Abstract:
An optical manifold for efficiently combining a plurality of blue LED outputs to illuminate a phosphor for a single, substantially homogeneous output, in a small, cost-effective package. Embodiments are disclosed that use a single or multiple LEDs and a remote phosphor, and an intermediate wavelength-selective filter arranged so that backscattered photoluminescence is recycled to boost the luminance and flux of the output aperture. A further aperture mask is used to boost phosphor luminance with only modest loss of luminosity. Alternative non-recycling embodiments provide blue and yellow light in collimated beams, either separately or combined into white.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/115,055 for “OPTICAL MANIFOLD FOR LIGHT-EMITTING DIODES” of Chaves et al. filed Apr. 25, 2005, the disclosure of which is incorporated herein by reference in its entirety. 
   Application Ser. No. 11/115,055 claims the benefit of U.S. Provisional Patent Application No. 60/658,713, filed Mar. 3, 2005, entitled OPTICAL MANIFOLDS FOR LIGHT-EMITTING, DIODES, which is incorporated by reference herein in its entirety. 
   Application Ser. No. 11/115,055 claims the benefit of U.S. Provisional Patent Application No. 60/614,565, filed Sep. 29, 2004, entitled OPTICAL MANIFOLDS FOR LIGHT-EMITTING DIODES, which is incorporated by reference herein in its entirety. 
   Application Ser. No. 11/115,055 claims the benefit of U.S. Provisional Patent Application No. 60/612,558, filed Sep. 22, 2004, entitled OPTICAL MANIFOLDS FOR LIGHT-EMITTING DIODES, which is incorporated by reference herein in its entirety. 
   Application Ser. No. 11/115,055 claims the benefit of U.S. Provisional Patent Application No. 60/564,847, filed Apr. 23, 2004, entitled OPTICAL MANIFOLDS FOR LIGHT-EMITTING DIODES, which is incorporated by reference herein in its entirety. 

   STATEMENT REGARDING FEDERALLY FUNDED RESEARCH AND DEVELOPMENT 
   This invention was supported in part by the National Energy Technology Laboratory Award No. DE-FC26-05NT42341. The Government may have certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to light-emitting diodes (LEDs), and more particularly to light collection/distribution systems that utilize one or more LEDs. 
   2. Description of Related Art 
   Light emitting diodes (LEDs) are a widely available, inexpensive, and efficient light source. For low light uses such as camping headlamps, one or two LEDs provide adequate light. However, to utilize LEDs for applications that require more light, such as automobile headlamps, it is necessary to combine the outputs of a plurality of LEDs. The LED prior art is less than satisfactory regarding the combination of the luminous outputs of a plurality of emitter-chips. Physical chip-adjacency can indeed produce a larger light source, but heat-removal limitations reduce the total luminance. Also, there is little continuity of illuminance between the adjacent emitters, leaving dark zones between the individual emitters. LEDs are available from a wide variety of suppliers, and in commercially available LEDs the emitters themselves have pronounced variations in luminance. For example, some suppliers (e.g., the OSRAM Corporation of San Jose, Calif. and the Cree Corporation of Santa Barbara, Calif.) manufacture high-power LEDs with wires and bonding pads that block light from the top of the emitting chip. In contrast, high-power LEDs from the Lumileds Corporation of San Jose, Calif. exemplify flip-chips, which have no wires or bonds that would otherwise block light emission in front. Even these, however, show great luminance variations across the emitter. The Luxeon I and Luxeon III LEDs by Lumileds, for example, can vary in luminance by a factor of ten from center to edge, with random patterns in between that differ from one chip to the next. Such undesirable patterning, whether on flip-chips or front-wired chips, can cause detrimental artifacts in the beams of collimating or condensing lenses. Although diffusers can be placed over such lenses, diffusers lose 15% of the light and give the beam a fuzzy edge. A more efficient method of source homogenizing, one that preserves sharp edges, would be a significant advance in illumination optics. Although thin-film LEDs have greatly improved uniformity over conventional on-substrate LEDs, there are fundamental reasons why they will always have nonuniform illuminance, because of inherently nonuniform current distribution downward through the active, light-generating layer. Using larger soldered electrodes causes more useless surface recombination at their juncture with the LED, so that electrodes must be kept small. In contrast, the optical transformer described herein places a premium on a corner location for the current-feed, amplifying the nonuniformity. Because the untreated sawed edges of the LED chip will cause surface recombination, current cannot be allowed to reach them, so that the LED cannot be illuminated all the way to its edge. It would be an advantage to provide an optical transformer that alleviates luminance inhomogeneities inherent to LEDs. 
   Beyond making a single source uniform, a better optical method is needed for combining the outputs of spatially separate LED chips, which are easier to cool than when closely packed. Such an optical source-combination device should optimally produce a uniform luminance with sharp edges. Besides easier thermal management, optical source-combination is needed that makes unnoticeable the individual variations or even failures of any of the LEDs. 
   The LED prior art is also less than satisfactory regarding the geometry of phosphor utilization in LEDs, such as for LEDs that generate white light. A phosphor coating of a quarter-millimeter (250 microns) or more directly onto a one-mm blue chip will necessarily increase source area, sometimes by a factor of four, and thus reduce luminance. The application of phosphor to such small chips necessarily results in color-temperature variations across each chip and between them as well. Also, much of the phosphor output backscatters; that is, it shines wastefully back into the chip, which is relatively absorptive. Finally, the phosphor must withstand the chip&#39;s high operating temperature, and differential thermal expansion poses adhesion problems, greatly reducing output if the phosphor should work loose. Although a thinner phosphor layer would have less problem with stress, as well as more luminance, only one manufacturer, Lumileds Corporation, for example, has the advanced phosphor deposition technology for the conformal 25-micron coating of their white LEDs, ten times thinner than the rest. (Laboratory samples from other companies have been exhibited but the processes have not been proven to be commercially viable at this time.) Even these devices vary in color-temperature, across their faces as well as from chip to chip. 
