Hybrid ray-mode parametrization of high frequency propagation in an open waveguide with bilinear transverse bilinear transverse refractive index: numerical results and quality assessment

Numerical reference solutions are generated by summing a large number of trapped and leaky modes, and are then examined to identify observables. After confirming qualitatively that the much simpler and efficient ray parametrization models are the basic features of the observed signal, quantitative evaluations are performed to assess the capability of the hybrid ray-mode algorithm to recover all relevant features of the reference field with adequate accuracy and numerical efficiency. Such features include uniform corrections near isolated ray caustics, replacement of illegitimate ray fields (and their pileup of caustics in the surface boundary layer) by a few surface guided modes, and mode cluster substitution for the transitional ray field that grazes the profile slope discontinuity, and therefore splits into two beam-like fields refracted out of, and back into, the duct. For the development of the parametrizations see ibid., vol.39, no.6, p.780-8 (1991)