Uniform illumination system

• US 7,072,096 B2
• Filed: 12/13/2002
• Issued: 07/04/2006
• Est. Priority Date: 12/14/2001
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Digital Optics International Corporation
• Inventors: Holman, Robert L., Cox, Arthur
• Primary Examiner(s): Ben, Loha
• Application Number:
  US10/319,800
• Publication Number:
  US 20040080938A1
• Time in Patent Office: 1,299 Days
• Field of Search: 359/618, 359/619, 359/621, 359/622, 359/623, 359/624, 359/625, 359/631, 359/633, 359/634, 359/501, 359/298, 359/457, 359/599, 385/4, 362/243, 362/242, 362/31, 362/245, 362/328, 362/331, 349/9, 349/62, 349/65, 349/112, 349/64, 349/66, 353/20, 353/31, 353/33, 353/34, 353/94
• US Class Current: 359/298
• CPC Class Codes: F21S 41/12 characterised by the type of emitted light
• CPC Class Codes: F21S 41/141 Light emitting diodes [LED]
• CPC Class Codes: F21S 8/08 with a standard F21S6/00 takes precedence
• CPC Class Codes: F21W 2102/00 Exterior vehicle lighting devices for illuminating purposes
• CPC Class Codes: F21W 2131/10 Outdoor lighting
• CPC Class Codes: F21W 2131/406 for theatres, stages or film studios
• CPC Class Codes: F21Y 2105/10 comprising a two-dimensional array of point-like light-generating elements
• CPC Class Codes: F21Y 2115/10 Light-emitting diodes [LED]
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0066 in the form of an LED array
• CPC Class Codes: G02B 27/0994 Fibers, light pipes optical fibers per se G02B6/02
• CPC Class Codes: G02B 27/1026 for use with reflective spatial light modulators
• CPC Class Codes: G02B 27/1033 having a single light modulator for all colour channels
• CPC Class Codes: G02B 27/1046 for use with transmissive spatial light modulators
• CPC Class Codes: G02B 27/1053 having a single light modulator for all colour channels
• CPC Class Codes: G02B 27/1066 for enhancing image performance, like resolution, pixel numbers, dual magnifications or dynamic range, by tiling, slicing or overlapping fields of view
• CPC Class Codes: G02B 27/1073 characterized by manufacturing or alignment methods
• CPC Class Codes: G02B 27/123 The splitting element being a lens or a system of lenses, including arrays and surfaces with refractive power
• CPC Class Codes: G02B 27/126 The splitting element being a prism or prismatic array, including systems based on total internal reflection
• CPC Class Codes: G02B 27/145 having sequential partially reflecting surfaces
• CPC Class Codes: G02B 27/147 : using averaging effects by spatially variable reflectivity on a microscopic level, e.g. polka dots, chequered or discontinuous patterns, or rapidly moving surfaces G02B27/1086 takes precedence
• CPC Class Codes: G02B 27/149 : using crossed beamsplitting surfaces, e.g. cross-dichroic cubes or X-cubes
• CPC Class Codes: G02B 27/283 : used for beam splitting or combining
• CPC Class Codes: G02B 5/045 : Prism arrays
• CPC Class Codes: G02B 6/0028 : Light guide, e.g. taper
• CPC Class Codes: G02B 6/0031 : Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0043 : provided on the surface of the light guide
• CPC Class Codes: G02B 6/0053 : Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02F 1/133603 : with LEDs
• CPC Class Codes: G02F 1/133604 : with lamps
• CPC Class Codes: G02F 1/133605 : including specially adapted reflectors
• CPC Class Codes: H01L 25/0753 : the devices being arranged next to each other
• CPC Class Codes: H01L 2924/00 : Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 : Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H04N 9/3105 : for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/315 : Modulator illumination systems general applications of lighting devices F21V; general optical systems G02B; lamp houses for projectors not peculiar to the presence of an electronic spatial light modulator G03B21/20

Abstract

A compact and efficient optical illumination system featuring planar multi-layered LED light source arrays concentrating their polarized or un-polarized output within a limited angular range. The optical system manipulates light emitted by a planar light emitters such as electrically-interconnected LED chips. Each light emitting region in the array is surrounded by reflecting sidewalls whose output is processed by elevated prismatic films, polarization converting films, or both. The optical interaction between light emitters, reflecting sidewalls, and the elevated prismatic films create overlapping virtual images between emitting regions that contribute to the greater optical uniformity. Practical illumination applications of such uniform light source arrays include compact LCD or DMD video image projectors, as well as general lighting, automotive lighting, and LCD backlighting.

