Geometrical model for the design of gradient-index-rod lens coupling devices.

Gaussian beam propagation in a gradient-radial-index medium is presented and discussed. A simple geometrical method for modeling the Gaussian beam inside the gradient-index medium has been developed. The results with this method and those predicted by wave optics have been compared in a number of practical cases. Results show the validity of the ray approach. This is also confirmed by experimental tests on a high-power laser-fiber coupler.