Resonant Excitation Analysis of the Absorption Enhancement of L-Shaped Metasurfaces in Midinfrared Band

Surface plasmon waveguides have attracted a lot of attention in recent years due to their ability to conduct light in the subwavelength scale. A large number of metallic structures have been used as waveguides and applied in integrated photonic circuits. Among these structures, the metal-insulator-metal surface plasmon waveguide is considered to have unique advantages. Compared to other waveguide forms, it is more compact and thus easier to integrate into optical circuits. For these reasons, we investigated the transmission properties of surface plasmon waves in metal-insulator-metal waveguides and built a MIM absorber consisting of gold and dielectric. We developed an interference model for the MIM absorber and concluded that the interactions between the metal patch and the substrate are not negligible in the near field. In addition, magnetic resonance plays an equally important role in approaching uniform absorption. Absorption spectra with different structural parameters, incidence angles, and polarizations were investigated. A sharp absorption peak was also found to be caused by the Rayleigh anomaly. The study reported in this paper contributes to further understanding of the physical properties of the MIM absorber, and we expect to refine the theoretical model in the future to eliminate the bias caused by near-field coupling.