Angle-Sensitive Metasurfaces for Lens-Free Compound-Eye Cameras

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Title: Metasurfaces for Lens-Free Compound-Eye Cameras Non-Technical Description:This project aims at developing a new camera technology featuring extreme size miniaturization, inspired by the compound-eye vision modality that is commonly found in nature in small invertebrates such as insects and crustaceans. Compound eyes typically consist of a curved array of many imaging elements (including lenses and photoreceptors), each oriented so as to detect light incident along a different direction. The full image of the object being visualized is then reconstructed from the combined inputs of all such elements. The optoelectronic implementation of this vision modality is generally complicated by its curved architecture, since standard optoelectronic devices are based on planar substrates. The compound-eye vision modality represents the optimally adapted solution to provide wide-angle field of view with negligible distortion within the smallest possible package. Furthermore, compound eyes can create focused images of objects at arbitrary distances without the need for any focal-length adjustment, and thus offer nearly infinite depth of field and extremely high acuity to motion. The proposed cameras could therefore provide an enabling technology for a wide range of imaging applications where small size, large field of view, and high temporal resolution are of particular importance. Specific examples include machine vision (e.g., for obstacle avoidance and autonomous navigation), surveillance, and endoscopic medical imaging. The proposed activities will also promote education through the training of graduate and undergraduate students in a wide range of topics within nanophotonics, optoelectronics, and image processing. Related curriculum development efforts will impact students in other disciplines.Technical Description:The proposed research will leverage recent advances in nanophotonics and metamaterials to develop a planar lens-free compound-eye camera consisting of a planar array of imaging pixels. The angle selectivity of each pixel is provided by specially designed arrays of metallic nanoparticles (optical metasurfaces) patterned on the surface of each photodetector. The key innovation of the proposed research is the development of metasurfaces that can selectively transmit into their substrate only light incident along a single geometrically tunable direction (within a small range). Light incident along any other direction will be reflected. With this arrangement, lens-free compound-eye cameras can be implemented using existing CMOS or CCD image-sensor arrays. Each pixel will be coated with a different metasurface designed to allow for the detection of light from a different direction. The proposed angle-sensitive photodetectors will be designed via full-wave numerical simulations, fabricated on silicon substrates, and characterized through angle-resolved photocurrent measurements. Arrays of these devices will then be developed for a proof-of-concept demonstration of their imaging capabilities. Advanced computational imaging algorithms will be employed to optimize the image reconstruction from the combined signals of the individual sensors. In addition to the potential technological impact of the proposed cameras, this research will also advance the science and technology of optical metasurfaces through the exploration of novel designs and applications, and will create new research opportunities in the emerging field of computational imaging.