Active modulation of terahertz hybrid metal-graphene electromagnetically induced transparency metasurface

Electromagnetically induced transparency (EIT) metasurfaces (MTSs) at terahertz (THz) frequencies face challenges in achieving high transmission and active modulation due to the high loss tangent of common substrates, mutual coupling between adjacent units, and inefficient active modulation methods. This work presents a novel hybrid metal-graphene EIT MTS structure on a liquid crystal polymer (LCP) substrate which has low loss tangent and low dielectric constant. The metal part of the MTS unit consists of a zigzag bright-mode resonator and two center symmetric split-ring dark-mode resonators, which can enhance transmission to 0.75 by suppressing coupling between adjacent units. To achieve dynamic manipulation, two T-shaped graphene strips are embedded in the dark-mode gaps and gated via an ion gel layer. By tuning graphene’s sheet resistance, a remarkable amplitude modulation depth of 43% and a significant group delay of 16 ps were demonstrated in the simulation. As verification, a prototype device with 2400 EIT MTS units was fabricated on an LCP substrate and demonstrated a maximum amplitude modulation depth of 42%, which is almost consistent with simulated results. This work paves a new way for graphene devices on flexible LCP films and provides a new method for THz EIT devices with high transmission and active modulation.