All-fiber laser pump reflector based on a femtosecond-written inner cladding Bragg grating

We report on the writing of chirped cladding Bragg gratings using 400 nm femtosecond pulses and the phase-mask inscription technique in the pure silica inner cladding of the gain fiber. The usefulness of such a fiber component is demonstrated as a pump reflector in a cladding-pumped all-fiber laser. A reflectivity of 53% for the residual pump power guided in the highly multimode 125 mu m fiber's cladding is achieved, allowing for significant pump recycling in the fiber laser cavity which therefore optimizes the overall laser performances. As proof of concept, adding this pump reflector at the output of a 25 W erbium-doped fiber laser operating near 1.6 mu m increased its slope efficiency according to the launched pump power from 17% to 23%, with the beneficial effect of reducing by 25% the optimal gain fiber length. This new, to the best of our knowledge, fiber laser component would have a great impact on the efficiency and cost of high-power cladding-pumped fiber laser systems. (C) 2019 Optical Society of America