Artificial reality system having Bragg grating

1. An optical assembly comprising:

a waveguide; and

a Bragg grating configured to couple light into or out of the waveguide, wherein the Bragg grating comprises a plurality of layer pairs, wherein at least one layer pair comprises a first material having a first refractive index and a second layer having a second refractive index, wherein properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency and a substantially the same diffraction angle for light of at least two colors, wherein the properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency for light of three colors, wherein each layer pair of the plurality of layer pairs comprises the first material and the second material, and wherein a thickness of each layer pair of the plurality of layer pairs is substantially the same.

2. The optical assembly of claim 1 , wherein the Bragg grating comprises a reflective Bragg grating.

3. The optical assembly of claim 1 , wherein the Bragg grating comprises a transmissive Bragg grating.

4. The optical assembly of claim 1 , wherein the properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency for first light having a first wavelength and second light having a second wavelength, wherein the first wavelength is different from the second wavelength by at least about 50 nm.

5. The optical assembly of claim 1 , wherein the light of three colors comprises light having a wavelength of between about 430 nm and about 450 nm, light having a wavelength of between about 525 nm and about 550 nm, and light having a wavelength of between about 650 nm and about 675 nm.

6. The optical assembly of claim 1 , wherein the Bragg grating exhibits substantially similar diffractive efficiency for light of at least two colors, for a diffraction order of the first light that is different than a diffraction order of the second light.

7. The optical assembly of claim 1 , wherein the properties comprise at least one of the first refractive index, the second refractive index, an average of the first refractive index and the second refractive index, or a thickness of each layer pair of the plurality of layer pairs.

8. The optical assembly of claim 1 , wherein the plurality of layer pairs defines a major plane, wherein the waveguide defines a major plane, and wherein the major plane of the plurality of layer pairs is oriented at a non-parallel and non-perpendicular angle to the major plane of the waveguide.

9. The optical assembly of claim 1 , wherein the Bragg grating is an input coupling grating.

10. The optical assembly of claim 1 , wherein the Bragg grating is an output coupling grating.

11. The optical assembly of claim 1 , wherein the Bragg grating is an input coupling grating, further comprising an output coupling grating, wherein the output coupling grating comprises:

a second plurality of layer pairs, wherein a second layer pair of the second plurality of layer pairs comprises a third material having a third refractive index and a fourth layer having a fourth refractive index, and wherein properties of the output coupling grating are selected so that the output coupling grating exhibits a substantially similar diffractive efficiency and a substantially the same diffraction angle for light of at least two colors.

12. The optical assembly of claim 1 , further comprising a projector configured to direct light into the waveguide via the Bragg grating.

13. A head mounted display comprising:

a projector; and

an optical assembly comprising:

a waveguide; and

a Bragg grating configured to couple light into or out of the waveguide, wherein the Bragg grating comprises a plurality of layer pairs, wherein a layer pair comprises a first material having a first refractive index and a second layer having a second refractive index, wherein properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency and a substantially the same diffraction angle for light of at least two colors, wherein the properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency for light of three colors, wherein each layer pair of the plurality of layer pairs comprises the first material and the second material, and wherein a thickness of each layer pair of the plurality of layer pairs is substantially the same, and wherein the projector is configured to direct light into the waveguide.

14. The head mounted display of claim 13 , wherein the properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency for light having a wavelength of between about 430 nm and about 450 nm, light having a wavelength of between about 525 nm and about 550 nm, and light having a wavelength of between about 650 nm and about 675 nm.

15. The head mounted display of claim 13 , wherein the properties comprise at least one of the first refractive index, the second refractive index, an average of the first refractive index and the second refractive index, or a thickness of each layer pair of the plurality of layer pairs.

16. The head mounted display of claim 13 , wherein the plurality of layer pairs defines a major plane, wherein the waveguide defines a major plane, and wherein the major plane of the layer pair is oriented at a non-parallel and non-perpendicular angle to the major plane of the waveguide.

17. The head mounted display of claim 13 , wherein the Bragg grating is an input coupling grating, further comprising an output coupling grating, wherein the output coupling grating comprises:

a second plurality of layer pairs, wherein a second layer pair of the second plurality of layer pairs comprises a third material having a third refractive index and a fourth layer having a fourth refractive index, and wherein properties of the output coupling grating are selected so that the output coupling grating exhibits a substantially similar diffractive efficiency for light of at least two colors.

18. A method comprising:

determining properties of a Bragg grating so that the Bragg grating exhibits a substantially similar diffractive efficiency and a substantially the same diffraction angle for light of at least two colors, wherein the properties of the Bragg grating are determined so that the Bragg grating exhibits a substantially similar diffractive efficiency for light of three colors, wherein the Bragg grating is configured to couple light into or out of a waveguide, wherein the Bragg grating comprises a plurality of layer pairs, wherein at least one layer pair comprises a first material having a first refractive index and a second layer having a second refractive index, wherein each layer pair of the plurality of layer pairs comprises the first material and the second material, and wherein a thickness of each layer pair of the plurality of layer pairs is substantially the same; and

assembling the Bragg grating with a waveguide.