Photodarkening of 488nm-pumped Sm3+-doped germanosilicate fiber laser

Photodarkening in samarium doped germanosilicate fiber and laser by downconversion is studied. Appreciable photodarkening occurs in the fiber and we attribute the effect to color centres which are both related to Sm₂O₃ and GeO₂. An energy level scheme has been illustrated to explain the photodarkening mechanism.