Claims

1. An image display system, comprising:

means for generating image information including a spatial light modulator; and

a light source system for directly illuminating said spatial light modulator comprised of;

a one-dimensional array of substantially parallel emitting channels located behind said spatial light modulator, said array having an output area and shape arranged to at least match the aperture size of said spatial light modulator, each channel of said array having an emitting width W defined by the projected length of emitting material enclosed by said channel, as measured perpendicular to the axis of said channel and as viewed from above said array, adjacent of transparent regions of equal intra-channel separation W′

, with the separation W′

being substantially less than the width W and equal to the shortest distance between said emitting material of any one said channel and said emitting material of any adjacent said channel;

a first light directing layer including a parallel array of at least one of transparent dielectric micro prisms and aspheric semi-cylinders on a transparent substrate, said substrate arranged parallel to an output plane of said emitting channels and between the output plane of said emitting channels and the input side of said spatial light modulator, separated from said emitting channel output plane by an optical distance G1, with the optical distance G1 being less than the width W;

a second light directing layer disposed between said first light directing layer and said spatial light modulator arranged parallel to and above said first light directing layer by an air-gap of thickness S1, with the thickness S1 being substantially less than W+W′

, said second light directing layer including one or more of a holographic diffuser sheet, a bulk diffuser sheet, a surface diffuser sheet, a lenticular lens diffuser sheet, and a reflective polarizer film; and

a light reflecting layer located behind a rear side of said emitting channels a distance Y from a rear side emitting plane, the distance Y being substantially less than the separation W′

, said light reflecting layer including at least one of a white diffuse reflecting material, a specular reflecting material, a prismatic reflecting material, a structured transparent reflecting material, a bulk diffuser, a holographic diffuser, and a flat substantially transparent substrate.

2. The image display system as defined in claim 1 wherein said spatial light modulator comprises a direct view transmissive liquid crystal display (LCD).

3. The image display system as defined in claim 1 wherein said spatial light modulator comprises a passive alphanumeric appliqué

such as found in conventional EXIT signs.

4. The image display system as defined in claim 1 wherein said spatial light modulator comprises a photographic transparency.

5. The image display system as defined in claim 1 wherein said first light directing layer includes a plastic sheet of substantially parallel grooves whose cross-section forms a contiguous array of micro prisms.

6. The image display system as defined in claim 5 wherein said first light directing layer includes a plastic sheet of substantially 90-degree micro prisms, said micro-prisms being about 50 microns center to center.

7. The image display system as defined in claim 1 wherein said first light directing layer includes a sheet of substantially parallel short-focal length plastic cylinder lenses.

8. The image display system as defined in claim 7 wherein said first light directing layer includes a sheet of aspheric plastic cylinder lenses whose cross-sectional shape can be inscribed within a prism whose apex angle is approximately 90 degrees full angle.

9. The image display system as defined in claim 1 wherein said second light directing layer consists of a single holographic diffuser sheet whose output angle specification, when asymmetric, is made widest in the plane perpendicular to the axes of said emitting channels.

10. The image display system as defined in claim 1 wherein said second light directing layer comprises two holographic diffuser sheets positioned at least one of touching each other and separated from each other by an air-gap thickness in the range of 1 to 3 mm.

11. The image display system as defined in claim 1 wherein said second light directing layer includes a reflective polarizer film whose polarization transmission axis has been aligned parallel with the direction of any input polarizers transmission axis that can be coupled to said spatial light modulator.

