High-density illumination system Number:7,520,642 from the United States Patent and Trademark Office (PTO) owispatent 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 array of electrically-interconnected LED chips positioned within the input apertures of a corresponding array of shaped metallic reflecting bins using at least one of elevated prismatic films, polarization converting films, micro-lens arrays and external hemispherical or ellipsoidal reflecting elements. Practical applications of the LED array illumination systems include compact LCD or DMD video image projectors, as well as general lighting, automotive lighting, and LCD backlighting.<H illumination, density, High, density, il, 7520642.html, Patent, pto, 7520642

Title: High-density illumination system

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 array of electrically-interconnected LED chips positioned within the input apertures of a corresponding array of shaped metallic reflecting bins using at least one of elevated prismatic films, polarization converting films, micro-lens arrays and external hemispherical or ellipsoidal reflecting elements. Practical applications of the LED array illumination systems include compact LCD or DMD video image projectors, as well as general lighting, automotive lighting, and LCD backlighting.

Patent Number: 7,520,642 Issued on 04/21/2009 to Holman, et al.

Inventors: Holman; Robert L. (Evanston, IL), Cox; Arthur (Park Ridge, IL)
Assignee: Digital Optics International Corporation (Evanston, IL)

Appl. No.: 11/784,046

Filed: April 5, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
11089314	Mar., 2005	7210806
10763816	Jan., 2004	6871982
60442624	Jan., 2003

Current U.S. Class: 362/328 ; 349/61; 362/19; 362/245; 362/331; 362/800

Current International Class: F21V 5/00 (20060101)

Field of Search: 362/19,242-245,328,331,343,545,800 349/61

References Cited [Referenced By]

U.S. Patent Documents


4947291	August 1990	McDermott
5361190	November 1994	Roberts et al.
6871982	March 2005	Holman et al.
7210806	May 2007	Holman et al.

Primary Examiner: Husar; Stephen F
Attorney, Agent or Firm: Foley & Lardner LLP

Parent Case Text

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/089,314, filed Mar. 23, 2005, now U.S. Pat. No. 7,210,806, which is a continuation of Ser. No. 10/763,816 filed Jan. 22, 2004, now U.S. Pat. No. 6,871,982, which claims priority to U.S. Patent Application 60/442,624 filed Jan. 24, 2003, incorporated herein by reference in its entirety.

Claims

What is claimed is:

1. An illuminating system, comprising: an electrical interconnection system for interconnecting at least one LED light emitting element to a power source; at least one LED light emitting element positioned on a common light-emitting plane; a first light redirecting element disposed above the at least one LED light-emitting element on said common light emitting plane, each said first light redirecting element including at least one diffusing medium, a diffusing layer, and a component, said component selected from the group consisting of a metallically reflecting bin and a lens system, said metallically reflecting bin having a circular or rectangular cross-section with mathematically curving shape necessitated by meeting the geometrical relationship between input and output aperture sizes, A.sub.inSin .sup.2.theta..sub.in=A.sub.outSin.sup.2.theta..sub.out, where A.sub.inis: if circular, the area of the reflecting bin inlet .pi.r.sub.in.sup.2, r.sub.in being the radius of the bin's inlet opening, and if rectangular, (x.sub.in)(y.sub.in) .theta..sub.in is the maximum half-angle emitted by the at least one LED at bin's input opening disposed above it, the full beam angle being 2.theta..sub.in, A.sub.out is the area of the aperture existing at the bin's ideal height H given as if circular, H=(r.sub.in+r.sub.out)/Tan.theta..sub.out with r.sub.out being the diameter of the bin's ideal output aperture, and .theta..sub.out is the corresponding output beam's half-angle, the beam's full angle being 2.theta..sub.out; if rectangular, H being the larger of H.sub.1=0.5(x.sub.in+x.sub.out)/Tan.theta..sub.out,x and H.sub.2=0.5 (y.sub.in+y.sub.out)/Tan.theta..sub.out,y with x.sub.out and y.sub.out being the aperture edge sizes, .theta..sub.out,x and .theta..sub.out,y being the corresponding output beam half-angles in each orthogonal meridians; and H.sub.bin is the actual bin height of the metallically reflecting bin of the first light redirecting element, H.sub.bin is equal to or less than the ideal bin height H; a second light redirecting element disposed beyond said first light redirecting element comprised of at least one condensing element having effective focal length F and an elevation above said first light redirecting means in the range 0 to 2 F above the output plane of said first light redirecting layer: said at least one condensing element of the second light redirecting layer selected from the group consisting of a Fresnel lens, two sequentially stacked Fresnel-type cylindrical lenses where the axes of each form an angle of 90-degrees with each other, a reflecting plane having a circular or rectangular cutout that allows for a substantial portion of the emitted light to pass outwards without change in brightness or angular direction, and two sequentially stacked lenticular lenses where the axes of each form an angle of 90-degrees with each other; and an output aperture disposed beyond said second light redirecting element, said output aperture containing at least one of a clear window and a spatial light modulator.

2. The illuminating system as defined in claim 1 wherein the first light redirecting element comprises metallically reflecting bins having a clear output aperture and a clear input aperture formed by at least one mathematically-tapered metallically reflecting sidewall extending therebetween, centers of each said metallically reflecting bin being centered on a center of a corresponding one of the LED light emitting element.

3. The illuminating system as defined in claim 1 wherein said first light redirecting element comprises at least one of lenses and systems of lenses centered on the center of a corresponding one of the LED light emitting element.

4. The illuminating system as defined in claim 1 wherein said first light redirecting element comprises at least one of a passive diffuser, a holographic diffuser and active diffuser including a transparent phase holding secondary diffuser spherical particles that fluoresce and/or scatter the light passing through the particles, the center of each said passive and active diffuser centered on a center of the corresponding one of the LED light emitting element.

5. The illuminating system as defined in claim 1 wherein said second light redirecting element is disposed a distance above said output plane of said first light redirecting element approximately equal to said effective focal length F of said second light redirecting element.

6. The illuminating system as defined in claim 1 wherein said effective focal length F of said second light redirecting element is greater than the distance H.sub.bin in which said output plane of said first light redirecting element stands above said common light emitting plane of said first light redirecting element, and in which the distance between said second light redirecting element and said output plane of said first light redirecting element falls in the range between 0 and 0.25 F.

