Deep‐Subwavelength Coupling‐Induced Fano Resonances in Symmetric Terahertz Metamaterials

Abstract

Fano resonances in metamaterials have attracted intense attention due to their sharp asymmetric spectral feature and low radiative loss channel. Typically, Fano resonances are excited in metamaterials with broken structural symmetry in a planar configuration. In article no. 1900310, Karmakar et al. experimentally demonstrate the excitation of Fano resonances in a geometrically symmetric metamaterial structure operating in the strong, deep sub-wavelength coupling regime at terahertz frequencies. The proposed structure consists of a vertically stacked symmetric resonator array separated by an ultrathin polyamide spacer. Such metastructures can strongly support highly localized, intense electromagnetic fields confined inside subwavelength volumes. The authors further show that the resonance linewidth and the field strengths could be engineered by tailoring the near-field coupling through the ultrathin spacer layer. Such exotic features of perfectly symmetric Fano resonators provide an ideal playing ground for strong light–matter coupling resulting in realization of ultrasensitive sensors, slow light devices, and energy efficient ultrafast terahertz modulators.