Abstract

Excited-state absorption (ESA) of the pump at 980 nm is not considered to be important for Er³⁺-doped fiber amplifiers (EDFAs), because the positions of the Er³⁺ energy levels do not permit the absorption of a 980nm photon from the metastable ⁴I_13/2 level.¹ It has been suggested recently, however, that ESA may in fact have some effect on the performance of EDFAs, especially at higher output powers.²'⁴ The origin of the effect can be seen in Fig. 1, where a 980-nm photon is absorbed from the ⁴I_11/2 level. If Er³⁺ is pumped in the 980-nm or a shorter wavelength band, this state has small but finite population even for oxide glasses.

© 1992 Optical Society of America