Authors: M. Bernier, R. Vallée, B. Morasse, C. Desrosiers, A. Saliminia, and Y. Sheng
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 4×10−3 was obtained and the accompanying photo-induced losses were subsequently removed by thermal annealing, resulting in a low loss (<0.1dB), stable and high reflectivity (>40dB) FBG. Based on this FBG, a monolithic Ytterbium fiber laser operating at 1073 nm with slope efficiency of 71% and output power of 13W was demonstrated.