CHARACTERIZATION OF CLUSTERS IN RARE-EARTH-DOPED FIBERS BY TRANSMISSION MEASUREMENTS

We show theoretically that the absorption saturation behavior of clust ered rare earth-doped fibers depends strongly on the percentage and/or the size of the clusters, which can form the basis for a simple diagn ostic tool. When applied to published transmission measurements in Er- Al-P-doped fibers, this technique indicates low percentages of cluster s in fibers co-doped With P and/or AI. In Nd-doped fibers with no codo pants, it shows the presence of a high percentage of large clusters. E stimates of the time constant and strength of the cross relaxation pro cess in Nd and Er clusters are inferred from these measurements.