Diffraction grating with a variable refractive index using ion implantation

1. A method comprising:

receiving a substrate having a material disposed on the substrate;

exposing the material to ion implantation, wherein:

the ion implantation is non-uniform, and

the ion implantation forms a varying refractive index in different regions of the material; and

etching or imprinting the material to form structures in the material to create an optical device that includes a plurality of ridges and a plurality of grooves,

wherein a first ridge of the plurality of ridges in a first region of the optical device and a second ridge of the plurality of ridges in a second region of the optical device have different refractive indices.

2. The method of claim 1 , wherein the optical device is a grating.

3. The method of claim 1 , wherein exposing the material to ion implantation is performed before etching or imprinting the material.

4. The method of claim 1 , wherein etching or imprinting the material is performed before exposing the material to ion implantation.

5. The method of claim 1 , wherein the non-uniform ion implantation follows a smooth function.

6. The method of claim 5 , wherein the smooth function is continuously increasing or decreasing to form a gradient.

7. The method of claim 1 , further comprising applying an overcoat to the structures in the material.

8. The method of claim 7 , wherein the overcoat is characterized by a varying refractive index.

9. The method of claim 8 , wherein the overcoat has a refractive index gradient in an opposite direction as a refractive index gradient of the material.

10. The method of claim 7 , wherein the ion implantation varies in three dimensions.

11. An optical device comprising:

a substrate;

a material disposed on the substrate;

a plurality of ridges and a plurality of grooves formed in the material; and

a varying refractive index in the material created by ion implantation,

wherein a first ridge of the plurality of ridges in a first region of the optical device and a second ridge of the plurality of ridges in a second region of the optical device have different refractive indices.

12. The optical device of claim 11 , wherein a maximum refractive index of the material minus a minimum refractive index of the material is equal to or greater than 0.5 and/or equal to or less than 1.0.

13. The optical device of claim 11 , wherein the plurality of ridges and the plurality of grooves are part of a grating.

14. The optical device of claim 11 , further comprising an overcoat on the material.

15. The optical device of claim 14 , wherein:

the overcoat has a first direction of increasing refractive index;

the material has a second direction of increasing refractive index; and

the first direction is opposite the second direction.

16. The optical device of claim 11 , wherein the material has an index of refraction that varies in two dimensions.

17. The optical device of claim 11 , wherein the material has an index of refraction that varies in three dimensions.

18. A system comprising:

an optical source for an augmented-reality display;

a waveguide;

an input 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 output coupler comprising:

a substrate;

a material disposed on the substrate, wherein the material has a varying refractive index created by ion implantation; and

a plurality of ridges and a plurality of grooves formed in the material, wherein a first ridge of the plurality of ridges in a first region of the output coupler and a second ridge of the plurality of ridges in a second region of the output coupler have different refractive indices.

19. The system as recited in claim 18 , wherein the plurality of ridges and the plurality of grooves are part of a grating.

20. The system as recited in claim 18 , wherein the varying refractive index varies in two dimensions.