LAUSR

We report on the design, realization and testing in pulsed amplification regime of a double-cladding, large mode area, polarization maintaining, solid core photonic bandgap fiber with Yb-doped core obtained from a Sol-Gel -made material. A specific hetero-structuration of the cladding has been applied to efficiently reject the higher-order modes, making the fiber single-mode in practice. When used as the last stage of a high power fiber amplifier, more than 90 W average power has been extracted at 1.03 $\mu$m wavelength with a slope efficiency of 75 % with respect to the absorbed pump power. These performances were obtained for a 6 m-long piece of fiber bent on a radius smaller than 12.5 cm. A mode field diameter of 35 $\mu$m is reported for the amplified beam with very good spatial quality and polarization extinction ratio.