Pixel-level 3D nanophotonic structures for multi-modality image sensors

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Consumer cameras typically capture a two-dimensional (2D) image of a scene, or record a movie. Specialized optical imaging devices can also capture additional information such as the polarization of the light or even a three-dimensional (3D) image of objects in a scene. This extra information is helpful in a wide range of applications, such as in sensors for self-driving cars, for identifying different types of cells and tissues in biomedical imaging, or for keeping a richer historical record than is offered by a simple 2D image. While devices already exist that can record 3D and polarization information, they are typically much larger and bulkier than a standard cell phone camera. In this proposal, approaches to significantly reduce the size and weight of such devices will be studied. This involves not only new optical designs, but also new approaches to the processes of designing and constructing 3D optical devices out of building blocks that are much smaller than the wavelength of light. In addition to enabling particularly small devices, such small building blocks interact with light based on different physical principles than those that apply to large optics. The research will be incorporated into a course at the University of Arizona, and undergraduate students and high school teachers will also partake in the research. Native American students and their educators, who are often disadvantaged in terms of their exposure to science and engineering, will be a major demographic target.Technical: The goal of this proposal is to use three-dimensional (3D) nanophotonics to enable imaging devices with angle, wavelength, and polarization sensitivity in significantly more compact and lighter weight systems than is currently possible. In existing angle-sensitive 3D light-field imaging approaches, the diffraction limit imposes a minimum useful pixel size. Although not previously demonstrated, nanophotonics offers the potential to significantly reduce the minimum pixel size, which can in turn allow for reductions in the size of any external optics. Novel high-speed optimization-based algorithms will be used to design 3D nanophotonic structures composed of metallic and/or dielectric nanoparticle building blocks. On individual pixels, different structures will selectively receive incoming light with specific incidence angles, polarizations, and/or wavelengths. Photonic nanostructures that cover entire blocks of pixels will also be designed to sort incoming light based on incidence angle, wavelength, and polarization. The nanostructures will be fabricated using an optical tweezer-based rapid prototyping approach. Colloidal nanoparticle building blocks will be chemically functionalized to bind when brought in contact with each other using the optical tweezers. After the nanophotonic structures have been fabricated on the image sensors, they will be tested under well-controlled lighting conditions using monochromatic laser sources directed at particular angles with particular polarizations, as well as in everyday broad-band, wide-field scenes. A compact and light-weight multimodality imaging device will be created. Its performance will be compared to existing light field imagers, hyperspectral imagers, and polarimeters.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.