基于四分之一波片的偏振转换全息超表面

To address the challenge of simultaneously achieving high polarization conversion efficiency and high-quality image reconstruction in near-infrared polarization holographic devices, this paper proposes a polarization-conversion holographic metasurface based on quarter-wave plates (QWP). The device adopts a metal-insulator-metal (MIM) gap-surface-plasmon (GSP) configuration, in which anisotropic meta-atoms satisfying the QWP condition are designed to realize the conversion from circularly polarized light to linearly polarized light. In addition, a 2×2 superpixel strategy is introduced to improve wavefront reconstruction quality and device performance. In the design process, inverse phase retrieval of the target image is carried out using a gradient-descent-based method, and the imaging characteristics of the device are analyzed based on Fresnel diffraction theory and three-dimensional finite-difference time-domain simulations. The results show that, compared with the single-pixel scheme, the 2×2 superpixel design exhibits superior holographic imaging performance, with the peak signal-to-noise ratio improved by 1.05 dB, the contrast-to-noise ratio and edge sharpness improved by 45.9% and 21.9%, respectively, and the polarization conversion efficiency improved by 9.7%. These findings indicate that collaborative superpixel design can effectively enhance the overall performance of QWP-based polarization-conversion holographic metasurfaces, and provide a useful reference for the design of near-infrared polarization-control and holographic devices.