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偏振转换和聚焦的超表面
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Abstract:
高阶偏振(Higher-order Polarization)光束的生成及其聚焦特性一直备受研究关注。MATLAB的理论仿真结果表明，在相同入射条件下，高阶偏振相比于线偏振、圆偏振、径向偏振和角向偏振光束，其聚焦光斑光强分布的半高全宽(FWHM)更小，这在超分辨领域具有潜在的应用。本文基于超表面的传输矩阵理论和传输相位理论，提出了一种超表面设计，利用时域有限差分模拟(FDTD)对超表面进行仿真模拟，仿真结果表明，本文设计出的超表面实现了偏振转换和聚焦。本文推导了适用于线偏振到高阶偏振转换的通用理论，通过选择超表面微元材料和相位响应，允许将任意波长的入射光波的线偏振转换为任意阶数和任意初始极化角度的高阶偏振光束。通过精心选择聚焦层超表面相位轮廓，实现对转换得到的高阶偏振光束的聚焦，取得了突破瑞利衍射极限的致密光斑。通过合理设计超表面，得到了各个NA处的最优聚焦光斑。利用这种方法，本文能够研究高阶偏振光束的聚焦特性，减小其在焦点区域的光斑，或深入研究焦点区域光强分布特性，从而大幅拓展了高阶偏振光束的研究范围。
The generation of higher-order polarization (HOP) beams and their focusing characteristics have been of great interest. Matlab theoretical simulation results show that under the same incidence conditions, HOP has a smaller half-height-full width (FWHM) of the focused spot intensity distribution than linear, circular, radial, and angular polarized beams. This has potential applications in the field of super-resolution. In this paper, we propose a metasurface design based on the transmission matrix theory and transmission phase theory of the metasurface. We simulate the metasurface using finite-difference simulation in the time domain (FDTD), and the simulation results show that our designed metasurface achieves polarization conversion and focusing. We derive a general theory applicable to the conversion of linear polarization to higher-order polarization. This permits the conversion of linear polarization of an incident light wave of any wavelength into a higher-order polarized beam of any order and any initial polarization angle by choosing the micrometric material and phase response of the metasurface. By carefully selecting the phase profile of the focusing layer metasurface, we achieve the focusing of the converted higher-order polarized beam, and obtain a dense spot that breaks through the Rayleigh diffraction limit. By rationally designing the metasurface, we obtain the optimal focusing spot at each NA. Using this method, we are able to study the focusing characteristics of higher-order polarized beams, reduce the spot in the focal region, or study the light intensity distribution characteristics in the focal region in depth. This greatly expands the research scope of higher-order polarized beams.
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