Wide angle imaging directional backlights

• US 10,330,843 B2
• Filed: 10/11/2016
• Issued: 06/25/2019
• Est. Priority Date: 11/13/2015
• Status: Active Grant

• Current Assignee: Reald Spark, LLC
• Original Assignee: Reald Spark, LLC
• Inventors: Robinson, Michael G., Woodgate, Graham J.
• Primary Examiner(s): Bruce, David V
• Application Number:
  US15/290,543
• Publication Number:
  US 20170139097A1
• Time in Patent Office: 987 Days
• CPC Class Codes: B29D 11/00596 Mirrors
• CPC Class Codes: G02B 27/0093 with means for monitoring data relating to the user, e.g. head-tracking, eye-tracking
• CPC Class Codes: G02B 30/33 involving directional light or back-light sources
• CPC Class Codes: G02B 30/34 Stereoscopes providing a stereoscopic pair of separated images corresponding to parallactically displaced views of the same object, e.g. 3D slide viewers
• CPC Class Codes: G02B 5/09 Multifaceted or polygonal mirrors , e.g. polygonal scanning mirrors; Fresnel mirrors
• CPC Class Codes: G02B 6/002 by shaping at least a portion of the light guide, e.g. with collimating, focussing or diverging surfaces
• 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 6/0048 with stepwise taper
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: H04N 13/305 using lenticular lenses, e.g. arrangements of cylindrical lenses
• CPC Class Codes: H04N 13/312 the parallax barriers being placed behind the display panel, e.g. between backlight and spatial light modulator [SLM]
• CPC Class Codes: H04N 13/32 using arrays of controllable light sources; using moving apertures or moving light sources

Abstract

An imaging directional backlight apparatus includes a waveguide and a light source array for providing large area directed illumination from localized light sources. The waveguide may include a stepped structure. The steps may 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, providing discrete illumination beams exiting from the top surface of the waveguide. Viewing windows are formed through imaging individual light sources and define the relative positions of system elements and ray paths. The uncorrected system creates non-illuminated void portions when viewed off-axis preventing uniform wide angle 2D illumination modes. The input end may have microstructures arranged to remove this non uniformity at wide angles. The microstructures may have reduced reflectivity for parts of the input end that contribute to stray light in privacy and autostereoscopic modes.

Claims

1. A directional backlight for a transmissive spatial light modulator, comprising:

a waveguide comprising an input end; and

an array of light sources at different input positions in a lateral direction across the input end, the light sources being arranged to input light into the waveguide through the input end, the light sources having light emitting areas with respective lateral extents,

the waveguide further comprising first and second, opposed guide surfaces for guiding the input light along the waveguide, and a reflective end facing the input end for reflecting the input light guided from the input end back through the waveguide, wherein the second guide surface is arranged to deflect light reflected from the reflective end through the first guide surface as output light, the reflective end has positive optical power in the lateral direction, and the waveguide is arranged to image the light sources in the lateral direction so that the output light from the light sources is directed into respective optical windows that are distributed in the lateral direction in dependence on the input positions of the light sources,

wherein the light sources include at least one pair of adjacent light sources arranged at input positions offset from the optical axis of the reflective end, wherein, within the pair, the light source closest to said optical axis is inclined with the normal to the lateral extent of its light emitting area inclined towards said optical axis and the light source furthest from said optical axis is inclined with the normal to the lateral extent of its light emitting area inclined away from said optical axis.

2. A directional backlight according to claim 1, wherein the input end of the waveguide comprises a pair of inclined input facets extending across the light emitting areas of the respective light sources of said pair.

3. A directional backlight according to claim 1, wherein the normal to the lateral extent of the light emitting area of said inclined light sources are inclined at angles to the lateral direction in a range from 15°

to 45°

.

4. A directional- backlight according to claim 2, wherein said input facets are each shaped as an array of curved sections having cusps therebetween, and the angles of the curved sections at the cusps, with respect to a direction along the light emitting area of the light source across which the input facet extends, are in a range from a first lower limit of 15°

to a first upper limit of 60°

.

5. A directional backlight according to claim 4, wherein the first lower limit is 35°

.

6. A directional backlight according to claim 5, wherein the first upper limit is 50°

.

7. A directional backlight according to claim 4, wherein the first upper limit is 50°

.

8. A directional backlight according to claim 2, wherein the input end includes an intermediate facet extending between the inclined input facets.

