Guided propagation in a step-index, multi-mode fiber: effect of index difference variation on allowable TM propagation constants

A method for measuring optical wavefronts is proposed by properly sampling the light amplitude distribution with a two-dimensional periodic mask. At the Talbot planes, where a reference wavefront (spherical or plane) would originate replicas of the aperture, distortions of the resulting selfimages take place. These intensity patterns are detected and processed for obtaining the required wavefront information. The approach is illustrated with some experimental results.