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;
creating a grating in the film; and
exposing the grating to an energy gradient, as part of a process to form a refractive-index gradient in the grating corresponding to the energy gradient.
2. The method of claim 1 , further comprising exposing the grating to a compound as part of the process to form the refractive-index gradient.
3. The method of claim 2 , wherein the compound has a higher refractive index than the film had before the film is exposed to the compound.
4. The method of claim 1 , further comprising forming an overcoat on the grating.
5. The method of claim 1 , wherein:
the film is an imprint resist; and
creating the grating in the film comprises imprinting the film with a template to create the grating.
6. The method of claim 1 , wherein:
creating the grating comprises using photolithography to remove at least a portion of the film to form the grating.
7. The method of claim 1 , wherein the film comprises a reactive monomer.
8. The method of claim 1 , wherein the film comprises a photoacid generator.
9. The method of claim 1 , wherein the energy gradient is a thermal gradient.
10. The method of claim 1 , wherein the energy gradient is a light gradient.
11. The method of claim 10 , further comprising using a gray-tone mask and UV light to form the light gradient.
12. The method of claim 1 , further comprising:
exposing the film to flood UV light; and/or
depositing a moiety that has a lower refractive index than the film.
13. The method of claim 1 , further comprising incorporating a depolymerizable oligomer or polymer into the film.
14. The method of claim 1 , wherein:
the film comprises a metal oxide sol-gel precursor; and
the energy gradient is a thermal gradient produced by a hot plate.
15. The method of claim 1 , wherein:
the method further comprises integrating the grating into a device used in a virtual reality and/or an augmented-reality system; and
the virtual reality and/or the augmented-reality system comprises:
an optical source,
a waveguide,
an optical coupler configured to couple light from the optical source into the waveguide, and
an output coupler configured to couple light out of the waveguide;
the waveguide is a planar waveguide; and
the grating is part of the output coupler.