TE modes of graded-index slab waveguides

An analysis of the TE modes of a slab waveguide with graded refractive-index distribution is presented. The refractive index is approximated by a piecewise-linear distribution for which exact solutions of the guided-wave problem can be obtained. For multimode guides, useful approximate solutions can be worked out with the help of the Wentzel-Kramers-Brillouin (WKB) approximation. A formula is given for the total number of guided TE modes supported by the waveguide. The coupling efficiency of a prism coupler is investigated by studying the radiation losses of the guided modes escaping from the waveguide through the coupling prism. It is found that the radiation losses of the modes of the graded-index waveguide are more nearly constant than those of the asymmetric slab waveguide.