Holographic meta-lenses for point-spread function engineering

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The point-spread function of an optical imaging system (that is, its response to a point light source) can be designed to achieve imaging modalities unattainable in conventional imaging systems based on refractive lenses. Conventionally, point-spread functions have been shaped by using apertures and optical phase masks, leading to functions such as improved resolution in microscopy, extended depth of field over which an object can stay in focus, and three-dimensional tracking of moving objects. The proposed program will explore a new paradigm of engineering point-spread functions by using flat “meta-lenses”, which are nano-structured thin films that are able to locally change the amplitude, phase, and polarization of light due to strong light-mater interactions. Powerful new imaging modalities will be invented by jointly designing meta-lenses and image processing algorithm as an integrated imaging system. The flat form factor of meta-lenses allows them to be fabricated with mature planar fabrication technologies developed by the integrated circuit industry and benefit from economies of scale. Optical imaging components and systems demonstrated in this program may have important implications for a variety of applications in machine vision, biomedical imaging, and holographic technology. The project will train graduate and undergraduate students to carry out innovative and in-depth research at the intersection between nanotechnology, materials sciences, and photonics. The project, with the support of Columbia Engineering School’s Outreach Program, will broaden participation in science and engineering by providing summer research opportunities to undergraduate students from diverse backgrounds. In addition, the project will promote a collaborative effort between scientists and artists in producing engaging and educational illustrations of scientific discoveries that are more accessible to the general public.The project will explore a new paradigm of engineering point-spread functions by holographic meta-lenses: single or multi-layered nano-structured thin films that can provide complete, independent, and sub-wavelength control of the phase, amplitude, and polarization of optical near-field for multivariate manipulation of optical far-field over a large wavelength and angular range. The holographic meta-lenses will be composed of a library of complex and sub-wavelength pixels or “meta-atoms”. The project will investigate: the structural dispersion engineering to create meta-atoms that provide the maximum allowable phase dispersion for controlling light over a continuous wavelength of a broad spectrum; the structurally birefringent and multi-component meta-atoms to provide complete and independent control of optical phase, amplitude, and polarization; and the multi-layered metasurface systems for wide-angle optical control. The research work will study fundamental limitations of optical control to establish the degree to which one optical parameter (phase, amplitude, or polarization of light at a certain wavelength) can be controlled by a unit volume of a structured material and to explore the design rules for creating a structured material with minimal volume to control multiple optical parameters independently and completely. To illustrate the promise of the new paradigm of point-spread function engineering, the project will demonstrate a few examples of holographic meta-lenses showing functions that are beyond the capabilities of conventional imaging systems based on refractive components and single-layer, phase-only metasurfaces.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.