The polarization of light is crucial for numerous optical applications ranging from quantum information processing to biomedical sensing due to the fundamental role of polarization as another intrinsic characteristic of optical waves, which is uncorrelated with the amplitude, phase, and frequency. However, conventional optical waveplates that enable polarization control are based on the accumulated retardation between two orthogonally polarized electric fields when light propagates a distance much larger than its wavelength in birefringent materials, resulting in bulky configurations and limited functionalities. Optical metasurfaces, ultrathin arrays of engineered meta-atoms, have attracted increasing attention owing to their unprecedented capabilities of manipulating light with surface-confined configurations and subwavelength spatial resolutions, thereby opening up new possibilities for revolutionizing bulky optical waveplates with ultrathin planar elements that feature compactness, integration compatibility, broadband operation bandwidths, and multiple functionalities. Herein, we review the recent progress in metasurface-enabled optical waveplates, which covers both basic principles and emerging applications. We provide an overview of metasurface-based conventional half- and quarter-waveplates as well as their use in wavefront shaping applications, followed by a discussion of advanced waveplates, including multifunctional waveplates and all-polarization generators. We also discuss dynamic waveplates based on active metasurfaces. Finally, we conclude by providing our outlook in this emerging and fast-growing research field.

中文翻译：

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超表面启用光波片的最新进展

光的偏振对于从量子信息处理到生物医学传感等众多光学应用至关重要，因为偏振的基本作用是光波的另一个固有特性，与振幅、相位和频率无关。然而，当光在双折射材料中传播的距离远大于其波长时，实现偏振控制的传统光学波片基于两个正交偏振电场之间的累积延迟，导致结构庞大且功能有限。光学超表面，工程超原子的超薄阵列，由于其前所未有的表面受限配置和亚波长空间分辨率操纵光的能力而引起了越来越多的关注，从而为使用具有紧凑性、集成兼容性、宽带操作带宽和多种功能的超薄平面元件彻底改变笨重的光学波片开辟了新的可能性。在这里，我们回顾了超表面光学波片的最新进展，涵盖了基本原理和新兴应用。我们概述了基于超表面的传统半波片和四分之一波片以及它们在波前整形应用中的使用，然后讨论了先进的波片，包括多功能波片和全偏振发生器。我们还讨论了基于有源超表面的动态波片。最后，我们总结了我们对这个新兴和快速发展的研究领域的展望。