Metasurfaces are ultrathin metamaterials consisting of planar electromagnetic (EM) microstructures (e.g., meta-atoms) with pre-determined EM responses arranged in specific sequences. Based on careful structural designs on both meta-atoms and global sequences, one can realize homogenous and inhomogeneous metasurfaces that can possess exceptional capabilities to manipulate EM waves, serving as ideal candidates to realize ultracompact and highly efficient EM devices for next-generation integration-optics applications. In this paper, we present an overview on the development of metasurfaces, including both homogeneous and inhomogeneous ones, focusing particularly on their working principles, the fascinating wave-manipulation effects achieved both statically and dynamically, and the representative applications so far realized. Finally, we also present our own perspectives on possible future directions of this fast-developing research field in the conclusion.

A thin screen exhibiting dynamically switchable transmission/absorption functionalities is highly desired in practice. However, a trilayer transmissive metasurface with active elements controlled in a uniform manner cannot exhibit independently controlled transmission and absorption properties due to intriguing interplays between the scattering and absorbing properties in systems exhibiting inversion symmetries. This motivates to employ the coupled‐mode theory to establish a generic phase diagram for such transmissive metasurfaces with active elements loaded in different layers tuned independently and to guide researchers design tunable metadevices with completely decoupled transmission/absorption responses. Based on such a phase diagram, a microwave metasurface is designed/fabricated with PIN diodes incorporated, and it is experimentally demonstrated that its functionality can switch from perfect transparency to perfect absorption, controlled by external voltages applied across the diodes. In addition to finding immediate applications in practice (e.g., smart radomes), the results of this study also provide a new type of tunable meta‐atom for building metasurfaces with flexible wave‐front control abilities.

Dynamical controls on terahertz (THz) wavefronts are crucial for many applications, but available mechanism requests tunable elements with sub‐micrometer sizes that are difficult to find in the THz regime. Here, different from the local‐tuning mechanism, we propose an alternative approach to construct wavefront‐control meta‐devices combining specifically designed metasurfaces and globally tuned graphene layers. Coupled‐mode‐theory (CMT) analyses reveal that graphene serves as a tunable loss to drive the whole meta‐device to transit from one functional phase to another passing through an intermediate regime, exhibiting distinct far‐field (FF) reflection wavefronts. As a proof of concept, we design/fabricate a graphene meta‐device and experimentally demonstrate that it can reflect normally incident THz wave to pre‐designed directions with different polarizations under appropriate gating voltages. We finally design a graphene meta‐device and numerically demonstrate that it can generate vectorial THz beams with continuously varying polarization distributions upon gating. These findings pave the road to realizing a wide range of THz applications, such as sensing, imaging, and wireless communications.

Reflecting light to a predetermined nonspecular direction is an important ability of metasurfaces, which is the basis for a wide range of applications (e.g., beam steering/splitting and imaging). However, anomalous reflection with 100% efficiency has not been achieved at optical frequencies yet, because of losses and/or insufficient nonlocal control of light waves. Here, we propose an all-dielectric quasi–three-dimensional subwavelength structure, consisting of multilayer films and metagratings, to achieve perfect anomalous reflections at optical frequencies. A complex multiple scattering process was stimulated by effectively coupling different Bloch waves and propagating waves, thus offering the metasystem the desired nonlocal control on light waves required by perfect anomalous reflections. Two perfect anomalous reflectors were demonstrated to reflect normally incident 1550-nm light to the 40°/75° directions with absolute efficiencies of 99%/99% in design (98%/88% in experiment). Our results pave the way toward realizing optical metadevices with desired high efficiencies in realistic applications.

Scanning focused light with corrected aberrations holds great importance in high-precision optical systems. However, conventional optical systems, relying on additional dynamical correctors to eliminate scanning aberrations, inevitably result in undesired bulkiness and complexity. In this paper, we propose achieving adaptive aberration corrections coordinated with focus scanning by rotating only two cascaded transmissive metasurfaces. Each metasurface is carefully designed by searching for optimal phase-profile parameters of three coherently worked phase functions, allowing flexible control of both the longitudinal and lateral focal position to scan on any custom-designed curved surfaces. As proof-of-concept, we engineer and fabricate two all-silicon terahertz meta-devices capable of scanning the focal spot with adaptively corrected aberrations. Experimental results demonstrate that the first one dynamically scans the focal spot on a planar surface, achieving an average scanning aberration of 1.18% within the scanning range of ±30°. Meanwhile, the second meta-device scans two focal points on a planar surface and a conical surface with 2.5% and 4.6% scanning aberrations, respectively. Our work pioneers a breakthrough pathway enabling the development of high-precision yet compact optical devices across various practical domains.