Grating-based backlight employing reflective grating islands

1. A grating-based backlight comprising:

a light guide configured to guide a light beam at a non-zero propagation angle between a first surface and a second surface of the light guide; and

a plurality of reflective grating islands spaced apart from one another and optically coupled to the light guide, a reflective grating island of the plurality comprising a reflection mode diffraction grating configured to diffractively couple out a portion of the guided light beam as a coupled-out light beam,

wherein the coupled-out light beam is directed away from the first surface of the light guide at a predetermined principal angular direction.

2. The grating-based backlight of claim 1 , wherein the reflection mode diffraction grating comprises a dielectric diffraction grating adjacent to a reflective material layer.

3. The grating-based backlight of claim 1 , wherein the reflection mode diffraction grating comprises a reflective metal diffraction grating.

4. The grating-based backlight of claim 1 , wherein the reflective grating island is between the first surface and the second surface of the light guide.

5. The grating-based backlight of claim 1 , wherein the reflective grating island is at the second surface of the light guide.

6. The grating-based backlight of claim 5 , wherein the reflection mode diffraction grating of the reflective grating island comprises diffractive features at the second surface of the light guide and a reflective material layer, the diffractive features comprising one or both of grooves in the second surface and ridges on the second surface of the light guide and the reflective material layer being on the second surface to cover the diffractive features.

7. The grating-based backlight of claim 1 , wherein the reflection mode diffraction grating of the reflective grating island comprises a multibeam diffraction grating configured to diffractively couple out the portion of the guided light beam as a plurality of coupled-out light beams, coupled-out light beams of the coupled-out light beam plurality having different principal angular directions from one another.

8. The grating-based backlight of claim 7 , wherein the different principal angular directions of the coupled-out light beams correspond to respective view directions of different views of a three dimensional (3D) electronic display.

9. A three-dimensional (3D) electronic display comprising the grating-based backlight of claim 7 , the 3D electronic display further comprising:

a light source optically coupled to an input of the light guide, the light source being configured to provide collimated light to be guided as the light beam; and

a light valve configured to modulate a coupled-out light beam of the coupled-out light beam plurality, the light valve being adjacent to the first surface of the light guide,

wherein the principal angular direction of the coupled-out light beam corresponds to a view direction of the 3D electronic display, the modulated light beam representing a pixel of the 3D electronic display in the view direction.

10. A three-dimensional (3D) electronic display comprising:

a plate light guide configured to guide a light beam at a non-zero propagation angle within the plate light guide;

an array of reflective grating islands optically coupled to the plate light guide, a reflective grating island of the array comprising a reflective mode multibeam diffraction grating configured to diffractively couple out a portion of the guided light beam as a plurality of coupled-out light beams having different principal angular directions from one another that correspond to respective view directions of different views of the 3D electronic display; and

a light valve array configured to modulate the coupled-out light beams of the plurality of coupled-out light beams, the modulated coupled-out light beams representing pixels of the different views of the 3D electronic display.

11. The 3D electronic display of claim 10 , further comprising a light source optically coupled to an input of the plate light guide, the light source being configured to provide collimated light to the plate light guide input, wherein the plate light guide is configured to guide the collimated light as a collimated light beam at the non-zero propagation angle.

12. The 3D electronic display of claim 11 , wherein the light source comprises a first light emitting diode (LED) configured to provide red light, a second LED configured to provide green light, and a third LED configured to provide blue light, each of the red light, the green light and the blue light being provided as a different color collimated light beam by the light source, and wherein the plate light guide is configured to guide each of the different color, collimated light beams at a respective different color-specific, non-zero propagation angle.

13. The 3D electronic display of claim 10 , wherein the reflective mode multibeam diffraction grating of the reflective grating island comprises a chirped diffraction grating having curved diffractive features.

14. The 3D electronic display of claim 10 , wherein the reflective grating island is between a first surface of the plate light guide and a second surface of the plate light guide, the light valve array being adjacent to the first surface.

15. The 3D electronic display of claim 10 , wherein the reflective grating island is at a second surface of the plate light guide opposite to a first surface adjacent to the light valve array, and wherein the reflective grating island further comprises a reflective material layer configured to cover diffractive features of the reflective mode multibeam diffraction grating, the diffractive features comprising one or both of grooves in the second surface and ridges on the second surface.

16. A method of grating-based backlight operation, the method comprising:

guiding a light beam in a light guide at a non-zero propagation angle between a first surface and a second surface of the light guide; and

diffractively coupling out a portion of the guided light beam as a coupled-out light beam using a plurality of reflective grating islands, the coupled-out light beam being directed out and away from the first surface of the light guide at a predetermined principal angular direction,

wherein the reflective islands of the plurality are spaced apart from one another and optically coupled to the light guide, a reflective grating island of the plurality comprising a reflection mode diffraction grating.

17. The method of grating-based backlight operation of claim 16 , wherein the reflection mode diffraction grating of the reflective grating island comprises one of a dielectric diffraction grating adjacent to a reflective material layer and a reflective metal diffraction grating.

18. The method of grating-based backlight operation of claim 16 , wherein the reflection mode diffraction grating of the reflective grating island comprises a multibeam diffraction grating configured to diffractively couple out the portion of the guided light beam as a plurality of coupled-out light beams, coupled-out light beams of the coupled-out light beam plurality having different principal angular directions from one another.

19. The method of grating-based backlight operation of claim 18 , wherein the different principal angular directions of the coupled-out light beams correspond to respective view directions of different views of a three dimensional (3D) electronic display.

20. The method of grating-based backlight operation of claim 16 , further comprising modulating the coupled-out light beam using a light valve, the modulated coupled-out light beam forming a pixel of an electronic display.