Spin-encoded Wavelength-space Multitasking Janus Metasurfaces 

The fruitful progress toward light manipulation in reflective (R) or transmissive (T) geometry (half-space) has facilitated strong aspiration to achieving full-space electromagnetic wave control in both R and T channels. Although it promises large-capacity and integrated functionality, yet imposes prohibitive difficulty and big challenging for extreme wave control (direction of arrival in full space) via an ultrathin flat device. As of today, very limited demonstrations were reported for single-band and linear-polarization operation, significantly limiting the exploitable degree of freedoms (DoFs) for real-world applications. Herein, we report for the first time a triple-layer wavelength-space multitasking scheme for wide-angle and large-capacity detection. Two anisotropic sub-meta-atoms are engineered with high quality factor and simultaneous in-plane and out-of-plane symmetry breaking, facilitating four R and two T spin-conversion channels with high efficiency and insulation. The chirality-assisted Fano effect gives rise to the wide-angle operation and boosted channels. Above features and released DoF would be extraordinary beneficial for large-capability and angle-engineered advanced device. Two proof-of-concept metadevices, i.e., large-scanning kaleidoscopic-beam generator and a wide-angle large-capacity reverser for multi-target tracking, are devised to verify the significance. Numerical and experimental results have approved predesigned advanced functions at six channels with measured efficiency over 75%. Our findings in multi-DoF multitasking of metasurfaces could stimulate great interest in radar applications with versatile beam generation and multi-channel integration.