12. The image display system as defined in claim 1 wherein said emitting channels comprise a hollow, thin-walled structure, made of glass, approximately rectangular in cross-section, and whose inside walls have been coated with a fluorescent phosphor material.

13. The image display system as defined in claim 12 wherein said emitting channels are attached to each other in a continuous serpentine manner by means of short interconnecting channel sections perpendicular to the axis of the interconnected parallel sections.

14. The image display system as defined in claim 12 wherein said emitting channels have substantially equal emitting widths falling between 10 and 15 mm and substantially equal transparent separation regions falling within the range of 1 to 5 mm in width.

15. The image display system as defined in claim 1 wherein said emitting channels are formed within and between two substantially flat transparent plates.

16. An illuminating system comprising:

a planar array composed of two or more light emitting diode chips, the same substantially identically sized with largest lateral dimension LL, each said light emitting diode chip separated from neighboring chips by a substantially equal center-to-center spacing W+W′

being less than or equal to a distance 2 LL;

a flat mounting plate disposed behind said array of said light emitting diode chips, providing support and electrical interconnection means for said light emitting diode chips;

a first light redirecting layer of thickness H+G1′

, disposed above said flat mounting plate, comprising an array of substantially same-sized tapered holes, sidewalls of each said hole slanting outwards from a first opening having first edges of a length greater than or equal to LL, to a second opening having second edges of length W+W′

, said sidewalls being smooth and reflective, said second openings having said second edges substantially contiguous with one another; and

with each said first opening containing at least one of said light emitting diode chips in said planar array;

a second light redirecting layer comprising a transparent dielectric medium whose top surface contains a regular array of substantially contiguous v-shaped grooves with each groove having a smooth sidewall, substantially equal groove angle, and substantially equal groove depth, said second light redirecting layer disposed a first elevation G1′

+H above said array of said light emitting diode chips; and

a third light redirecting layer disposed above said second light redirecting layer, including at least one of a light scattering diffuser, a quarter-wave phase retardation film, and a polarizer for at least one of absorbing and reflecting light of a first polarization state and transmitting light of a second polarization state orthogonal to said first polarization state.

17. The illuminating system as defined in claim 16 wherein said light emitting diode chips are approximately square with said largest lateral dimension LL lying between 0.2 mm and 3.0 mm on a side.

18. The illuminating system as defined in claim 17 wherein said light emitting diode chips have transparent substrates and both electrical contacts located on a same side of said transparent substrate.

19. The illuminating system as defined in claim 17 wherein said light emitting diode chips are electrically interconnected to said electrical interconnection means on said flat mounting plate.

20. The illuminating system as defined in claim 17 wherein each of said light emitting diode chips in said planar array emits substantially a same color of light.

21. The illuminating system as defined in claim 17 wherein each of said light emitting diode chips in said planar array emits a spectrum of colors approximating white.

22. The illuminating system as defined in claim 16 wherein said light emitting diode chips in said planar array have center-to-center spacing W+W′

within a range no less than about 1.5 LL and no greater than about 2 LL.

23. The illuminating system as defined in claim 16 wherein said first light redirecting layer is coated with a highly reflective metallic film.

24. The illuminating system as defined in claim 23 wherein said highly reflective metallic film is at least one of protected silver, enhanced aluminum, and aluminum.

25. The illuminating system as defined in claim 23 wherein said same-size tapered holes are filled with transparent dielectric material of refractive index greater than 1.45 and less than 1.55 at visible light wavelengths.

26. The illuminating system as defined in claim 23 wherein said first light redirecting layer of said thickness H+G1′

, first edge length greater than or equal to LL of said first opening and said second edge length W+W′

of said second opening are interrelated geometrically by said sidewall'"'"'s slant angle α

measured from the normal to the surface of said first light redirecting layer substantially as Tan α

=(W+W′

−

LL)/(2(H+G1′

)).

27. The illuminating system as defined in claim 16 wherein a spatial distribution of output light emitted from said second light redirecting layer results from overlapping virtual images of said light emitting diodes and said sidewalls of said first light redirecting layer.