   It would be an advantage if the phosphor could be situated away from the LED; particularly, it would be an advantage if the phosphor layer in a LED device was positioned remotely enough to be unaffected by the temperature variations of the LED itself. Such a phosphor target could then be as small as the combined area of the separate LED chips, to maximize luminance. Conventional arrays of white LEDs suffer from variations in color temperature. In order to overcome this problem manufacturers employ expensive binning procedures. However, with the current state-of-the-art LEDs, there is still considerable variation in the color temperature, even using tight bins. Further, since an array of close-packed LEDs in practice has a spacing that is typically one or more chip widths between chips, simple application of phosphor over the entire array would result in a diluted, highly uneven luminance. 
   Achieving higher white luminance from an LED, with uniformity and color-consistency, is critical for LED market penetration into general lighting uses, where the lower power consumption and longer life of LEDs can greatly contribute to energy conservation. Larger and more efficient phosphor coatings can be utilized if they can be separate from their blue-light sources. Such an advance could particularly benefit automotive headlamps, where current white LEDs are marginal at best in luminance. In fact, color temperature variations across a beam could lead to excess blue light, which is ophthalmologically hazardous. 
   In some applications it is advantageous to produce a number of smaller size sources from a single larger source. This is useful for example when an optical design is difficult to mold because the optical component would be too thick and/or too large. If such a large single source is separated into a number of smaller size sources of the same total area, the same lens design can be used for each such source, just scaled down to a moldable size. It would also be desirable that these smaller sources are more uniform than the larger parent source, or that they have a prescribed luminance output. 
   In other applications it would be useful to change the shape of a single source or multiple sources to another shape, such as from a square to a rectangle of a substantially equal area or vice versa. This is useful for such applications as LED headlamps where it is desirable to generate rectangular sources with aspect ratios (length to width) of between two to one to six to one. Such a method must, of course, preserve source luminance as much as possible. 
   Finally, it is desirable to have a highly efficient means of producing white LED light sources without the use of phosphors, by combining two or more LEDs of a different wavelength into a single homogeneous source. Traditionally, the approach has been to use three different colored LEDs to make white light, commonly a red, a green, and a blue LED. However, the traditional optical approaches do not produce a rectangular or square uniform light source using such RGB light sources. It would be beneficial to have means of producing a light source combining more than three LED wavelengths. Additionally, it would be useful to have a means of producing such light sources where the chromaticity of the light source is adjustable. 
   SUMMARY OF THE INVENTION 
   Embodiments of optical manifolds are described herein that provide the ability to efficiently combine a plurality of LED outputs into a single output that is substantially homogeneous, in a small, cost-effective package that may be made of a dielectric material. Optical manifolds are described that can be used to combine multiple LEDs of the same color to provide a high flux and high intensity output beam, or can be used to generate a multi-wavelength beam. For example, a red, green, and blue LED can be combined to make a “white” output. Embodiments are also disclosed that use a single LED or multiple LEDs and a remote phosphor coating arranged so that backscattered photoluminescence is recycled to the output. The optical manifolds use principles of nonimaging optics, and are designed to substantially alleviate luminance variations on the emitting surfaces of LEDs, and provide a substantially uniform light source. In addition, these optical manifolds can be used to produce a variety of non-square shaped light sources using square-shaped LEDs, including rectangular and asymmetric high flux light sources. These high-flux sources are useful for many applications such as for solid state lighting automobile headlamps. For example, for this application it is desirable to have a uniform rectangular LED-based light source with length to width ratio of 4 to 1. This is achievable with the optical manifold described herein. Solid-state lighting in general, and light-emitting diodes in particular, will find new applications through the benefits of the optical transformer described herein. To provide, for example a white LED, an optical system is disclosed for delivering the light of one or more blue chips to a spatially separate phosphor. Such a phosphor target could then be as small as the combined area of the separate chips, to maximize luminance. The phosphor layer is positioned remotely enough to be unaffected by the temperature variations of the LED itself. 
   The optical transformer described herein relates generally to utilizing the principles of non-imaging optics to fulfill the above-discussed illumination-engineering needs, via the origination of a new type of optical manifold. The edge-ray principle of non-imaging optics sets forth the surfaces of minimal increase of source etendue, a central quantity of non-imaging optics. Etendue is the product of source area A s  and the projected solid angle of the source&#39;s output, multiplied by the square of the refractive index n of the optical medium surrounding the source:
 
E=n 2 A s  sin 2  θ
 
where θ is the off-normal angle of the solid conical angle which is equivalent to the source&#39;s radiation pattern. A diffuse Lambertian emission into 2π steradians is represented by θ=90°. This diffuse output is characteristic of the emission from an LED chip itself.
 
   An ideal optical system conserves etendue, so that the enlarged output area of an ideal collimator leads to its usefully high intensity within a narrow beam angle, while the small size of the focal spot of a solar concentrator leads to the usefully multiplied flux from its wide beam angle. 
