Diffraction grating with a variable refractive index formed using an energy gradient
An optical device with a variable index of refraction is formed by exposing a film to an energy gradient. The optical device has angular selectivity. The optical device can be used as an output coupler for a waveguide used in a virtual-reality and/or augmented-reality apparatus.
1. A method of creating an optical device with a variable index of refraction for angular selectivity, the method comprising:
depositing a film on a substrate, wherein the film includes a block copolymer;
exposing the film to ultra-violet (UV) light using a gray-tone mask;
developing the film using a solvent to create a variable refractive index in the film; and
patterning the film to create an optical structure after developing the film.
2. The method of claim 1 , wherein depositing the film comprises:
spin-coating the film on the substrate; and
annealing the film to produce self-assembled block copolymer domains.
3. The method of claim 1 , wherein the film includes poly(styrene-block-methyl methacrylate) (PS-b-PMMA).
4. The method of claim 3 , wherein exposing the film to UV light decomposes poly(methyl methacrylate) (PMMA) blocks in the film.
5. The method of claim 3 , wherein developing the film using the solvent develops more PS-b-PMMA domains in areas of the film exposed to more UV light.
6. The method of claim 1 , wherein exposing the film to the UV light comprises exposing the film to UV light having a dose between 0.1 and 100 J/cm 2 .
7. The method of claim 1 , wherein the solvent includes acetic acid or isopropanol.
8. The method of claim 1 , wherein patterning the film comprises:
applying a photoresist to the film;
selectively exposing the photoresist;
partially removing the photoresist based on selectively exposing the photoresist; and
etching the film to create the optical structure.
9. The method of claim 1 , wherein the optical structure includes an optical grating.