Dual control of amplitude and phase in a multilayer terahertz metasurface for transmission and reflection modulation.

Current metasurfaces encounter challenges in achieving precise control over transmittance-reflection mode conversion. This study presents a multilayer metasurface structure that incorporates dual amplitude and phase control, utilizing vanadium dioxide () and Dirac semimetals (DSMs) as tunable materials. By adjusting the orientation angle of the split-ring resonator (SRR) in the intermediate layer and modifying the Fermi energy level of the DSMs, precise dual control of amplitude and phase can be attained. When is in its insulating phase with a DSM Fermi level of 500 meV, the metasurface exhibits notable transmission characteristics, enabling refraction and focusing at 0.6 THz while demonstrating remarkable insensitivity to the incident angle. Conversely, when transitions to the metallic phase and the Fermi level of the DSMs is decreased to 1 meV, the metasurface displays significant reflection characteristics, facilitating the generation of vortex beam and multi-beam vortices. This multilayer metasurface holds considerable promise for applications in terahertz.