   The optical transformer described herein offers a new kind of optical manifold that provides etendue-limited illumination for collimated backlights, etendue-limited combination of plurality of light sources, and etendue-limited phosphor utilization. The useful fulfillment of these important tasks by the optical transformer described herein marks a new stage of LED evolution. For example, other photoluminescent materials besides phosphors can be used with the optical transformer described herein more easily than directly on LEDs, such as the photoluminescent semiconductor AlInGaP. 
   Some embodiments disclosed herein utilize total internal reflection only, and thus do not need metallic reflector coatings to be applied to their surfaces. Further embodiments comprise injection-molded sub-sections that are assembled into a complete manifold for producing a large “virtual chip” from the emission of several LED chips of smaller size. The virtual chip has better uniformity of luminance and color than the actual chips, and can be configured with usefully restricted angular output. Also, controlled non-uniformity can be engineered along with such angular restrictions, enabling an intensity prescription to be met by placing the focal plane of a projection lens on the manifold output. 
   The reversibility of light paths dictates that the embodiments disclosed herein could equally well be used to disperse a large source by transforming it into several smaller ones, as with a single LED illuminating numerous instruments on an automotive dashboard. With the optical transformer described herein it would be easy to have a backup LED that also fed the optical manifold for the dashboard. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of this invention, reference is now made to the following detailed description of the embodiments as illustrated in the accompanying drawing, wherein: 
       FIG. 1A  is a cross-sectional view of a thin-film LED with an adjacent compound parabolic concentrator (CPC) reflector; 
       FIG. 1B  is a magnified cross-sectional view of part of  FIG. 1A , showing the LED with a diffuse reflector in contact with the active epitaxy layer; 
       FIG. 2A  is a cross-sectional view of two thin-film LEDs and a prism coupler; 
       FIG. 2B  is a cross-sectional view of an optical manifold  44  that utilizes the prism coupler shown in  FIG. 2A , including two thin-film LEDs immersed in smaller CPCs, each with a prism coupler, and a large CPC; 
       FIG. 3A  is a side view of an optical manifold comprising a plurality of square CPCs arranged in a 2×2:1 configuration; 
       FIG. 3B  is an end view of an optical manifold comprising square CPCs in a 2×2:1 configuration; 
       FIG. 4A  is a side view of a 2×4:1 optical manifold for eight LEDs and a 2:1 rectangular output, also comprising a mixing rod; 
       FIG. 4B  is another side view of a 2×4:1 optical manifold for eight LEDs and a 2:1 rectangular output, also comprising a mixing rod; 
       FIG. 5A  is a perspective view from the input side of a 4×4 optical manifold that feeds the output of sixteen blue LEDs through a blue-pass filter; 
       FIG. 5B  is a perspective view of the manifold of  FIG. 5A  from the output side, where the blue-passed light is condensed onto a patch of highly uniform phosphor; 
       FIG. 6  is a cross-section of an angular compressor; 
       FIG. 7A  is view of prior art, including a corner turner; 
       FIG. 7B  is a ray trace of the prior art shown in  FIG. 7A ; 
       FIG. 7C  is a cross-section of an angle-rotator of the optical manifold. 
       FIG. 7D  is an alternative embodiment of an angle-rotator similar to that in  FIG. 7C ; 
       FIG. 7E  is a ray tracing of an angle-rotator such as shown in  FIG. 7D ; 
       FIG. 8  is a cross-section of a source-shifter comprising two modified angle rotators; 
       FIG. 9A  is a cross-section of a half-width source shifter; 
       FIG. 9B  is a cross-section of a full-width source shifter; 
       FIG. 10  is a perspective view of a luminance shifter; 
       FIG. 11A  is an exploded, perspective view of another embodiment of an optical manifold that defines a monolithic etendue-squeezer; 
       FIG. 11B  is a perspective view of the resulting monolithic etendue-squeezer shown in exploded view in  FIG. 11A ; 
       FIG. 11C  is another perspective view of the monolithic etendue-squeezer shown in  FIGS. 11A and 11B ; 
       FIG. 12  is a perspective view of a monolithic 9:1 etendue-squeezer; 
       FIG. 13A  is a cross-section of a luminance transfer duct with an optically inactive surface; 
       FIG. 13B  is a cross-section of an angle-rotating luminance duct similar to the embodiment of  FIG. 13A ; 
       FIG. 14  is a cross-section of an angle-rotating luminance duct that has symmetrically placed ports; 
       FIG. 15  is a cross-section of a 4:1 duct with an inactive surface; 
       FIG. 16  is a cross-sectional view of a bilaterally symmetrical duct with two inactive surfaces; 
       FIG. 17A  is a cross-sectional view of a composite system comprising four joined ducts with the configuration of  FIG. 15 ; 
       FIG. 17B  is a cross-sectional view of another embodiment of an optical manifold in a further composite system; 
       FIG. 17C  is a cross-sectional view of another embodiment of an optical manifold in a composite system, also including a phosphor-coated surface; 
       FIG. 18A  is a cross-sectional view of an alternative optical manifold that includes dielectric CPCs, illustrating the drawbacks of joining two CPCs at 90°; 
       FIG. 18B  is a cross-sectional view of an alternative optical manifold that includes two dielectric CPCs as in  FIG. 18A , illustrating how an air gap prevents rays from escaping; 
       FIG. 19  is a cross-sectional view of another alternate configuration, including a phosphor-coated surface. 
   

   Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
   DETAILED DESCRIPTION 
   This invention is described in the following description with reference to the Figures, in which like numbers represent the same or similar elements. 
