Ytterbium fiber laser based on first-order fiber Bragg gratings written with 400 nm femtosecond pulses and a phase-mask.

A Fiber Bragg grating of 369 nm pitch was inscribed in a germanium-free double-clad ytterbium doped silica fiber using a femto-second pulse train at 400 nm wavelength and a phase mask. The photo-induced refractive index modulation of higher than 4 x 10(-3) was obtained and the accompanying photo-induced losses were subsequently removed by thermal annealing, resulting in a low loss (<0.1 dB), stable and high reflectivity (>40 dB) FBG. Based on this FBG, a monolithic Ytterbium fiber laser operating at 1073 nm with slope efficiency of 71% and output power of 13 W was demonstrated.