Flat spectral response gratings using high index materials
An example head-mounted display device includes a plurality of optical elements in optical communication. The optical elements are configured to project an image in a field of view of a user wearing the head-mounted display device. A first optical element is configured to receive light from a second optical element. The first optical element defines a grating at along a periphery of the first optical element. The grating includes a plurality of protrusions extending from a base portion of the first optical element. The protrusions include a first material having a first optical dispersion profile for visible wavelengths of light. The grating also includes 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 has a second optical dispersion profile for visible wavelengths of light.
1. A system comprising:
a plurality of optical elements in optical communication, the plurality of optical elements being stacked in a first direction, and the plurality of optical elements being configured, during operation, to project an image in a field of view of a user,
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 binary grating at along a periphery of the first optical element, the binary grating comprising:
a plurality of protrusions extending from a base portion of the first optical element and towards the second optical element in the first direction, the protrusions comprising a first material having a first refractive index for a visible wavelength 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 refractive index for the visible wavelength of light,
wherein there is an absence of the second material on the first surfaces of the protrusions.
2. The system of claim 1 , wherein the second material comprises titanium dioxide (TiO 2 ).
3. The system of claim 2 , wherein the first material comprises silicon carbide (SiC).
4. The system of claim 2 , wherein the first material comprises lithium niobate (LiNbO 3 ).
5. The system of claim 1 , wherein the base portion of the first optical element comprises the first material.
6. The system of claim 1 , wherein the base portion of the first optical element comprises the same material as the plurality of protrusions.
7. The system of claim 1 , wherein the base portion of the first optical element is integrally formed with the plurality of protrusions.
8. The system of claim 1 , wherein each protrusion has a substantially rectangular cross-section.
9. The system 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 system of claim 9 , wherein the first height is greater than the second height.
11. The system of claim 10 , wherein the first height is approximately 90 nm.
12. The system of claim 11 , wherein the second height is approximately 80 nm.
13. The system of claim 1 , wherein the binary grating repeats according to a period along a length of the base portion of the first optical element.
14. The system of claim 13 , wherein the period corresponds to a length of approximately 208 nm.
15. The system of claim 1 , wherein each protrusion has a substantially equal width.
16. The system of claim 1 , wherein each protrusion has a width of approximately 140 nm.
17. A method comprising:
providing a first optical element comprising a binary grating formed along a first surface of the first optical element, the binary grating comprising:
a plurality of protrusions comprising a first material having a first refractive index for a visible wavelength of light, and each of the protrusions comprising a first surface opposite a 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 refractive index for the visible wavelength 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, such that the first optical element and the second optical element are stacked in a first direction, and such that the plurality of protrusions of the first optical element extend from the base portion of the first optical element and towards the second optical element in the first direction.
18. The method of claim 17 , wherein the second material comprises titanium dioxide (TiO 2 ).
19. The method of claim 18 , wherein the first material comprises silicon carbide (SiC).
20. The method of claim 18 , wherein the first material comprises lithium niobate (LiNbO 3 ).