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

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