Bilayer Dielectric Metasurfaces for Non‐Multiplexing Full‐Space Terahertz Wavefront Control

ABSTRACT Metasurfaces, as two‐dimensional ultrathin artificial structures, have significantly facilitated the manipulation of electromagnetic waves. Recent advances show that metasurface functionalities can be further promoted from performing in only the transmission/reflection space to simultaneously and independently in both spaces. However, related studies so far mostly rely on electromagnetic multiplexing strategies where two intrinsically incident waves are required, i.e., the transmission and reflection functionalities are realized at different electromagnetic parameter conditions. Here, we demonstrate a bilayer all‐dielectric metasurface design scheme based on Si‐SiO 2 ‐Si meta‐atoms capable of achieving non‐multiplexing full‐space 1‐bit phase control for wavefront engineering of one incident wave in the terahertz regime. Three types of full‐space metasurface devices are experimentally characterized, which can perform holographic imaging, beam focusing, and beam diffusion in the transmission space, while exhibiting ±first‐order diffraction in the reflection space, respectively. The results exhibit excellent agreement with the theory. Our design offers a promising route for flexible and compact full‐space terahertz wavefront control devices.