Tailoring Electromagnetic Responses in Terahertz Metasurface by Breaking the Structural Symmetry in T‐Shaped Resonators

Abstract

Herein, the design of terahertz metasurface with symmetric T‐shaped resonators and the corresponding bright and dark modes are reported on. It is demonstrated that the dark mode evoked by breaking the structural symmetry is insensitive to the X‐polarized electric field and a typical electromagnetically induced transparency (EIT) effect is also observed in the numerical simulation when introducing a relatively low structural asymmetry where the dark and bright modes are modified to the same frequency. To explain the underlying mechanism, theoretical calculations based on the coupled Lorentz oscillator model are performed. In terms of the desirable fittings with the simulation results, it is confirmed that there exists the dark mode in the symmetric T‐shaped resonators and the coupling between the bright and dark modes enhanced by the structural–symmetry breaking is responsible for the observed EIT effect. It is shown in the results further that the structural asymmetry degree has close relation with the coupling strength resonance and can thereby greatly affect the oscillation resonance splitting in frequency that it is reflected by the change of the bandwidth of the transparency window. In addition, the experimental spectra showing the characteristic of broadband transparency window are explained by the excitation of the dark mode whose frequency deviates from the bright mode.

A terahertz metasurface biosensor based on electromagnetically induced transparency for fingerprint trace detection

“…6,7 Recently, electromagnetically induced transparency (EIT) arising from quantum interference in three-level atomic systems has been extended to metasurfaces for the realizations of slow-light devices, 8,9 absorbers, 10 modulators, 11 and biosensors. 12,13 In 2008, Zhang et al 9 demonstrated a plasmonic metamaterial to investigate theoretically EIT phenomena resulting from a radiative element coupled with a subradiant (dark) element. Gu et al 11 achieved an active optical control of EIT metasurface by integrating photoconductive silicon.…”

“…Gu et al 11 achieved an active optical control of EIT metasurface by integrating photoconductive silicon. Kang et al 12 proposed a T-shaped EIT resonator, which was attributed to the coupling between bright and dark modes as well as to the structural-symmetry breaking. More recently, EIT metamaterials are especially attractive for bio-sensing applications because of their multiple resonance modes, including two absorption dips and one transparency peak.…”