Complex degree of spatial coherence in an optical fiber: theory and experiment

Abstract

The modulus and the phase of the complex degree of spatial coherence at the exit face of a coherently excited optical fiber have been analyzed, taking into account interference between modes. The pointwise correlation between two axially symmetrical points across the fiber core exhibits an undulating behavior, varying with longitudinal coordinate as cos(βl − βk)z. It was found that the mean values for the modulus and the phase can be obtained by averaging over the undulating period. This theory has been confirmed by an experiment that measures the spatial coherence using a computer-aided wave-front-reversing interferometer.