基于光学超构表面的彩色图案和超构透镜的设计与实现

Design and Implementation of Colorful Display and Metalens Based on Optical Metasurfaces

靳铭珂

11749101

硕士

材料学

李贵新

2019-06-01

2019-07-10

哈尔滨工业大学

深圳

现代生产生活中，光学器件和光学系统处处可见。二十世纪激光的发明极大地丰富了光与物质相互作用的研究，而近几十年来，得益于纳米技术的发展，超构材料又让光学系统的设计和应用重焕新生，极大地丰富了光学的内涵。光学超构材料是指一类由尺度远小于其工作波长的功能单元构成的结构化材料，虽然它仍以自然界中存在的材料为基础，但其亚波长的人工设计让诸多在传统材料看来“绝无可能”的光学现象成为现实，也为新颖光学器件的设计提供了前所未有的手段和自由度。近年来，为解决三维超构材料中损耗大、加工难的问题，二维光学超构表面应运而生。光学超构表面是一种准二维的超构材料，在二维尺度上由亚波长超构功能单元构成，能灵活有效地实现对光偏振、振幅和相位的调控，实现特定的光学功能。传统光学器件对光相位的调控依赖于光通过块状光学器件时累计产生的光程差异，而光学超构表面利用亚波长功能单元的共振及贝里几何相位等原理，能在二维界面上引入突变的相位，由此实现对光波的调控，为设计和实现平面光学元件带来了广阔空间。本论文结合金属等离激元理论、电介质谐振理论和贝里几何相位理论等，分别用金属铝和电介质氮化硅设计和实现了彩色显示超构表面和超构透镜，并对其光学性能进行了实验测量。超构表面彩色显示相较于传统染料的显著优点即其颜色鲜艳而持久。本论文利用铝纳米棒-二氧化硅-铝三明治反射式结构实现超构表面彩色显示。首先，结合金属等离激元理论，利用FDTD电磁仿真软件针对红（630 nm）、绿（540 nm）、蓝（450 nm）三个波长优化设计了三组具有窄带响应的超构功能单元，并分析超构功能单元的几何参数变化对其光学转换效率的影响。然后，根据目标彩色图片的三个颜色通道和对应强度，结合马吕斯定律和贝里几何相位原理，将三种超构单元组合排布生成超构表面。最后，制备该光学超构表面并实验验证了其彩色显示功能。超构透镜可用平面结构取代厚重的传统透镜，其灵活的设计和易于集成的天性使其具有极高的应用价值。本论文用介质材料设计实现了一个透射式超构透镜，其功能单元由氮化硅纳米柱组成。超构透镜直径为500 m，数值孔径0.05，焦距5 mm，工作波长为532 nm。首先，结合电介质谐振理论，利用FDTD软件针对532 nm工作波长优化设计了具有高转化效率的氮化硅纳米柱单元，并分析其几何参数对光学转化效率的影响。然后，基于惠更斯原理和费马原理计算超构透镜所需的相位分布，利用贝里几何相位设计超构表面来实现该相位分布。最后，制备该超构透镜并实验表征了其聚焦特性。本文详细阐述了上述两种超构表面的制备方法并分析了工艺参数对样品结构的影响。首先利用电子束蒸镀制备铝膜和二氧化硅薄膜，等离子体增强化学气相沉积（PECVD）制备氮化硅薄膜，并用椭偏仪标定其厚度和折射率。然后利用电子束曝光技术实现超构功能单元排布图案的转移。最后，利用剥离技术或者感应等离子体刻蚀技术（ICP）刻蚀完成超构表面的制备。

Nowadays, optical devices and optical systems are everywhere in modern industry and daily life. Laser, as invented in twentieth century, has greatly enriched studies of the interactions between light and matter. In the past decades, benefited from the development on nanotechnology, metamaterials have rejuvenated the design and application of optical systems, flourished the subject of optics. Optical metamaterials are artificial structural materials composed of structures at a scale much smaller than their working wavelength. Although based on natural materials, metamaterials can achieve many anomalous optical phenomena that are “impossible” for natural materials and provide unprecedented degrees of freedom to design innovative optical components, ascribed to their subwavelength design. In recent years, two-dimensional metasurfaces emerged to overcome the obstacles encountered by three-dimensional metamaterials, such as lossy and difficult to fabricate. Metasurfaces are quasi-2D structured interface composed of subwavelength nanostructures which can be used to efficiently manipulate the amplitude, phase and polarization of light, therefore realize desired optical functionalities. The phase manipulation of conventional optical devices depends on the optical phase differences accumulated when the light passes through the bulk optical devices. Instead, by using the resonances of the subwavelength structure and principles such as the geometric Berry phase, metasurfaces can introduce abrupt phase change on the interface, making it possible to manipulate the phase of light and realize planar optical devices at ease. In this thesis, by combining theories such as surface plasmon polariton, dielectric resonance, geometric Berry phase and so on, we design and realize colorful display and metalens based on aluminum and silicon nitride metasurfaces, respectively. The optical performances of the two metasurface components are experimentally characterized. Compared with traditional dyes, one distinguished advantage of metasurface colorful display is its endurance. In this thesis, he metasurface colorful display is based on reflective metasurface, comprising a sandwiched structure of aluminum nanorods, silica spacer and aluminum mirror. The FDTD simulation software is used for optimizing three types of unit cell with narrow band characteristics at three wavelengths: red (630 nm), green (530 nm) and blue (450 nm). The influence of varying geometric parameters of the unit cell on the optical conversion efficiency is analyzed. The three channels of the target color image and the corresponding intensities are then mapping into the distributions of three optimized unit cell to forms the metasurface, according to the Malus’s law and the geometric Berry phase. Finally, we fabricate the optical metasurface and experimentally demonstrated its capability for colorful display. Metalens can replace the bulky conventional lens by using planar design. Its design flexibility and easy-to-integrate nature hold great potential for practical applications. In this thesis, we design and fabricate a dielectric transmission metalens based on silicon nitride nanopillars. The diameter of the designed metalens is 500 µm, the numerical aperture (N.A.) is 0.05, the focal length 5 mm, and the working wavelength 532 nm. We first optimize the unit cell with high conversion efficiency at wavelength of 532 nm by using the FDTD software, and the theory of dielectric resonance. The influence of varying geometric parameters of the unit cell on the optical conversion efficiency is numerically analyzed. Then, according to the Huygens principle, the Fermat principle and geometric Berry phase, the phase distributions of the metalens can be calculated and mapped into the design of metasurface. Finally, we fabricated the metalens and measured their optical focusing performances. This thesis also presents the detailed fabrication processes of the optical metasurfaces and analyses the influences of the process parameters on performances of the fabricated samples. Firstly, Electron Beam Evaporation is used to prepare the aluminum film and the silica spacer, the Plasma-Enhanced Chemical Vapor Deposition is used for depositing the silicon nitride films. The thicknesses and the refractive indices of the films are characterized by using the Spectroscopic Ellipsometry. Next, the pattern transformation is performed by Electron Beam Lithography. At last, the metal lift-off process is used for fabricating the aluminum metasurface, and the Induction Couple Plasma Reactive Ion Each for the silicon nitride metasurface.

光学超构材料 光学超构表 彩色图案 超构透镜

optical metamaterials optical metasurfaces colorful display metalens

中文

联合培养

南方科技大学

靳铭珂. 基于光学超构表面的彩色图案和超构透镜的设计与实现[D]. 深圳. 哈尔滨工业大学,2019.