CURVATURE INDUCED MODE-COUPLING IN LARGE-CORE OPTICAL FIBERS WITH STEP REFRACTIVE-INDEX PROFILES

A simple ray model is developed to approximate the output beam angle increase caused by a symmetric bend with variable curvature in a large core optical fibre beam delivery system of the type commonly used in laser material processing. The results are compared with experiments using curved fibres in the shape of half-cycle cosines with different rates of curvature change. The theoretical model was supported by experiment, and is sufficiently simple for application in the design of an optical fibre beam delivery system.