Liquid crystal display system with internally reflecting waveguide for backlighting and non-Lambertian diffusing

• US 5,838,403 A
• Filed: 02/14/1996
• Issued: 11/17/1998
• Est. Priority Date: 02/14/1996
• Status: Expired due to Term

• Current Assignee: Luminit LLC
• Original Assignee: Physical Optics Corporation
• Inventors: Jannson, Joanna L., Jannson, Tomasz P., Lerner, Jeremy M.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Parker, Kenneth
• Application Number:
  US08/601,133
• Time in Patent Office: 1,007 Days
• Field of Search: 349/65, 349/62, 349/64, 349/67, 359/599, 385/901, 385/129, 385/130, 385/146, 362/26, 362/29, 362/27
• US Class Current: 349/65
• CPC Class Codes: G02B 6/0018 Redirecting means on the surface of the light guide
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened 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 6/0061 to provide homogeneous light output intensity
• CPC Class Codes: G02F 1/133607 the light controlling member including light directing or refracting elements, e.g. prisms or lenses
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

Systems and methods for providing an LCD with a collimated backlight and a non-Lambertian diffuser are described. An LCD system includes: an illumination source for producing light; a collimating waveguide optically connected to the illumination source, the collimating waveguide including a top surface, an incident end and a plurality of substantially parallel optical elements for redirecting light from the incident end to, and through, the top surface, each of the plurality of substantially parallel optical elements including a first facet that is nonparallel to the top surface and a second facet that is nonparallel to the top surface; a reflector optically connected to the light source and optically connected to the collimating waveguide, the reflector (1) at least partially surrounding the illumination source, and (2) reflecting light from said illumination source to said incident end by direct reflection; a liquid crystal display optically connected to the collimating waveguide; and a non-Lambertian diffuser optically connected to the liquid crystal display for directing light from said liquid crystal display. The light from the reflector is directly incident upon the incident end. The systems and methods provide advantages in that the light from the LCD is bright and homogenous.

Claims

1. An apparatus, comprising:

an illumination source for producing light;

a first collimating waveguide optically connected to said illumination source, said first collimating waveguide including a top surface, an incident end and a first plurality of substantially parallel optical elements for redirecting light from said incident end to, and through, said top surface by total internal reflection, each of said first plurality of optical elements including a concave first facet that is nonparallel to said top surface and a second facet that is nonparallel to said top surface, said second facet being concave with respect to said top surface;

a second collimating waveguide optically connected to said first collimating waveguide, said second collimating waveguide including an upper surface and a second plurality of optical elements for redirecting light from said top surface through said upper surface;

a diffuser for homogenizing light optically connected to said second collimating waveguide; and

a reflector optically connected to said light source and optically connected to said first distributed wedge collimating waveguide, said reflector (1) at least partially surrounding said illumination source, and (2) reflecting light from said illumination source to said incident end by direct reflection.

2. The apparatus of claim 1, further comprising a nonimaging optic between said illumination source and said incident surface, said nonimaging optic being optically connected to said illumination source and said first collimating waveguide.

3. The apparatus of claim 1, wherein said diffuser includes a light shaping holographic surface diffuser having at least one diffuser characteristic selected from the group consisting of directional and off-axis.

4. A backlight comprising:

a collimating waveguide having a light input end, a top surface, a bottom surface, and opposing sides;

said bottom surface converging toward said top surface in a direction along said backlight away from said light input end;

said bottom surface comprising a plurality of straight facets having a density ρ

distributed along said bottom surface in a direction along said backlight away from said light input end and extending at least part way between said opposing sides;

each said straight facet having a straight facet bottom surface which converges toward said top surface in a direction along said backlight away from said light input end at an angle γ

less than approximately 5°

;

each said straight facet bottom surface of each said straight facet being parallel to each said straight facet bottom surface of each other said straight facet;

said collimating waveguide reflecting light rays entering said light input end in accordance with total internal reflection and entering with an angle greater than said total internal reflection critical angle;

said facets causing light rays entering said light input end and having an angle near said total internal reflection critical angle to exit said top surface at an angle nearly tangential to said top surface.

