Evidence of Tm impact in low-photodarkening Yb-doped fibers.

Sylvia Jetschke, Sonja Unger, Anka Schwuchow, Martin Leich, Julia Fiebrandt, Matthias Jäger, Johannes Kirchhof

Index: Opt. Express 21(6) , 7590-8, (2013)

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Abstract

In contrast to Yb/Al-doped fibers, the influence of very low Tm(2)O(3) concentrations (≥ 0.1 mol-ppm) on photodarkening (PD) is clearly detectable in Yb/P-doped fibers that are known to show little degradation effects. For Tm(2)O(3) additions of more than 50 mol-ppm, the measured PD loss is even similar to Yb/Al-doped fibers with comparable rare earth concentrations. Our work reveals the risk of color center generation by pumping at wavelengths of 915 nm or 976 nm even in Al-free Yb-doped fibers and emphasizes the importance of high purity of raw materials for the preparation of Yb laser fibers with expected very low PD.