Wide angle imaging directional backlights

• US 20160306099A1
• Filed: 04/13/2016
• Published: 10/20/2016
• Est. Priority Date: 04/13/2015
• Status: Active Grant

• Current Assignee: Reald Spark, LLC
• Original Assignee: RealD Incorporated
• Inventors: Robinson, Michael G., Woodgate, Graham J.
• Granted Patent: US 10,459,152 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B29D 11/00269 Fresnel lenses
• CPC Class Codes: B29D 11/00596 Mirrors
• CPC Class Codes: G02B 5/09 Multifaceted or polygonal mirrors , e.g. polygonal scanning mirrors; Fresnel mirrors
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0043 provided on the surface of the light guide
• CPC Class Codes: G02B 6/0048 with stepwise taper
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/009 of the light source in the package G02B6/0021 takes precedence

Abstract

An imaging directional backlight apparatus including a waveguide, a light source array, for providing large area directed illumination from localized light sources. The waveguide may include a stepped structure, in which the steps may further include extraction features optically hidden to guided light, propagating in a first forward direction. Returning light propagating in a second backward direction may be refracted, diffracted, or reflected by the features to provide discrete illumination beams exiting from the top surface of the waveguide. In operation, luminance streaks and bright illumination regions may be formed due to undesirable imaging characteristics from the structure of the Fresnel mirror. Fresnel mirror draft facets and reflective facet microstructures are provided that achieve reduction of visibility of light streaks and bright illumination regions.

Claims

1. A directional waveguide comprising:

an input end;

first and second opposed, laterally extending guide surfaces for guiding light along the waveguide; and

a reflective end facing the input end for reflecting the input light back along the waveguide, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light,

wherein the reflective end is a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets providing the Fresnel reflector with positive optical power laterally, and, in at least a center region of the Fresnel reflector, the depth of the draft facets parallel to the optical axis of the reflective end being greater than the depth of the reflective facets.

2. A directional waveguide according to claim 1, wherein the pitch of the reflective facets laterally across the reflective end is constant.

3. A directional waveguide according to claim 1, wherein the width of the reflective facets laterally across the reflective end is at most 0.5 mm.

4. A directional waveguide according to claim 1, wherein the depth of each of the draft facets is at least 0.5 μ

m.

5. A directional waveguide according to claim 1, wherein the height of the reflective end between the first and second guide surfaces has a profile that is flat.

6. A directional waveguide according to claim 1, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to direct light guided along the waveguide in directions allowing exit through the first guide surface as the output light and intermediate regions between the light extraction features that are arranged to guide light along the waveguide.

7. A directional waveguide according to claim 6, wherein the second guide surface has a stepped shape in which said light extraction features are facets between the intermediate regions.

8. A directional waveguide according to claim 6, wherein the light extraction features have positive optical power in the lateral direction.

9. A directional backlight comprising:

a directional waveguide according to claim 1; and

an array of input light sources arranged at different input positions in a lateral direction across the input end of the waveguide and arranged to input light into the waveguide.

10. A directional display device comprising:

a directional backlight according to claim 9; and

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

11. A directional display apparatus comprising:

a directional display device according to claim 10; and

a control system arranged to control the light sources.

12. A directional waveguide comprising:

an input end;

first and second opposed, laterally extending guide surfaces for guiding light along the waveguide; and

a reflective end facing the input end for reflecting the input light back along the waveguide, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light,

wherein the reflective end is a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets providing the Fresnel reflector with positive optical power laterally, wherein the internal angles between adjacent draft facets and reflective facets are the same.

13. A directional waveguide according to claim 12, wherein the internal angles are in the range from 90 to 100 degrees.

14. A directional waveguide according to claim 12, wherein each reflective facet is laterally straight.

15. A directional waveguide according to claim 12, wherein each reflective facet is laterally curved.

16. A directional waveguide according to claim 12, wherein each reflective facet has a microstructure arranged to provide lateral angular diffusion of the light reflected therefrom.

17. A directional waveguide according to claim 16, wherein said microstructure comprises a plurality of curved sub-facets.

