Competence Center for Specialty Optical Fibers

We investigated photodarkening (PD) parameters of Yb/Al-doped silica fibers in dependence on the concentration of additional rare earth ions like Tm or Er. It is found that both, Tm and Er cause a decrease of Yb inversion followed by a reduction of PD in the case of Er, whereas Tm-codoping with more than 10 mol-ppm can strongly accelerate the process and also increase the PD loss. However, contrary to [1], we conclude that the typical PD behavior of Yb/Al fibers is an intrinsic feature of this fiber type and not caused by trace impurities of Tm (< 1 mol-ppm) that are unintentionally incorporated by the raw materials during fiber preparation.