Suppression of photo-darkening effect in Yb-doped silica glass fiber by co-doping of group 2 element

•We fabricated Yb-doped silica fibers co-doped group 2 elements by using the zeolite method.•Mg co-doped Yb-doped silica fiber show superior resistance to photo-darkening effect.•The mechanism of photo-darkening effect was studied by considering the valence states in silica glasses.

We found that co-doping of group 2 element effectively suppresses the photo-darkening (PD) effect in Yb-doped silica glass fiber and Mg co-doped Yb-doped silica glass fiber (YbMgSGF) is the most effective. This phenomenon is well understood on the basis of bond valence concept in the glass. In our model, Mg2 + ion with Al3 + stabilizes Yb3 + valence state with charge compensation in the silica glass and Mg2 + could smoothly match silica glass network because the ionic radius is the closest to the radii of Al3 + and Si4 +. YbMgSGF is not only a promising Yb-doped optical fiber for high power fiber laser, but also for ultimate short length fiber lasers. This technique could also be applied to reduce PD effect in the other rare-earth ion doped fibers, such as Tm, Tb, Eu, and Sm.