Metasurfaces for polarization-field manipulation

Polarization is a fundamental degree of freedom of light and plays a crucial role in optical communications, quantum information, three-dimensional displays, super-resolution imaging, biomedical sensing, and optical information security. Conventional polarization-control technologies rely primarily on discrete components, including birefringent crystals, dichroic materials, wave plates, and spatial light modulators, which are generally bulky, difficult to integrate, and limited in multiplexing capability. Metasurfaces, two-dimensional optical platforms composed of subwavelength artificial micro- and nanostructures, offer a promising route to overcoming these limitations. In this review, the fundamental mechanisms of metasurface-enabled polarization-field manipulation and the representative approaches to the generation, modulation, and application of polarization fields were systematically summarized. First, the capabilities of metasurfaces for controlling the phase, amplitude, frequency, and polarization of light were outlined. Next, the physical mechanisms underlying the manipulation of linear, circular, and elliptical polarization states and complex vectorial light fields were discussed, with emphasis placed on geometric phase, propagation phase, anisotropic responses, and spin–orbit coupling. Recent advances in vector beam generation, longitudinal evolution of polarization states, polarization multiplexing and information encryption, full-Stokes polarimetric imaging, and reconfigurable polarization control were then reviewed. It is shown that metasurfaces enable multi-degree-of-freedom light-field manipulation in ultrathin devices, and significant application potential is demonstrated in multi-channel optical information processing, on-chip polarization devices, structured-light communication, and intelligent imaging. Overall, metasurfaces enable multidimensional light-field manipulation with ultrathin devices and hold substantial potential for multichannel optical information processing, on-chip polarization components, structured-light communication, and intelligent imaging.