Fast and accurate method for calculation of polarised modes in semiconductor rib waveguides

A new semivectorial ´spectral index´ (SI) method for finding the guided modes of semiconductor rib waveguides is described. The results are shown by comparison to be of the same accuracy as well established finite difference calculations. A useful by-product is a contour map of the principal field component. The propagation constants are found using novel transcendental equations which are easy to set up and are given here explicitly. These discriminate clearly between the TE and TM modes and are variational in nature.