A tunable terahertz metasurface with function of polarization conversion and circular dichroism

A tunable and multifunctional electromagnetic control metasurface is proposed. The metasurface comprises the graphene sheet and gold open ring, enabling multiband cross-polarization conversion (CPC) and line-to-circular polarization conversion (LTCPC). Simultaneously, it can achieve circular dichroism (CD) with amplitude of 0.99 at 2.28 THz, along with the capability for near-field imaging. The physical mechanism of operation is studied by analyzing surface current distribution and electric field. In addition, because the metasurface exhibits chiral characteristics, appropriate rotation can induce a phase gradient, facilitating a phase coverage of 0–360°. Based on the tunable phase gradient of metasurface, anomalous reflection and vortex beams can be realized.