Optical waveguide beam splitter with polarization volume gratings for display

1. An optical device for providing illumination light, the optical

device comprising:

an optical waveguide including a first surface and an opposing second surface; and

a plurality of polarization selective elements disposed adjacent to the optical waveguide and extending on the first surface or the second surface of the optical waveguide so that a respective polarization selective element:

receives light in a first direction, and

redirects a first portion of the light in a second direction, wherein a second portion, distinct from the first portion, of the light undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide.

2. The optical device of claim 1 , wherein:

the respective polarization selective element is a polarization volume grating.

3. The optical device of claim 1 , wherein:

the optical device also includes a spatial light modulator positioned adjacent to the first surface.

4. The optical device of claim 3 , wherein:

the respective polarization selective element is a reflective grating positioned adjacent to the second surface of the optical waveguide; and

redirecting the first portion of the light in the second direction includes directing the first portion of the light in the second direction such that the first portion of the light exits the optical waveguide through the first surface.

5. The optical device of claim 3 , wherein:

the respective polarization selective element is a transmission grating positioned adjacent to the first surface of the optical waveguide and between the first surface of the optical waveguide and the spatial light modulator; and

redirecting the first portion of the light in the second direction includes transmitting the first portion of the light in the second direction.

6. The optical device of claim 1 , wherein:

the respective polarization selective element is switchable between different states, including a first state and a second state distinct from the first state;

the first state causes the respective polarization selective element to redirect the first portion of the light in the second direction, wherein the second portion of the light undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide; and

the second state causes the respective polarization selective element to transmit the received light such that the received light undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide.

7. The optical device of claim 6 , wherein:

the first state causes the first portion of the light in the second direction to illuminate a respective region of a spatial light modulator; and

the second state causes the respective polarization selective element to forgo illuminating the respective region of the spatial light modulator.

8. The optical device of claim 1 , further including a light source positioned to provide the light into the optical waveguide toward the respective polarization selective element.

9. The optical device of claim 8 , wherein the light source defines an optical axis that is parallel to an optical axis of the optical waveguide.

10. The optical device of claim 8 , wherein the light source defines an optical axis that is tilted with respect to an optical axis of the optical waveguide.

11. The optical device of claim 8 , further including a tapered light guide positioned between the light source and the optical waveguide, the tapered light guide configured to direct the light provided by the light source into the optical waveguide.

12. The optical device of claim 8 , further including a diffuser positioned between the light source and the optical waveguide.

13. An optical device for providing illumination light, the

optical device comprising:

an optical waveguide; and

a plurality of polarization selective elements disposed adjacent to the optical waveguide so that a respective polarization selective element:

receives light in a first direction, and

redirects a first portion of the light in a second direction, wherein a second portion, distinct from the first portion, of the light undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide, wherein:

the plurality of polarization selective elements includes a first polarization selective element and a second polarization selective element;

the first polarization selective element receives first light and redirects a first portion of the first light in the second direction, wherein:

a second portion of the first light, distinct from the first portion of the first light, undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide as second light, and

a ratio between the first portion and the second portion of the first light has a first value; and

the second polarization selective element receives the second light and redirects a first portion of the second light in the second direction, wherein:

a second portion of the second light, distinct from the first portion of the second light, undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide, and

a ratio between the first portion and the second portion of the second light has a second value distinct from the first value.

14. The optical device of claim 13 , wherein the first polarization selective element has a first thickness, the second polarization selective element has a second thickness greater than the first thickness, and the second value is greater than the first value.

15. The optical device of claim 13 , wherein the first polarization selective element has a first duty cycle, the second polarization selective element has a second duty cycle, the second duty cycle is greater than the first duty cycle, and the second value is greater than the first value.

16. The optical device of claim 13 , wherein:

the plurality of polarization selective elements includes a third polarization selective element positioned so that the second polarization selective element is positioned between the first polarization selective element and the third polarization selective element; and

the third polarization selective element receives the second portion of the second light as third light and redirects a first portion of the third light in the second direction, wherein:

a second portion of the third light, distinct from the first portion of the third light, undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide, and

a ratio between the first portion and the second portion of the third light has a third value.

17. The optical device of claim 16 , wherein:

the optical waveguide has a first end positioned to receive the light and a second end opposite to the first end;

the optical device also includes a polarization-maintaining reflector assembly positioned adjacent to the second end; and

the second value is greater than the first value and the third value.

18. The optical device of claim 13 , wherein the first portion of the first light is received by a first region of a spatial light modulator and the first portion of the second light is received by a second region of the spatial light modulator distinct from the first region of the spatial light modulator.

19. The optical device of claim 18 , wherein the first portion of the first light has a first intensity when incident on the first region and the first portion of the second light has a second intensity corresponding to the first intensity when incident on the second region.

20. A method for providing illumination light, the method comprising:

receiving light in a first direction with a respective polarization selective element of a plurality of polarization selective elements disposed adjacent to an optical waveguide and extending on a first surface or an opposing second surface of the optical waveguide; and

redirecting, with the respective polarization selective element, a first portion of the light in a second direction, wherein a second portion, distinct from the first portion, of the light undergoes total internal reflection, thereby continuing to propagate inside the optical waveguide.