7. The illuminating system as defined in claim 1 wherein said effective focal length F of said second light redirecting element is chosen to change said output beam angles emitting from said first light redirecting element, and in which the distance between said second light redirecting element and said output plane of said first light redirecting element falls approximately in the range of 0.5 F and 1.5 F.

8. An illuminating system, comprising: an electrical interconnection system for interconnecting at least one LED light emitting element to a power source; at least one LED light emitting element positioned on a common light-emitting plane; a first light redirecting element disposed above the at least one LED light-emitting element on said common light emitting plane, each said first light redirecting element including at least one diffusing medium, a diffusing layer, and a component, said component selected from the group consisting of a metallically reflecting bin and a lens system, said metallically reflecting bin having a circular or rectangular cross-section with mathematically curving shape necessitated by meeting the geometrical relationship between input and output aperture sizes, A.sub.inSin.sup.2.theta..sub.in=A.sub.outSin.sup.2.theta..sub.out, where A.sub.in is (x.sub.in)(y.sub.in); .theta..sub.in is the maximum half-angle emitted by the at least one LED at bin's input opening disposed above it, the full beam angle being 2.theta..sub.in, A.sub.out is the area of the aperture existing at the bin's ideal height H given as H being the larger of H.sub.1=0.5 (x.sub.in+x.sub.out)/Tan.theta..sub.out,x and H.sub.2=0.5 (y.sub.in+y.sub.out)/Tan.theta..sub.out,y with x.sub.out and y.sub.out being the aperture edge sizes, .theta..sub.out,x and .theta..sub.out,y being the corresponding output beam half-angles in each orthogonal meridians; and H.sub.bin is the actual bin height of the metallically reflecting bin of the first light redirecting element, H.sub.bin is equal to or less than the ideal bin height H; a second light redirecting element disposed beyond said first light redirecting element comprised of at least one condensing element having effective focal length F and an elevation above said first light redirecting means in the range 0 to 2 F above the output plane of said first light redirecting layer: said at least one condensing element of the second light redirecting layer selected from the group consisting of a Fresnel lens, two sequentially stacked Fresnel-type cylindrical lenses where the axes of each form an angle of 90-degrees with each other, a reflecting plane having a circular or rectangular cutout that allows for a substantial portion of the emitted light to pass outwards without change in brightness or angular direction, and two sequentially stacked lenticular lenses where the axes of each form an angle of 90-degrees with each other; and an output aperture disposed beyond said second light redirecting element, said output aperture containing at least one of a clear window and a spatial light modulator.

9. The illuminating system as defined in claim 8 wherein the first light redirecting element comprises metallically reflecting bins having a clear output aperture and a clear input aperture formed by at least one mathematically-tapered metallically reflecting sidewall extending therebetween, centers of each said metallically reflecting bin being centered on a center of a corresponding one of the LED light emitting element.

10. The illuminating system as defined in claim 8 wherein said first light redirecting element comprises at least one of lenses and systems of lenses centered on the center of a corresponding one of the LED light emitting element.

11. The illuminating system as defined in claim 8 wherein said first light redirecting element comprises at least one of a passive diffuser, a holographic diffuser and active diffuser including a transparent phase holding secondary diffuser spherical particles that fluoresce and/or scatter the light passing through the particles, the center of each said passive and active diffuser centered on a center of the corresponding one of the LED light emitting element.

12. The illuminating system as defined in claim 8 wherein said second light redirecting element is disposed a distance above said output plane of said first light redirecting element approximately equal to said effective focal length F of said second light redirecting element.

13. The illuminating system as defined in claim 8 wherein said effective focal length F of said second light redirecting element is greater than the distance H.sub.bin in which said output plane of said first light redirecting element stands above said common light emitting plane of said first light redirecting element, and in which the distance between said second light redirecting element and said output plane of said first light redirecting element falls in the range between 0 and 0.25 F.

14. The illuminating system as defined in claim 8 wherein said effective focal length F of said second light redirecting element is chosen to change said output beam angles emitting from said first light redirecting element, and in which the distance between said second light redirecting element and said output plane of said first light redirecting element falls approximately in the range of 0.5 F and 1.5 F.

Description

BACKGROUND OF THE INVENTION

The present invention, which is an expansion on inventions described in a previously filed application, entitled Uniform Illumination System filed on Dec. 14, 2001, Ser. No. 10/319,800, and which is incorporated by reference herein, is concerned generally with a thin and compact multi-layered optical system and method for generating well-organized output illumination from a one or two-dimensional array of discrete light emitting diodes (LEDs), the output light spread uniformly over the system's aperture while emanating from a uniquely multi-layered system comprised of reflecting bins and elevated light directing films. The present invention focuses centrally on the beneficial interactions between the geometric parameters of a thin array of metallically-reflecting bins, each having four tapered sidewalls meeting at an input aperture containing an LED, and the geometric parameters of orthogonally oriented prism sheets (and/or polarization converting sheets) placed above them. The previous invention described the basic geometric configurations of such multi-layers, while the present invention explores their performance differences, and in doing so, sets forth two specific embodiments related to directed LED lighting and illumination, as well as adding means for additional efficiency gains by the external recycling of otherwise wasted light. The first LED light source array embodiment trades optical efficiency to achieve output beams having the highest practical density of lumens, making very high-power illumination applications such as occur in video projectors practical at the soonest opportunity. In this non-etendue-preserving embodiment, interactions between reflecting bins and elevated prism sheets, polarization-converting films and/or micro-lens arrays cause beneficial spatial overlap of bin outputs that increase the array's effective lumen density. The second LED light source array embodiment achieves highest possible optical efficiency, allowing high-brightness illumination applications using the fewest possible LEDs and/or the lowest amounts of electrical power. In this etendue-preserving embodiment, shaped reflecting bins are combined with elevated micro-lenses and polarization converting films to manipulate the illumination pattern especially for square or rectangular illumination targets. Accordingly, the field of illumination produced by the particular optical systems containing these multi-layered emitting arrays provide a suitable illuminating beam for projecting an electronic image (as from an LCD or DMD) onto a screen, or the illumination itself composed of separately-controlled image pixels, the sum of which at any instant forming a spatially modulated image to be viewed directly, as in LED image displays for signage and video. The field of directed illumination may also be used as a means of general illumination, as in lighting fixtures and luminaries. More particularly, the multi-layer optical system that achieves this favorable performance consists of a heat extraction layer, an electronic back plane containing a regular one or two-dimensional array of electronically interconnected LEDs (preferably flip-chip style), an micro-fabricated array of contiguous (or nearly contiguous) reflecting bins with shaped or plane tapered sidewalls, one bin surrounding each LED (or group of LEDs), and a sequence of at least one additional optical light directing layer positioned above or at a preferred spacing from the reflecting bin apertures, the layer construction designed in conjunction with the geometry of the underlying reflecting bins, so as to maximize the light source array's output power and field coverage within a particular angular range, or within a particular angular range and polarization state. An additional layer or layers, in configurations that needing some additional diffusive mixing, can be conventional light spreading materials such as holographic diffusers, lenticular diffusers, lens arrays, bulk or surface scattering diffusers, opal glass, or ground glass, added to improve spatial uniformity.