   Glossary of Terms and Acronyms 
   The following terms and acronyms are used throughout the detailed description:
         angle rotator a device that delivers luminance from one plane to another lying at a tilt to the first   CPC compound parabolic concentrator   cross-CPC a three-dimensional (3-D) configuration having a 2-D CPC profile in two orthogonal directions   dome of LED an approximately spherical LED cover made of transparent dielectric materials   edge-ray principle the foundational principle of non-imaging optics, whereby a defining set of rays from the edge of an aperture are guaranteed to be delivered to the edge of another aperture, but the first aperture is not imaged onto the second   etendue the optical manifestation of entropy, defined as the product of source area A s  and the projected solid angle of the source&#39;s output, multiplied by the square of the refractive index n of the optical medium surrounding the source   ITO indium tin oxide   LED light emitting diode, a direct converter of low-voltage direct current to light in a narrow spectral band   luminaire a light source and functionally associated light-control apparatus, such as a reflector or a shade   luminance shifter a device that delivers luminance to a different transverse coordinate   NA numerical aperture   phosphor a photoluminescent material that emits light in response to external excitation, often continuing after the excitation ceases   phosphor patch a component having a given size and shape that contains phosphor. It can comprise phosphor or phosphor dispersed in an encapsulant, such as a silicone fluid. The phosphor patch can also be made as a composite material where a phosphor layer (with or without an encapsulant) is deposited on a suitable transparent substrate, such as a sheet or film in a volume production process.   thin film LED an LED that comprises very thin layers and emits nearly 100% of its radiation from its top face   TIR total internal reflection       

   Overview 
   For purposes of explanation, an “optical manifold” resembles the exhaust manifold of engines. In an optical manifold, channels are provided that either combine multiple light outputs into a single output, or distribute a single output over space. This term can designate a device for fiber optic fan-in and fan-out, such as in U.S. Pat. Nos. 6,850,684, 6,847,774, 6,832,032, 6,655,848, 6,556,754, and 6,549,710 by Simmons et al. This multi-input, multi-output function is an informational task that is distinct from the efficient distribution of illumination. In fiber-optics parlance, such distribution is sometimes called ‘fan-in’ and ‘fan-out’, denoting the joining of several optical paths into one. 
   The distinction between ‘fan-in’ and ‘fan-out’ is important when reversibility is considered. That is, some such fiber-optic devices cannot be functionally interchanged, because some light on the reverse paths may spread out and be internally lost. However, it is an advantage to have a system that reversibly conveys light, so that its embodiments are operable in both directions. Thus the embodiments of the optical manifold described herein operate in both light-distribution, from a high-power source to many points of application, as well as light combining, of many sources into one large synthetic source with the same luminance as its input sources. 
   The term “optical manifold” was used in U.S. Pat. No. 4,362,361 by Campbell, et al., but therein this term denotes a partially reflective coating that repeatedly allows a small part of a laser beam to escape reflection as it tunnels inside a slab, so that multiple beams are made from one. This usage differs from what has become the conventional usage, in that “optical manifold” now denotes branching many-to-one light paths. 
   U.S. Pat. No. 6,186,650 discloses an “optical manifold” of branching waveguides, with numerous embodiments illustrated. It is believed that an actual ray tracing of these structures, however, would show considerable leakage, as shown by  FIG. 19A  and  FIG. 19B  in that patent. Moreover, it is believed that this prior art does not conserve etendue, giving outputs that are much weaker than the input. This is because the squared-off endings of the ports will cause much of the guided light therein to be reflected backwards. 
   Etendue, like entropy, is a measure of optical disorder, basically being the product of spatial extent and angular extent. Increasing the etendue of light can be considered as the optical equivalent of turning work into waste-heat, where the optical work would be the luminance of light-emission, and the waste-heat would be the useless dispersion of this light. An “etendue-limited” optical device is one that delivers light with nearly the original luminance, once inevitable reflections and scatterings are accounted for. The optical transformer described herein is etendue-limited, in that the input area-angle product is preserved for light passing through it. Some embodiments of the optical transformer described herein receive light from a plurality of sources to create a large, highly uniform synthetic source that may prove highly useful in the art of illumination. Other embodiments form distributed lighting systems, as in vehicle dashboards, that preserve both luminosity and etendue, enabling fewer LED sources to be necessary to accomplish the illumination task. 
   One example of an etendue-limited optical element is the compound parabolic concentrator (CPC), disclosed by Winston in U.S. Pat. No. 4,002,499. Another is the compound elliptic concentrator (CEC), disclosed by Winston in U.S. Pat. No. 3,957,031. Both of these can be utilized as a building block of the optical transformer described herein. A recent case is the corner-turning element disclosed by Fein in U.S. Pat. No. 6,819,687, which is etendue-limited only for angles well under the critical angle (NA&lt;1). Designed for use with the angular limitations of fiber-optic illumination, this device has significant limitations that are surpassed by a similar-looking but geometrically different angle-turning component of the optical transformer described herein. Fein&#39;s device is intended for the NA=0.5 range of fiber-optic illumination, so that light in the NA=1 range, which is that of the optical transformer described herein, would leak out of it. The optical transformer described herein has the NA=1 range because this enables it to convey four times the irradiance of NA=0.5 systems such as Fein&#39;s. A further limitation of Fein&#39;s device is the NA=1 that its design permits, because its primary application is right-angle turns in biomedical settings, for which two 45°-turners are utilized at NA=0.5. In contrast, the angle-rotating components of embodiments of the optical transformer described herein have very little leakage at any arbitrary turning angle of the NA=1 light it conveys, so that the 90° angle rotators illustrated herein could as easily be extended to comprise a 360° device suitable for a helical configuration, should such a novel requirement arise. This flexibility enables optical transformer embodiments described herein to address the entire span of applications of both light combining and light distribution, with maximal flux, something yet to be accomplished by the prior art. This flexibility is further exemplified by embodiments of the optical manifold disclosed herein comprising two opposing angle-rotators acting as luminance shifters, another useful component of systems with arbitrary branching patterns of distributed illumination. 
