Efficient double-clad thulium-doped fiber laser with a ring cavity

We have constructed a novel ring cavity for a double-clad thulium-doped fiber laser, by placing the fiber's 45 degrees angle-polished output end before the input end and relaunching the pump and the laser power into the fiber. This design can reduce reabsorption by using short fibers without loss of pump efficiency. The dependence of the laser's performance on the fiber's length and the output coupler's reflectivity is investigated experimentally and theoretically. With an 80-cm-long fiber, 2.7-W single-mode continuous-wave output is generated for 11.5 W of launched pump power. (C) 2001 Optical Society of America.