Highly efficient Er,Yb-doped fiber laser with 188W free-running and > 100W tunable output power

Efficient high-power operation of an erbium-ytterbium co-doped fiber laser cladding-pumped by two spatially-multiplexed and polarization combined 975 nm diode-stacks is reported. Up to 188 W of continuous-wave output at 1.57 microm was generated with a beam-quality factor (M;2) of 1.9 and an overall slope efficiency with respect to launched pump power of 41% (and 43% for output powers <120W). Tunable operation was demonstrated by use of an external cavity containing a diffraction grating and a maximum output power of 108 W at 1538 nm was generated for a launched pump power of ~ 336 W. The operating wavelength was tunable from 1531 to 1571 nm, with >100W output power over a tuning range of 36 nm from 1532 nm to 1568 nm.