   Another improvement provided herein regards manufacturability of optical transformers. In the prior art, such as exemplified in Fein, all the surfaces must be optically active on such optical angle-turning devices. This makes it difficult to have points of injection for a part without introducing lossy surface defects on the optically active surfaces. Optical transformers are described herein that overcome this problem by providing inactive surfaces along the length of the device that can be used for points of injection. The inactive surfaces can be used as a means of holding the devices, and they can be freely modified into a wide range of shapes, without affecting the shape of the active surfaces of the device. The inactive surfaces are deliberately created by the pattern of ray distribution within the angle-rotator, providing an envelope of non-interaction with the light field, within which non-lossy attachments may be made. 
   DESCRIPTION 
   A better understanding of the features and advantages of the optical transformer described herein will be obtained by reference to the following detailed description and accompanying drawings, which set forth illustrative embodiments in which the principles of the invention are utilized. 
   An optical manifold is described herein that receives light from a plurality of solid-state sources and combines them into a single virtual-source output having little more etendue than the sum of the inputs. When the sources have different dominant wavelengths, the output light has the chromaticity of their colorimetric mixture. Due to the reversibility of light, the same shape of manifold could be used to disperse the light from a single large solid-state source among multiple virtual sources. 
   Two solid-state light sources in particular are contemplated for the optical transformer described herein: thin LEDs and dome-packaged high-power LEDs. Their packaging geometry dictates differing configurations of injection means for the optical transformer described herein. The prior art encompasses several types of injector means, including CPCs and immersion lenses, as well as conventional domed packaging. 
     FIG. 1A  is a cross-sectional view of an optical manifold including a thin-film LED  10  comprising a light-emitting layer  11 , reflective means  12 , and a window  13 . The LED  10  is embedded in a protective transparent epoxy  14 . An external CPC reflector  15  is accurately situated on the surface of epoxy  14  so that it just straddles window  13  over LED  10 , which is typically about a millimeter across. One advantage of the optical manifold described herein is that it allows more efficient cooling of larger (or multiple) LEDs. The difficulty of cooling larger or multiple chips is one of the motivations for the optical transformer described herein. (Electricity and heat sinks are not shown.) 
   Thin-film LEDs, such as the LED  10  shown in  FIG. 1A , emit nearly 100% of their output flux from the top surface of the device. Such devices have been produced in the laboratory and have been shown to the public by, for example OSRAM Semiconductors of Regensburg, Germany, which has begun producing them commercially in red and yellow with green and blue by the middle of the year 2005. A variety of thin emitter technologies are currently proposed by OSRAM Corporation of San Jose, Calif., including Indium Gallium Aluminum Phosphide (InGaAlP) and Indium Gallium Nitride (InGaN). All the emitting architectures shown by OSRAM Semiconductors to date use a wire bond on their top surface. The current thickness of the emitting layer in these devices is on the order of 0.1 microns and the overall chip depth is two to five microns. Therefore the side emissions from these devices are quite small, so they are ideally suitable for use in many of the embodiments of this invention. 
     FIG. 1A  further shows source-point  11   s  emitting edge-ray  16 , which just clears the upper edge of CPC  15 . Also shown is edge ray  17   e  emitted horizontally, thereby intercepting the base of reflector  15 , from which it is reflected into ray  17   r , which in turn just clears the upper edge of CPC  15 . The 45° design angle is shown. It applies to both direct ray  16  and reflected ray  17   r . Double-arrow  18  denotes the width of the virtual source generated by CPC  15 . Its width is 1/sin 45° times the width of emitting layer  11 , thus preserving etendue. 
   Although  FIG. 1A  shows CPC  15  as a hollow metal reflector, it could as well be filled with a dielectric such as cast epoxy. If the 45° design angle would be slightly reduced to the critical angle (40°), the CPC would become slightly taller, and extreme rays  16  and  17   r  would be refracted to horizontal, for a planar air-interface across the top of CPC  15 . Such a filled CPC would couple the LED into air with transverse magnification equal to the refractive index of the transparent filling material. (The area is increased by the factor of n 2 .) For greater magnifications, a narrower design angle is needed. When that angle is reduced to 10°, reflector  15  can be dispensed with, since total internal reflection suffices. 
   U.S. Pat. No. 3,739,217 by Bergh and Saul teaches that the extraction of light from within a high-index-of-refraction body can be increased by roughening either a front emitting surface or a back surface of the high-index layer, where this roughened back surface interfaces with a reflective layer. However, the Bergh et al. patent does not specify the reflector-material nor does it indicate whether the reflector should be in direct contact with all surfaces of the high-index body. The Bergh et al. patent appears to indicate in its  FIGS. 2 and 3  that there is an air gap between the illuminated body and the back reflector. 
