Flat spectral response gratings using high index materials

1. A head-mounted display device comprising:

a plurality of optical elements in optical communication, the plurality of optical elements being configured, during operation of the head-mounted display device, to project an image in a field of view of a user wearing the head-mounted display device,

wherein a first optical element of the plurality of optical elements is configured to receive light from a second optical element of the plurality of optical elements;

wherein the first optical element defines a grating at along a periphery of the first optical element, the grating comprising:

a plurality of protrusions extending from a base portion of the first optical element, the protrusions comprising a first material having a first optical dispersion profile for visible wavelengths of light, and each of the protrusions comprising a first surface opposite the base portion of the first optical element; and

a second material disposed between at least some of the plurality of protrusions along the base portion of the first optical element, the second material having a second optical dispersion profile for visible wavelengths of light,

wherein there is an absence of the second material on the first surfaces of the protrusions.

2. The head-mounted display device of claim 1 , wherein the second material is titanium dioxide (TiO 2 ).

3. The head-mounted display device of claim 2 , wherein the first material is silicon carbide (SiC).

4. The head-mounted display device of claim 2 , wherein the first material is lithium niobate (LiNbO 3 ).

5. The head-mounted display device of claim 1 , wherein the base portion of the first optical element comprises the first material.

6. The head-mounted display device of claim 1 , wherein the base portion of the first optical element is composed of the same material as the plurality of protrusions.

7. The head-mounted display device of claim 1 , wherein the base portion of the first optical element is integrally formed with the plurality of protrusions.

8. The head-mounted display device of claim 1 , wherein each protrusion has a substantially rectangular cross-section.

9. The head-mounted display device of claim 1 , wherein each protrusion extends a first height above a surface of the base portion of the first optical element, and

wherein the second material extends a second height above the surface of the base portion of the first optical element, the second height being different from the first height.

10. The head-mounted display device of claim 9 , wherein the first height is greater than the second height.

11. The head-mounted display device of claim 10 , wherein the first height is approximately 90 nm.

12. The head-mounted display device of claim 11 , wherein the second height is approximately 80 nm.

13. The head-mounted display device of claim 1 , wherein the grating repeats according to a period along a length of the base portion of the first optical element.

14. The head-mounted display device of claim 13 , wherein the period corresponds to a length of approximately 208 nm.

15. The head-mounted display device of claim 1 , wherein each protrusion has a substantially equal width.

16. The head-mounted display device of claim 1 , wherein each protrusion has a width of approximately 140 nm.

17. The head-mounted display device of claim 1 , wherein the first and second optical dispersion profiles reduce variations between a first diffraction efficiency of the grating with respect to a first wavelength of incident light, a second diffraction efficiency of the grating with respect to a second wavelength of incident light, and a third diffraction efficiency of the grating with respect to a third wavelength of incident light with respect to a range of incident angles compared to a grating composed of only the first material.

18. The head-mounted display device of claim 17 , wherein the first wavelength corresponds to first color in the visible spectrum, wherein the second wavelength corresponds to a second color in the visible spectrum, and wherein the third wavelength corresponds to third color in the visible spectrum, the first color, the second color, and third color being different from one another.

19. The head-mounted display device of claim 18 , wherein the first color is red, the second color is green, and the third color is blue.

20. The head-mounted display device of claim 17 , wherein the range of incident angles is approximately −20° to 20°.

21. A method of constructing a head-mounted display device, the method comprising:

providing a first optical element comprising a grating formed along a first surface of the first optical element, the grating comprising:

a plurality of protrusions comprising a first material having a first optical dispersion profile for visible wavelengths of light, and each of the protrusions comprising a first surface opposite the base portion of the first optical element, and

a second material deposited between at least some of the plurality of protrusions along the first surface of the first optical element, the second material having a second optical dispersion profile for visible wavelengths of light,

wherein there is an absence of the second material on the first surfaces of the protrusions; and

positioning the first optical element in optical communication with a second optical element in the head-mounted display device.