9. A directional backlight according to claim 8, wherein said intermediate facet is each shaped as an array of curved sections having cusps therebetween, and the angles of the curved sections at the cusps, with respect to the lateral direction, are in a range from a second lower limit of 15°

to a second upper limit of 34°

.

10. A directional backlight according to claim 9, wherein the second lower limit is 20°

.

11. A directional backlight according to claim 10, wherein the second upper limit is 30°

.

12. A directional backlight according to claim 9, wherein the second upper limit is 30°

.

13. A directional backlight according to claim 4, wherein said curved sections are conic sections.

14. A directional backlight according to claim 4, wherein the curved sections are concave with respect to the light guide.

15. A directional backlight according to claim 4, wherein the curved sections are convex with respect to the light guide.

16. A directional backlight according to claim 1, wherein the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are arranged to reflect light from the light sources.

17. A directional backlight according to claim 1, further comprising a control system arranged to control the light sources.

18. A directional backlight according to claim 17, the control system being arranged, on selective operation of a first light source to direct light into an optical window, to simultaneously operate a second light source that directs light reflected by the reflective end and then by a side of the waveguide into an outer portion of the waveguide that fails to be illuminated by the first light source.

19. A directional display device comprising:

a directional backlight according to claim 1; and

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

20. A directional backlight for a transmissive spatial light modulator, comprising:

a waveguide comprising an input end; and

an array of light sources at different input positions in a lateral direction across the input end, the light sources being arranged to input light into the waveguide through the input end, the light sources having light emitting areas with respective lateral extents that do not cover the entirety of the input end in the lateral direction,

the waveguide further comprising first and second, opposed guide surfaces for guiding the input light along the waveguide, and a reflective end facing the input end for reflecting the input light guided from the input end back through the waveguide, wherein the second guide surface is arranged to deflect light reflected from the reflective end through the first guide surface as output light, the reflective end has positive optical power in the lateral direction, and the waveguide is arranged to image the light sources in the lateral direction so that the output light from the light sources is directed into respective optical windows that are distributed in the lateral direction in dependence on the input positions of the light sources,

wherein the input end comprises at least one reflection reduction region in the lateral direction, outside the lateral extents of the light emitting areas of the light sources, within which the input end is shaped in the lateral direction as an array of curved sections having cusps therebetween, the angles of the curved sections at the cusps with respect to the lateral direction being in a range from a lower limit of 15°

to an upper limit of 34° and

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 reflected by the reflected end 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.

21. A directional backlight according to claim 20, wherein the lower limit is 20°

.

22. A directional backlight according to claim 21, wherein the upper limit is 30°

.

23. A directional backlight according to claim 20, wherein the upper limit is 30°

.

24. A directional backlight according to claim 20, wherein said curved sections are conic sections.

25. A directional backlight according to claim 20, wherein the curved sections are concave with respect to the light guide.

26. A directional backlight according to claim 20, wherein the curved sections are convex with respect to the light guide.

27. A directional backlight according to claim 20, wherein the curved sections are identical.

28. A directional backlight according to claim 20, wherein the light sources have light emitting areas with respective lateral extents that are separated, and the input end comprises plural reflection reduction regions arranged between the lateral extents of the light sources.

29. A directional backlight according to claim 20, wherein the array of light sources are at different input positions in a lateral direction across a central part of the input end, and the input end comprises reflection reduction regions outside the central part of the input end.

30. A directional backlight according to claim 20, wherein the light extraction features and the intermediate regions alternate with one another in a stepped shape.

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

32. A directional backlight according to claim 20, wherein the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are arranged to reflect light from the light sources.

33. A directional display device comprising:

a directional backlight according to claim 20; and

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

34. A directional backlight according to claim 33, 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 reflected by the reflected end 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.

35. A directional backlight according to claim 34, wherein the light extraction features and the intermediate regions alternate with one another in a stepped shape.

36. A directional backlight according to claim 34, wherein the light extraction features have positive optical power in the lateral direction.

