An optical system comprising: an optical element comprising a metasurface (1418, 1518, 1618), the metasurface (1418, 1518, 1618) comprising a plurality of nanostructures (1420, 1520, 1620) forming repeating unit cells, wherein, as seen in a top-down view, each unit cell comprises: a plurality of first nanostructures having first lengths and first widths, wherein the first lengths are elongated in a first direction, and wherein the first widths differ from one another; and a plurality of second nanostructures having second lengths and second widths, wherein the second lengths are elongated in a second direction, and wherein the second widths differ from one another, wherein the second direction crosses the first direction; and an antireflection coating for the optical element comprising the metasurface, the antireflection coating comprising: a layer of an optically transparent material having a refractive index greater than 1 and less than a refractive index of a material comprising the metasurface, wherein the layer of optically transparent material is conformally disposed over the nanostructures (1420, 1520, 1620) of the metasurface, and the layer of optically transparent material follows contours of the nanostructures (1420, 1520, 1620) without completely filling volumes separating each of the nanostructures (1420, 1520, 1620), wherein the unfilled volumes that separate the first nanostructures from the second nanostructures are of a different volume from the unfilled volumes that separate the first nanostructures or that separate the second nanostructures. a plurality of first nanostructures having first lengths and first widths, wherein the first lengths are elongated in a first direction, and wherein the first widths differ from one another; and a plurality of second nanostructures having second lengths and second widths, wherein the second lengths are elongated in a second direction, and wherein the second widths differ from one another, wherein the second direction crosses the first direction; and an antireflection coating for the optical element comprising the metasurface, the antireflection coating comprising: a layer of an optically transparent material having a refractive index greater than 1 and less than a refractive index of a material comprising the metasurface, wherein the layer of optically transparent material is conformally disposed over the nanostructures (1420, 1520, 1620) of the metasurface, and the layer of optically transparent material follows contours of the nanostructures (1420, 1520, 1620) without completely filling volumes separating each of the nanostructures (1420, 1520, 1620), wherein the unfilled volumes that separate the first nanostructures from the second nanostructures are of a different volume from the unfilled volumes that separate the first nanostructures or that separate the second nanostructures. a layer of an optically transparent material having a refractive index greater than 1 and less than a refractive index of a material comprising the metasurface, wherein the layer of optically transparent material is conformally disposed over the nanostructures (1420, 1520, 1620) of the metasurface, and the layer of optically transparent material follows contours of the nanostructures (1420, 1520, 1620) without completely filling volumes separating each of the nanostructures (1420, 1520, 1620), wherein the unfilled volumes that separate the first nanostructures from the second nanostructures are of a different volume from the unfilled volumes that separate the first nanostructures or that separate the second nanostructures.