Currently available illumination systems capable of achieving equivalent brightness uniformity (and lumen density) using only conventional optical elements, do so with at least 2 times fewer lumens per square millimeter, less efficiently (in terms of brightness), and in considerably thicker and less well-integrated packaging structures. Currently available LED illumination systems use arrays of discretely packaged LED devices, or LED chips on interconnection planes disposed below conventional refractive optical elements (whose effective optical collection range is limited). By comparison, the uniqueness of the present invention relates to the fact that its compartmentalized packaging layer and its cooperatively designed optical over-layers are both made to be continuous elements for the entire array--and whose choice of materials and their geometry achieves significantly enhanced performance. Designing the reflecting bins and the optical layers above them interactively, and by means of a realistic and experimentally validated computer model, is found to maximize optical output compared with more conventional designs. The increase in the performance of such LED light source arrays is not an obvious step despite previous use of LEDs in arrays, in reflective packages, and in conjunction with many types of conventional secondary optical elements.

Such compact LED illumination systems are of primary interest for the projection of images onto screens from such spatial light modulators as reflective and transmissive LCDs and DMDs. LED illumination is considered superior to the commonly used discharge lamps with regard to operating lifetime, which increases nearly 100-fold, and also because the conductive heat generated in the LEDs is easier to extract than the radiative heat given off by a gas discharge. Using LEDs in place of short-arc discharge lamps, however, is not straightforward for several reasons. Discharge lamps generate 60 (white) lumens per watt at 130-150 watts, and today's projection systems have rather low end-to-end optical efficiencies in the range of 15% and less. Imagining the use of today's best high-power LEDs at light levels of 7000 to 9000 lumens seems quite difficult, given that best emission efficacies are only in the range of only 15-25 lumens per watt. What's more, manufacturing economies keep typical LCD and DMD image apertures less than 1.2'' on the diagonal, and such devices cannot make effective use of light at angles above +/-12 degrees. This means that the total effective illumination area for the +/-90 degree emitting LEDs has to be less than 19.28 mm.sup.2, or for the standard image 4:3 aspect ratio, less than a rectangular area 5.07 mm by 3.80 mm. While such jumbo chips might become available in the distant future, the largest chips known today are square and not yet larger than 1 mm or 2 mm on an edge (as manufactured by LumiLeds, San Jose, Calif.). Even were such jumbo chips available, the challenge would still be to convert all its generated lumens to the +/-12-degrees needed in practical image projectors with high enough efficiency and spatial illumination uniformity. At today's best LED lumen density of 50 lumens/mm.sup.2, the total lumen yield from such a small illumination aperture would not be nearly enough after projection system transmission losses to reach competitive projection screen powers, which must be at least 1000 white-field lumens for many product applications of commercial interest.

The basic approach for overcoming this limitation has been described previously and involves using spatially separated high lumen density multi-layered arrays of separated red, green and blue LEDs, these arrays arranged and designed to concentrate their output emissions to a particular range of narrowed output angles (and polarization states) that can be handled efficiently by the conventional optics of a modern image projection system. Once so-created and integrated with the respective reflective or transmissive LCDs (or reflective digital micro-mirror devices, DMDs or DLPs as trade marked by Texas Instruments), the LED array output beams are mixed using the standard dichroic mixing cubes that allow the single-colored beam apertures to be superimposed on each other.

The present invention extends the basic approach to specific very high lumen density illuminator embodiments that enable with the best of the forthcoming high-power flip-chip LEDs, a wide range of compact and practical image projectors.

The present invention also extends to very low power, potentially hand held image projectors suitable for battery operation.

Such compact high lumen density LED illumination systems are also of interest for certain traffic signals and alerts, interior lighting, street lighting, stage and theatrical lighting, automotive head and tail lighting, safety warning lights, the backlighting of LCD screens and certain fiber optic medical illuminators.

These same compact high lumen density multi-layered illumination systems may be adapted for their intrinsic ability to display pixelized images directly, where in each reflecting bin within the light source array involved contains one each of a red, green and blue LED, and wherein every LED in the array is individually-addressed.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide an improved high lumen density illumination system and method of use.

It is another object of the invention to provide a multi-layered packaging means for a high lumen density light source panel structure containing a sparse two dimensional array of light emitting diode chips on a layer that provides discrete, thin-film electrical interconnections to the diodes, and that isolates one or more diode chips within separate specularly reflecting compartments, the compartments themselves arranged in a corresponding two-dimensional array that is covered with a stack of optical layers, one of which is a mechanical spacer including the bins themselves that allows light transmission from each compartment to reach two light directing layers that include linear arrays of prism-like grooves made in a clear plastic material, the grooves in each layer aligned at 90-degrees to one another.

It is a further object of the invention to provide a sufficiently high lumen density light source panel system and method for providing an efficient and homogeneous beam of directional illumination to LCD and DMD spatial light modulators within compact video projection systems.

It is also an object of the invention to provide a multi-layered packaging means that combines a layer composed of an array of metallically reflecting bins having four tapered sidewalls, the bottom aperture of each bin containing one or more flip-chip LEDs protruding into the bin from an electrically interconnected back plane, the interior of each bin either filled with air or a clear dielectric encapsulant, the bin apertures covered with a thin film stack consisting of two prism sheet layers and optionally a quarter wave phase retardation layer and a reflective polarizing layer.

