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 (<i>V</i><i>O</i>₂) 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 <i>V</i><i>O</i>₂ 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 <i>V</i><i>O</i>₂ 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.