Coherently combined 20 W at 2000 nm from a pair of thulium-doped fiber lasers

We experimentally demonstrated coherent beam combining of a pair of thulium-doped fiber lasers using an all-fiber Fox-Smith resonator. We built two thulium-doped fiber lasers from PM fibers and pumped them at 793 nm. Each laser provided a power of more then 10 W at a wavelength of 2000 nm with a slope efficiency of more then 0.5. Then a compound Fox-Smith resonator was created using the PM coupler. More then 20 W of laser power was obtained due to a constructive interference at the output of the laser while a slope efficiency decreased to 0.35. Stable CW output signal was achieved despite the fact that the individually operated lasers had tendency to self-pulsations.