An ultra-wideband plasmonic reflector based on local resonant bandgap and Bragg bandgap

Unlike previous reports that utilized periodic modulation of insulation layer thickness or dielectrics, we propose the use of split ring resonators (SRRs) and their arrays to modulate the propagation characteristics of MIM plasmon waveguides. Due to the strong resonance backscattering of SRR, resonance transmission valleys appear in the transmission spectra of MIM waveguides. Changing the size of SRR can achieve continuously adjustable positions of resonance transmission valleys. The introduction of SRRs periodic arrays will result in two bands (bandgaps) with transmission minimum in the transmission spectra. Combining the dependence of the two bandgaps on the array period and the field distribution, the two bandgaps are Bragg bandgaps and local resonance bandgaps, respectively. By modulating the local resonance bandgap, the Bragg bandgap can be tuned. The introduction of local bandgap increases the degree of freedom to modulate the transmission characteristics of MIM waveguides. Combining local resonant bandgap and Bragg bandgap can significantly increase the reflection bandwidth, achieve broadband filtering, and facilitate the miniaturization of waveguide devices.