Evidence of enhanced hypersensitive transition in erbium-doped fibers with different Al/sub 2/O/sub 3/ content

Precise spectroscopic absorption measurements of erbium-doped aluminosilicate fibers with different Al/sub 2/O/sub 3/ content were performed with the Judd-Ofelt analysis. From the Judd-Ofelt analysis, the /spl Omega//sub 2/ parameters of Er/sup 3+/ ions in these fibers were found to be about three times as large as those in aluminosilicate bulk glasses. The enhancement of the /spl Omega//sub 2/ parameters led to much stronger line strength of hypersensitive transitions in a fiber form than in a bulk glass form. This indicates that the distortion of the ligand field around the Er/sup 3+/ ions are more enhanced in a fiber form than in a bulk glass form. Furthermore, the /spl Omega//sub 6/ and the /spl Omega//sub 2/ parameters increased with an increase of q content up to 20 000 ppm. This Al/sub 2/O/sub 3/-content dependence of the /spl Omega//sub 6/ parameter was consistent with that of the line strength and the spontaneous emission probabilities of the transition corresponding to the /sup 4/I/sub 13/2//spl rarr//sup 4/I/sub 15/2/.