5. The backlight of claim 4, wherein said facets cause light rays entering said light input end and having an angle near said total internal reflection critical angle to exit said top surface at an angle of approximately 2γ

.

6. The backlight of claim 4, wherein each said straight facet bottom surface is reflective to prevent light from leaking from each said straight facet bottom surface.

7. The backlight of claim 4, wherein each said straight facet bottom surface is metalized to prevent light from leaking from each said straight facet bottom surface.

8. The backlight of claim 4, wherein light leaks from each said straight facet bottom surface and from said top surface.

9. The backlight of claim 4, wherein each said straight facet extends between said opposing sides.

10. The backlight of claim 4, wherein said density ρ

of said straight facets varies as a function of a distance from said light input end.

11. The backlight of claim 10, wherein said density ρ

of said straight facets is such that an intensity of emitted light is uniform across a length of said backlight.

12. The backlight of claim 10, wherein each said straight facet bottom surface is metalized to prevent light from leaking from each said straight facet bottom surface.

13. The backlight of claim 4, further comprising a diffuser optically coupled to said top surface for homogenizing light exiting said top surface.

14. The backlight of claim 13, further comprising a non-Lambertian second diffuser optically coupled to said light input end for reducing reflection from said light input end.

15. The backlight of claim 4, further comprising a non-Lambertian diffuser optically coupled to said light input end for reducing reflection from said light input end.

16. The backlight of claim 4, further comprising a liquid crystal display optically coupled to said collimating waveguide.

17. The backlight of claim 16, further comprising a non-Lambertian diffuser optically coupled to said liquid crystal display for directing light from said liquid crystal display.

18. The backlight of claim 17, further comprising a second diffuser optically coupled to said top surface for homogenizing light exiting from said top surface.

19. The backlight of claim 18, further comprising a non-Lambertian third diffuser optically coupled to said light input end for reducing reflection from said light input end.

20. The backlight of claim 4, further comprising a spatial light modulator optically coupled to said collimating waveguide.

21. The backlight of claim 4, further comprising a light source optically coupled to said light input end.

22. The backlight of claim 21, further comprising a reflector optically coupled to said light source and optically coupled to said light input end of said collimating waveguide, said reflector at least partially surrounding said light source and reflecting light from said light source to said light input end by direct reflection, wherein light from said reflector is directly incident upon said light input end.

23. The backlight of claim 4, further comprising a second collimating waveguide optically coupled to said collimating waveguide, said second collimating waveguide including an upper surface and a second plurality of facets for redirecting light exiting said top surface through and out said upper surface at an angle substantially greater than 2γ

and approximately normal to said top surface.

24. A backlight comprising:

a collimating waveguide having a light input end, a top surface, a bottom surface, and opposing sides;

said bottom surfaces converging toward said top surface in a direction along said backlight away from said light input end;

said bottom surface comprising a plurality of straight facets having a density ρ

distributed along said bottom surface in a direction along said backlight away from said light input end and extending at least part way between said opposing sides;

each said straight facet having a straight facet bottom surface which converges toward said top surface in a direction along said backlight away from said light input end at an angle less than approximately 5°

;

each said straight facet bottom surface of each said straight facet being parallel to each said straight facet bottom surface of each other said straight facet;

said collimating waveguide reflecting light rays entering said light input end in accordance with total internal reflection and at an angle greater than a total internal reflection critical angle;

said facets causing light entering said light input end and having an angle near said total internal reflection critical angle to exit said top surface at an angle nearly tangential to said top surface and of approximately 2γ

;

a second collimating waveguide optically coupled to said collimating waveguide, said second collimating waveguide including an upper surface and a second plurality of facets for redirecting light exiting said top surface through and out said upper surface at an angle substantially greater than 2γ and

approximately normal to said top surface;

a non-Lambertian diffuser optically coupled to said second collimating waveguide for directing light exiting said second collimating waveguide.

