Metasurfaces with asymmetric gratings for redirecting light and methods for fabricating

A method for forming a multi-level metasurface, the method comprising:

• providing an optically transmissive substrate;
• providing an optically transmissive layer over the substrate;
• and
• patterning the optically transmissive layer to define a plurality of unit cells on a lower level of the metasurface, each unit cell comprising, as seen in a top-down view:
• a laterally-elongated first nanobeam having a first width;
• and
• a laterally-elongated second nanobeam spaced apart from the first nanobeam, the second nanobeam having a second width larger than the first width,
• wherein heights of the first and the second nanobeams are in a range between 10 nm to 450 nm, and
• forming an upper level of the metasurface by depositing a layer of material on a top of each of the first and the second nanobeams, wherein the material of the layer of material defines a gap between the first and the second nanobeams, wherein material forming the layer of material is different from material forming either of the first or the second nanobeams.

An optical system comprising:

• an optically transmissive substrate comprising a multi-level metasurface comprising a lower level and an upper level, the lower-level comprising:
• a plurality of unit cells, each unit cell comprising, as seen in a top-down cross-sectional view:
• a laterally-elongated first nanobeam having a first width;
• and
• a laterally-elongated second nanobeam spaced apart from the first nanobeam, the second nanobeam having a second width larger than the first width,
• wherein a pitch of the unit cells is 10 nm to 1 μm,
• wherein the upper-level comprises a layer of material on a top of each of the first and the second nanobeams, wherein material forming the layer of material is different from material forming either of the first or the second nanobeams.

A method for forming a multi-level metasurface, the method comprising:

• providing an optically transmissive substrate;
• providing an optically transmissive layer over the substrate;
• patterning the optically transmissive layer to define a grating comprising a plurality of unit cells on a lower level of the metasurface, each unit cell comprising, as seen in a top-down view:
• a laterally-elongated first nanobeam having a first width;
• and
• a laterally-elongated second nanobeam spaced apart from the first nanobeam, the second nanobeam having a second width larger than the first width,
• wherein a pitch of the unit cells is 10 nm to 1 μm, and
• forming an upper level of the metasurface by depositing a layer of material on a top of each of the first and the second nanobeams, wherein the material of the layer of material defines a gap between the first and the second nanobeams, wherein material forming the layer of material is different from material forming either of the first or the second nanobeams.