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 outcouple 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, or polarized and unpolarized light, with a similar level of efficiency. The diffraction gratings and waveguides may include a transmissive layer and a metal layer. The diffraction grating may comprise a blazed grating.
1. A waveguide comprising:
a substrate configured to propagate light within the waveguide by total internal reflection; and
at least one diffraction grating on the substrate, each diffraction grating comprising:
a grating pattern on a side of the substrate, the grating pattern comprising material different than the substrate;
a first layer disposed over at least a portion of the grating pattern on the side of the substrate, the first layer comprising an optically transmissive material; and
a second layer comprising metal disposed on the side of the substrate over both the grating pattern and the first layer, such that the first layer is between the grating pattern and the second layer, and such that the diffraction grating has a first diffraction efficiency for light having a first state over a range of angles of light incident thereon and a second diffraction efficiency for light having a second state over the range of angles of light incident thereon,
wherein the grating pattern, the first layer, and the second layer are on the side of the substrate configured as an incident side,
wherein at least one of the first state or the second state is a polarization state, and
wherein the first diffraction efficiency is 1 to 2 times the second diffraction efficiency.
2. The waveguide of claim 1 , wherein the substrate has an index of refraction of at least 1.9.
3. The waveguide of claim 1 , wherein the grating pattern comprises polymer.
4. The waveguide of claim 1 , wherein the grating pattern comprises imprintable material.
5. The waveguide of claim 1 , wherein the grating pattern comprises material having a refractive index of 1.4 to 1.95.
6. The waveguide of claim 1 , wherein the grating pattern comprises material having a refractive index that is lower than a refractive index of the substrate.
7. The waveguide of claim 1 , wherein the grating pattern comprises a blazed grating pattern.
8. The waveguide of claim 7 , wherein the first layer is disposed on one side of the diffractive features of the blazed grating pattern and not on another side of the diffractive features.
9. The waveguide of claim 1 , wherein the first layer comprises one or more of titanium dioxide (TiO 2 ), zirconium dioxide (ZrO 2 ), or silicon carbide (SiC).
10. The waveguide of claim 1 , wherein the second layer comprises one or more of aluminum, silver, gold, copper, aluminum silicate (AlSi), or an alloy of at least two of these.
11. The waveguide of claim 1 , wherein the first and second states comprise transverse electric and transverse magnetic polarizations, respectively.
12. The waveguide of claim 1 , wherein one of the first and second states is unpolarized.
13. The waveguide of claim 1 , wherein the first layer comprises at least one of a dielectric material or a semiconductor material.
14. The waveguide of claim 1 , wherein the first layer comprises a high refractive index material having a refractive index from 1.9 to 3.5.
15. The waveguide of claim 1 , wherein the range of angles spans at least 12 degrees.
16. The waveguide of claim 1 , wherein the range of angles spans at least 22 degrees.
17. The waveguide of claim 1 , wherein the second layer is conformally disposed to at least partly conform to a shape of the grating pattern.
18. The waveguide of claim 1 , wherein the first layer includes at least two sublayers of different materials having different refractive indices.
19. The waveguide of claim 18 , wherein at least one of the sublayers comprises titanium dioxide (TiO 2 ), and at least a different one of the sublayers comprises silicon dioxide (SiO 2 ).
20. The waveguide of claim 1 , wherein the first diffraction efficiency is within 10% of the second diffraction efficiency.