On-chip Metasurface Polarimeter Array for full Stokes Polarization Imaging

毫不夸张地说，成像传感器的发展已经对我们的生活产生了深远的影响，从智能手机的相机到最先进的医疗成像设备，甚至到太空探索。除了光的强度和颜色外，光的特点还在于它的偏振状态，这种偏振状态会受到物体的发射、散射或透射的影响。检测光偏振已被证明是各种应用的必要条件，如生物医学诊断，遥感，目标检测和天文学。然而，尽管图像传感器的灵敏度、速度、像素密度和颜色范围不断提高，但在单片集成传感器上还没有实现全偏振成像的能力。本项目是开发一种芯片集成成像传感器阵列，即偏振成像阵列，不仅可以检测光的强度和颜色，还可以检测光的完整偏振状态。这种紧凑的系统可以进一步集成到许多便携式系统中，用于临床诊断，实时环境监测网络，或用于实地研究和研究的智能手机偏振仪。通过整合研究和教育，该项目旨在激励和培养纳米光子学和纳米技术领域的下一代科学家和工程师，以应对健康、安全、环境问题和空间探索方面的重大挑战。特别是，该提案旨在通过让本科生参与研究，向K-12学生展示研究成果和夏季充实计划，促进科学和工程（特别是代表性不足的群体）的参与。本课题的科学目标是研究集成人工工程平面光学器件实现片上偏振成像传感器阵列的可行性。传统的偏振传感和成像系统非常笨重，需要移动部件，这使得最小化变得困难。此外，由于场景中的运动，这些系统还存在帧率降低和极化信息提取不准确的问题。单片集成偏振成像系统已经得到了广泛的研究；然而，这些偏振成像系统存在各种局限性，例如像素尺寸大，成像质量下降，与硅技术缺乏兼容性以及精度差。所提出的技术充分利用了纳米光子学和纳米制造的前沿发展，为片上极化传感和成像应用提供了显著改进的解决方案。所有的探测元件都是基于直接集成在硅光电探测器上的亚波长厚结构实现的。在可见光范围内，所有偏振探测元件的偏振消光比和透射效率分别为30%和40%。本项目开发的制造工艺与CMOS技术兼容，并且可以很好地容忍几十纳米的横向对准误差。所有这些检测元件都可以制作到亚微米尺寸，同时仍然保持相当好的性能，适用于大规模廉价的CMOS生产。该项目将实现具有高灵敏度和精度的片上偏振成像传感器阵列。此外，该研究将使深入了解集成超表面平面光学片的基本器件物理和制造技术，这对于实现具有其他独特性能和前所未有功能的超紧凑光学系统至关重要。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。

It is no exaggeration to say that the development of imaging sensors has made profound impact on our life, from a smartphone camera to the most advanced medical imaging equipment, and even to space exploration. Besides its intensity and color, light is also characterized by its polarization state that can be affected by emission, scattering or transmission of an object. Detecting light polarization has been proven to be essential for various applications such as biomedical diagnostics, remote sensing, target detection and astronomy. Yet, despite the fact that the sensitivity, speed, pixel density and color range of image sensors have been continuously improved, the capability of full-polarization imaging, hasn't been realized on monolithically integrated sensors. This project is to develop a chip-integrated imaging sensor array, or in another word, polarimetric imaging array, to detect not only light intensity and color but also the complete polarization state of light. Such a compact system can be further incorporated into many portable systems for clinic diagnostics, real time environmental monitoring network, or a smartphone polarimeter for field study and research. By integrating research and education, the project is aimed to inspire and cultivate the next-generation of scientists and engineers in nanophotonics and nanotechnology to address grand challenges in health, security, environmental issues and space exploration. In particular, the proposal aims to promote participation in science and engineering (esp. under-represented groups) by engaging undergraduate students in research, showcasing research to K-12 students through outreach and a summer enrichment program. The scientific objective of this project is to investigate the feasibility of integrating artificially engineered planar optics to realize on-chip polarimetric imaging sensor array. Conventional polarimetric sensing and imaging systems are very bulky and require moving parts, which makes it difficult for minimization. Moreover, these systems also suffer from reduced frame rate and inaccuracy of extracted polarization information due to motion in the scene. Monolithic integrated polarimetric imaging systems have been extensively studied; however, these polarimetric imaging systems have various limitations, such as large pixel size, degradation in imaging quality, lack of compatibility with silicon technology and poor accuracy. The proposed technology fully exploits the cutting-edge development in nanophotonics and nanofabrication to provide significantly improved solutions for on-chip polarimetric sensing and imaging applications. All the detection elements are realized based on subwavelength-thick structures directly integrated onto silicon photodetectors. The polarization extinction ratios and transmission efficiency are 30 and 40% in the visible range for all polarization detection elements, respectively. The fabrication process developed in this project is compatible with CMOS technology, and well tolerates a lateral alignment error as large as tens of nanometers. All these detection elements can be made down to submicrometer size while still maintaining reasonably good performance, feasible for large-scale inexpensive CMOS production. The project will lead to the realization of on-chip polarimetric imaging sensor arrays with high sensitivity and accuracy. Moreover, the research will enable an in-depth understanding of the fundamental device physics and fabrication techniques involved in integrating metasurface flat optics on chip, which is essential for realizing ultra-compact optical system with other unique properties and unprecedented functionalities.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.