Pump Wavelength Dependence of Photodarkening in Yb-Doped Fibers

Photodarkening in Yb-doped fibers is known to be dependent of Yb population inversion. In addition to this dependence, we report that pump wavelength selection plays a significant role in photodarkening dynamics. It is found that 976 nm pump source can lead to more severe photodarkening effects than 916 nm pumping at the same inversion levels. This observation is consistent in Yb-doped fibers with various compositions. Our work reveals pump wavelength is another determinant factor of photodarkening besides the inversion level and emphasizes the importance of pump wavelength selection in high power Yb-doped fiber lasers and amplifiers.