Collaborative Research: Photon Funnels -- A Fundamentally New Concept for Concentrating Light

在任何光学系统中，收集和聚光都是必不可少的过程。传统的透镜收集光线并将其集中到一个点，但是当光线从不同的角度或不同的位置照射时，聚光点会移动。因此，当光源移动时，传感器和探测器可能会损失能量，并且光学设备的效率通常受到透镜或透镜系统的角度接受度的限制。在这个项目中，中佛罗里达大学和德克萨斯大学埃尔帕索分校的一个合作团队将探索一种全新的聚光方法，这种方法被称为“光子漏斗”，它基于空间工程光学晶格。光子通道将被设计成利用一种叫做“自准直”的光学现象来控制光在工程晶格内的传播方式。采用结合理论、模拟、制造和光学测试的协作方法，该团队将开发基础知识，使科学家和工程师能够为无数应用设计光子通道。对社会的好处将包括成像、光学探测和传感、电信和能量收集的新技术。这个跨学科的项目将为研究学生提供光学工程、物理、化学、材料科学、设计和仿真方面的前沿训练。与项目相结合的教育外展活动将把研究的兴奋带给更广泛的社区，并将有助于提高对科学和技术的了解，并鼓励年轻人在相关领域从事职业。研究目标是：1)对光子通道和更普遍的自准直、空间变化的晶格产生基本的理解；2)建立光子通道的基本性能极限；3)确定互易性在多大程度上限制了它们的光收集能力；4)创建工程师可以在自己的应用程序中使用的设计规则。光子通道是波长尺度的非周期三维晶格，其中的单元胞在空间上定向变化，通过自准直将光引导到单个集中区域。因为光子漏斗是通过自准直的方式工作的，所以它们不受斯涅尔定律的约束，所以原则上它们可以收集和集中所有位置、所有角度和所有偏振的入射光。没有现有的技术提供这种非凡的能力。光子通道和空间变晶格是通过空间改变光学晶格的结构来设计的，同时保持了单位细胞的自准直特性。空间变晶格与光子晶体、超材料以及基于梯度折射率和变换光学的器件有着根本的不同。空间可变晶格不需要奇异的特性——比如高折射率、负折射率或小于1——这使得空间可变晶格更容易制造，而且本质上更容易制造。该项目将改变工程师设计光学系统的方式，因为他们可以在某些应用中搁置传统的射线光学，而使用光子漏斗来集中光线。光子漏斗和空间可变晶格提供了巨大的潜力，因为多种功能可以集成到一个设备中，包括光的收集和集中，紧密的光束弯曲，波长分离，以及偏振，相位和功率的控制。

Collecting and concentrating light is an essential process in any system utilizing optics. Conventional lenses collect light and concentrate it to a spot, but the concentration spot moves as light rays strike at different angles or different positions. As a result, sensors and detectors can lose energy as a source moves, and the efficiency of an optical devices is often limited by the angular acceptance of a lens or lens system. In this project, a collaborative team at the University of Central Florida and the University of Texas at El Paso will explore a fundamentally new approach for concentrating light called "photon funnels," which is based on spatially engineered optical lattices. Photon funnels will be designed to leverage an optical phenomenon called "self-collimation" to control how light propagates within an engineered lattice. Using a collaborative approach that combines theory, simulation, fabrication, and optical testing, the team will develop fundamental knowledge that enables scientists and engineers to design photon funnels for a myriad of applications. The benefits to society will include new technologies for imaging, optical detection and sensing, telecommunications and energy harvesting. This interdisciplinary project will give research students cutting-edge training in optical engineering, physics, chemistry, materials science, and design and simulation. Educational outreach activities integrated with the project will bring the excitement of the research to the broader community and will help to improve understanding of science and technology and encourage youth to pursue careers in related fields.The research goals are to: 1) generate fundamental understanding of photon funnels and more generally self-collimating, spatially-variant lattices; 2) establish the fundamental performance-limits of photon funnels; 3) determine to what extent reciprocity limits their light collecting ability; and 4) create design-rules that engineers can use for their own applications. Photon funnels are wavelength-scale aperiodic three-dimensional lattices in which the unit cells are spatially varied in orientation to direct light via self-collimation to a single concentration zone. Because photon funnels work via self-collimation, they are not bound by Snell's law, so in principle they could collect and concentrate light incident at all positions, all angles, and all polarizations. No existing technology offers this extraordinary capability. Photon funnels and spatially-variant lattices are designed by spatially varying the structure of an optical lattices while preserving the self-collimating properties of the unit cells. Spatially-variant lattices are fundamentally different from photonic crystals, metamaterials, and devices based on graded-index and transformation optics. Spatially-variant lattices do not require exotic properties - like refractive index that is high, negative, or less than one - which makes spatially-variant lattices simpler to fabricate and inherently more manufacturable. The project will transform how engineers design optical systems because they could set aside traditional ray optics in certain applications and use photon funnels to concentrate light. Photon funnels and spatially-variant lattices offer tremendous potential because multiple functions can be integrated into a single device, including light collection and concentration, tight beam bending, wavelength separation, and control of polarization, phase, and power.