18. A directional waveguide according to claim 12, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to direct light guided along the waveguide in directions allowing exit through the first guide surface as the output light and intermediate regions between the light extraction features that are arranged to guide light along the waveguide.

19. A directional waveguide according to claim 18, wherein the second guide surface has a stepped shape in which said light extraction features are facets between the intermediate regions.

20. A directional waveguide according to claim 18, wherein the light extraction features have positive optical power in the lateral direction.

21. A directional backlight comprising:

a directional waveguide according to claim 12; and

an array of input light sources arranged at different input positions in a lateral direction across the input end of the waveguide and arranged to input light into the waveguide.

22. A directional display device comprising:

a directional backlight according to claim 21; and

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

23. A directional display apparatus comprising:

a directional display device according to claim 22; and

a control system arranged to control the light sources.

24. A directional waveguide comprising:

an input end;

first and second opposed, laterally extending guide surfaces for guiding light along the waveguide; and

a reflective end facing the input end for reflecting the input light back along the waveguide, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light,

wherein the reflective end is a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets providing the Fresnel reflector with positive optical power laterally, each reflective facet having a microstructure arranged to provide lateral angular diffusion of the light reflected therefrom.

25. A directional waveguide according to claim 24, wherein said microstructure comprises a plurality of curved sub-facets.

26. A directional waveguide according to claim 24, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to direct light guided along the waveguide in directions allowing exit through the first guide surface as the output light and intermediate regions between the light extraction features that are arranged to guide light along the waveguide.

27. A directional waveguide according to claim 26, wherein the second guide surface has a stepped shape in which said light extraction features are facets between the intermediate regions.

28. A directional waveguide according to claim 26, wherein the light extraction features have positive optical power in the lateral direction.

29. A directional backlight comprising:

a directional waveguide according to claim 24; and

an array of input light sources arranged at different input positions in a lateral direction across the input end of the waveguide and arranged to input light into the waveguide.

30. A directional display device comprising:

a directional backlight according to claim 29; and

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

31. A directional display apparatus comprising:

a directional display device according to claim 30; and

a control system arranged to control the light sources.

32. A directional waveguide comprising:

an input end;

first and second opposed, laterally extending guide surfaces for guiding light along the waveguide; and

a reflective end facing the input end for reflecting the input light back along the waveguide, the second guide surface being arranged to deflect the reflected input light through the first guide surface as output light, and the waveguide being arranged to direct the output light into optical windows in output directions that are distributed in a lateral direction in dependence on the input position of the input light,

wherein the reflective end is a Fresnel reflector comprising alternating reflective facets and draft facets, the reflective facets providing the Fresnel reflector with positive optical power laterally, and the draft facets being arranged to have a lower reflectivity than the reflective facets.

33. A directional waveguide according to claim 32, wherein, along the direction into the waveguide away from the reflective end, the draft facets are inclined inwardly towards the optical axis of the Fresnel reflector.

34. A directional waveguide according to claim 32, wherein the reflective facets are coated with a reflective material and wherein the draft facets are not coated with the reflective material.

35. A directional waveguide according to claim 32, wherein the first guide surface is arranged to guide light by total internal reflection and the second guide surface comprises a plurality of light extraction features oriented to direct light guided along the waveguide in directions allowing exit through the first guide surface as the output light and intermediate regions between the light extraction features that are arranged to guide light along the waveguide.

36. A directional waveguide according to claim 35, wherein the second guide surface has a stepped shape in which said light extraction features are facets between the intermediate regions.

37. A directional waveguide according to claim 35, wherein the light extraction features have positive optical power in the lateral direction.

38. A directional backlight comprising:

a directional waveguide according to claim 32; and

an array of input light sources arranged at different input positions in a lateral direction across the input end of the waveguide and arranged to input light into the waveguide.

39. A directional display device comprising:

a directional backlight according to claim 38; and

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

40. A directional display apparatus comprising:

a directional display device according to claim 39; and

a control system arranged to control the light sources.