37. A directional backlight for a transmissive spatial light modulator, comprising:

a waveguide comprising an input end; and

an array of light sources at different input positions in a lateral direction across the input end, the light sources being arranged to input light into the waveguide through the input end, the light sources having light emitting areas with respective lateral extents;

the waveguide further comprising first and second, opposed guide surfaces for guiding the input light along the waveguide, and a reflective end facing the input end for reflecting the input light guided from the input end back through the waveguide, wherein the second guide surface is arranged to deflect light reflected from the reflective end through the first guide surface as output light, the reflective end has positive optical power in the lateral direction, and the waveguide is arranged to image the light sources in the lateral direction so that the output light from the light sources is directed into respective optical windows that are distributed in the lateral direction in dependence on the input positions of the light sources,

wherein across a lateral extent of the input end aligned with the light emitting area of at least one of light sources, the input end is shaped in the lateral direction as an array of curved sections having cusps therebetween, the array of curved sections including asymmetric curved sections having different angles at the cusps on either side thereof, with respect to a direction along the aligned light emitting area of the light source, the higher of said different angles being in a range from a first lower limit of 35°

to first upper limit of 90°

, and the lower of said different angles being in a range from a second lower limit of 15°

to a second upper limit of 34°

.

38. A directional backlight according to claim 37, wherein the first lower limit is 45°

, or 60°

.

39. A directional backlight according to claim 38, wherein the first upper limit is 85°

.

40. A directional backlight according to claim 37, wherein the first upper limit is 85°

.

41. A directional backlight according to claim 37, wherein the second lower limit is 20°

.

42. A directional backlight according to claim 38, wherein the second upper limit is 30°

.

43. A directional backlight according to claim 37, wherein the second upper limit is 30°

.

44. A directional backlight according to claim 37, wherein the asymmetric curved sections are divided into first asymmetric curved sections wherein the higher of said different angles is on a first side of the asymmetric curved sections and second asymmetric curved sections wherein the higher of said different angles is on a second, opposite side of the asymmetric curved sections.

45. A directional backlight according to 44, wherein the first asymmetric curved sections and the second asymmetric curved sections alternate with each other across the array of curved sections.

46. A directional backlight according to claim 37, wherein the upper of said different angles and the lower of said different angles are identical for each asymmetric curved section.

47. A directional backlight according to claim 37, wherein the array of curved sections include further curved sections, interspersed with the asymmetric curved sections, the angles of the further curved sections at the cusps with respect to the lateral direction being in a range from the first lower limit to the first upper limit.

48. A directional backlight according to claim 37, wherein said curved sections are conic sections.

49. A directional backlight according to claim 37, wherein the curved sections are concave with respect to the light guide.

50. A directional backlight according to claim 37, wherein the curved sections are convex with respect to the light guide.

51. A directional backlight according to claim 37, wherein the light sources have light emitting areas with respective lateral extents that are separated, and the input end comprises at least one reflection reduction region arranged outside the lateral extents of the light sources, within which the input end is shaped in the lateral direction as an array of curved sections having cusps therebetween, the angles of the curved sections at the cusps with respect to the lateral direction being in a range from a lower limit of 15°

to an upper limit of 34°

.

52. A directional backlight according to claim 37, wherein said at least one of light sources is at an input position offset from the optical axis of the reflective end.

53. A directional backlight according to claim 37, wherein the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are arranged to reflect light from the light sources.

54. A directional backlight according to claim 37, further comprising a control system arranged to control the light sources.

55. A directional backlight according to claim 54, the control system being arranged, on selective operation of a first light source to direct light into an optical window, to simultaneously operate a second light source that directs light reflected by the reflective end and then by a side of the waveguide into an outer portion of the waveguide that fails to be illuminated by the first light source.

56. A directional display device comprising:

a directional backlight according to claim 37; and

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

57. A directional backlight for a transmissive spatial light modulator, comprising:

a waveguide comprising an input end; and

an array of light sources at different input positions in a lateral direction across the input end, the light sources being arranged to input light into the waveguide through the input end, the light sources having light emitting areas with respective lateral extents,

the waveguide further comprising first and second, opposed guide surfaces for guiding the input light along the waveguide, and a reflective end facing the input end for reflecting the input light guided from the input end back through the waveguide, wherein the second guide surface is arranged to deflect light reflected from the reflective end through the first guide surface as output light, the reflective end has positive optical power in the lateral direction, and the waveguide is arranged to image the light sources in the lateral direction so that the output light from the light sources is directed into respective optical windows that are distributed in the lateral direction in dependence on the input positions of the light sources,

wherein across a lateral extent of the input end aligned with the light emitting area of at least one of light sources, the input end is shaped in the lateral direction as an array of teeth that are each shaped with a convex curved section on one side the tooth and a concave curved section on the other side of the tooth.

