  Wide-angle optical functionality is crucial for implementation of advanced
imaging and image projection devices. Conventionally, wide-angle operation is
attained by complicated assembly of multiple optical elements. Recent advances
in nanophotonics have led to metasurface lenses or metalenses, a new class of
ultra-thin planar lenses utilizing subwavelength nanoantennas to gain full
control of the phase, amplitude, and/or polarization of light. Here we present
a novel metalens design capable of performing diffraction-limited focusing and
imaging over an unprecedented > 170 degree angular field of view (FOV). The
lens is monolithically integrated on a one-piece flat substrate and involves
only a single layer of metasurface that corrects third-order Seidel aberrations
including coma, astigmatism, and field curvature. The metalens further features
a planar focal plane, which enables considerably simplified system
architectures for applications in imaging and projection. We fabricated the
metalens using Huygens meta-atoms operating at 5.2 micron wavelength and
experimentally demonstrated aberration-free focusing and imaging over the
entire FOV. The design concept is generic and can be readily adapted to
different meta-atom geometries and wavelength ranges to meet diverse
application demands.
