Yb^3+-doped silica glass rod with high optical quality and low optical attenuation prepared by modified sol-gel technology for large mode area fiber

We report on a modified sol-gel method combined with an innovative high-temperature melting technology for the preparation of Yb3+-doped silica glass rods (circle divide 3-18 mm) with high optical quality and low background loss. We prepared Al-Yb, Al-P-Yb, Al-FYb, and Al-P-F-Yb doped silica glass rods for large mode area fibers (LMA) with a high laser power and low core numerical aperture (0.02). We were able to successfully solve the doping homogeneity problem caused by the volatility of P and F. More importantly, we developed a purification technology and successfully reduced the optical attenuation to 0.05 dB/m. An Al-Yb co-doped silica photonic crystal fiber (PCF) with a core diameter of 100 mu m was fabricated for laser behaviour characterization. In the continuous wavelength laser measurement, a laser output slope efficiency of 83.3% was obtained from the fabricated PCF. To our knowledge, this is the highest slope efficiency derived from a Yb3+-doped silica PCF prepared by a non-CVD method. In the pulse amplification laser experiment, an average amplified power of 310 W with a peak power of 1.5 MW and a pulse duration of 21 ps were achieved.