Effect of Gyrotropic Substrates on the Surface Plasmon Polaritons Guided by Metal Films of Finite Width

The propagation characteristics of surface plasmon polariton modes in metal-strip plasmonic waveguides with gyrotropic (magneto-optic) substrate material has been numerically studied. The method of line formalism has been adopted for computing the dispersion of fundamental symmetric and antisymmetric modes supported by the structure. The magneto-optic substrate has been chosen such that the resulting propagating modes exhibit nonreciprocal dispersion, enabling their application in many optical devices. Fundamental pair modes of surface plasmon polaritons supported by metal strips, which have degeneracy properties with isotropic dielectric substrates, have been found to be nondegenerate in our case. These modes show different trends in the dispersion with variation of metal film thickness, compared to that in an asymmetric strip waveguide with isotropic substrate. A nonreciprocal phase shift of 0.5-14 rad/mm is achievable for antisymmetric modes that are localized near the gyrotropic interface.