Metasurface Polarization Information Encoding

Significance Since the successful demonstration of versatile wavefront shaping on metasurfaces by F. Capasso et al. at Harvard University in 2011, metasurfaces as a two-dimensional artificial electromagnetic material composed of an array of lightweight nano -scatters at the subwavelength scale have garnered significant attention as an ultra -compact planar optics platform for light -field manipulation. The original metasurfaces utilize the plasmonic resonance effect demonstrated by metals to manipulate the phase of electromagnetic waves, enabling phenomena such as anomalous refraction, reflection, planar focusing, and shaping of special light beams. Subsequently, metasurfaces based on all -dielectric micro-nanostructures with Mie-type resonances are proposed, which significantly improves their efficiency and lays the foundation for the practical applications of planar optical elements. By altering the material and structural parameters of the unit cell of the a metasurface, various physical properties such as phase, amplitude, polarization, and frequency of light waves can be flexibly modulated, resulting in precise control over the diffraction and polarization properties of light.Metasurfaces are significant in both academic and industrial communities. They exhibit broad application prospects in various fields, including VR/AR near -eye displays, multidimensional computational imaging, autonomous driving, in -vehicle photography/ displays, information coding, and encryption.According to their functionalities, metasurface optical elements can be classified into two major categories: metasurface diffraction optical elements and metasurface polarization optical elements. Metasurface imaging lenses, metasurface beam shapers, and metasurface holographic elements are examples of diffractive optical elements. These elements achieve wavefront shaping by primarily modulating the phase of the incident light by spatially varying meta -atoms. With the continuous advancement of metasurfaces, the metasurface polarization optical elements have emerged as another prominent class of metasurface optical elements. Metasurface polarization optical elements are thin film optical elements comprising micro-nanostructured metallic or dielectric meta-atoms with local polarization responses. Such meta -atoms typically possess strong anisotropy and circular dichroism, allowing them to perform polarization conversion and projection operations at nanoscale. Unlike traditional polarization optical elements such as waveplates and polarizers, metasurface polarization optical elements manipulate the phase or amplitude of light of different polarization components through the anisotropy in its structure, rather than the anisotropic material. Consequently, they possess more precise and flexible characteristics, allowing for pixelated encoding of the polarization state of light at subwavelength scales.In recent years, owing to the extension of its applications and the advent of the big data, there is an increase in demand for information security and capacity. In this context, the use of metasurfaces in conjunction with polarization information for precise control of optical field information has garnered significant research interest, particularly in high -density image information coding and anti -counterfeiting encryption. Therefore, we conducted a comprehensive review of recent research articles on metasurface polarization optical elements and particularly focused on polarization information encoding, with the aim of providing valuable insights into the future developments in this field.Progress First, we explain the various types of metasurface polarization optical elements, such as metasurface waveplates (Fig. 1), metasurface polarizers (Fig. 2), and metasurface polarizing beam splitters (Fig. 3), thus highlighting their exceptional performance in polarization control. Next, we delve into the applications of micro-metasurface polarization optical elements for pixelated polarization information encoding. These applications use the Malus metasurface (Fig. 4) that enables point -by -point encoding of the near -field polarization state spatial distribution: the Malus metasurface (Fig. 5) combined with other degrees of freedom for enhanced control and some applications based on Malus metasurfaces (Fig. 6). Subsequently, we introduce polarization holography and vector holography metasurfaces for spatially encoding far -field polarization states, which encompass metasurface polarization multiplexing holography (Fig. 7), metasurface vectorial holography (Fig. 8), metasurface full -color vectorial holography (Fig. 9), and metasurface Jones matrix vectorial holography (Fig. 10). On the metasurface platform, the highly controllable polarization response of meta -atoms provides a universal method to manipulate the polarization state of the far -field wavefront, thereby achieving multifunctional and high-performance holographic applications and particularly demonstrating significant capabilities in information encryption. Last, we briefly discuss the current challenges in the further development of metasurface polarization optical elements. While metasurface polarization optics has shown immense potential in information multiplexing, storage, hiding, encryption, and anti -counterfeiting, its application for advancements in the large-scale production, industrialization, and practical usability of metasurface information encoding and encryption technologies in everyday life requires intensive research.Conclusions and Prospects In conclusion, metasurface polarization optical elements offer new avenues for efficient, secure, and flexible optical information coding and transmission. Compared to traditional polarization optical elements relying on anisotropic crystal materials, metasurface polarization optical elements require only isotropic materials for their construction. Through the anisotropic characteristics of the meta -atoms at the subwavelength scale, they achieve flexible, diverse, and integrated control of light polarization states. The metasurface polarization information encoding technology has significant value for application in the fields of information encryption, optical imaging, and display, and it contributes to the advancement of optical devices and systems.