28. The illuminating system as defined in claim 27 wherein said second light redirecting layer contains prismatic brightness enhancement film, whose equal groove angles are nominally 90 degrees and whose groove depths are generally in the range between 15 microns and 25 microns.

29. The illuminating system as defined in claim 27 wherein said smooth sidewalls have equal groove angles lying between 85 and 110 degrees.

30. The illuminating system as defined in claim 29 wherein said transparent dielectric medium is made free of birefringence effects.

31. The illuminating system as defined in claim 16 wherein said third light redirecting layer is composed of two sub-layers, the first sub-layer being a quarter-wave phase retardation film and the second sub-layer being a reflective polarizing film.

32. The illuminating system as defined in claim 31 wherein said first sub-layer is disposed above said second light redirecting layer, and said second sub-layer disposed above said first sub-layer.

33. The illuminating system as defined in claim 31 wherein said reflective polarizing film comprises a DBEF type film arranged to reflect substantially all light in a first linear polarization state and reflect substantially all light in a second linear polarization state.

34. The illuminating system as defined in claim 33 wherein said quarter-wave phase retardation film comprises a stretched polymeric multi-layer, whose optical property converts light beams transmitting through with said first linear polarization state into light with a first circular polarization state and light transmitting through with said second linear polarization state into light with a second circular polarization state, both when said retardation film'"'"'s polar axis is oriented at 45-degrees to said light beam'"'"'s plane of polarization.

35. An image projection system comprising:

a projection lens having an acceptance angle +/−

ω

;

a color mixing system having a first, second and third input faces and a single output face, with first second and third light beams of first second and third emitting colors respectively provided to said first, second and third input faces respectively, and then combined as a single output beam of light passing through said single output face, said output beam of light formed as a superposition of said first, second and third input beams;

first, second and third LCD micro-displays having respective first, second and third image apertures of equal rectangular horizontal and vertical edge dimensions H and V;

first, second and third angle transforming sub-systems, each of the sub-systems including at least one of a first, second and third positive lens, a first, second and third concave mirror, a first, second and third polarizing beam splitter, a first, second and third quarter-wave phase retardation layer;

first, second and third planar light source arrays, each said array including an array of equally spaced light emitting diode chips respectively of first, second and third emitting;

color, a flat interconnection plate, an array of hollow bins having tapered specularly-reflecting sidewalls, first and second light redirecting layers, a quarter-wave phase retardation film and a polarization-selective reflector, with each said hollow bin disposed about each of said light emitting diode chips, said first and second light redirecting layers disposed above said array of hollow bins; and

said projection lens focused on each said rectangular image aperture, said first, second and third angle-transforming sub-systems collecting input illumination from said first, second, and third planar light source arrays, respectively, each over an equal input angular range +/−

β

, said first, second and third angle-transforming sub-systems functioning to convert respectively said first, second and third input illumination each from angle +/−

β

to first, second and third light beams of first, second and third output illumination angle +/−

ω

, while simultaneously redirecting said first, second and third light beams respectively to said first, second and third image apertures of said first, second and third LCD micro-displays.

36. The image projection system of claim 35 wherein said first, second and third LCD micro-displays comprise transmissive elements each located at said first, second, and third input faces of said color mixing system and simultaneously at or near the respective first focal planes of said first, second and third positive lenses.

37. The image projection system of claim 36 wherein said first, second and third emitting colors comprise respectively red, green and blue.

38. The image projection system of claim 37 wherein said color mixing system is selected from the group of a dichroic X-cube and a Philips prism arrangement.

39. The image projection system of claim 36 wherein said first, second and third planar light source arrays are disposed respectively substantially in second focal planes of said first, second and third positive lenses.

40. The image projection system of claim 39 wherein said first, second and third positive lenses include at least one of a first glass, a second glass, and a third bulk glass or plastic condensing lens, and a first Fresnel lens, a second Fresnel lens, and a third Fresnel lens.

