Light input for directional backlight
A directional backlight may include a light guiding apparatus including at least one transparent optical waveguide for providing large area collimated illumination from localized light sources. The waveguide is arranged in a first part and a second part with a light injection aperture between the respective parts. Such controlled illumination may provide for efficient, multi-user autostereoscopic displays as well as improved 2D display functionality including high brightness displays and high display efficiency.
1. A directional backlight comprising:
a waveguide comprising first and second, opposed guide surfaces for guiding input light along the waveguide, wherein the second guide surface comprises at least two parts each extending partway along the waveguide, being separated perpendicular to a lateral direction by an input aperture; and
an array of light sources arranged to generate input light and to inject the input light through the input aperture into the waveguide at respective input positions in the lateral direction across the waveguide, wherein
the waveguide further comprises a reflective end arranged to reflect the input light back through the waveguide to each of the parts of the second guide surface,
the first guide surface is arranged to guide light by total internal reflection,
each of parts of the second guide surface comprises a plurality of light extraction features that extend linearly and parallel to each other and intermediate regions between the light extraction features that are arranged to direct light through the waveguide without extracting it, the light extraction features being oriented to deflect the input light after reflection from the reflective end in directions allowing exit through the first guide surface as output light through the first guide surface, and
the reflective end has positive optical power in the lateral direction so that the waveguide directs the output light from the light sources into optical windows in output directions that are positioned in the lateral direction in dependence on the input position of the input light.
2. A directional backlight according to claim 1 , wherein the array of light sources is disposed behind one of the parts of the second guide surface.
3. A directional backlight according to claim 2 , further comprising a light shield arranged between the array of light sources and the one of the parts of the second guide surface behind which the array of light sources is disposed.
4. A directional backlight according to claim 1 , further comprising a respective rear reflector arranged behind each of the parts of the second guide surface, each rear reflector comprising an array of reflective facets arranged to reflect light from the array of light sources, that is transmitted through the light extraction features of the waveguide, back through the waveguide to exit through the first guide surface into said optical windows.
5. A directional backlight according to claim 1 , wherein the input aperture comprises an input facet extending between the two parts of the second guide surface, the array of light sources being arranged along the input facet.
6. A directional backlight according to claim 1 , wherein the directional backlight further comprises an injection waveguide portion arranged between the array of light sources and the input aperture to guide input light from the array of light sources to the input aperture for injection of the input light through the input aperture.
7. A directional backlight according to claim 6 , wherein the injection waveguide portion is a separate element from the waveguide.
8. A directional backlight according to claim 7 , wherein the injection waveguide portion is index matched with the waveguide.
9. A directional backlight according to claim 6 , wherein the injection waveguide portion is formed integrally with the waveguide.
10. A directional backlight according to claim 6 , wherein the two parts of the second guide surface overlap in a direction along the waveguide.
11. A directional backlight according to claim 6 , further comprising a light combiner arranged between the injection waveguide portion and the input aperture, and a further array of light sources arranged to generate input light at a predetermined input position in a lateral direction across the waveguide, the further array of light sources being arranged to inject the input light into the waveguide through the light combiner, the further array of light sources being closer to the reflective end than the first-mentioned array of light sources.
12. A directional backlight according to claim 1 , wherein the directional backlight further comprises a further array of light sources arranged to generate input light at a predetermined input position in a lateral direction across the waveguide, the further array of light sources being arranged to inject the input light into the waveguide through the second guide surface partway along the waveguide at a position that is different from the first mentioned array of light sources.
13. A directional backlight according to claim 1 , wherein the waveguide has a facing end facing the reflective end, and the directional backlight further comprises a further array of light sources that is arranged to inject further input light through the facing end into the waveguide.
14. A directional backlight according to claim 1 , comprising plural sets of a waveguide and array of light sources each arranged in the same manner, the waveguides being tiled.
15. A directional backlight according to claim 14 , wherein the waveguides include waveguides that are tiled in a direction perpendicular to the lateral direction with their ends opposite from the reflective end abutting.
16. A directional backlight according to claim 15 , wherein the waveguides that are tiled are integrally formed.
17. A directional backlight according to claim 15 , further comprising a respective rear reflector arranged behind each of the parts of the second guide surface, each rear reflector comprising an array of reflective facets arranged to reflect light from the array of light sources at least one light source, that is transmitted through the light extraction features of the waveguide, back through the waveguide to exit through the first guide surface into said optical windows, the rear reflectors extending continuously behind the abutting ends.
18. A directional backlight according to claim 14 , wherein the waveguides include waveguides that are tiled in the lateral direction.
19. A directional backlight according to claim 18 , wherein the waveguides that are tiled in the lateral direction are connected by a hinge allowing folding of the waveguides.
20. A directional backlight according to claim 1 , wherein the second guide surface has a stepped shape comprising facets, that are said light extraction features, and the intermediate regions.
21. A directional backlight according to claim 1 , wherein the array of light sources are arranged in a curve.
22. A display device comprising:
a directional backlight according to claim 1 ; and
a transmissive spatial light modulator arranged to receive the output light from the first guide surface and to modulate it to display an image.
23. A display apparatus comprising:
a display device according to claim 22 ; and
a control system arranged to selectively operate the light sources to direct light into varying optical windows corresponding to said output directions.
24. A display apparatus according to claim 23 , being an autostereoscopic display apparatus wherein the control system is further arranged to control the display device to display temporally multiplexed left and right images and synchronously to direct the displayed images into optical windows in positions corresponding to left and right eyes of an observer.
25. A display apparatus according to claim 24 , wherein
the control system further comprises a sensor system arranged to detect the position of an observer across the display device, and
the control system is arranged to selectively operate the light sources to direct the output light into at least one optical window selected in dependence on the detected position of the observer.