【作者】 陈晨；

【导师】 李涛；

【作者基本信息】 南京大学 ， 光学工程， 2021， 博士

【摘要】 超构表面是一种基于亚波长结构单元局域地控制光的波长、相位、偏振等特性实现对光场调控的平面光学设计,它具有超薄超轻的结构特征和多功能灵活调控的优势,为新型高度集成化的光学元件开发提供了新方案。迄今,人们已经提出了多种超构表面相位调控原理,展示出诸如光束变换、全息、成像及其多种复用功能,有望实现光学系统小型化、集成化的同时,解决传统透镜成像和全息成像的一些如成像景深、信息通道扩展等关键性问题,进一步增强和丰富光学系统的功能,拓展其应用前景。本文围绕超构表面的成像及全息技术展开,以光的波长、偏振及相位为调控维度,从原理设计、功能演示、应用开发多方面入手,解决了传统层析成像当中景深有限及机械移动的问题,丰富了超构表面波前调控器件的功能性,进一步提升了手性光学器件的性能。具体内容包括:1、详细分析了超构表面的色散特性,创新性地提出了利用超构表面的大色散,以波长作为调控维度实现透镜的无机械变焦及光谱层析功能。提出了针对具体成像过程的广义消球差相位设计,显著提高了成像的横向及纵向分辨率。设计并加工了工作在可见光的氮化镓超构透镜,对其性能进行了详细的表征。在实验上演示了无机械光谱变焦、3D切片样品层析成像及蛙卵细胞的显微光谱层析成像,并与传统衍射透镜在信噪比、效率等方面做了详细的比较。该光谱层析方案一方面可以解决传统折射器件景深受限的问题,另一方面也可以显著提升器件的集成度与稳定性,在生物组织等层析成像方面有巨大的潜力。2、将几何相位与传播相位结合,提出实现偏振与相位同时调控的设计方法。研制了工作在蓝光470 nm的氮化硅超构表面,实验上首先验证了同偏振态与正交偏振态相位独立调控的能力,演示了偏振依赖的全息成像。进一步加入偏振调控,构建出具有1/4波片性能的波前调控器件,演示了高效的透镜成像及全息等功能。设计并验证了庞加莱球上其他任意偏振态(椭圆偏振态)的透镜及成像,展示了该方案丰富的偏振及波前调控能力。该设计方法可进一步提高手性成像器件的集成度,有望应用于矢量全息等方面。3、提出了一种基于平面手性超构原子的相位调制方法,实现了偏振解耦的复用全息功能。不同于常用的几何相位全局性调控特征,该方法是通过打破每个单元的镜像对称性和高阶旋转对称性来实现圆偏振光下的相位调控。研制了相应的硅超构表面,在980 nm波长下验证了这类手性超构原子在单个圆偏振光下的波前调控能力和宽带高效特性,进一步设计并验证了无串扰的自旋解耦的全息功能。此外,将手性超构原子与几何相位相结合,以更少的单元种类实现了相同的自旋解耦的功能,并验证了手性超构原子带来的更大设计自由度和更优性能。该方法丰富了超构表面的设计原理,有望进一步提升手性光学器件的性能。更多还原

【Abstract】 Metasurfaces consisting of subwavelength dielectric or metallic antannas are emerging as the most attractive flat optical design which reshape the light field by manipulating the polarization,phase,amplitude and wavelength of the electromagnetic wave.Metasurfaces have ultrathin and ultralight features and can manipulate the light with multi-functionalities in a more flexible way.So far,researchers have developed several phase modulation principles,and domenstrated a varity of applications such as beam transformation,hologram,imaging and other multiplexing functionalities.Metasurfaces not only meet the tendency for miniaturization,lightweight and integration,but also can solve some key problems in traditional lens imaging and holographic imaging,such as limited depth of field,limited information capacity and encryption.It can further spur and enrich the function of the optical system,strengthen and expand its practical applications.Focusing on the metalens imaging and meta-hologram,this thesis provides effective ways through the manipulation of spectral response,polarization and phase of the light to realize non-mechanical tomographic imaging,enriches the functionality of the wave modulation devices,and improves the performances of chiral optical devices.The particular contents include:1.The dispersion properties of the metasurfaces are analyzed.We innovatively proposed to utilize the large dispersion of the metalens to realize the non-mechanical optical zoom and spectral tomographic imaging.Generalized aplanatic phase design for imaging process is proposed,which significantly improves the lateral and longitudinal resolution of imaging.A gallium nitride metalens operating in visible band was designed and fabricated.Its dispersion properties and broadband resolutions were characterized.In the experiment,we demonstrated the non-mechanical spectral zoom,microscopy spectral tomography for 3D slice sample and frog eggs.The comparison with the traditional diffraction lens in terms of signal-to-noise ratio,efficiency and other aspects were performed.This method not only expands the limited depth of field of traditional refraction devices,but also significantly improves the integration and stability of the imaging devices,which has great potential in the field of biological tissue tomography.2.Combining the geometric phase with the propagation phase,the design method for simultaneously controlling the polarization and the phase is proposed.We developed the fabrication technology of silicon nitride metasurfaces working at the wavelength of470 nm.The independent phase manipulation ability of the light with the same polarization state and the orthogonal polarization state was firstly verified experimentally,and polarization-dependent holographic imaging was demonstrated.A metalens and meta-hologram with 1/4 wave plate functionality were constructed and demonstrated with high efficiency by adding the polarization control.Lens focusing and imaging with other arbitrary polarization states on the Poincaré sphere(elliptic polarization states)were designed and verified.It demonstrated the rich polarization and wavefront regulation capabilities of this scheme.This design method can further improve the integration of chiral imaging devices and is expected to be applied to vector holography.3.A phase modulation method based on planar chiral meta-atoms is proposed,and the spin-decoupled meta-holograms are realized.Different from the global effect of the geometric phase,this method is based on the local effect which breaks the mirror symmetry and high order(n>2)rotational symmetry of the plannar meta-atom to realize the phase control of the circularly polarized light.By developing the fabrication of the silicon metasurfaces working under the wavelength of 980 nm,the wavefront control ability of this kind of chiral meta-atoms with a single circular polarized light incidence was verified.Experiment results show the broadband and efficient characteristics.Furthermore,independent holographic images were demonstrated with negligible polarization crosstalk.In addition,combining the chiral meta-atoms with the geometric phase,the same spin-decoupled function were realized with less kinds of meta-atoms.Moreover,the more degrees of freedom and the better performances of the chiral metaatoms were verified through comparison experiments.This method enriches the design principle of metasurfaces and is expected to further improve the performance of chiral optical devices.更多还原