Triple Fano resonances in plasmonic heptamer nano-hole arrays: Symmetric and asymmetric structures

Abstract

The optical properties of gold heptamer-arranged nanoholes array have been studied numerically, for both symmetric and asymmetric structures. This array supports three Fano resonances arising from the excitation of localized surface plasmon polaritons (LSPPs), propagating surface plasmon polaritons (PSPPs), or/and waves related to Wood's anomaly (WA). To study the nature of each Fano resonance, electromagnetic near-field distributions have been computed, and the effects of the geometrical parameters has been carried out. In addition, the sensing performance of the structure has been examined, revealing that the highest bulk sensitivity (400 nm/RIU) and surface sensitivity (2 nm/nm) belong to LSPP Fano resonance, whereas, the highest figure of merit (24 RIU−1) is obtained by a coupled WA-PSPP Fano resonance, which is only supported by the asymmetric structure.