Pixel-controlled programmable metasurface as phase-type spatial terahertz modulator

Reconfigurable intelligent surfaces (RISs) transcend the passive response limitations of conventional metasurface resonators by integrating active materials into metasurface elements, enabling a more flexible control of electromagnetic wave properties. However, RISs devices operating in the terahertz (THz) regime continue to face significant challenges in structural design and multifunctional implementation, particularly regarding optically-addressed THz RISs devices with independent pixel-level encoding, which remain experimentally underexplored. Here, we propose a compact and relatively efficient transmissive programmable metasurface device functioning as a phase-type spatial THz modulator, which enables separate encoding of each pixel within a 50×50 resolution array, thereby achieving dynamic generation and reconfiguration of THz wavefronts. The spatial modulation of the pump pulse intensity locally activates the vanadium dioxide integrated meta-atoms across the metasurface and, thus, defines the specifically designed phase modulation of the cross-polarized transmission. Dynamic wavefront manipulation is then realized by switching the spatial intensity distribution of the pump pulse. Proof-of-concept experiments demonstrate that the same programmable metasurface can perform three distinct functionalities—zoom lens, tunable vortex beam generator, and dynamic hologram. The amplitude conversion efficiency of the device was experimentally measured to be 27%. The programmable scheme demonstrated here paves the way toward miniaturized, integrated, and multifunctional THz optical devices.