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

Fano resonances in metamaterials attract 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. Herein, the excitation of Fano resonance in geometrically symmetric metamaterial structure operating in the strong, deep sub-wavelength coupling regime at terahertz frequencies is experimentally demonstrated. The structure consists of vertically stacked symmetric resonator array separated by an ultrathin polyimide spacer. Such meta-structures can strongly support highly localized, intense electromagnetic field confined inside the sub-wavelength volumes. It is further shown that the resonance linewidth and the field strengths can 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.