Display device with diffraction grating having reduced polarization sensitivity
Diffraction gratings provide optical elements in head-mounted display systems to, e.g., incouple light into or out-couple light out of a waveguide. These diffraction gratings may be configured to have reduced polarization sensitivity. Such gratings may, for example, incouple or outcouple light of different polarizations with similar level of efficiency. The diffraction gratings and waveguides may include a transmissive layer and a metal layer. The diffraction grating may comprises a blazed grating.
1. A head-mounted display system comprising:
a head-mountable frame;
a light projection system configured to output light to provide image content;
a waveguide supported by the frame, the waveguide comprising a substrate configured to guide at least a portion of the light from said light projection system coupled into said waveguide;
a first diffraction grating on at least one surface of the substrate, the first diffraction grating comprising material different than the substrate;
a first layer disposed over at least a portion of the first diffraction grating on an incident side of the waveguide, the first layer comprising an optically transmissive material; and
a second layer comprising metal disposed on the incident side of the waveguide over both the first diffraction grating and the first layer, such that the first layer is between the first diffraction grating and the second layer, and such that said first diffraction grating has a first diffraction efficiency for a first polarization state over a range of angles of light incident thereon and a second diffraction efficiency for a second polarization state over the range of angles of light incident thereon, the first diffraction efficiency being from 1 to 1.2 times the second diffraction efficiency.
2. The head-mounted display system of claim 1 , wherein the substrate comprises material having an index of refraction of at least 1.9.
3. The head-mounted display system of claim 1 , wherein the first diffraction grating material comprises polymer.
4. The head-mounted display of claim 1 , wherein the first diffraction grating material comprises imprintable material.
5. The head-mounted display system of claim 1 , wherein the first diffraction grating material has a refractive index of 1.4 to 1.95.
6. The head-mounted display system of claim 1 , wherein the first diffraction grating material has a refractive index that is lower than said substrate.
7. The head-mounted display system of claim 1 , wherein said first diffraction grating comprises a blazed diffraction grating.
8. The head-mounted display system of claim 1 , wherein the first layer comprises titanium dioxide (TiO 2 ), zirconium dioxide (ZrO 2 ) or silicon carbide (SiC).
9. The head-mounted display system of claim 1 , wherein said first diffraction grating comprises a blazed diffraction grating, and wherein the first layer is disposed on one side of the diffractive features of the blazed diffraction grating and not on another side of the diffractive features.
10. The head-mounted display system of claim 1 , wherein the first and second polarization states comprise transverse electric and transverse magnetic polarizations, respectively.
11. The head-mounted display system of claim 1 , wherein one of the first and second polarization states is unpolarized.
12. The head-mounted display system of claim 1 , wherein the first layer comprises at least one of a dielectric material or a semiconductor material.
13. The head-mounted display system of claim 1 , wherein the first layer comprises a high refractive index material having a refractive index from 1.9 to 3.5.
14. The head-mounted display system of claim 1 , wherein the range of angles is at least 12 degrees.
15. The head-mounted display system of claim 14 , wherein the range of angles is at least 22 degrees.
16. The head-mounted display system of claim 1 , wherein the range of angles is between ±6 degrees with respect to the plane of the substrate.
17. The head-mounted display system of claim 16 , wherein the range of angles is between ±11 degrees with respect to the plane of the substrate.
18. The head-mounted display system of claim 1 , wherein said waveguide is included in an eyepiece configured to direct light to an eye of a user wearing said head mounted display.
19. The head-mounted display system of claim 1 , wherein the second layer is conformally disposed to at least partly conform to a shape of the first diffraction grating.
20. The head-mounted display system of claim 1 , wherein the first layer includes at least two sublayers of alternating materials having different refractive indices.