It is still another object of the invention to provide an improved system and a method for designing the geometry of the prism sheets operating in conjunction with the geometry of an underlying LED-containing bin structure, such that output light concentration within a selected angular range is increased maximized.

It is yet another object of the invention of provide an improved system and method for fabricating relatively thin arrays of metallically reflecting bins made with an open lattice of input and output apertures.

It is further an object of the invention of provide an improved system and method of designing thin arrays of metallically-reflecting bins whose geometry and sidewall shape is adjusted so as to maximize the angular and polarization state recycling brought about by reflective means external to the bins themselves.

It is still an additional object of the invention to provide an improved system and method for constructing a hemispherical reflector within a planar LED array based projector system such that the hemispherical reflector is formed on the inside wall of a cylindrical element whose axis lies along the optical axis of the projection system.

It is yet one other object of the invention to provide an improved system and method for collecting and reusing light emitted by a planar LED light source whose output angles miss the input aperture of an angle transforming condensing lens such that the higher angle light is instead intercepted by two sets of orthogonal and metallically reflecting sidewalls having ellipsoidal curvature, one focal line of each sidewall lying in the plane of the LED light source aperture, the other focal line of each sidewall lying on an input edge of a substantially transparent light pipe positioned between the LED light source array and the condensing lens, the light pipe fitted with a distribution of light re-directing means that allow a portion of the collected light to be directed out from the light pipe and into the input aperture of the condensing lens.

It is additionally an object of the invention to provide an improved system and method for coupling planar multi-layered LED bin arrays to LCD or DMD micro-displays by means of a secondary angle transforming or condensing element whose front and rear focal lengths are matched to the approximate locations of the array's output aperture and the display's input aperture.

It is yet an additional object of the invention to provide an improved system and method for coupling a planar LED array light source to LCD or DMD micro-displays by means of a secondary angle transforming element and an external hemispherical reflector positioned to collect and recycle all emitted light not collected by the transforming element's aperture.

It is one further object of the invention to provide a compact means for efficiently recovering, re-circulating and reusing wide-angle output light from a multi-layered LED light source array by means of an externally positioned reflector having either continuous or faceted spherical radius.

It is yet one further object of the invention to provide a compact means for efficiently recovering, re-circulating and reusing wide-angle output light from a multi-layered LED light source array by means of an externally positioned four-sided ellipsoidal reflector in conjunction with an elevated transparent light pipe having a partially structured surface plane

It is yet a further object of the invention to provide an improved system and method for forming the sloping sidewalls of metallically reflecting bin arrays such that the sidewall reflections while non-scattering in nature, serve to randomize angular direction of the resulting light rays.

It is one other object of the invention to provide an improved system and method for forming the LED and encapsulant surfaces within and a part of metallically reflecting bin arrays such that the associated reflections, while non-scattering in nature, serve to randomize angular direction of the reflected light rays.

It is a further object of the invention to provide an improved system and method for efficiently transmitting light of one polarization from an LED light source system through the input aperture of an LCD micro-display device, while recycling and reusing light of the orthogonal polarization state by means of reflective polarizer and quarter-wave phase retardation planes, one associated with the input aperture of an angle transforming element, the other the output aperture of a metallically reflecting LED light source array, combined with a hemispherical reflecting element, the focus of whose metallically reflecting interior is at or near the center-point of the LCD aperture.

It is one more object the invention to provide an improved system and method for making a high efficiency multi-layered LED light source array wherein one layer is a contiguous array of metallically reflecting four-sided bins whose sidewall curvatures maximize the LED flux that is conveyed from input to output aperture in each X and Y meridian, while parallel layers above this one are secondary light directing layers including two orthogonal cylindrical lenses or lens arrays whose cylinder axes are aligned in parallel with the bin array's orthogonal aperture diagonals, a quarter-wave phase retardation layer and a wide-band reflective polarizer layer.

It is one more object the invention to provide an improved system and method for making a silicon substrate containing a pattern of electrically conductive circuitry enabling the electrical bonding and interconnection of one or two-dimensional arrays of physically separated flip chip LEDs, arranged in rows and columns.

It is an additional object the invention to provide an improved system and method for making one or two-dimensional arrays of metallically reflecting bins having sloped or tapered sidewalls whose arrangement allows physical through-holes in the array defining both input and output apertures, the associated input aperture array spatially arranged so that each input aperture matches the size and shape of each LED chip in a corresponding array so that when brought together each LED chip fits simultaneously through each corresponding input aperture without mechanical interference blocking such a fit so that each chip thereby protrudes into each bin.

It is also an additional object of the invention to provide a compact means for efficiently converting un-polarized output light from a multi-layered LED light source array into substantially polarized output light using the metallically-reflecting nature of the reflecting bins involved and the metallically-reflecting nature of the LED's electrodes, in conjunction with elevated polarization converting films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A illustrates in schematic cross-section a multi-layered planar LED light source array in which LED chips are contained in an array of containers located beneath contiguous bins having plane tapered reflecting sidewalls whose bin apertures are beneath an upper and lower prism sheet.

FIGS. 1B illustrates in schematic cross-section a multi-layered planar LED light source array in which LED chips placed within contiguous bins having plane tapered reflecting sidewalls whose bin apertures are beneath an upper and lower prism sheet.

FIG. 2A illustrates in schematic cross-section a multi-layered planar LED light source array in which LEDs are placed in the apertures of contiguous bins having curved reflecting sidewalls whose bin apertures are beneath a polarization selective reflecting plane.

FIG. 2B illustrates a perspective view of a contiguous bin having four orthogonal mathematically shaped sidewalls.

FIG. 2C illustrates a perspective view of a contiguous bin having a single mathematically shaped sidewall with optional vertical boundary walls.

FIG. 3A illustrates in schematic cross-section a multi-layered planar LED light source array in which flip-chip LEDs are arranged in a regular array on a planar circuit plane, each LED protruding through the input aperture of an array of contiguous bins having plane tapered reflecting sidewalls whose bin apertures are beneath a stack of films containing a lower and upper prism sheet.

FIG. 3B provides greater detail of the schematic cross-section of FIG. 3A specifically with regard to the insertion of a sub-mounted flip-chip LED into the secondary layer of contiguous micro-reflecting bins.

