Analytical model of terahertz metasurface for enhanced amplitude modulation

Optically-driven terahertz (THz) modulation generally requires excitation of excessively large photoconductivity of active components, which poses huge challenges for realization and practical applications. With the aid of an analytical circuit model, we demonstrate an approach to alleviate the trade-off between large amplitude modulation and use of low photoconductivity in complementary split-ring resonator modulators. As revealed by analytical results and verified by full-wave simulation, the maximum modulation depth and needed photoconductivity are determined by the inductance and gap resistance of the structure, respectively. Therefore, by tailoring its inductance and resistance via geometry adjustment, both improvement of modulation efficiency and reduction of photoconductivity are simultaneously realized. A large amplitude modulation similar to 0.5 is achieved with an ultralow conductivity of 2000 S m(-1). The proposed approach might offer a guideline for structure design of THz devices with various active components.