Coupled-mode equations for multimode waveguide systems in isotropic or anisotropic media

Coupled-mode theory for parallel waveguides is extended to include systems with multimode guides. The basic set of coupled differential equations is similar to that for single-mode guides, but the matrices are more broadly defined to allow for coupling among all the modes. Cases of anisotropic dielectric waveguides and/or an anisotropic embedding medium are also considered.