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 (NW1); and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width (NW2) larger than the first width (NW1), 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 disposed on a second level directly on the first and second nanobeams , 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 (NW1); and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width (NW2) larger than the first width (NW1), 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 disposed on a second level directly on the first and second nanobeams , 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 (NW1); and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width (NW2) larger than the first width (NW1), 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 (NW1); and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap (Gap), the second nanobeam having a second width (NW2) larger than the first width (NW1), 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 disposed on a second level directly on the first and second nanobeams , 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. <EOS>