1.1 kW, beam combinable thulium doped all-fiber amplifier

A 1.1 kW CW fiber amplifier emitting at 1.95µm and phase modulated at 5 GHz, with 51% optical conversion efficiency and near diffraction limited beam quality (M2<1.1) is demonstrated. The fiber amplifier consists of 9m of active 20/400um thulium doped fiber, and 2m of passive delivery fiber. Several limiting nonlinearities critical to maintaining coherence were analyzed, including stimulated Brillouin Scattering and modulation instability. To our knowledge, this is the first kw-class thulium doped fiber amplifier operating with narrow linewidth.