Microscale concave interfaces for structural reflective coloration

在日常生活中，人类和机器依靠不同的颜色来处理重要信息。随着现代物理学的发展，我们对颜色产生的认识大大扩展，不同的颜色现象能够被表征；其中一些包括光学色散（例如棱镜诱导的彩虹），光谱选择性吸收（例如化学颜料和共振光子结构）和薄膜干涉（例如气泡和油膜）。结构色尤其依赖于优化其几何形状来产生颜色，而不是利用颜料或染料。这些结构着色策略吸引了相当大的科学和工业利益，因为他们独特的能力来操纵光的流动。特别是，最近提出了一种由微尺度凹界面（MCI）引入的全内反射（TIR）干涉，不同于传统的着色工艺。人们相信，将这种新的颜色产生机制整合到大规模显示器和传感器中是令人兴奋的，但实现起来却充满挑战。这个NSF项目将首先进行基础和实验相结合的研究，以阐明这种MCI的物理机制。主要的重点是探索这种新的MCI结构的明确的物理机制，将通过制造和系统的实验表征来验证。在这些新的光学界面结构的基础上，将探索用于光探测和测距（LIDAR）应用的混合可见光和红外显示技术。这种新的反射色彩策略的实现有望在信息和显示应用中产生重要的技术突破。拟议的微光学结构将促进研究和发展，对交通安全，国家安全和保持全球领先地位的光子技术产生更广泛的影响。这项研究将与布法罗大学（UB）的教育项目紧密结合。这项研究将为绿色光电器件和高级设计实现的新课程的发展提供信息。这项研究以及当前和未来的技术趋势将呈现给更广泛的受众，包括K-12教师和学生，以及公众。研究者团队开发了一种新的MCI结构，它可以实现独特的反射结构颜色，即在不同的外部光学照明条件下，它可以分别实现彩色逆反射和虹彩反射。认为这种结构显色平台不同于传统的物理过程，可以探索新的彩色显示技术和应用。虽然普遍认为这种新的反射色是由TIR在凹界面内部引入的，但对其显色机理仍缺乏完整而准确的解释。这个NSF项目将首先进行基础和实验相结合的研究，通过全面的理论建模和实验验证来阐明这种MCI的物理机制。采用射线追踪和光相干叠加相结合的建模策略来揭示MCI结构的光干涉机理。利用该组合模型系统地研究了通过控制几何和折射率参数来实现颜色的可调性。基于对新着色机制的基本理解，研究者将开发交通标志样本，以探索未来自动驾驶系统遥感/成像的智能标志。特别是，来自激光雷达系统的激光的飞行时间将被系统地表征，以揭示MCI在未来自动驾驶仪应用中的潜力。由于红外诱导的反射特性，这种类型的新结构特别适用于低光环境（例如夜间交通标志，广告牌，娱乐暗室装饰等），并且有望解决当前激光雷达系统中使用的深度学习视觉分类的强大物理世界攻击。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In everyday life, humans and machines rely on different colors to process important information. As modern physics advanced, our understanding of color generation expanded greatly, and different coloration phenomena were able to be characterized; some of which include optical dispersion (e.g. prism-induced rainbows), spectrally selective absorption (e.g. chemical pigments and resonant photonic structures), and thin-film interference (e.g. bubble and oil membranes). Structural colors in particular rely on optimizing their geometry to produce color, rather than utilize pigments or dyes. These structural coloration strategies have attracted considerable scientific and industrial interests because of their unique ability to manipulate the flow of light. In particular, a total internal reflection (TIR) interference introduced by microscale concave interfaces (MCI) was recently proposed, different from conventional coloration processes. It was believed that the incorporation of this new color creation mechanism into large scale displays and sensors is exciting but challenging to achieve. This NSF project will first perform a combined fundamental and experimental research to clarify the physical mechanism of this MCI. The major focus is to explore unambiguous physical mechanism of this new MCI structure, which will be validated through fabrication and systematic experimental characterization. Building upon these new optical interface structures, hybrid visible and infrared display technologies will be explored for light detection and ranging (LIDAR) applications. Realization of this new reflective coloration strategies is expected to yield important technological breakthroughs in information and display applications. The proposed micro-optics structure will foster the research and development with the broader impact on traffic safety, national security and sustaining the global leadership in photonics technologies. This research will be closely integrated with educational programs at University at Buffalo (UB). The research will inform development of new courses on Green Optoelectronic Devices and Senior Design Implementation. The research and current and future technology trends will be presented to a broader audience including K-12 teachers and students, and the general public.The investigator’s team developed a new MCI structure that can realize a unique reflective structural color, i.e., under different external optical illumination conditions, it can realize colorful retroreflection and iridescent reflection, respectively. It was believed that this type of structural coloration platform is different from conventional physical processes and can enable the exploration of new color display technologies and applications. Although it is generally agreed that this new reflective color is introduced by TIR inside the concave interface, a complete and accurate explanation to the coloration mechanism is still missing. This NSF project will first perform a combined fundamental and experimental research to clarify the physical mechanism of this MCI using thorough theoretical modeling and experimental validation. A combined ray-tracing and light coherent superposition modeling strategy will be developed to reveal the optical interference mechanism of the MCI structure. The color tunability by controlling the geometric and refractive index parameters will be investigated systematically using this combined modeling. Building upon the fundamental understanding of the new coloration mechanism, the investigator will develop traffic sign samples to explore smart signs for future remote sensing/imaging for autopilot systems. In particular, the time-of-flight of the laser from the LIDAR system will be characterized systematically to reveal the potential of the MCI in future autopilot applications. Due to the TIR-induced retroreflection feature, this type of new structure is especially suitable for low light environment (e.g. night-time traffic signs, advertisement boards, darkroom decoration for entertainment, etc.) and is promising to address the robust physical-world attacks on current deep learning visual classification used in LIDAR systems.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.