FIG. 4A contains a perspective view of an array of contiguous plane-walled reflecting bins, such as that represented in the schematic cross-section of FIGS. 3A-B.

FIG. 4B contains a perspective view of the tool structure used to form the array of reflecting bins illustrated in the perspective of FIG. 4A.

FIG. 5A is a schematic cross-section of the front view of a one-bin region of the multi-layered LED light source array of FIGS. 3A-B.

FIG. 5B is a schematic cross-section of the side view of a one-bin region of the multi-layered LED light source array of FIGS. 3A-B.

FIG. 5C is a perspective view of the two prism sheets as located above the bin arrays illustrated for example in FIGS. 1A, 3A-B and 5A-C.

FIG. 6A is an illustrative exploded view of the basic flip chip LED structure as modeled herein, showing a substrate layer, an epitaxial coating, the plane of rays immersed within the epitaxial material, and the reflecting electrode structure.

FIG. 6B illustrates a top view of the reflecting electrode's striped structure.

FIG. 6C is an illustrative perspective view of the basic flip chip LED structure as modeled herein, showing, including in particular, its location and attachment to a mounting circuit.

FIG. 7 represents the graphical results in total effective output lumens of a 40-bin LED light source array structured as in FIGS. 3 and 5 as a function of bin depth and the type of films elevated above the bins.

FIG. 8 represents the graphical results in total effective output lumens of a 40-bin LED light source array structured as in FIGS. 3 and 5 as a function of the apex angle of prism sheets used and the bin depth.

FIG. 9 represents the graphical results in total effective lumens of an optimized 40-bin LED light source array structured as in FIGS. 3 and 5 as a function of the apex angle of prism sheets used

FIG. 10 represents the graphical results in total effective lumens of a 40-bin LED light source array structured as in FIGS. 3A-B and 5A-C as a function of both the apex angle of prism sheets used and bin depth.

FIG. 11 is a schematic cross-section illustrating the mechanism of polarization recovery and reuse in an LED light source array structured as in FIGS. 3A-B and 5A-C showing the trajectories of illustrative optical rays as a function of their polarization.

FIG. 12 represents graphical results in total included lumens per bin for an LED light source array structured as in FIGS. 3A-B and 5A-C (curves A and B) contrasted with an array of bins, each of which designed to preserve etendue (curves C and D).

FIGS. 13 is a schematic cross-section illustrating the geometrical relations in a projection system combining the LED light source array of FIGS. 3A-B and 5A-C with a secondary angle transforming element and an imaging device (either an LCD or DMD).

FIG. 14 represents graphical results in total effective lumens of two types of LED light source array structures, one having straight-walled bins and one having curved wall bins, both as a function of prism sheet apex angle.

FIG. 15A is a schematic cross-section illustrating geometry and ray paths for the optical system of FIG. 13 combined with a hemispherical light-recycling reflector.

FIG. 15B shows in a magnified cross-sectional view the type of LED bin array as illustrated in FIGS. 3A-B that can be used in the system of FIG. 15A without optical over layers.

FIG. 15C shows a single LED bin that can be used in the system of FIG. 15A without optical over layers.

FIG. 15D shows the type of LED bin array illustrated in FIGS. 3A-B that can be used in the system of FIG. 15A with the addition of optical over layers.

FIG. 15E shows a graphic illustration one type of commercially available LED package structure that can be used singly or in a tight array within the system represented in FIG. 15A.

FIG. 16A shows a perspective view of the hemispherical reflector sidewall as represented in FIG. 15A.

FIG. 16B shows a side view of the hemispherical reflector sidewall as represented in FIG. 15A.

FIG. 16C shows a top view of the hemispherical reflector sidewall as represented in FIG. 15A.

FIG. 16D shows a perspective side view of an alternative cylindrically segmented hemispherical reflector that can be used in the system represented in FIG. 15A.

FIG. 17 shows a schematic cross-section of the cylindrically segmented hemispherical reflector shown in FIG. 16D as used in the system represented in FIG. 15A.

FIG. 18 is a schematic cross-section illustrating geometry and ray paths for the optical system of FIG. 13 combined with a corner-cube-based light-recycling reflector.

FIG. 19A is the schematic cross-section of a single tapered reflecting bin with constituent LED chip showing illustrative optical ray paths for LED emission and the behavior of incoming light rays.

FIG. 19B shows a magnified view of the tapered reflecting sidewall's surface flatness as represented in the schematic of FIG. 19A.

FIG. 20 is the schematic cross-section of a single tapered reflecting bin with constituent LED showing the geometrical effects of refraction by a single prism sheet elevated above, with illustrative optical ray paths shown both for LED emission and an incoming light ray.

FIG. 21A shows a magnified cross-sectional view of a triangularly rippled surface boundary between the transparent dielectric fill and air within the output aperture of a micro-reflecting bin such as that shown in FIG. 20.

FIG. 21B shows another magnified cross-sectional view of a rib-like rippled surface boundary between the transparent dielectric fill and air within the output aperture of a micro-reflecting bin such as that shown in FIG. 20.

FIG. 21C shows yet another magnified cross-sectional view of a cylindrically or spherically rippled surface boundary between the transparent dielectric fill and air within the output aperture of a micro-reflecting bin such as that shown in FIG. 20.

FIG. 21D is the schematic cross-section of a single tapered reflecting bin with constituent LED chip showing illustrative optical ray paths for LED emission and an incoming light rays as affected by the existence of rippled surface structures.

FIG. 21E is the magnified schematic cross-section of a single tapered reflecting bin with constituent LED chip in the vicinity of the LED showing illustrative optical ray paths for LED emission and an incoming light rays as affected by the existence of rippled surface structures of the LED's epitaxial layer, metallic reflecting electrodes and supporting substrate.

FIG. 22A is a schematic cross-section of an optical system combining the LED light source array of FIGS. 3A-B and 5A-C with a secondary angle transforming element, a structured light pipe plate and a four-sided elliptical reflector.

FIG. 22B is the associated perspective view of the schematic cross-section shown in FIG. 22A.

FIG. 23A is a more detailed schematic cross-section of the side view of the optical system represented in FIG. 22A-B showing its geometric positioning within the optical system of FIG. 13.

FIG. 23B is a perspective view of on of the mathematically shaped reflecting sidewalls shown in FIG. 23A.

