An optical system suitable for use in a display comprising: an optically transmissive substrate having a surface; a multilevel metasurface on the surface, the metasurface comprising, as seen in a top-down view: a grating comprising a plurality of unit cells, each unit cell comprising: first level nanobeams comprising: a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width larger than the first width, wherein heights (hnm) of the first and the second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less, second level nanobeams (2030a, 2030b) disposed on a second level directly on the first and second nanobeams (2020a, 2020b), the second level nanobeams formed of an optically transmissive material; and masses of the optically transmissive material, the masses located between neighboring first level nanobeams and having height of 10 nm to 600 nm, wherein the optically transmissive material has a refractive index higher than 1.6. an optically transmissive substrate having a surface; a multilevel metasurface on the surface, the metasurface comprising, as seen in a top-down view: a grating comprising a plurality of unit cells, each unit cell comprising: first level nanobeams comprising: a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width larger than the first width, wherein heights (hnm) of the first and the second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less, second level nanobeams (2030a, 2030b) disposed on a second level directly on the first and second nanobeams (2020a, 2020b), the second level nanobeams formed of an optically transmissive material; and masses of the optically transmissive material, the masses located between neighboring first level nanobeams and having height of 10 nm to 600 nm, wherein the optically transmissive material has a refractive index higher than 1.6. first level nanobeams comprising: a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width larger than the first width, wherein heights (hnm) of the first and the second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less, a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width larger than the first width, wherein heights (hnm) of the first and the second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less, 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 μm where the refractive index is 3.3 or less, second level nanobeams (2030a, 2030b) disposed on a second level directly on the first and second nanobeams (2020a, 2020b), the second level nanobeams formed of an optically transmissive material; and masses of the optically transmissive material, the masses located between neighboring first level nanobeams and having height of 10 nm to 600 nm, wherein the optically transmissive material has a refractive index higher than 1.6.