Light homogenization

1. A device for homogenizing light, comprising:

a waveguide having a first waveguide surface and a second waveguide surface parallel to the first waveguide surface; and

a partially reflective element located between the first waveguide surface and the second waveguide surface, wherein the partially reflective element has a lateral area extending parallel to the first waveguide surface, wherein the partially reflective element has a reflective axis parallel to a surface normal of the waveguide, and wherein the partially reflective element overlaps some but not all of the first waveguide surface.

2. The device of claim 1 , wherein the partially reflective element is configured to reflect light incident on the partially reflective element at a first reflectivity for a first set of incidence angles and to reflect light incident on the partially reflective element at a second reflectivity for a second set of incident angles, the first reflectivity being different from the second reflectivity.

3. The device of claim 1 , wherein:

the waveguide comprises a first layer having parallel plane surfaces and a second layer having parallel plane surfaces;

the device further comprising an interior plane surface of the parallel plane surfaces of the first layer that abuts an interior plane surface of the parallel plane surfaces of the second layer;

the first waveguide surface is a plane surface of the first layer opposite the interior plane surface of the parallel plane surfaces of the first layer; and

the second waveguide surface is a plane surface of the second layer opposite the interior plane surface of the parallel plane surfaces of the second layer.

4. The device of claim 3 , wherein:

the first layer and the second layer have matched indices of refraction; and

the partially reflective element is a partially reflective element disposed on one or both of the interior plane surface of the parallel plane surfaces of the first layer or the interior plane surface of the parallel plane surfaces of the second layer.

5. The device of claim 3 , wherein:

the first layer has an index of refraction different from that of the second layer; and

the partially reflective element is a boundary condition associated with the first layer and the second layer.

6. The device of claim 1 , wherein the partially reflective element is configured to reflect between 10% and 90% of light incident on the partially reflective element.

7. The device of claim 1 , wherein the partially reflective element comprises a partially reflective plate disposed within the waveguide, the partially reflective plate comprising a plate surface parallel to the first waveguide surface.

8. The device of claim 1 , wherein the partially reflective element comprises a first partially reflective plate and a second partially reflective plate disposed within the waveguide, each of the first and second partially reflective plates comprising a plate surface parallel to the first waveguide surface, and each of the first and second partially reflective plates being configured to reflect between 10% and 90% of light incident on a respective one of the first and second partially reflective plates.

9. The device defined in claim 1 , wherein the partially reflective element comprises a partially reflective element selected from the group consisting of: a hologram in a grating medium, a plate, a metallic coating, a dielectric coating, and a boundary between a pair of dielectric layers with mismatched indices of refraction.

10. A device comprising:

a waveguide having a first waveguide surface and a second waveguide surface parallel to the first waveguide surface;

a partially reflective element located between the first waveguide surface and the second waveguide surface, the partially reflective element having a reflective axis parallel to a surface normal of the waveguide; and

a light coupling device disposed within the waveguide, the light coupling device comprising:

a grating medium,

a first grating structure within the grating medium, the first grating structure being configured to reflect light of a wavelength and a first incidence angle about a first reflective axis offset from the surface normal, and

a second grating structure within the grating medium, the second grating structure being configured to reflect light of the wavelength and a second incidence angle about a second reflective axis offset from the surface normal, wherein the second incidence angle is different than the first incidence angle.

11. The device of claim 10 , wherein the first grating structure comprises a hologram.

12. The device of claim 10 , wherein the first grating structure comprises a non-holographic diffractive optical element.

13. The device of claim 10 , wherein the partially reflective element at least partially overlaps the grating medium in a direction orthogonal to a plane of the first waveguide surface.

14. A device comprising:

a waveguide having a first waveguide surface and a second waveguide surface parallel to the first waveguide surface; and

a partially reflective element located between the first waveguide surface and the second waveguide surface,

wherein the partially reflective element comprises:

a grating medium,

a first grating structure within the grating medium, the first grating structure being configured to reflect light of a wavelength and a first incidence angle about a first reflective axis parallel to a surface normal of the waveguide, and

a second grating structure within the grating medium, the second grating structure being configured to reflect light of the wavelength and a second incidence angle about a second reflective axis parallel to the surface normal, wherein the second incidence angle is different from the first incidence angle.

15. The device of claim 14 , wherein the first grating structure comprises a hologram.

16. The device of claim 14 , wherein the partially reflective element is configured to reflect between 10% and 90% of the light of the wavelength incident on the grating medium.

17. The device of claim 14 , wherein each of the first incidence angle and the second incidence angle has a value between 65° and 77° with respect to the surface normal.

18. The device of claim 14 , wherein the partially reflective element is configured to allow a majority of light of the wavelength to pass through the grating medium at a third incidence angle different from the first incidence angle and the second incidence angle.

19. A head mounted display device, comprising:

a light source for providing image-bearing light; and

an optical lens comprising,

a light input section of the optical lens for receiving the image-bearing light;

a waveguide disposed within the optical lens operatively coupled to the light input section, the waveguide having a first layer with a first waveguide surface and a second layer with a second waveguide surface parallel to the first waveguide surface;

a partially reflective element located in a third layer of the waveguide between the first waveguide layer and the second waveguide layer, the partially reflective element having a reflective axis parallel to a surface normal of the waveguide and having a lateral area extending parallel to the first waveguide surface; and

a light coupling device operatively coupled to the waveguide medium.

20. The head mounted display device defined in claim 19 , wherein the partially reflective element comprises a partially reflective element selected from the group consisting of: a hologram in a grating medium, a plate, a metallic coating, a dielectric coating, and a boundary between a pair of dielectric layers with mismatched indices of refraction.