[en] The coupling between the high order localized resonant mode and diffraction mode in meta-molecule arrays consisting of three identical split ring resonators (SRRs) in each cell was demonstrated numerically with finite difference time domain method. By introducing both the near-field interaction and diffraction coupling mechanism, two types of interesting resonant modes are observed. One is the excitation of the second and the third-order plasmon resonance simultaneously with linear polarized light at normal incidence. The other one is a dark plasmonic state with sharper line shape produced by the third-order plasmon resonance and diffraction coupling. These resonant modes based on the ‘designed’ coupling scheme present higher quality factors than those in hybridized plasmonic state due to the electric dipole interaction, which is of great interest for application in the field of nanophotonic devices such as sensing, detector and spaser. (paper)

[en] The non-linear responses of optical materials offer useful mechanisms for optical switching, novel optical sources, and harmonic frequency conversion. However, the non-linear response of traditional materials is usually extremely weak and requires high input power for excitation. In this study, we theoretically propose a scheme for enhancing the third harmonic generation (THG) efficiency and output power of layered graphene disks array by introducing a plasmonic antibonding state with enhanced oscillation strength due to plasmonic coupling. We verify that, the THG efficiency of a double-layer stacked graphene/SiO₂ disk structure under relatively low input intensity can be significantly enhanced more than one order of magnitude with appropriate design, as compared with monolayer patterned graphene nanostructure. We also demonstrate that the THG efficiency can be further improved by optimizing the geometry parameters such as spacer distance and Fermi energy. Our results offer an effective mechanism for significantly improving THG efficiency in the mid-infrared and terahertz ranges, thereby paving the way for new frequency converters and modulators in optical communication and signal processing. (paper)