Design and experimental demonstration of 3-bit digital coding metasurfaces for terahertz wave manipulation

Future communication systems are expected to support massive numbers of users with high spectral and energy efficiency through high-integration, low-cost, and low-power-consumption devices and systems. Digital coding metasurfaces, serving as a bridge between the digital and electromagnetic (EM) domains, have garnered significant attention due to their potential in enabling novel communication architectures. In this work, we design, fabricate, and experimentally characterize three types of 3-bit digital coding metasurfaces by encoding the phase sequences along the x- and y-directions, including metalenses, focusing optical vortex (FOV) generators, and superposed FOV generators. The proposed metalenses realize efficient wavefront modulation and focusing within a compact planar architecture. Furthermore, the FOV generators produce vortex EM waves carrying orbital angular momentum (OAM), offering an effective approach to enhancing communication capacity. In addition, the superposed FOV generators, formed by combining different topological charges (TCs), provide new opportunities for spectrum utilization, interference suppression, and communication security. Both simulated and measured results exhibit excellent agreement with theoretical predictions, confirming the superior performance of the proposed 3-bit digital coding metasurfaces. The demonstrated design approach, featuring flexible EM wave manipulation and a simplified design process, paves the way for more intelligent, flexible, and efficient communication systems.