Effects of F- on the optical properties of Yb3+-doped large mode area silica fiber prepared by sol-gel method

Yb-Al co-doped rod glass introducing with F- as the large core of photonic crystal fiber (PCF) was prepared by solgel method combined with high temperature sintering, and the rod without F^- was fabricated as the comparison. The refractive index and homogeneity of the rods, and the attenuation, laser properties of the fibers have been investigated to confirm the effects of F^- in the fibers. The results show that introducing F^- in the fiber core can obviously decrease the refractive index of Yb³⁺ doped silica glass, and the beam quality of the PCF has been greatly improved by the lower NA of core.