基于群论的晶格扰动介质纳米孔阵列多重Fano共振机理及演变

Group theory based formation mechanism and evolution of multiple Fano resonances in dielectric nanohole arrays with lattice-perturbed

基于全介质超构材料独特的电磁属性,提出了一种晶格扰动介质纳米孔阵列超构表面来激发近红外区域的多重Fano共振.结合群论深入探究了该超构表面在其原胞为方形晶格构型与方形晶格对称性被破坏两情况下多重Fano共振的形成机理及演变规律.研究表明,在方形晶格超构表面中,外部辐射连续体分别与由正入射平面波直接激发的双重简并模式共振干涉形成双重Fano共振,且该共振与原胞中是否含孔及孔的形状无关,在晶格扰动超构表面中,原本不耦合的非简并模式由正入射平面波激发出来并与外部辐射连续体干涉形成Q值更高的三重Fano共振.进一步探讨了正入射平面波的xy极化方向对上述五重Fano共振的影响,结果表明,双重简并模式Fano共振偏振无关,三重非简并模式Fano共振偏振依赖.本文将为利用方形晶格构型的超构表面实现多重Fano共振的激发及演变提供有效的理论参考.

Based on the electromagnetic properties of all-dielectric optical metamaterial,an all-dielectric metasurface of lattice-perturbed nanohole array is proposed to excite a multiple Fano resonance in the near-infrared region.Combined with the group theory,the formation mechanism and evolution law of multiple Fano resonances in this structure when its unit cell is a square lattice configuration and the square lattice symmetry is broken are explored in depth.The results show that double degenerate mode directly excited by the normal incident plane wave is coupled to vertical free-space radiation continuum to form double Fano resonance when unit cell is symmetrical,while the uncoupled non-degenerate modes excited by the normal incident plane wave is coupled to vertical free-space radiation continuum to form triple Fano resonance with higher Q factor when the symmetry is broken.Numerical simulation is used to explore the influences of x-polarized and y-polarized plane wave on the above Fano resonances,and the results show that the Fano resonance of double degenerate resonance is polarization independent,while the non-degenerate resonance is polarization dependent.The findings in this work can provide an effective theoretical reference for designing other square lattice metasurface to realize the excitation and evolution of multiple Fano resonances.