Evaluation of parasitic upconversion mechanisms in Er/sup 3+/-doped silica-glass fibers by analysis of fluorescence at 980 nm

The behavior of modulated and unmodulated upconversion fluorescence in Er/sup 3+/-doped silica-glass optical fibers pumped at 1480 nm has been experimentally and theoretically investigated. It is found to be consistent with a model where the upconversion fluorescence is generated by homogeneous and inhomogeneous energy-transfer upconversion. Model calculations indicate an upper limit of a homogeneous upconversion coefficient of 10/sup -23/ m/sup 3//s in fiber, and a negligible cross-section for excited-state absorption at 1480 mn.<
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