     FIG. 1B  is a magnified view of the LED  10  of  FIG. 1A , showing emitting layer  11  comprising thin (approximately 0.1 microns) active layer  11   a  situated in the middle, InGaN layer  11   u  above it, and layer  11   b  below it. Window  13  can be seen to have slanted edge  13   w  to prevent light-escape.  FIG. 1B  further shows an approach to enhancing the luminous extraction efficiency of a top-emitting LED (or of a predominantly top-emitting LED) wherein electrically conductive reflective layer  12  also acts to power epitaxy layer  11 , with which it is in direct contact. Roughened interface  11   i  is the contact surface. This roughening can be achieved on the epitaxy layer  11  by chemical etching or other well-known methods. Once the epitaxy layer is roughened, the reflective layer  12  can be deposited thereupon by vacuum, sputtering, or other deposition methods. 
   The material properties of reflector layer  12  must be precisely specified to match with the properties of the epitaxy layer. For example, where an electrically conductive reflective layer is needed, a metallic material is best, and its index must have the proper complex value to achieve a high diffuse reflectance. For a blue LED using an epitaxy layer of GaInN or GaN for example, the visible-wavelength index of refraction of both GaInN and GaN is about 2.54. Calculating the reflectance of such a metal layer involves using the complex index of refraction in the Fresnel-reflection equations, so that both the real and imaginary components of the index of refraction of a candidate material are critical. The reflectance for rays striking at a zero incidence angle can provide a metric for choosing appropriate materials. A suitable equation for carrying out such an analysis is:
 
 R =[( N   epi   −N   s ) 2   +k   s ]/[( N   epi   +N   s ) 2   +k   s   2 ]
 
where:
         R is the reflectance at zero incidence at the interface of the epitaxy and the metal layer,   N epi  is the index of refraction of the epitaxy,   N s  is the real part of the index of refraction of the metal, and   k s  is the imaginary part of the index of refraction of the metal.       

   Assuming that the epitaxy layer has index 2.54, the metal needs the real component to be low and the imaginary component high. Silver has a low real component (0.12) and a very high imaginary component, over wavelengths ranging from 450 nm (k=2.47) to 700 nm (k=4.52). At 550 nm a thick layer of silver has an index of refraction (real) of approximately 0.12 and an imaginary value of 3.34. Plugging these values into the aforementioned equation yields a reflectance of 0.93. By way of comparison a layer of aluminum would have a much lower reflectance in contact with GaInN, as it has a real value of 0.76 and an imaginary value of 5.32 at 550 nm. In this case the reflectance at the interface of the two materials, for zero incidence angle rays, can be calculated by the same equation as 0.80. This is a very significant difference, especially with the extraction efficiency of the device having a non-linear relationship to the reflectance of this layer, because internal rays in the epitaxy undergo many boundary reflections before being either absorbed or extracted from the layer. Thus a small improvement in the reflectance of this bottom interface layer can produce a large improvement in the external quantum efficiency of the LED. 
   Such a reflective layer may also be made of dielectric materials using multi-layer approaches, particularly the Bragg reflector, common to the industry. However, electrical conductive paths known as vias must be introduced somewhere through this otherwise non-conductive layer, in order to power the semi-conductor. The use of a dielectric layer however may increase the internal resistance of the device and therefore increase the internal heat generated for a given applied voltage. Further, it is known that it is very difficult to design a Bragg reflector which has high reflectance for a wide range of wavelengths and incidence angles. This is especially a problem for LEDs which employ conformal phosphor coatings on the die. Thus silver may be deemed a superior solution over a dielectric reflector as it performs well over a wide range of incidence angles and wavelengths. 
   U.S. Pat. No. 6,784,462 teaches how to make an “omni-directional” back reflector with very high reflectance for an LED by combining a quarter wavelength layer of Indium Tin Oxide (ITO) in front of a layer of silver. The thin film approach in the &#39;462 patent, however, assumes that the silver and ITO layers are smooth, precluding any roughening of the bottom of the LED proper, known as the ‘epitaxial layer’ because it is made atop a substrate, by an atomic beam in a vacuum. Because of extensive light trapping within a cube of high-index material, a standard LED geometry, achieving maximum extraction efficiency makes it imperative to have a roughened surface at the interface where the reflector is in contact with the epitaxial layer. This is needed to achieve high diffuse reflectance, which causes trapped light to be randomly redirected for another chance at escape. Further, ITO has a much lower electrical conductance than silver, which may be a disadvantage for some designs. 
   Getting trapped light scattered out before it is absorbed makes it desirable to have either a bottom diffuse reflector or a top scattering layer incorporated with layer  11   u  of  FIG. 1A . A combination where both approaches are employed can also be utilized. However, one can introduce too much scattering in the device when both a top and bottom scattering layer are used and thus reduce the device extraction efficiency. It can be shown that without top scattering introduced into layer  11   u , that a perfect reflector such as described in U.S. Pat. No. 6,784,462 will not perform as well as the diffuse silver reflector described herein. Further, in many instances it is desirable to have a smooth interface at the top of layer  11   u  and one cannot introduce a scattering or diffusing layer on its interface or below its top emitting surface. In these instances the rear diffuse reflector proves most beneficial and has been stated herein, will outperform even a 100% perfect specular reflector. 
   Furthermore, silver will lose its reflectivity if not properly protected from contact with air or corrosive materials (it is highly reactive with sulfur), so it must be sealed by suitable protective layer. Typically, if the silver is sandwiched between the epitaxial layer and a suitable substrate such as Germanium, then no noticeable degradation of this material takes place as it is hermetically sealed. If edge protection is required there are many suitable materials known to those skilled in this field of semi-conductor design. 
