We have constructed a novel ring cavity for a double-clad thulium-doped fib
er laser, by placing the fiber's 45 degrees angle-polished output end befor
e 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 Optica
l Society of America.