Multifunctional All‐Silicon Terahertz Chiral Metasurfaces via Integrated Moiré and Spin‐Decoupled Phase Engineering

ABSTRACT We present a reconfigurable all‐silicon terahertz (THz) chiral metasurface (RTCM) integrating phase‐induced chiral meta‐devices with Moiré phase engineering, to address insufficient dynamic tunability and dimension‐limited light field manipulation in existing THz metasurfaces. Conventional THz components, such as refractive lenses and off‐axis parabolic mirrors, suffer from wavefront aberrations and limited imaging resolution, while existing metasurfaces lack the ability to simultaneously deliver varifocal lensing and spin‐selective transmission. Our RTCM device adopts two cascaded metasurfaces: One with rectangular meta‐atoms enables spin‐decoupled phase modulation, embedding random phase and focusing phase into orthogonal circular polarization (CP) channels respectively; The other with cylindrical meta‐atoms maintains polarization‐insensitive propagation phase control. Adjusting their relative rotation angle regulates broadband circular dichroism (CD) response (80 GHz bandwidth) and axial focal length. The initial RTCM achieves over 4.6× dynamic zoom ratio, 34.42−7.43 λ focal length range, and below −14.02 dB average crosstalk. An improved version with an offset phase factor realizes full‐rotation reconfigurable CD, 34.99% average focusing efficiency, and −13.79 dB average crosstalk at 0.5 THz. This mechanically reconfigurable design, free of external voltages or active materials, is highly suitable for portable THz systems and holds significant potential in non‐destructive testing and biomedical imaging.