   Regarding the matter of a roughened back-reflector made of silver, computer simulations thereof, using well-known Monte-Carlo ray-tracing techniques, show that the optical transformer described herein will greatly benefit from having this feature in the LEDs that illuminate its embodiments, particularly those disclosed below that recycle the emission of a phosphor. 
   This roughened-silver reflector can of course greatly benefit thin-film LEDs whether or not used in conjunction with the optical transformer described herein. Referring again to  FIG. 1B , another such LED optical improvement is the reduction of the absorptance of lower epitaxy-layer  11   b , where the majority of luminosity losses occur within epitaxy layer  11 . As an epitaxy, this layer is typically deposited on a sapphire crystal. In the production of thin-film LEDs the epitaxy wafer is removed from the sapphire. (A summary of the processes needed to remove the InGaN wafer from the sapphire substrate was described by Dr. K. Streubel of OSRAM-Opto in a presentation titled “Thin-film Technology for Light Emitting Diodes” at Intertech LEDs 2004 conference in San Diego, Calif., USA, Oct. 20-22, 2004.) 
   The absorption of the lower layer is not essential to its function, and seems to be confined to the superficial atomic crystal-planes, several tens of nanometers out of the layer&#39;s total thickness of 5,000 nm. According to the research of S. Schad and B. Neubert of the University of Ulm in Germany, described in their paper “Absorption in InGaN-on-Saphire Based Light-Emitting Diodes”, Annual Report 2003, Optoelectronics Department, University of Ulm, the first thin layer of an InGaN-type LED grown on a sapphire substrate, approximately 65 nm, is responsible for most of the absorptance of the InGaN LED in the blue wavelength. They theorize that the remaining semi-conductor material grown on the substrate is highly transparent. These planes were so near the sapphire that their crystal structure and absorptance greatly increased. In some embodiments, neither layer  11   a  nor  11   u  has this thin absorptive layer. Precise removal of this strained sub-layer is possible with magnetorheological polishing, greatly reducing the absorptance and thereby enhancing the LED&#39;s external quantum efficiency. 
   A separate possibility for enhancing that efficiency is to cause the front layer  11   u  of  FIG. 1B  to have bulk-scattering characteristics, rather than the complete transparency typical of such a layer. A study using a ray-tracing model showed that the introduction of a scattering coefficient of 100/mm into layer  11   u  gives an approximately 40% increase in efficiency for a SMD-type LED, where layer  11   u  does not have any appreciable scattering and does not have a phosphor layer in contact with it. Similar improvements are seen for a dome type monochrome LED. If the scattering coefficient is increased to 200/mm, a very slight improvement is seen. Whereas beyond this level there is reached a point where the performance degrades from the maximum. The use of a means of scattering in the front layer typically does not have a beneficial effect on performance when it is used in conjunction with the roughened back-reflector approach already discussed. There is a very slight improvement to the extraction efficiency if a roughened-back reflector is used in combination with layer  11   u  having a 10/mm scattering coefficient. Beyond this level of front scattering the performance falls below either single approach. 
   The optical manifolds disclosed herein that recapture back-scattered light can be enhanced significantly when the extraction efficiency of the LED is high. Particularly, it is believed that the remote phosphor embodiments described herein will outperform the prior art in terms of external quantum efficiency, particularly conformal-phosphor LEDs. The performance of the novel optical systems disclosed herein can be improved dramatically when they are used in conjunction with top-emitting or substantially top-emitting LEDs, particularly those which employ a highly reflective back layer with modest scattering. 
     FIG. 2A  is a cross-sectional view of a prism coupler  40  that has an interior angle adapted to the critical angle α C  of the prism material. Thin LED  41  sends Lambertian emission across airgap  41   a , wherein it is confined between upper edge ray  41   e  and lower edge ray  41 L. Thin LED  42  emits across airgap  42   a  and enters prism  40 , wherein its Lambertian emission becomes confined to half-angle α C , between upper edge ray  42   e  and lower edge ray  42 L. The purpose of interior angle  40 A being 2α C  becomes apparent when ray  41   e  is seen to internally reflect off air gap  42 , to join ray  42 L. Thus the internally reflected light fills the angle space outside the edge rays of the incoming light. 
     FIG. 2B  is a cross-sectional view of an optical manifold  44  that utilizes the prism coupler shown in  FIG. 2A . The optical manifold  44  comprises a dielectric CPC  44   c  and a conjoined prism block  44   b . The thin LED  45  is immersed in a dielectric CPC  45   c , which is wider at airgap  45   a , across which it shines Lambertian light into manifold  44 , wherein refraction confines it to critical angle α C . A similar approach is used with LED  46 , CPC  46   c , and airgap  46   a . The prism coupler then receives two inputs of radiation spanning an angle 2α C , through  45   a  and  46   a , and transforms them into a fully Lambertian pattern at  44   b  (about ±90° full angle). A CPC  44   c  expands from its width at block  44   b  to its exit face  44   a . This enables all the light to exit as Lambertian emission  44   e , forming a “virtual chip”. An exit surface at  44   b  would trap light beyond critical angle α C , hence the use of CPC  44   c.    
