title: Influence of Tm- or Er-codoping on the photodarkening kinetics in Yb fibers.
abstract: We investigated photodarkening (PD) parameters of Yb/Al-doped silica fibers as a function of the concentration of additional rare earth ions like Tm or Er. It was found that both Tm and Er cause a decrease in 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) unintentionally incorporated by the raw materials during fiber preparation.
authors.affiliation: Institute of Photonic Technology, Albert-Einstein-Str 9, 07745 Jena, Germany. sylvia.jetschke@ipht-jena.de
authors.forename: Sylvia
authors.initials: S
authors.lastname: Jetschke
authors.forename: Martin
authors.initials: M
authors.lastname: Leich
authors.forename: Sonja
authors.initials: S
authors.lastname: Unger
authors.forename: Anka
authors.initials: A
authors.lastname: Schwuchow
authors.forename: Johannes
authors.initials: J
authors.lastname: Kirchhof