Excited-state absorption and gain measurement at 1.3 /spl mu/m in Nd/sup 3+/ doped silica fibers with different codopants: effect of cesium on ESA cross section

A study of the excited state absorption (ESA) spectrum around 1.3 /spl mu/m in Nd/sup 3+/ doped fibers is presented. Several fibers are characterized with different codopants including germanium, aluminum, and cesium and their effects on the spectrum of the radiative transitions are studied. We found an important variation of the magnitude of the ESA cross section giving rise to gain (0.032 dB/mW) at 1.34 /spl mu/m.