58. A directional backlight according to claim 57, wherein said curved sections are conic sections.

59. A directional backlight according to claim 57, wherein, at cusps between the convex curved sections and the concave curved sections, each of the convex curved sections and the concave curved sections has a shallow angle at the cusp at one end thereof in a range from 0°

to 20° and

has a steep angle at the cusp at the other end thereof in a range from 45°

to 90°

.

60. A directional backlight according to claim 57, wherein said teeth are identical.

61. A directional backlight according to claim 57, wherein the light sources have light emitting areas with respective lateral extents that are separated, and the input end comprises at least one reflection reduction region arranged outside the lateral extents of the light sources, within which the input end is shaped in the lateral direction as an array of curved sections having cusps therebetween, the angles of the curved sections at the cusps with respect to the lateral direction being in a range from a lower limit of 15°

to an upper limit of 34°

.

62. A directional backlight according to claim 57, 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 reflected by the reflected end 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.

63. A directional backlight according to claim 62, wherein the light extraction features and the intermediate regions alternate with one another in a stepped shape.

64. A directional backlight according to claim 62, wherein the light extraction features have positive optical power in the lateral direction.

65. A directional backlight according to claim 57, wherein said at least one of light sources is at an input position offset from the optical axis of the reflective end.

66. A directional backlight according to claim 57, wherein the waveguide further comprises sides, extending between the input end and the reflective end and between the guiding surfaces, that are arranged to reflect light from the light sources.

67. A directional backlight according to claim 57, further comprising a control system arranged to control the light sources.

68. A directional backlight according to claim 67, the control system being arranged, on selective operation of a first light source to direct light into an optical window, to simultaneously operate a second light source that directs light reflected by the reflective end and then by a side of the waveguide into an outer portion of the waveguide that fails to be illuminated by the first light source.

69. A directional display device comprising:

a directional backlight according to claim 57; and

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

70. A directional backlight for a transmissive spatial light modulator, comprising:

a waveguide comprising an input end; and

an array of light sources at different input positions in a lateral direction across the input end, the light sources being arranged to input light into the waveguide through the input end, the light sources having light emitting areas with respective lateral extents,

the waveguide further comprising first and second, opposed guide surfaces for guiding the input light along the waveguide, and a reflective end facing the input end for reflecting the input light guided from the input end back through the waveguide, wherein the second guide surface is arranged to deflect light reflected from the reflective end through the first guide surface as output light, the reflective end has positive optical power in the lateral direction, and the waveguide is arranged to image the light sources in the lateral direction so that the output light from the light sources is directed into respective optical windows that are distributed in the lateral direction in dependence on the input positions of the light sources,

wherein across a lateral extent of the input end aligned with the light emitting area of at least one of light sources, the input end is shaped in the lateral direction as an array of curved sections having cusps therebetween, the angles of the curved sections at the cusps with respect to the lateral direction being in a range from a lower limit of 35°

to an upper limit of 90°

, and

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 reflected by the reflected end 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.

71. A directional backlight according to claim 70, wherein the lower limit is 45°

.

72. A directional backlight according to claim 71, wherein the upper limit is 75°

.

73. A directional backlight according to claim 71, wherein the upper limit is 75°

.

74. A directional backlight according to claim 70, wherein the curved sections are conic sections.

75. A directional backlight according to claim 70, wherein the curved sections are concave with respect to the light guide.

76. A directional backlight according to claim 70, wherein the curved sections are convex with respect to the light guide.

77. A directional backlight according to claim 70, wherein the light sources have light emitting areas with respective lateral extents that are separated, and the input end comprises at least one reflection reduction region arranged outside the lateral extents of the light emitting areas, within which the input end is shaped in the lateral direction as an array of curved sections having cusps therebetween, the angles of the curved sections at the cusps with respect to the lateral direction being in a range from a lower limit of 15°

to an upper limit of 34°

.

78. A directional backlight according to claim 70, wherein the light extraction features and the intermediate regions alternate with one another in a stepped shape.

79. A directional backlight according to claim 70, wherein the light extraction features have positive optical power in the lateral direction.

80. A directional backlight according to claim 70, further comprising a control system arranged to control the light sources.

81. A directional backlight according to claim 80, the control system being arranged, on selective operation of a first light source to direct light into an optical window, to simultaneously operate a second light source that directs light reflected by the reflective end and then by a side of the waveguide into an outer portion of the waveguide that fails to be illuminated by the first light source.

82. A directional display device comprising:

a directional backlight according to claim 70; and

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