41. The image projection system of claim 35 wherein said first and second light redirecting layers each comprise an upper surface structured with a contiguous array of similarly v-shaped micro-grooves, a groove axis of said first light redirecting:

layer aligned orthogonal to a groove axis of said second light redirecting layer, said v-shaped grooves of said second light redirecting layers disposed above said v-shaped grooves of said first light redirecting layer, and peaks of both said v-shaped grooves facing away from said array of hollow bins.

42. The image projection system of claim 41 wherein said contiguous array of similarly v-shaped grooves is composed of substantially the same groove angle, γ

.

43. The image projection system of claim 42 wherein the angle γ

between adjacent groove sidewalls is about 90-degrees.

44. The image projection system of claim 43 wherein said contiguous array of similarly v-shaped grooves comprises a prismatic BEF film.

45. The image projection system of claim 41 wherein said projection lens is disposed beyond said single output face of said color mixing system.

46. The image projection system of claim 45 wherein said acceptance angle +/−

ω

is +/−

12 degrees.

47. The image projection system of claim 45 wherein said acceptance angle +/−

ω

is greater than +/−

8 degrees and less than +/−

20 degrees.

48. The image projection system of claim 41 wherein said first, second and third planar light source arrays each provide the major portion of their illumination within said equal angular range +/−

β

, +/−

β

being between +/−

20 degrees and +/−

40-degrees.

49. The image projection system of claim 35 wherein said first, second and third LCD micro-displays comprise reflective types of micro-displays and each being located at a first face of said first, second, and third polarizing beam splitters, said first, second and third planar light source arrays each emitting polarized light respectively of said first, second and third emitting colors and disposed at a second face of said first, second and third polarizing beam splitters, said second face being disposed 90-degrees to said first face, a first, second and third mirror set being located at a third face of said first, second and third polarizing beam splitters, said third face being opposite to said second face, and a fourth face of said first, second and third polarizing beam splitters being opposite to said first face and disposed adjacent to said first, second, and third face of said color mixing system.

50. The image projection system of claim 49 wherein said first, second and third LCD micro-displays comprise a liquid crystal on silicon (LCOS) type structure.

51. The image projection system of claim 49 wherein said first, second and third polarizing beam splitters are each formed by two 90-degree glass or plastic prisms joined together with optically transparent adhesive applied to a polarization selective coating deposited or affixed to one prism'"'"'s hypotenuse face.

52. The image projection system of claim 49 further including a generally cubic hollow frame to support a multi-layer glass or plastic plate occupying its slanting diagonal plane, said multi-layer glass or plastic plate including, in addition to said glass or plastic plate, at least one of a polarization-selective reflector, an absorption polarizer, and an optically transparent adhesive.

53. The image projection system of claim 35 wherein said first, second and third emitting colors are substantially red, green and blue.

54. The image projection system of claim 49 wherein said first, second and third mirror sets comprise said first, second and third concave mirror and said first, second and third quarter-wave phase retardation film, said first, second and third quarter-wave film disposed on a plane facing the mirror surface of said first, second and third concave mirrors, and said first, second and third concave mirrors functioning to focus through said first, second and third polarizing beam splitters onto the aperture planes of said first, second and third planar light source arrays and also onto said aperture planes of said first, second, and third LCD micro-displays.

55. The image projection system of claim 54 wherein said first, second and third concave mirrors include at least one of a metallically-reflecting spherical surface, a metallically-reflecting aspherical surface, a metallically-reflecting Fresnel surface, and having a metallically-reflecting mirror plane disposed behind a convexly-shaped dielectric medium.

56. An illumination system comprising,

a color mixing system having a first, second and third input faces and a single output face, with the mixing system functioning to provide first, second and third light beams of first, second and third emitting colors, respectively, provided to said first, second and third input faces, respectively, and then combined as a single output beam of light passing through said single output face, said output beam formed as a superposition of said first, second and third input beams;

first, second and third planar light source arrays, each including an array of equally spaced light emitting diode chips respectively of first, second and third emitting color, a flat interconnection plate, an array of hollow bins having tapered specularly-reflecting sidewalls with each said hollow bin disposed about each said light emitting diode, a first and second light redirecting layers, said first and second light redirecting layers disposed above said array of hollow bins; and

said first, second and third planar light source arrays each located at said first, second, and third input faces of said color mixing system.

