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

Abstract

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.

Reconfigurable metamaterials for optoelectronic applications

“…Along with the rapid development of micro-fabrication technologies, the realization of typical reconfigurable metamaterial devices has become mature. Most of reconfigurable metamaterials reported in literatures are based on periodic resonator arrays on semiconductor substrates, such as periodic SRR, [59] asymmetric SRR, [60] chiral-shaped metamaterial, [61] three-dimensional stacked metamaterial, [62] line segment-shaped metamaterial, [63] and complementary electric SRR [64] as shown in Figure 2. The metamaterial configurations can be designed to possess different electromagnetic properties, e.g.…”

“…The proposed diversified metamaterial configurations. They are (a) periodic SRR, [59] (b) asymmetric SRR, [61] (c) chiralshaped metamaterial, [62] (d) three-dimensional stacked metamaterial, [63] (e) line segment-shaped metamaterial, [64] and (f) and complementary electric SRR. [65] in the symmetric structure, such as Fano resonance as shown in Figure 2(b).…”

“…This Fano resonance can be tuned by changing the thickness of dielectric layer between metamaterials as shown in Figure 2(e). [64] Figure 2(f) shows the complementary electric SRR structures, which metal patterns are replaced by the perforated regions compared with the typical electric SRR structures. These kind of complementary electric SRR structures are named as "complementary metamaterials."…”

Magnetotransport‐Induced Non‐Contact Terahertz Detection of Weak Magnetic Fields in Optically Thin Frequency‐Agile Superlattice Metasurfaces

“…due to its low associated energy. [27][28][29][30] However, realization of THz resonant magnetic field sensor is rather a tough call, as skin-depth of metals at THz is usually around a hundred of nanometer, where magnetotransport and spin-rectification, flow of spin-polarized currents, and spin-diffusion between different magnetic domains (layers) are generally difficult to control. [31][32][33][34] Very recently, researchers have demonstrated unique possibility to realize THz magnetotransport-based meta-structures using optically thin (sub-skin depth) structure, where application of magnetic field increased the spectral contrast of resonances.…”

Ultrasensitive specific sensor based on all-dielectric metasurfaces in the terahertz range

“…7 Fano type resonances are then introduced into the metallic metasurfaces to further improve the Q factor, which usually means stronger electromagnetic eld connement and higher sensitivity. 8,9 A maximum sensitivity of >1 THz/RIU have been achieved at the Fano mode in the THz band. 10 However, the Q-factors of metalbased resonant systems are limited to <$10 due to inevitable non-radiative loss.…”