Terahertz 4D Bessel Beam Steering and Near‐Field Communications by Cascaded Metasurfaces

ABSTRACT Bessel beams, renowned for their non‐diffracting and self‐healing capabilities, are emerging as a compelling candidate for next‐generation wireless signal transmission, especially in near‐field terahertz systems. Bilayer dielectric metasurfaces with relative in‐plane rotation have been extensively explored for dynamic beam steering, offering advantages such as light weight, low power consumption, and large apertures. However, they still face challenges in controlling additional degrees of freedom beyond beam direction. Here, we propose a novel approach using three cascaded metasurfaces, each integrating multiple phase functions, to achieve 4D Bessel beam steering. By relative rotation among the three layers, we demonstrate independent control over non‐diffracting propagation distance, dynamic switching between 0th‐ and 1st‐order Bessel beams, 360° azimuthal scanning, and ±40° elevational scanning. Experimental results confirm the meta‐device's effectiveness in variable‐distance point‐to‐point near‐field wireless communications and the self‐healing properties. This advancement in multi‐dimensional modulation of Bessel beams is crucial for near‐field mobile communications with increased information capacity.