FIG. 24A is a perspective view of a slab-type structured light pipe plate.

FIG. 24B is a perspective view of a light pipe plate with plane beveled end faces.

FIG. 24C is a perspective view of a light pipe plate with truncated plane beveled end faces.

FIG. 25A is a schematic cross-section of the effects of light pipe structure on illustrative total internally reflecting light rays.

FIG. 25B is a magnified view of the lower light pipe surface as depicted in FIG. 25A and the effect of a mesa-like surface structure on the process of total internal reflection.

FIG. 25C is a perspective view of the mesa-like surface structure depicted in FIG. 25B.

FIG. 26 is the schematic cross-section of a variation on the optical system of FIGS. 1A-B3 that includes a hemispherical reflector for the recycling and reuse of polarized light.

FIG. 27 is a generalized schematic cross-section of the optical systems based on FIGS. 13, 15A-E, 17, 18, 22A-B, 23A-B, and 26 incorporating planar LED light source arrays of FIGS. 3A-B and 5A-C.

FIG. 28A is another generalized schematic cross-section of the optical systems based on FIGS. 13, 15A-E, 17, 18, 22A-B, 23A-B, and 26 incorporating the planar LED light source arrays of FIGS. 3A-B and 5A-C as well as other possible LED array structures.

FIG. 28B shows a magnified cross-sectional view of the micro-reflecting LED bin array type of FIG. 3A as one possible choice for use in the optical system of FIG. 28A without optical over-layers.

FIG. 28C shows the magnified view of a single LED bin that can be used in the system of FIG. 28A without optical over layers.

FIG. 28D shows the type of LED bin array illustrated in FIG. 3B that can be used in the system of FIG. 28A with the addition of optical over layers.

FIG. 28E shows a graphic illustration one type of commercially available LED package structure that can be used singly or in a tight array within the system represented in FIG. 28A.

FIG. 29A is the schematic side view cross-section of a multi-layered planar LED light source array in which flip-chip LEDs are arranged in a regular array on a planar circuit plane, each LED protruding through the input aperture of an array of contiguous bins having curved reflecting sidewalls designed so as to preserve etendue from input to output aperture and whose bin apertures are located beneath an elevated stack of polarization converting films.

FIG. 29B is a perspective view of the multi-layered planar LED light source array depicted in FIG. 30A.

FIG. 30A shows the Lambertian angular output distribution of an LED light source, such as the micro-reflecting array depicted in FIG. 30B.

FIG. 30B is a schematic cross-section of an LED array of truncated etendue-preserving micro-reflecting bins whose centers have been pushed closer together than physically possible, with the reflector truncation line placed at the onset of reflector overlap.

FIG. 31 A shows the non-Lambertian angular output distribution of an LED light source such as that of FIG. 31B whose behavior has been modified so as to increase light emission at lower angles at the expense of light emission at higher angles.

FIG. 31B is the schematic cross-section of the truncated LED array shown in FIG. 30B with the addition of two prism sheets elevated above the array to replace the overlapping reflector region that had been removed as the result of the truncation.

FIG. 32A shows the schematic top view of a 3.times.3 LED light source array composed of the contiguous etendue-preserving reflector bins as illustrated in FIGS. 29A-B with light output (.about.93 lumens) as represented for the case when only the center LED has been lighted.

FIG. 32B shows the schematic top view of a 3.times.3 LED light source array composed of the contiguous etendue-preserving reflector bins as illustrated in FIGS. 29A-B with light output shown for the case when all 9 LEDs have been lighted.

FIG. 33A shows the top view of a 3.times.3 LED light source array composed of the contiguous non-etendue-preserving reflector bins and elevated prism sheets shown in FIGS. 3A-B and 5A-C and depicts the 9-bin array's light output for the case when only the center LED has been lighted.

FIG. 33B is a perspective view of the 3.times.3 LED light source array of FIG. 33A.

FIG. 34 shows the graphical result of the fraction of total effective lumens produced by the single lighted bin of the LED light source array of FIGS. 33A-B as a function of the size of the output square area considered, for light within two similar angular ranges (+/-25-degrees, triangles .DELTA.; +/-30-degrees, squares, .quadrature.).

FIG. 35A is a schematic representation of one type of sub-mounted flip-chip LED having a hexagonal sub-mount circuit with positive and negative contacts on opposing hexagonal points.

FIG. 35B is a schematic representation of one type of sub-mounted flip-chip LED with square sub-mount circuit.

FIG. 35C is a schematic representation of another type of sub-mounted flip-chip LED having a hexagonal sub-mount circuit with positive and negative contacts on opposing hexagonal edges.

FIG. 35D is a schematic back-side representation of an illustrative series-parallel electrical interconnection circuit applied to the bottom of the metallically reflecting bin arrays shown in the cross-sections of FIGS. 3A-5C and 29A-B, the bin arrays used as a means of attaching and interconnecting an array of the discretely sub-mounted flip-chip type LEDs shown in FIGS. 35A-C.

FIG. 35E illustrates by means of a cross-sectional view how a sub-mounted LED of FIGS. 35A-C is assembled to the micro-reflecting bin array depicted in FIG. 35D.

FIG. 36 is a schematic representation of the micro-reflecting bin array of FIG. 35D except for the use of a different series-parallel electrical interconnection circuit.

FIG. 37 is the schematic representation of another illustrative series-parallel electrical interconnection circuit applied to the top surface of a planar substrate for the purpose of attaching and interconnecting an array of un-mounted flip-chip LEDs for use with the bin arrays of FIGS. 3A-5C and 29A-B.

FIG. 38 is the schematic representation of the completely parallel electrical interconnection circuit applied to the top surface of a planar substrate circuit for the purpose of attaching and interconnecting an array of un-mounted flip-chip LEDs for use with the bin arrays of FIGS. 3A-5C and 29A-B.

FIG. 39 shows graphical results for the lumens produced by a single 1.6 mm bin in the optimized LED light source array of FIGS. 3A-B and 5A-C as a function of the enclosed angular range of emitted output for three LED bin array cases: no elevated prism sheets, elevated prism sheets with 90-degree prisms and elevated prism sheets with optimized 104-degree prisms.

FIG. 40 is a schematic representation of the top view of an 8.times.8 bin LED light source array with all 64 LEDs operating, showing the spatial output percentage contributed by each 1.6 mm square bin region.

