Spin‐Encoded Wavelength‐Direction Multitasking Janus Metasurfaces

Abstract The fruitful progress toward light manipulation in reflective (R) or transmissive (T) geometry (half‐space) has facilitated strong aspiration towards full‐space wave control. Although R–T synergistic strategy promises large‐capacity and integrated functionality, it imposes difficulty and challenges for direction of arrival (DoA) in full space via an ultrathin flat device. As of today, very limited demonstrations are reported for single‐wavelength and linear‐polarization operation in full space, significantly limiting the exploitable degrees of freedom (DoFs) for real‐world applications. Herein, a triple‐layer wavelength‐direction multitasking scheme for wide‐angle and large‐capacity DoA is reported, which is pivotal for blind‐free radar detection. By engineering two anisotropic sub‐meta‐atoms with high quality factor and simultaneous in‐plane and out‐of‐plane symmetry breaking, four R and two T spin‐conversion channels are achieved in wide‐angle operation with high efficiency and insulation. Above features and released DoFs would be extraordinarily beneficial for large‐capability and angle‐engineered advanced applications. Two proof‐of‐concept metadevices, i.e., a large‐scanning kaleidoscopic‐beam generator and a wide‐angle reverser for multi‐target tracking, are devised to verify the significance. Numerical and experimental results show predesigned functions at six channels with measured efficiency over 75%. The findings in achieving multi‐DoF multitasking can stimulate great interest in radar applications with versatile forming beams and multi‐channel integration.