Photodarkening-Induced Absorption and Fluorescence Changes in Yb Fibers

We study the photodarkening effect in a double clad ytterbium-doped silica fiber fabricated by modified chemical vapor deposition and solution doping. A common measurement technology for photodarkening is used to study the photodarkening-induced absorption spectra. We present a fast and simple method to observe the PD effect by measurement of the fluorescence spectra. The method proposed here can be used to observe the influence for a short time, and thus reduces the requirements of system stability and heat management. It is obtained that under the condition of 45.5% Yb ion inversion level, photodarkening-induced excessive loss at an equilibrium state is above 4.5 dB/m and florescence intensity degradation is above 10% after 500 min pumping at 1041 nm for the home-made normal Yb/Al co-doped silica fiber.