The propagating mode characteristics of an equilateral triangular dielectric waveguide whose top and bottom regions have different refractive indices were investigated using the ray-optics method based on the geometrical optics approximation and the wave-optics method. In the ray-optics approach, the guiding modes were obtained by imposing the field amplitude and phase conditions as ray travels along the guide. In the wave-optics approach, the propagating modes were obtained by applying Marcatili's approximation to the equilateral triangular guide.;Our results have useful applications in a variety of integrated optical devices.;The accuracies of the computed propagation constants obtained by these methods were tested by comparing ours with those given by James and Yeh curves for a triangular core fiber. The ray-optics method gives better results than the wave-optics method near the cutoff region.
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