Experimental evidence of differences in the absorption spectra of clustered and isolated ions in erbium doped fibers

The absorption spectra of clustered and isolated ions in erbium-doped germanosilicate fibers have been experimentally studied. The ground state absorption spectra broaden as the degree of erbium-ion clustering increases, indicating that the absorption spectra of clustered ions is significantly different from that of the homogeneous ions. This is confirmed by comparing the broadened absorption spectra with the fibre unbleachable loss spectrum; a direct measurement of the clustered ions. This is the first experimental evidence indicating different absorption cross-sections for the two species of ions in germanosilicate glass, an assumption used in the theoretical description of self-pulsing in erbium doped fiber lasers, but in direct contradiction to the pair-induced quenching model widely used to characterise EDFAs