BEAM DELIVERY BY LARGE-CORE FIBERS - EFFECT OF LAUNCHING CONDITIONS ON NEAR-FIELD OUTPUT PROFILE

For large-core optical fibers of a few meters length, which are typical of those used in beam del systems for high-power Nd:YAG lasers, it is shown that the near-field profile of the output beam is strong function of the launching conditions. The output profile depends on both the input spot size an its alignment relative to the fiber axis. A simple theoretical model is developed for step-index fiber th shows that the output profile depends on the distribution of guided power between meridional modes an groups of skew modes. A relationship is hence derived between the launching conditions and the output profile. The predictions of the theoretical model are consistent with experiment.