FIG. 41A is a schematic representation of the top view of the central 6.times.6 bin portion of the 8.times.8 bin LED light source array of FIG. 40, showing the total lumens contributed by each 1.6 mm square bin region when one binned LED in the array emits half as many lumens as all others.

FIG. 41B is a schematic representation of the top view of an illustrative 3.times.3 bin array portion of the 6.times.6 bin array depicted in FIG. 41B, showing the detailed lumen contributions from neighboring bins in the array.

FIG. 42A is a schematic representation of the etendue-preserving bins of FIGS. 29A-B supplemented by two elevated cylindrical lenses whose cylinder axes are aligned with bin-aperture diagonals to improve diagonal-meridian field coverage.

FIG. 42B is a schematic representation of the etendue-preserving bins of FIGS. 29A-B supplemented by two elevated lenticular lens arrays whose cylinder axes are aligned with bin-aperture diagonals to improve diagonal-meridian field coverage.

FIG. 43 is a schematic cross-section of an illustrative video projection system for three reflective LCDs, based on the focal plane optical system layout of FIGS. 1A-B3 and the planar light source arrays of FIGS. 3A-B, 5A-C, 11, 29A-B and 42A-B.

FIG. 44 shows graphical results for the white lumen screen output of the projection system of FIG. 43 using the non-etendue-preserving LED light source arrays of FIGS. 3A-B, 5A-C and 11 as a function of both the condensing element's effective focal length in air and the total number of 1.6 mm bins in each (red, green and blue) array.

FIG. 45 is a schematic cross-section of an illustrative video projection system for three transmissive LCDs based on the focal plane optical system layout of FIG. 13 including the planar light source arrays of FIGS. 1A-3B, 5A-C, 11, 29A-B and 42A-B (shown illustratively with the etendue-preserving light source array of FIGS. 42A-B).

FIG. 46 is a schematic cross-section of an illustrative video projection system for a single transmissive LCD operated field-sequentially based on the focal plane optical system layout of FIG. 13 and the planar light source arrays of FIGS. 1A-3B, 5A-C, 11, 29A-B and 42A-B (shown illustratively with the etendue-preserving light source array of FIG. 42A-B).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventions relate to multi-layered packaging structures whose structural details maximize optical output from arrays of interconnected light emitting diodes (LEDs) over earlier multi-layered packaging structures. Specifically, the present inventions allow for the highest possible concentrations of output lumens per square millimeter of output aperture. This improvement leads to designs that allow earliest possible use of LED arrays as practical replacements for light bulbs in demanding applications such as video projection. This improvement also leads to related designs that use the minimum number of LEDs for the intended purpose.

Previous inventions, such as 10 in FIGS. 1A-B and 66 in FIG. 2A, have described the use of specially-shaped and sized reflecting bins surrounding each LED (or groups of LEDs) in the array with the bins arranged to work in conjunction with the design of certain reflective multi-layers placed just above them, such as for example prism sheets 4 and 6 in FIGS. 1A-B and reflective polarizer 56 in FIG. 2A. The shape of the reflecting sidewalls 2 (and in 22) in FIGS. 1A-B and 50 in FIG. 2A is adjusted to redirect output light towards the reflective multi-layers from LED 20 in FIGS. 1A-B (or the enclosed LED emitter 70 in FIG. 2A). Multiple reflections between reflective elements are then employed to transform the output angular distribution of light passing through the systems 10 and 66 in a favorable way for a variety of lighting applications. While this multi-layered approach provides a basis for achieving high-density output light from arrays of LEDs, no working relationship has yet been established for maximizing the array's output density.

The form introduced in FIGS. 1A-B and shown with flip-chip LEDs 20 uses shallow reflecting bins 12 with plane, tapered sidewalls 2. LED light enters bins 12 through aperture 24 from sub-bins 22 that contain the flip-chip LED (or LEDs) 20 and encapsulant 14, located just beneath the main bins. Flip-chip LEDs consist of transparent substrate layer 42 and epitaxial device layers 40 within which a diode is formed and light is generated. Electrical contacts (combined with highly-reflective under-surface mirror) 44 allow attachment to sub-mounts 24 and heat extraction layers. The sub-bins 22 surrounding the LED chips, also with shaped reflecting sidewalls 16, collect and convey LED light emitted through its substrate 42 and then through bin aperture 24 (and optional diffusing layer 8). One particular configuration is shown in FIGS. 1A-B in which the sub-bins 22 and main bins 12 are formed as a continuous entity, sharing common dielectric medium 18, and having the same sidewall slope 38 (angle .alpha. measured from the vertical).

The form of FIGS. 1A-B operates with its two prism sheets 4 and 6 elevated above the LEDs preferred heights G1'and G1'+G4 so that light reflected from the bins is controlled in both angle and spatial distribution. Additional reflective polarizer layers 28 are added when necessary to control output polarization as well. When the prisms are made to have 90-degree apex angles, output preference 36 is given to angles within +/-22.5 degrees. Beam uniformity depends on the factors of prism sheet spacing.

The analogous form of FIGS. 2A-C is one that replaces the role of the reflective angle-controlling prism sheets by the curved shape of the bin sidewalls 50. By doing so, output light from the bins is even more tightly controlled in angle, and polarization, by reflective interactions with polarizer layer 56 elevated above the bins.

While both structural forms of FIGS. 1A-B and FIGS. 2A-C yield angularly-directed output beams from seamlessly arranged output apertures, neither system's optical efficiency (expressed in output lumens falling within a specified angular range divided total LED lumens emitted) and output density (output lumens falling within a specified angular range divided by the aperture area) has been maximized.