57. The illumination system of claim 56 wherein said first, second and third emitting colors are respectively red, green and blue.

58. The illumination system of claim 56 wherein said color mixing system comprises a group of dichroic reflecting layers arranged on plates, on the required faces of an X-prism cube or on the required surfaces of a Philips prism.

59. The illumination system of claim 56 wherein said first light redirecting layer includes at least one of the following:

(a) a sheet of contiguous and substantially equivalent v-shaped grooves, (b) a negative cylindrical lens, (c) a lenticular array of negative cylindrical lenses, and (d) a negative cylindrical Fresnel lens.

60. The illumination system of claim 56 wherein said second light redirecting layer includes at least one of the following:

(a) a sheet of contiguous and substantially equivalent v-shaped grooves, (b) a negative cylindrical lens, (c) a lenticular array of negative cylindrical lenses, and (d) a negative cylindrical Fresnel lens.

61. The illumination system of claim 56 wherein said array of equally spaced light emitting diode chips is composed of at least two light emitting diode chips identically sized with largest lateral dimension LL, each said light emitting diode chip separated from neighboring chips by a substantially equal center-to-center spacing W+W′

, W+W′

being less than or equal to 2 LL.

62. The illumination system of claim 61 wherein said light emitting diode chips are approximately square with said largest lateral dimension LL lying between 0.2 mm and 3.0 mm on a side.

63. The illumination system as defined in claim 62 wherein each of said light emitting diode chips has a transparent substrate and both electrical contacts located on a same side of said transparent substrate.

64. The illumination system as defined in claim 62 wherein said light emitting diode chips are electrically interconnected to said flat interconnection plate.

65. The illumination system as defined in claim 64 wherein said flat interconnection plate is made predominately of silicon and contains metallic circuitry electrically insulated from said silicon that provides electrical interconnection means for said light emitting diode chips.

66. The illumination system as defined in claim 56 wherein said array of hollow bins has tapered specularly-reflecting sidewalls, said array having thickness L, said array disposed above said flat interconnection plate, and said array of hollow bins comprising identically sized holes, each of said holes having sidewalls slanting outwards from a first opening having first edges of length LL, to a second opening having second edges of length W, substantially contiguous with one another;

with each said first opening containing one said light emitting diode chip in said planar light source array.

67. The illumination system as defined in claim 66 wherein said thickness L, first edges of length LL of said first opening and said second edges of length W of said second opening are interrelated geometrically by said sidewall'"'"'s average slant angle a measured from the normal to the surface of said first light redirecting layer approximately by the expression tan α

=(W−

LL/2 L.

68. The illumination system as defined in claim 66 wherein said hollow bins are filled with a dielectric medium having refractive index n between 1.45 and 1.6 for said first, second and third emitting colors.

69. The illumination system as defined in claim 66 wherein said second edges of length W calculated separately in both X and Y meridians are approximately equal to LL(n)/Sin β

where +/−

β

is the predominate range of angular illumination in each meridian in air for said first, second and third light beams having said first, second and third emitting colors respectively, and n being the refractive index of the dielectric medium filling each said hollow bin.

70. The illumination system as defined in claim 66 wherein said thickness L is approximately (W−

LL/(2 Tan β

′

), with β

′

=Sin<sup>−

1</sup> (Sin β

/n) where +/−

β

is the predominate range of angular illumination in air for said first, second and third light beams having said first, second and third emitting colors respectively, n being the refractive index of the dielectric medium filling each said hollow bin.

71. The illumination system as defined in claim 56 wherein said hollow bins are filled with a dielectric medium having refractive index n between 1.45 and 1.6 for said first, second and third emitting colors.