Antireflection coatings for metasurfaces
Antireflection coatings for metasurfaces are described herein. In some embodiments, the metasurface may include a substrate, a plurality of nanostructures thereon, and an antireflection coating disposed over the nanostructures. The antireflection coating may be a transparent polymer, for example a photoresist layer, and may have a refractive index lower than the refractive index of the nanostructures and higher than the refractive index of the overlying medium (e.g., air). Advantageously, the antireflection coatings may reduce or eliminate ghost images in an augmented reality display in which the metasurface is incorporated.
1. A display system comprising:
a waveguide assembly for receiving and outputting image light having image content, the waveguide assembly comprising a stack of waveguides, each waveguide comprising:
an optically transmissive substrate;
an incoupling optical element comprising a metasurface overlying the substrate, the metasurface comprising a plurality of nanostructures 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 comprising a layer of an optically transparent material conformally disposed over the nanostructures of the metasurface, wherein the optically transparent material has a refractive index less than a refractive index of the nanostructures, wherein the layer of the optically transparent material follows contours of the nanostructures without completely filling volumes separating each of the nanostructures such that a top surface of each waveguide is non-planar, and 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; and
an image injection device configured to direct the image light into each waveguide of the waveguide assembly via the metasurface of each incoupling optical element,
wherein the antireflection coating has a thickness configured to provide destructive interference between image light reflecting off a top surface of the antireflection coating and image light reflecting off a bottom surface of the antireflection coating,
wherein, as seen in the top-down view, incoupling optical elements of different ones of the waveguides are laterally offset from one another.
2. The display system of claim 1 , wherein the metasurface comprises a diffraction grating.
3. The display system of claim 2 , wherein the metasurface comprises an asymmetric diffraction grating.
4. The display system of claim 1 , wherein the metasurface comprises a Pancharatnam-Berry phase optical element (PBOE).
5. The display system of claim 1 , wherein the metasurface comprises multi-tier nanostructures.
6. The display system of claim 1 , wherein the optically transparent material comprises a polymer.
7. The display system of claim 6 , wherein the optically transparent material comprises photoresist.
8. The display system of claim 1 , wherein the optically transparent material has a refractive index from about 1.2 to about 2.
9. The display system of claim 1 , wherein a distance from a topmost surface of the nanostructures to a topmost surface of the antireflection coating is from about 10 nm to about 1 micron.
10. The display system of claim 9 , wherein a distance from a topmost surface of the nanostructures to a topmost surface of the antireflection coating is from about 30 nm to about 250 nm.