25. The backlight of claim 24, wherein said non-Lambertian diffuser provides a controllable output angle determined by surface features replicated in said non-Lambertian diffuser from speckle recorded in a photosensitive medium which determine angular output characteristics of said non-Lambertian diffuser.

26. The backlight of claim 24, wherein said second collimating waveguide is integral with said non-Lambertian diffuser.

27. The backlight of claim 25, wherein γ

is in the range 0.5°

-2.0°

.

58. The backlight of claim 27, wherein each of said plurality of curved facets are concave with respect to said top surface.

28. A backlight comprising:

a collimating waveguide having a light input end, a top surface, a bottom surface, and opposing sides;

said bottom surfaces converging toward said top surface in a direction along said backlight away from said light input end;

said bottom surface comprising a plurality of straight facets distributed along said bottom surface in a direction along said backlight away from said light input end and extending at least part way between said opposing sides;

each said straight facet having a straight facet bottom surface arranged substantially parallel to said bottom surface which converges toward said top surface in a direction along said backlight away from said light input end at an angle less than approximately 5°

; and

wherein said straight facet bottom surfaces cause light rays entering said light input end and having an angle near said total internal reflection critical angle to exit said top surface at an angle nearly tangential to said top surface.

29. The backlight of claim 28, wherein said bottom surface converges toward said top surface at an angle between 0.5°

to 2.0°

.

30. The waveguide of claim 28 wherein said collimating waveguide reflects light rays entering said light input end in accordance with total internal reflection and at an angle greater than a total internal reflection critical angle.

31. The waveguide of claim 28 wherein said straight facet bottom surfaces cause light rays entering said light input end and having an angle near said total internal reflection critical angle to exit said top surface at an angle to said top surface and of approximately 2γ

.

32. The waveguide of claim 28, wherein the facets have an density distribution along said bottom surface that varies as a function of a direction along said backlight away from said light input end.

33. The waveguide of claim 28, wherein each said straight facet bottom surface of each said straight facet is parallel to each said straight facet bottom surface of each other said straight facet.

34. The backlight of claim 28, wherein said facets cause light rays entering said light input end and having an angle near said total internal reflection critical angle to exit said top surface at an angle of approximately 2γ

.

35. The backlight of claim 28, wherein each said straight facet bottom surface is reflective to prevent light from leaking from each said straight facet bottom surface.

36. The backlight of claim 28, wherein each said straight facet bottom surface is metalized to prevent light from leaking from each said straight facet bottom surface.

37. The backlight of claim 28, wherein light leaks from each said straight facet bottom surface and from said top surface.

38. The backlight of claim 28, wherein each said straight facet extends between said opposing sides.

39. The backlight of claim 28, wherein said density ρ

of said straight facets varies as a function of a distance from said light input end.

40. The backlight of claim 39, said density ρ

of said straight facets is such that an intensity of emitted light is uniform across a length of said backlight.

41. The backlight of claim 39, wherein each said straight facet bottom surface is metalized to prevent light from leaking from each said straight facet bottom surface.

42. The backlight of claim 28, further comprising a diffuser optically coupled to said top surface for homogenizing light exiting said top surface.

43. The backlight of claim 42, further comprising a non-Lambertian second diffuser optically coupled to said light input end for reducing reflection from said light input end.

44. The backlight of claim 28, further comprising a non-Lambertian diffuser optically coupled to said light input end for reducing reflection from said light input end.

45. The backlight of claim 28, further comprising a liquid crystal display optically coupled to said collimating waveguide.

46. The backlight of claim 28, further comprising a non-Lambertian diffuser optically coupled to said liquid crystal display for directing light from said liquid crystal display.

