Directional Backlight

• US 20130321913A1
• Filed: 05/17/2013
• Published: 12/05/2013
• Est. Priority Date: 05/18/2012
• Status: Active Grant

• Current Assignee: Reald Spark, LLC
• Original Assignee: RealD Incorporated
• Inventors: Harrold, Jonathan, Woodgate, Graham J., Robinson, Michael G., Schuck, Miller H.
• Granted Patent: US 9,709,723 B2
• Time in Patent Office: Days
• US Class Current: 359/464
• CPC Class Codes: G02B 30/24 involving temporal multiplexing, e.g. using sequentially activated left and right shutters
• CPC Class Codes: G02B 30/33 involving directional light or back-light sources
• CPC Class Codes: G02B 30/36 using refractive optical elements, e.g. prisms, in the optical path between the images and the observer
• CPC Class Codes: G02B 6/0028 Light guide, e.g. taper
• CPC Class Codes: G02B 6/0048 with stepwise taper

Abstract

Disclosed is an optical inline light guiding apparatus which may include a substantially parallel planar light expansion section and a light extraction section comprising a stepped structure, in which the steps may be extraction features and guiding features. Such controlled illumination may provide for efficient, multi-user autostereoscopic displays with wide viewing freedom, high efficiency and low cross talk and other directional display uses.

Claims

1. A directional backlight comprising:

an array of light sources;

a light expansion waveguide section having an input end and opposed guide surfaces for guiding light along the waveguide, the array of light sources disposed at different input positions in a lateral direction across the input end of the light expansion waveguide section; and

a light extraction waveguide section arranged to receive light from the light expansion waveguide section, and comprising first and second, opposed guide surfaces for guiding light along the light extraction waveguide section, the first guide surface being arranged to guide light by total internal reflection and the second guide surface having a stepped shape comprising a plurality of facets and intermediate regions intermediate the facets, the intermediate regions being arranged to direct light through the light extraction waveguide section without extracting it, and the facets facing the light expansion waveguide section and oriented to reflect light guided through the light extraction waveguide section in directions allowing exit through the first guide surface into optical windows in output directions distributed in the lateral direction that are dependent on the input positions of the light sources.

2. A directional backlight according to claim 1, further comprising a diffuser extending across the first guide surface of the light extraction waveguide section.

3. A directional backlight according to claim 2, wherein the diffuser is an asymmetric diffuser that provides greater angular dispersion of light in a direction perpendicular to the lateral direction than in the lateral direction.

4. A directional backlight according to claim 1, comprising at least one window-forming optical element arranged to converge input light from the light sources in the lateral direction into said optical windows.

5. A directional backlight according to claim 4, further comprising a lens element between the light expansion waveguide section and the light extraction waveguide section that has positive optical power in the lateral direction and is a said window-forming optical element.

6. A directional backlight according to claim 5, wherein the lens element comprises two bodies of different refractive index having an interface shaped as a lens surface.

7. A directional backlight according to claim 5, wherein the light expansion waveguide section and the light extraction waveguide section have a gap between them, and the lens element is formed by at least one of an input end of the light extraction waveguide section and an output end of the light expansion waveguide section being shaped as a lens surface.

8. A directional backlight according to claim 5, wherein the facets extend linearly in the lateral direction.

9. A directional backlight according to claim 4, wherein the facets extend in the lateral direction and are curved to provide positive optical power in the lateral direction to form a said window-forming optical element.

10. A directional backlight according to claim 4, further comprising a Fresnel lens extending across the first guide surface of the light extraction waveguide section that is a said window-forming optical element.

11. A directional backlight according to claim 1, wherein the light expansion waveguide section and the light extraction waveguide section have a gap between them.

12. A directional backlight according to claim 1, wherein the light expansion waveguide section and the light extraction waveguide section are continuous.

13. A directional backlight according to claim 1, wherein the light expansion waveguide section widens in the lateral direction in the direction from the array of light sources to the light extraction waveguide section.

14. A directional backlight according to claim 1, wherein the light expansion waveguide section has a height in the direction perpendicular to the lateral direction that is smaller than the height of the light extraction waveguide section at an input end that is arranged to receive light from the light expansion waveguide section.

15. A directional backlight according to claim 1, wherein the light extraction waveguide section has said stepped shape in a light extraction region and further comprises a light guiding region between the light extraction region and the light expansion waveguide section wherein the first guide surface is arranged to direct light through the waveguide without extracting it.

16. A display device comprising:

a directional backlight comprising;

an array of light sources;

a light expansion waveguide section having an input end and opposed guide surfaces for guiding light along the waveguide, the array of light sources disposed at different input positions in a lateral direction across the input end of the light expansion waveguide section; and

a light extraction waveguide section arranged to receive light from the light expansion waveguide section, and comprising first and second, opposed guide surfaces for guiding light along the light extraction waveguide section, the first guide surface being arranged to guide light by total internal reflection and the second guide surface having a stepped shape comprising a plurality of facets and intermediate regions intermediate the facets, the intermediate regions being arranged to direct light through the light extraction waveguide section without extracting it, and the facets facing the light expansion waveguide section and oriented to reflect light guided through the light extraction waveguide section in directions allowing exit through the first guide surface into optical windows in output directions distributed in the lateral direction that are dependent on the input positions of the light sources; and

a transmissive spatial light modulator arranged to receive the light output from the light extraction waveguide section and to modulate it to display an image.

17. A display apparatus comprising:

a display device comprising;

a directional backlight comprising;

an array of light sources;

a light expansion waveguide section having an input end and opposed guide surfaces for guiding light along the waveguide, the array of light sources disposed at different input positions in a lateral direction across the input end of the light expansion waveguide section; and

a light extraction waveguide section arranged to receive light from the light expansion waveguide section, and comprising first and second, opposed guide surfaces for guiding light along the light extraction waveguide section, the first guide surface being arranged to guide light by total internal reflection and the second guide surface having a stepped shape comprising a plurality of facets and intermediate regions intermediate the facets, the intermediate regions being arranged to direct light through the light extraction waveguide section without extracting it, and the facets facing the light expansion waveguide section and oriented to reflect light guided through the light extraction waveguide section in directions allowing exit through the first guide surface into optical windows in output directions distributed in the lateral direction that are dependent on the input positions of the light sources; and

a transmissive spatial light modulator arranged to receive the light output from the light extraction waveguide section and to modulate it to display an image; and

a control system arranged to selectively operate the light sources to direct light into varying optical windows.

18. A display apparatus according to claim 17, 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 light into varying optical windows in dependence on the detected position of the observer.

19. A display apparatus according to claim 18, 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 selectively operate the light sources to direct the displayed left and right images into varying optical windows in positions corresponding to left and right eyes of an observer in dependence on the detected position of the observer.

20. A directional backlight comprising:

an array of light emitting elements; and

a waveguide for guiding light comprising;

a first light guiding region, comprising first and second substantially parallel planar surfaces; and

a second light guiding region comprising;

a first light guiding surface, wherein the first light guiding surface is substantially planar; and

a second light guiding surface, opposite the first light guiding surface, further comprising a plurality of guiding features and a plurality of extraction features, wherein the extraction features and the guiding features are connected to and alternate with one another respectively, further wherein the plurality of extraction features direct light to reflect and exit the light valve, wherein the extraction features are arranged so that light from the light emitting elements is directed by the extraction features with substantially the same directionality for extraction features across the plurality of extraction features.