On-chip Metasurface Polarimeter Array for full Stokes Polarization Imaging

可以毫不夸张地说，成像传感器的发展已经对我们的生活产生了深远的影响，从智能手机摄像头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，光的特征还在于其偏振状态，该偏振状态可以受到物体的发射、散射或透射的影响。检测光偏振已被证明是必不可少的各种应用，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已经不断提高，但是全偏振成像的能力还没有在单片集成的传感器上实现。本项目旨在研制一种芯片集成的成像传感器阵列，或者说偏振成像阵列，不仅可以检测光的强度和颜色，而且可以检测光的完整偏振状态。这种紧凑的系统可以进一步结合到用于临床诊断的许多便携式系统、真实的实时环境监测网络或用于现场学习和研究的智能手机偏振计中。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，通过外联和夏季充实计划向K-12学生展示研究，促进科学和工程（特别是代表性不足的群体）的参与。本计画的科学目标是探讨整合人工设计的平面光学元件以实现片上偏振影像感测器阵列的可行性。传统的偏振传感和成像系统非常庞大，需要移动部件，这使得它很难最小化。此外，由于场景中的运动，这些系统还遭受降低的帧速率和提取的偏振信息的不准确性。单片集成偏振成像系统已经得到了广泛的研究，然而，这些偏振成像系统具有各种限制，如大像素尺寸，成像质量下降，缺乏与硅技术的兼容性和精度差。所提出的技术充分利用了纳米光子学和纳米纤维的前沿发展，为片上偏振传感和成像应用提供了显着改进的解决方案。所有的检测元件都是基于直接集成到硅光电探测器上的亚波长厚度结构来实现的。所有偏振探测元件在可见光范围内的偏振消光比和透射效率分别为30%和40%。在这个项目中开发的制造工艺是兼容的CMOS技术，以及容忍的横向对准误差高达几十纳米。 所有这些检测元件都可以制作成亚微米尺寸，同时仍然保持相当好的性能，对于大规模廉价的CMOS生产是可行的。该项目将实现高灵敏度和高精度的片上偏振成像传感器阵列。此外，这项研究将使人们能够深入了解在芯片上集成超颖表面平面光学器件所涉及的基本器件物理和制造技术，这对于实现超该奖项反映了NSF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进行评估，被认为值得支持的搜索.

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.