  In this work, a numerical modal decomposition approach is applied to model
the optical field of laser light after propagating through a highly multi-mode
fiber. The algorithm for the decomposition is based on the reconstruction of
measured intensity profiles along the laser beam caustic with consideration of
intermodal degrees of coherence derived from spectral analysis. To enhance the
accuracy of the model, different approaches and strategies are applied and
discussed. The presented decomposition into a set of LP modes enables both the
wave-optical simulation of radiation transport by highly multi-mode fibers and,
additionally, the analysis of free-space propagation with arbitrarily modified
complex amplitude distributions.
