High-power fiber amplifier using a PM Yb-doped photodarkening-resistant LMA fiber with depressed-clad index profile design

摘要

Based on a depressed-clad index profile design, a PM Yb-doped large mode area (LMA) fiber with an effective mode area of 450 μm~2 was designed and fabricated. The fiber was used to amplify 10-ns pulses at 1064 nm with a repetition rate of 100 kHz, and an output energy higher than 200 μJ was obtained, within a bandwidth of 0.5 nm. The fiber was coiled on a 12-cm diameter mandrel to obtain a single-mode output having a measured M2 value of 1.04. The output polarization extinction ratio was higher than 20 dB. The photodarkening excess loss of the Ytterbium//Phosphorus Aluminum co-doped fiber was measured to be a factor 5 lower than that of a reference Ytterbium/Aluminum co-doped fiber. It is shown how a depressed-clad index profile design can improve higher-order mode filtering while keeping the coiling diameter practical for compact fiber amplifier packaging.