Surface plasmon polaritons on the thin metallic film coated with symmetrical and asymmetrical dielectric gratings

Surface plasmon polartions (SPPs) on the planar metallic film coated with dielectric gratings on both sides are studied theoretically and numerically. It is found that the coupling between SPP modes can be efficiently tuned by the relative shift of the gratings on the two sides, including both the symmetrical and asymmetrical cases. The absorption due to the excitation of SPPs can be enhanced or suppressed as the coupling of SPP modes varies. A coupled mode theory is employed to analyze the coupling between these SPP modes in addition to full-wave simulations. The results obtained by the coupled mode theory and numerical simulations agree well with each other. The investigation of coupled SPP modes may have potential applications in photonic devices.