a Yb concentration of 5.66 wt%, and absorption coefficient of 32 dB/cm at 980 nm. The figure of merit of the unsaturated absorption and gain per unit length of the YCDSF are 93% and 4.4 dB/cm, respectively. Based on the results of the numerical simulation, an all-fiber distributed Bragg reflector (DBR) laser using only a 1.5-cm-long YCDSF is experimentally demonstrated to have a maximum output power of 360 mW with a pump threshold power of 21 mW. The fiber laser also achieved an optical signal-to-noise ratio of 80 dB, a beam quality factor of 1.022 in two orthogonal directions and a slope efficiency of up to 50.5%. These results indicate that the all-fiber DBR laser has potential applications in high-quality seed sources and coherent optical communications.