Simple Model for Spatial Coherence of Light at the Output of a Multimode Fiber

A model for the spatial coherence function of a partially coherent light produced at the output of a step-index multimode fiber excited with a spatially coherent broadband source is developed. The field is represented as a sum of coherent and partially coherent parts, the former being a fully developed speckle and the latter is described by a “Jinc” degree of coherence and uniform intensity over the core of the fiber. The model correctly describes all available experimental data, including global degree of coherence, and is intuitive and simple.