Multiband Hybrid Metasurface for Enhanced Second-Harmonic Generation via Coupled Gap Surface Plasmon Modes

Abstract

A multiband hybrid metasurface supporting multiple gap-surface plasmon (GSP) and localized surface plasmon (LSP) modes is presented. The structure adopts a metal-dielectric-metal configuration consisting of an aluminum bottom layer, a silicon dioxide spacer, and a bar-disc hybrid resonator patterned in the top aluminum layer. Optimized geometrical parameters yield four distinct resonances across the near-infrared and telecommunication bands, arising from the interplay between GSP modes and LSP excitations. The reflectance spectra are systematically analyzed as functions of geometric parameters and polarization, demonstrating tunable multiband operation. Experimental measurements of the fabricated metasurface show good agreement with numerical predictions. Furthermore, the second-harmonic generation (SHG) response is numerically investigated, revealing enhanced SH emission at the resonance wavelengths due to strong electromagnetic field confinement within the metal-dielectric-metal cavity. The proposed metasurface provides a compact platform for multiband and multifunctional nanophotonic applications.

Figures (14)

• Figure 1: (a) Three-dimensional schematic of the proposed hybrid metasurface. The top $\mathrm{Al}$ layer consists of a bar--disc hybrid resonator, separated from an optically thick continuous bottom $\mathrm{Al}$ layer by a $\mathrm{SiO_{2}}$ dielectric spacer, forming a metal–dielectric–metal configuration that supports GSP modes. (b) Unit-cell geometry showing the structural parameters: bar width $a_1$, bar length $a_2$, disc radius $r_1$, bar-disc separation $d_1$, layer thicknesses $h_1$, $h_2$, and $h_3$, and lattice periods $P_x=P_y$.
• Figure 2: Simulated reflectance spectra of the isolated resonators. (a) Bar-only structure for varying bar width $a_1$. (b) Disc-only structure for varying disc radius $r_1$. (c) Reflectance spectra of the isolated bar and disc resonators with optimized geometrical parameters.
• Figure 3: Electromagnetic field distributions of the isolated bar resonator in the $x z$-plane at two resonant wavelengths. (a-b) Normalized electric-field distributions. (c-d) Corresponding normalized magnetic-field distributions.
• Figure 4: Electromagnetic field distributions of the isolated disc resonator in the $x z$-plane at two resonant wavelengths. (a-b) Normalized electric-field distributions. (c-d) Corresponding normalized magnetic-field distributions.
• Figure 5: Simulated absorptance and reflectance spectra of the hybrid metasurface for the optimized structural parameters, showing four resonant modes labeled $\mathrm{P}_{\mathrm{I}}$, $\mathrm{P}_{\mathrm{II}}$, $\mathrm{P}_{\mathrm{III}}$, and $\mathrm{P}_{\mathrm{IV}}$, occurring at wavelengths $\lambda_1=900\,\mathrm{nm}$, $\lambda_2=990\,\mathrm{nm}$, $\lambda_3=1075\,\mathrm{nm}$, and $\lambda_4=1465 \,\mathrm{nm}$, respectively.