An approach to model board-integrated multimode waveguides

Signal propagation within multimode waveguides with rectangular cross sections is modeled by an approximative determination of the propagating modes. Precondition for the approach is a small difference between the refractive indices of the waveguide's core and cladding leading to a small numerical aperture. The approximation yields good results for modes far away from cutoff. As the roughness between core and cladding of real board-integrated waveguides results in a stronger attenuation of the higher order modes compared to the modes of lower order, the approximation seems to be well suited for modeling this kind of waveguides.