Electromagnetic Manipulation Evolution from Stacked Meta‐Atoms to Spatially Cascaded Metasurfaces

Abstract Metasurfaces, known as planar two‐dimensional (2D) metamaterials, are proposed to overcome obstacles like high loss and bulky volume occurring with three‐dimensional (3D)metamaterials. Single‐layer structures face limited degrees of freedom, and cannot satisfy the growing functional demands for meta‐devices. To simplify the design process and gain more controllability, quasi‐2D structures are introduced into metasurfaces in the form of stacked meta‐atoms design or spatially cascaded metasurfaces. These configurations greatly expand the manipulation capability of metasurfaces and spawn a variety of functions and applications. In this review, the progress of metasurfaces with multi‐layer stacked meta‐atoms and spatially cascaded metasurfaces is presented. Progress is presented from metasurfaces with multi‐layer stacked meta‐atom configurations to spatially cascaded metasurfaces, focusing on the development of versatile applications for these quasi‐2D configurations. Special attentions are paid to the diffractive deep neural networks(D 2 NNs), and a category of recently developed cascaded metasurfaces introduces a brand‐new method into metasurface inverse designing as well as paves paths to all‐optical computing. Finally, the promising avenues for such metasurfaces are discussed.