The importance of maximizing LED array output can be illustrated by the difficult performance requirements presented by a modern LCD or DMD (DLP) video projector needing to deliver over 1000 white-field lumens to the (front or rear) projection screen. One common RGB white-field distribution is 60% green, 30% red and 10% blue, requires 600 green screen lumens, 300 red screen lumens, and 100 blue screen lumens. Suppose the projector uses three reflective LCDs at f/2.4, one for each color, each of whose aspect ratios are 4:3 and each of whose diagonal size is 1.2''. Taking the green channel as the critical example, with a 90% efficient projection lens and an 81% transmissive dichroic color-splitting cube, one finds that there must be 823.7 polarized green lumens at the reflective LCD within an angular range of +/-12-degrees (i.e. f/2.4). Then using the pseudo-Kohler polarizing beam-splitter type angle-transformer (25-degree to 12-degree) we've described previously, and that is explained later in more detail, one finds that the associated LED array illuminator must be capable of supplying 1170 polarized green lumens within +/-25-degrees. Any light generated in angles greater than +/-25-degrees cannot be viewed. Moreover, the 1170 lumen beam must be produced within a specific rectangular aperture area defined by fundamental geometric expressions related to the LCD's spatial and angular aperture. (Note: Square apertures may also be used, and this variation will be discussed further below.) Specifically, and from the well-known Sine Relation, the illumination aperture edges, X.sub.ILL and Y.sub.ILL, are as in equations 1 and 2. X.sub.ILL=X.sub.LCD Sin(12)/Sin(25) (1) Y.sub.ILL=Y.sub.LCD Sin(12)/Sin(25) (2)

Accordingly, with X.sub.LCD and Y.sub.LCD being 24.384 mm and 18.288 mm respectively, the LED illuminator aperture becomes approximately 12 mm by 9 mm (there is a more detailed discussion further below). Any light created outside this aperture area cannot fall usefully within the LCD aperture. So, for a sufficient number of green lumens to reach the screen, it must be practical to produce 1170 polarized green lumens within this particular 108-mm.sup.2 illumination-aperture area; those lumens confined to +/-25-degrees.

Doing so represents a significant challenge without deploying an array of LED chips within a suitably efficient high-density angle-controlling package.

As one indication of this difficulty, consider that the latest 5-watt high-power LED package manufactured by LumiLeds (as Luxeon.TM.) emits 120 un-polarized green lumens over a +/-90-degree Lambertian angular distribution from a domed circular lens (shown later) that is approximately 4 mm in diameter. Assuming for the moment that such 4 mm domes can be closed-packed (and they can't because of their external package and electrode design), it can be shown from geometry that the luminous effect of only a total of 7.5 lens domes can be accommodated within the illustrative 9 mm.times.12 mm illumination rectangle. These 7.5 domes produce 900 un-polarized lumens within +/-90-degree rather than the +/-25-degrees needed. LumiLeds reports in published data sheets that half this luminous power (450 lumens) exists within +/-60-degrees, which implies that only 107 un-polarized lumens exist within +/-25-degrees. Even allowing for 100% polarization conversion efficiency (about 50% is practical), such an array falls short of the projector need by more than a factor of ten.

The LED chips used by LumiLeds within this Luxeon.TM. package are 2 mm by 2 mm squares. Assuming the package is nearly 100% efficient in routing lumens generated by this chip into usable output, the 5-watt chip would be emitting at a density of 30 lumens/mm.sup.2. If electrical efficiency were no object (and it is), as many as 27 such super-chips could fit into the required 12 mm by 9 mm illumination aperture, yielding 3,240 un-polarized lumens over +/-90-degrees, or 1,620 un-polarized lumens over +/-60-degrees. The yield within +/-25-degrees would therefore be 385.8 un-polarized lumens, and with 50% conversion efficiency, 289.3 polarized lumens. Even such a monster array running at 135 watts falls short of the projector's green lumen need by a factor of four.

It has been established that the emitting density of these same high-power flip-chip LEDs is currently as high as 50 lumens/mm.sup.2, and that by 2004, with twice the power density (or less) able to be tolerated, will rise to the 100 lumens/mm.sup.2 level. Despite such advances, the monster array just described would generate 6,480 un-polarized green lumens over +/-90-degrees at 270-watts. This would produce 1157 polarized green lumens, which is just about the number needed. Yet, the wattage necessary for this is impractical, as total projector power for R-G-B would rise above 550 watts.

What is needed, even with the highest-performing LEDs, is a more angularly efficient LED illumination array than would exist by such conventional means.

The present inventions, shown in three basic forms, addressing this and related needs, are based on the two original forms shown in FIGS. 1A-B and in FIGS. 2B-C. Each better facilitates such practical high-lumen density applications, particularly video projection, where as it has been seen, very high numbers of lumens are required within a narrow angular range and a confined spatial area. The improved forms also facilitate practical applications in other areas, such as traffic signaling, where commercial priorities seek the costs reductions possible when using the fewest number of LEDs possible.

A. First Form: Shallow-Profile Multi-Layer LED Arrays Using Straight-Walled Bins and Modified Prism Sheets (As in FIGS. 3A-B and 5A-C)

The first form of the present invention is shown in FIGS. 3A-B, and involves the use of a continuous and regular array structure composed of shallow reflecting bins 82 with plane sidewalls 106 located just beneath a vertical stack of reflecting films covering the bin apertures that includes two orthogonally-oriented prism sheets 88 and 92 with modifications, and optionally, a quarter-wave phase retardation film 86 and a reflective polarizer 84. This compact form, an extension of the previous form shown in FIGS. 1A-B, achieves highest possible lumen density by permitting the densest allowable array of LED chips 118 on the systems 90 back plane 94. Rather than placing LED chips in arrays having empty spaces 105 between the LEDs that equal the size of the LEDs themselves, this structure allows a tighter packing of LEDs, limited by the bin's sidewall angle .alpha., 38, which depends on its constructive relationship with the design of the prism sheet layers 88 and 92.

Moreover, the spacing between the LED array and the modified prism sheets is set by the depth of the shallow reflecting bins 82, and not by a gap between the lowest prism sheet and the bin layer itself. As such, optimum performance depends on the geometric relationship existing between the bin and prism structures.

The LEDs used in this structure may be of any form or number, but are best made in the so-called flip-chip style 118, wherein a transparent substrate material 120 (currently sapphire) is combined with epitaxial layers 122 (currently gallium nitride based) whose structure and adjacent electrodes 114 and 116 act to form the p-n junctions that generate emitted light. Electrodes 114 and 116 have been made reflecting, so that any emitted light directed towards these elements reflects towards the transparent substrate layer, and thereby, outwards from the LED.

One particular advantage of orienting the LED chip with its electrodes facing downwards is that it reduces the difficulty of making electrical interconnection. In this case, a process known as solder-bumping is best used to re-flow solder material deposited between the LED electrodes and counter-positioned bars (or str