Photodarkening of alumosilicate and phosphosilicate Yb-doped fibers

Photodarkening of ytterbium-doped laser fibers is an important problem, as it is directly associated with the fiber lasers and amplifiers durability. The phenomenon manifests itself as the growth of optical losses in the process of fiber usage under the action of pump radiation. In this paper the comparison of the parameters of this process for alumosilicate and phosphosilicate Yb-doped fibers is performed for the first time. And it was found that normalized phosphosilicate fibers are a good alternative to alumosilicate ones, especially for the operation in case of high value of upper level population.