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Quantitative characterization of clustering in erbium-doped silica glass fibers

The current evidence for clustering of erbium ions in silica glass is reviewed, including experiments on fiber amplifier efficiency, excited state decay, and nonsaturable absorption in Er3+ pumped at 980 nm. Experiments performed by the authors on nonsaturable excited state absorption in Er3+ pumped at 980 nm add further evidence for clustering. It is found that the degree of clustering is much reduced with the addition of Aluminum to the glass. However, it is also found that ion-ion interactions can potentially limit amplifier efficiency even when no clustering is present.