Electric-field-coupled Inductive-capacitive Resonators for Terahertz Electromagnetically Induced Transparency Metamaterials

Electromagnetically induced transparency (EIT) metamaterials (MTMs) address the enhancement of non-linear susceptibility and the control of the light group velocity, which enable them to find many fascinating applications in non-linear optics, slow-light devices, and quantum memories. Typically, an EIT MTM unit is constructed of a cut-wire (CW) acted as a bright-mode resonator and some split-ring resonators (SRRs) operated as dark-mode resonators. In this work, two kinds of EIT MTMs based on electric-field-coupled inductive-capacitive (ELC) resonators with pure electric response rather than traditional SRRs with magnetic response are first proposed to mimic the EIT effect at terahertz (THz) frequencies. Both of the employed ELC resonators are axial and central symmetry instead of fourfold rotational symmetry, and thus they only couple to electric field component of the CWs in the proposed EIT MTMs. The Fano-type destructive interference between the CWs and ELC resonators leads to the EIT effect, which is verified by simulation and experimental results. In numerical simulation, the EIT MTM unit with two symmetric splits on the outer strip achieve an excellent transmission peak of 0.86 at 0.41THz, and the EIT MTM unit with a sharing capacitor on the inner strip has a well transmission peak of 0.66 at 0.44THz. As a verification, the former EIT MTM device was fabricated on a 100-µm thick liquid crystal polymer (LCP) substrate with a low loss tangent at THz frequencies. The measured results show a good consistency with the simulation results. This work provides a new method for the structural design of EIT MTMs, and opens up the possibility for some important functions of active EIT MTMs, such as the frequency shift of the EIT effect.