Abstract: We present rate equations describing the effects of clusters on Nd-doped fibers. Two models are presented, based on formalisms found in the literature. The first one, valid for any cluster size, describes the interaction between an excited ion and a ground state ion in proximity to each other as a non-radiative process referred to as cross relaxation. The second model, valid only for large clusters, describes this interaction as cooperative upconversion. The effects of clustering on two experimental applications are explored: nonlinear phase shift in all-optical fiber switches and cw transmission saturation behavior of clustered fibers. Both measurements suggest that in some fibers as many as 60% of the available dopant ions are clustered. The extent of clustering is experimentally linked to the concentration of Nd in the fibers tested, and perhaps to the use of co-dopants as well. !15
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