Polarization-multiplexing metasurfaces for tunable wavefront configurations via Moiré engineering

Abstract

Traditional tunable metasurfaces have evolved through mechanisms relying on external stimuli, such as electrical, thermal, or optical excitation, to dynamically control electromagnetic (EM) wavefronts. While these approaches enable functionalities like focal varying and polarization modulation, they suffer from inherent limitations, including energy inefficiency, structural complexity, and limited adaptability. Here, cascaded all-dielectric Moiré metasurfaces are introduced, which are capable of simultaneous polarization multiplexing and focal-length control for terahertz (THz) beams without external stimuli. Moiré device 1 combines polarization-insensitive (Layer 1) and polarization-sensitive (Layer 2) meta-atoms to independently tailor orthogonal circular polarization channels, including left-handed circular polarization (LCP) and right-handed circular polarization (RCP). Under circularly polarized illumination, it generates focused beams with distinct topological charges ( l =0 for LCP → RCP and l =1 for RCP → LCP ), while relative layer rotation enables continuous focal-length adjustment from 9.28 mm to 3.22 mm, accompanied by a numerical aperture (NA) increase from 0.54 to 0.88. Moiré device 2 extends this paradigm to orthogonal linear polarization (LP) channels, producing l =1 and l =0 beams under x -LP and y -LP illumination, with a zoom range of 8.42–3.11 mm and NA up to 0.88. Experimental results validate polarization-selective focusing with efficiency exceeding 15% and robust agreement with simulation results, and the calculated absolute percentage errors (APEs) are below 5.9% for focal length and 3% for NA. These values are consistent with the expected theoretical trends, demonstrating that the experimental results align well with the predicted performance. This reconfigurable system introduces additional control dimensions through mechanical adjustments to cascaded metasurfaces, paving the way for adaptive wavefront control and opening new avenues for next-generation optical technologies.