具有旋转变焦能力的双层大数值孔径超透镜
Dual-layer large-numerical-aperture metalenses with rotational zoom capability
- School of Physics, Sun Yat-sen University（中山大学物理学院）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
提出一种基于完整无像差相位函数的双层旋转超透镜设计，通过互补相位分布与旋转实现3:1连续变焦，最大数值孔径0.83，实验验证焦距调谐与近衍射极限聚焦。
AI中文摘要：
我们提出了一种基于完整理想无像差相位函数的非近轴设计策略，用于双层旋转变焦超透镜。通过采用精确的透镜相位表达式而非传统的抛物近似，该方法保留了对于大数值孔径（NA）工作至关重要的高阶相位贡献。变焦是通过在两个超表面层上设计互补的相位分布，并通过受控旋转动态调制其组合相位来实现的。为实现目标相位分布，我们设计了一种工作在10 GHz的介质超表面，采用排列在三角晶格中的陶瓷圆柱谐振器。对晶格周期、圆柱直径和高度的系统参数优化确保了完整的2π相位覆盖，同时保持透射率高于85%。由此产生的相位-几何映射为器件实现建立了可靠的单元库。利用该单元库，我们设计了双层超透镜，并通过时域有限差分（FDTD）模拟评估其性能。制造了一个孔径为300 mm的原型，并使用三维近场扫描测量进行了实验表征。模拟和实验均证实，随着旋转角度从-60°变化到60°，实现了连续的焦距调谐，对应的焦距范围为100至300 mm，变焦比为3:1。该器件实现了最大数值孔径0.83，测得的焦斑接近衍射极限。实验提取的焦距变化与理论预测和模拟结果非常吻合。
英文摘要：
We present a non-paraxial design strategy based on the full ideal aberration-free phase function for a dual-layer rotational zoom metalens. By adopting the exact lens phase expression rather than the conventional parabolic approximation, this approach preserves the higher-order phase contributions critical to large-NA operation. Zooming is achieved by engineering complementary phase distributions on two metasurface layers and dynamically modulating their combined phase via controlled rotation. To realize the target phase profiles, a dielectric metasurface operating at 10 GHz is designed using ceramic cylindrical resonators arranged in a triangular lattice. A systematic parametric optimization of lattice period, cylinder diameter, and height ensures a complete 2pi phase coverage while maintaining a transmission above 85%. The resulting phase-geometry mapping establishes a reliable unit-cell library for device implementation. Leveraging this library, the dual-layer metalens is designed and its performance evaluated through finite-difference time-domain simulations. A prototype with a 300 mm aperture is fabricated and experimentally characterized using three-dimensional near-field scanning measurements. Both simulations and experiments confirm that continuous focal-length tuning is achieved as the rotation angle varies from -60deg to 60deg, corresponding to a focal-length range of 100 to 300 mm and a zoom ratio of 3:1. The device achieves a maximum NA of 0.83, and the measured focal spots remain nearly diffraction-limited. The experimentally extracted focal-length variation agrees closely with theoretical predictions and simulations.