47. The backlight of claim 46, further comprising a second diffuser optically coupled to said top surface for homogenizing light exiting from said top surface.

48. The backlight of claim 47, further comprising a non-Lambertian third diffuser optically coupled to said light input end for reducing reflection from said light input end.

49. The backlight of claim 28, further comprising a spatial light modulator optically coupled to said collimating waveguide.

50. The backlight of claim 28, further comprising a light source optically coupled to said light input end.

51. The backlight of claim 39, further comprising a reflector optically coupled to said light source and optically coupled to said light input end of said collimating waveguide, said reflector at least partially surrounding said light source and reflecting light from said light source to said light input end by direct reflection, wherein light from said reflector is directly incident upon said light input end.

52. A backlight comprising:

a collimating waveguide having a light input end, a top surface, a bottom surface, and opposing sides, said bottom surface converging toward said top surface in a direction along said backlight away from said light input end, said bottom surface comprising a plurality of curved facets distributed along said bottom surface in a direction along said backlight away from said light input end and extending at least part way between said opposing sides, each said curved facet having a curved facet bottom surface, each said curved facet bottom surface being arranged to reflect a ray-bundle incident to said curved facet bottom surface, and wherein said ray-bundle comprises a plurality of light rays and wherein each of said light rays is reflected substantially normally to the top surface in a symmetrical distribution.

53. The backlight of claim 52, wherein said plurality of curved facets are arranged in an array distributed on said bottom surface.

54. The backlight of claim 52, wherein said plurality of curved facets are arranged in a segmented array.

55. The backlight of claim 52, wherein said plurality of curved facets are arranged into segments, each said segment being arranged parallel to each other said segment.

56. The backlight of claim 52, wherein said plurality of curved facets are distributed with an increasing density ρ

from said light input end.

57. The backlight of claim 52, wherein said density ρ

of said straight facets is such that an intensity of emitted light is uniform across a length of said backlight.

59. The backlight of claim 54, wherein said bottom surface converges towards said top surface at an angle less than about 5°

.

60. The backlight of claim 54, wherein said bottom surface converges toward said top surface at an angle of about 0.50°

-2.0°

.

61. The backlight of claim 54, wherein said collimating waveguide further comprises a second light input end opposing said light input end, said bottom surface further comprising a plurality of second curved facets each opposing said plurality of curved facets and each having a second curved facet bottom surface, each said second curved facet being arranged to reflect a second ray-bundle incident to said second curved facet bottom surface, and wherein said second ray-bundle comprises a plurality of light rays and wherein each of said light rays are reflected substantially normally to the top surface and in a symmetrically distribution.

62. The backlight of claim 61, wherein each said second curved facet is concave with respect to said top surface.

63. The backlight of claim 61, wherein each said curved facet and each said second curved facet is concave with respect to said top surface.

64. The backlight of claim 61, wherein each said curved facet and each said second curved facet is arranged with scalloped edges, said scalloped edges collimating skew light rays.

65. The backlight of claim 62, wherein each said curved facet and each said second curved facet are arranged to preferentially direct a light flux substantially normal to said top surface.

66. The backlight of claim 65, wherein light flux enters said waveguide collimator from said light input end and said second light input end.

67. A backlight comprising:

a collimating waveguide having a light input end, a top surface, a bottom surface, and opposing sides, said bottom surface converging toward said top surface in a direction along said backlight away from said light input end, said bottom surface comprising a plurality of curved facets having a density distributed along said bottom surface in a direction along said backlight away from said light input end and extending at least part way between said opposing sides, each said curved facet having a curved facet bottom surface, each said curved facet bottom surface being curved substantially in accordance with the equation;

##EQU33## where β

is the angle of a highest inclination incident ray and w and G are dimensions of said curved facet; and

said plurality of curved facets causing light entering said light input end and reflecting from said plurality of curved facets to reflect from each said curved facet bottom surface symmetrically with respect to an axis normal to said top surface.