Intermediate excited-state absorption in erbium-doped fiber strongly pumped at 980 nm

Abstract

We report the observation of fluorescence at 530 to 550 nm from erbium-doped germanosilicate fiber under strong pumping in the 980-nm band. The observed nonlinear dependence on pump power is shown to arise from a sequential two-photon absorption from the ground state to the ⁴F_7/2 state through the short-lived ⁴I_11/2 intermediate state. Rate-equation modeling shows that the pump power dependence of this intermediate excited-state absorption is influenced by population cycling induced by amplified spontaneous emission in the fiber from the metastable ⁴I_13/2 state.