  We report on the writing of chirped volume 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 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 cladding of the
highly multimode 125 microns fiber 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 micron 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
fiber laser component would have a great impact on the efficiency and cost of
high-power cladding-pumped fiber laser systems.
