Holographic meta-lenses for point-spread function engineering

光学成像系统的点扩展函数(即，其对点光源的响应)可以被设计成实现在基于折射透镜的传统成像系统中无法获得的成像形态。传统上，点扩展函数是通过使用光圈和光学相位掩模来成形的，这导致了诸如提高显微镜的分辨率、对象可以保持在焦点上的扩展景深以及运动对象的三维跟踪等功能。拟议的计划将探索一种新的工程化点扩散函数的范例，通过使用扁平的“亚透镜”，这是一种纳米结构的薄膜，由于强烈的光与物质的相互作用，能够局部改变光的幅度、相位和偏振。通过将准透镜和图像处理算法作为一个集成的成像系统进行联合设计，将发明强大的新成像模式。准透镜的扁平形状因素使其能够利用集成电路行业开发的成熟的平面制造技术来制造，并受益于规模经济。本项目中展示的光学成像组件和系统可能对机器视觉、生物医学成像和全息技术中的各种应用具有重要意义。该项目将培养研究生和本科生在纳米技术、材料科学和光子学的交叉点上进行创新和深入的研究。该项目在哥伦比亚工程学院外展计划的支持下，将通过为来自不同背景的本科生提供暑期研究机会，扩大对科学和工程的参与。此外，该项目将促进科学家和艺术家之间的合作，制作更容易为公众所了解的引人入胜的、具有教育意义的科学发现插图。该项目将探索利用全息元透镜实现工程化点扩散函数的新范例：单层或多层纳米结构薄膜，它可以对光学近场的相位、幅度和偏振进行完全、独立和亚波长的控制，从而在大波长和大角度范围内对光学远场进行多变量操纵。全息元透镜将由一个复杂的亚波长像素库或“元原子”组成。该项目将研究：结构色散工程，以创建为控制宽光谱连续波长的光提供最大允许的相位色散的准原子；结构双折射和多组分的准原子，以提供对光学相位、幅度和偏振的完全和独立的控制；以及多层亚表面系统，用于广角光学控制。这项研究工作将研究光学控制的基本限制，以确定一个光学参数(某一波长上的光的相位、幅度或偏振)可以在多大程度上受到单位体积的结构材料的控制，并探索创造出体积最小的结构材料以独立和完全地控制多个光学参数的设计规则。为了说明点扩散函数工程新范式的前景，该项目将展示几个全息亚透镜的例子，展示基于折射组件和单层、纯相位亚表面的传统成像系统所无法实现的功能。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The point-spread function of an optical imaging system (that is, its response to a point light source) can be designed to achieve imaging modalities unattainable in conventional imaging systems based on refractive lenses. Conventionally, point-spread functions have been shaped by using apertures and optical phase masks, leading to functions such as improved resolution in microscopy, extended depth of field over which an object can stay in focus, and three-dimensional tracking of moving objects. The proposed program will explore a new paradigm of engineering point-spread functions by using flat “meta-lenses”, which are nano-structured thin films that are able to locally change the amplitude, phase, and polarization of light due to strong light-mater interactions. Powerful new imaging modalities will be invented by jointly designing meta-lenses and image processing algorithm as an integrated imaging system. The flat form factor of meta-lenses allows them to be fabricated with mature planar fabrication technologies developed by the integrated circuit industry and benefit from economies of scale. Optical imaging components and systems demonstrated in this program may have important implications for a variety of applications in machine vision, biomedical imaging, and holographic technology. The project will train graduate and undergraduate students to carry out innovative and in-depth research at the intersection between nanotechnology, materials sciences, and photonics. The project, with the support of Columbia Engineering School’s Outreach Program, will broaden participation in science and engineering by providing summer research opportunities to undergraduate students from diverse backgrounds. In addition, the project will promote a collaborative effort between scientists and artists in producing engaging and educational illustrations of scientific discoveries that are more accessible to the general public.The project will explore a new paradigm of engineering point-spread functions by holographic meta-lenses: single or multi-layered nano-structured thin films that can provide complete, independent, and sub-wavelength control of the phase, amplitude, and polarization of optical near-field for multivariate manipulation of optical far-field over a large wavelength and angular range. The holographic meta-lenses will be composed of a library of complex and sub-wavelength pixels or “meta-atoms”. The project will investigate: the structural dispersion engineering to create meta-atoms that provide the maximum allowable phase dispersion for controlling light over a continuous wavelength of a broad spectrum; the structurally birefringent and multi-component meta-atoms to provide complete and independent control of optical phase, amplitude, and polarization; and the multi-layered metasurface systems for wide-angle optical control. The research work will study fundamental limitations of optical control to establish the degree to which one optical parameter (phase, amplitude, or polarization of light at a certain wavelength) can be controlled by a unit volume of a structured material and to explore the design rules for creating a structured material with minimal volume to control multiple optical parameters independently and completely. To illustrate the promise of the new paradigm of point-spread function engineering, the project will demonstrate a few examples of holographic meta-lenses showing functions that are beyond the capabilities of conventional imaging systems based on refractive components and single-layer, phase-only metasurfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.