Directional Phase and Polarization Manipulation Using Janus Metasurfaces

Abstract Janus metasurfaces, exemplifying two‐faced 2D metamaterials, have shown unprecedented capabilities in asymmetrically manipulating the wavefront of electromagnetic waves in both forward and backward propagating directions, enabling novel applications in asymmetric information processing, security, and signal multiplexing. However, current Janus metasurfaces only allow for directional phase manipulation, hindering their broader application potential. Here, the study proposes a versatile Janus metasurface platform that can directionally control the phase and polarization of terahertz waves by integrating functionalities of half‐wave plates, quarter‐wave plates, and metallic gratings within a cascaded metasurface structure. As a proof‐of‐principle, the study experimentally demonstrates Janus metasurfaces capable of independent and simultaneous control over phase and polarization, showcasing propagation direction‐encoded focusing and polarization conversion. Moreover, the directionally focused points are utilized with distinct polarization states for advanced applications in direction‐ and polarization‐sensitive detection and imaging. This unique strategy for simultaneous phase and polarization control with direction‐dependent versatility opens new avenues for designing ultra‐compact devices with significant implications in imaging, encryption, and data storage.