Uniform illumination system

• US 20040080938A1
• Filed: 12/13/2002
• Published: 04/29/2004
• 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
• Granted Patent: US 7,072,096 B2
• Time in Patent Office: Days
• US Class Current: 362/231
• 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:

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

and a light source system for directly illuminating said spatial light modulator consisting 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 match or exceed the aperture size of said spatial modulator, each channel of said array having an emitting width W defined by the projected length of emitting material enclosed by said channel, measured perpendicular to the axis of said channel and as viewed from above said array, adjacent transparent regions of equal intra-channel separation S, S being substantially less than W and equal to the shortest distance between said emitting material of any one channel and said emitting material of any adjacent channel;

a first light directing layer including parallel array of transparent dielectric micro prisms or aspheric semi-cylinders on a transparent substrate, said substrate arranged parallel to the 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 1, T being less than W;

a second light directing layer disposed between the 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 D, D being substantially less than W+S, said layer including one or more of a holographic diffuser sheet, a bulk diffuser sheet, a surface diffuser sheet, lenticular lens diffuser sheet and reflective polarizer film;

a light reflecting layer located behind the rear side of said emitting channels a distance G from the rear side emitting plane, G being substantially less than S, said layer including one or more of a white diffuse reflecting material, a specular reflecting material a prismatic reflecting material, a structured reflecting material, a bulk diffuser, and a holographic diffuser, and a flat substrate.

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

3. The image display system as defined in claim 1 wherein said spatial light modulator is a passive alphanumeric applique such as found in conventional EXIT signs.

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

5. The image display system as defined in claim 1 wherein said first diffusing layer includes a plastic sheet of 90-degree micro prisms, as manufactured by Minnesota Mining and Manufacturing Company under the trademark BEF.

6. The image display system as defined in claim 1 wherein said first diffusing layer includes a sheet of short-focal length plastic cylinder lenses.

7. The image display system as defined in claim 1 wherein said first diffusing 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.

8. The image display system as defined in claim 1 wherein said second diffusing layer consists of a single holographic diffuser sheet whose output angle specification, if not symmetric, is made widest in the plane perpendicular to the axes of said emitting channels.

9. The image display system as defined in claim 1 wherein said second diffusing layer consists of two holographic diffuser sheets, either touching each other, or separated from each other by an air-gap thickness in the range of 1 to 3 mm.

10. The image display system as defined in claim 1 wherein said second diffusing layer includes a reflective polarizer film whose polarization transmission axis has been aligned parallel with the direction of any input polarizers transmission axis that may be attached to or otherwise part of said spatial light modulator.

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

12. The image display system as defined in claim 11 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.

13. The image display system as defined in claim 11 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.

14. An illuminating system comprising:

a two-dimensional array on substantially equal horizontal and vertical center-to-center spacing consisting of one or more electrically interconnected light emitting diode chips of lateral dimensions L mm by W mm whose transparent substrate medium is of refractive index n₀;

a reflecting plane layer disposed behind said two-dimensional array of said electrically interconnected light emitting diode chips, providing means of support and electrical interconnection;

a first transparent spacer layer of finite thickness, comprising regions of a transparent dielectric medium of refractive index n₁ said dielectric medium encapsulating said light emitting diode chips;

a second transparent spacer layer of finite thickness, comprising a dielectric medium of refractive index n₂, the top surface of which contains a regular array of v-shaped smooth-sided grooves having equal groove angle and equal groove depth;

a third transparent spacer layer disposed just above said first transparent spacer layer of finite thickness, comprising a medium of refractive index n₂, said refractive index n₃ being less than said refractive index n₂;

a fourth transparent spacer layer disposed above said third transparent spacer layer of finite thickness, comprising a medium of refractive index n₄ being greater than said refractive index n₃, the bottom surface of which is a smooth plane, the top surface of which contains a regular array of v-shaped smooth-sided grooves having equal groove angle and equal groove depth;

and whose groove axes run substantially at a 90 degree angle to the groove axes of said second transparent layer;

a fifth transparent spacer layer disposed above said fourth spacer layer of finite thickness, comprising a medium of refractive index n₅, said refractive index n₅ being less than said refractive index n₄,

a sixth transparent spacer layer disposed above said fifth spacer layer of finite thickness, comprising a medium of refractive index n₆, said refractive index n₆ being greater than said refractive index n₅ and said groove angles being those measured between adjacent groove faces, said groove depth being the shortest distance measured from the bottom of said groove to the top of said groove; and

said sixth transparent spacer layer including at least one of a light scattering diffuser and a polarizer for absorbing or reflecting light of a first polarization state and transmitting light of a second polarization state orthogonal to said first polarization state.

15. The illuminating system as defined in claim-14 wherein said dimensions L mm and W mm of said electrically interconnected light emitting diode chips are approximately equal to L and lie between 0.2 mm and 2.0 mm on a side.

16. The illuminating system as defined in claim 15 wherein said center-to-center spacings are within a range no less than about 1.5L and no greater than about 2L.

17. The illuminating system as defined in claim 15 wherein said two-dimensional array consists of said electrically interconnected light emitting diode chips all emitting substantially the same color light.

18. The illuminating system as defined in claim 15 (wherein said two-dimensional array consists of clusters of three or more said light emitting diode chips, one emitting substantially red light, one emitting substantially green light and one emitting substantially blue light, the centers of said clusters separated from one another by said center-to-center spacings being no less than 1.5 times the minimum cluster size defined by the square area taken up by said electrically interconnected light emitting diodes located within said cluster, said electrically connected light emitting diodes within said cluster being separated from each other in all directions within said cluster by a space no smaller than about 1.5L.