The miniaturization of current image sensors is primarily limited by the volume of optical elements. Using a subwavelength patterned quasi-periodic structure known as a metasurface, we can build planar optical elements based on the principle of diffraction. This platform allows us to mimic complex, asymmetric curvatures with ease and is ideal for the adaptation of freeform optics to the micron scale. The implementation of freeform optics on metasurfaces allows for extreme miniaturization of optical components. In our research we have demonstrated metasurface based optical elements such as lenses, vortex beam generators, and cubic phase plates near visible frequencies. Our fabricated lenses achieved beam spots of less than 1 μm with numerical apertures as high as ~ 0.75. We observed a transmission efficiency of 90% and focusing efficiency of 40% in the visible wavelengths. In addition, we have demonstrated a dynamic metasurface optical system called the Alvarez lens with a tunable focal length range of over 2.5 mm corresponding to a change in optical power of ~1600 diopters with 100 m of total mechanical displacement.
Alan Zhan, Shane C. Colburn, and Arka Majumdar, "Dielectric metasurface-based freeform optics," Proc. SPIE 10113, High Contrast Metastructures VI, 1011306 (Presented at SPIE OPTO: January 31, 2017; Published: 20 February 2017); https://doi.org/10.1117/12.2261227.
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