     FIGS. 1A through 2B  show two-dimensional profiles acting on rays running in the plane of the Figures. In some practical embodiments a 3-dimensional system is formed by extruding such a profile orthogonally to its plane. The thickness of this extrusion distarice is typically equal or slightly larger than the width of the square chip. This will result in losses in the extrusion direction of rays not in the plane of the profile being extruded. Instead, a two-way cross-CPC can be used, with the same profile used in orthogonal directions. Examples of this are shown in  FIGS. 3A ,  3 B,  4 A,  4 B,  5 A, and  5 B. Critical to high system efficiency is the use of a transparent material with suitably low absorptance, because of the multi-pass nature of the passage of light within these embodiments. For example, polycarbonate, a routinely employed injection-molded plastic, has so much absorption that these embodiments will have serious losses, whereas acrylic does not. 
     FIG. 3A  is a perspective view of optical manifold  80 , a dielectric-filled 2×2:1 multi-CPC embodiment. It comprises four input cross-CPCs  81  and output cross-CPC  82 , all square in cross-section, as seen with dividing line  80   d . The cross-section of each of these four cross-CPCs  81  is selected so that immersed LEDs  83  will have all their light sent across plane  80   d  into cross-CPC  82 . 
     FIG. 3B  is another perspective view of optical manifold  80 , also showing exit surface  84 , which must connect to another device of similar refractive index, else some of the concentrated light will be returned by internal reflection. It is possible to join manifold  80  with some of the embodiments to be shown below. 
     FIG. 4A  is perspective view of a 2×4:1 optical manifold  90 , comprising a plurality of input cross-CPCs  91  that receive light from a corresponding plurality of immersed LEDs  92 , a rectangular mixing section  93  that receives the light from the plurality of cross-CPCs  91 , and a rectangular output cross-CPC  94  that receives light from the rectangular mixing section. 
     FIG. 4B  is another perspective view of the manifold  90  shown in  FIG. 4A , also including an approximately rectangular output surface  95  from the output cross-CPC  94 . 
     FIG. 5A  is a perspective view of a 4×4:1 optical manifold  100 , comprising a plurality of (in this embodiment sixteen) square dielectric input cross-CPCs  101 , a corresponding plurality of immersed LEDs  102  connected respectively to the cross-CPCs, and an approximately square output dielectric cross-CPC  103  coupled to collectively receive the light output from each of the cross-CPCs. Also shown is an immersed square filter  105 , installed for the case of blue LEDs  102 . In some embodiments, square filter  105  would be a blue-pass reflector applied across the input face of output CPC  103 , then optically joined to the array of input cross-CPCs  101 . Such a blue-pass reflector can be constructed in several ways well known to those skilled in this art, such as deposition of thin film multi-layer dielectric or other materials onto a suitable substrate, and through single or multi-layer reflection or transmission holographic coatings. In a 1981 publication (Miles, Webb, and Griffith, “Hemispheric-field-of-view, nonimaging narrow-band spectral filter”,  Optics Letters, Vol.  6#12 pp. 616-618 (December 1981) two hollow reflective CPCs are used face-to-face to collimate light into a narrow-band spectral filter and then condense the filtered light. Embodiments of the optical transformer described herein, in contrast, utilize a dielectric CPC instead of a hollow CPC. Another difference is using a short-pass filter or band-pass filter by which short wavelengths are transmitted and long wavelengths are reflected (rather than a narrow-band filter). For many applications, a band-pass filter with a lower cutoff below the working range of frequencies may be treated as equivalent to a short-pass filter. The embodiment of  FIG. 5A  has a plurality of input CPCs rather than a single CPC. The condenser CPC  103  has a phosphor target. Condenser CPC  103  combines and homogenizes the input from sixteen LEDs onto a single exit surface  104  on which the phosphor target resides. A novelty of the embodiment of  FIG. 5A  is the function of filter  105 , to reflect the back emission of phosphor  105 . This is the recycling principle of certain embodiments of optical transformer described herein, which is believed to be a novelty. 
     FIG. 5B  is another perspective view of the optical manifold  100  shown in  FIG. 5A , and in addition comprising an approximately rectangular exit face  104 . 
   It is desirable that the Lambertian distribution of an immersed LED be compressed to the critical angle, but expanding area in an etendue-conserving fashion. Equally important for building blocks of the optical manifolds of the optical transformer described herein are etendue-conserving ways to transport luminance at a high NA, which is typically around 1, while mixing it to achieve high uniformity and a constant color. The NA can be calculated using either of the following equations:
 
 NA=n  sin(π/2−θ C )= n √(1−1 /n   2 ),
     where θ C  is the critical angle of the material and n is the index of refraction of the material. This equation is useful for determining the NA of a system where the input ray bundle is already inside a dielectric media. In this instance the value n in the equation is greater than 1.0.   

   It is desirable that the Lambertian distribution of an immersed LED be compressed to the critical angle, but expanding area in an etendue-conserving fashion.  FIG. 6  shows distribution-transforming element  120 , with a wide-angle (±90°) port  121  marked by end-points  123  and  124 , and spatially wider narrower-angle port  122 , marked by end-points  125  and  126 . Point  127  is a point on the surface of element  120  between end points  123  and  125  from which a ray at the critical angle θ of the transparent medium composing element  120  will just exit from element  120  at end-point  126  on the opposite side. Point  128  is directly opposite point  127 . From end-point  123  to point  127 , the profile of element  120  is an ellipse with foci at opposite points  124  and  126 . Between end-point  125  and point  127  is a parabola with focus at point  124  and axis parallel to the ray running from point  127  to point  126 . The opposite side, from end-point  124  to point  128  and from point  128  to end-point  126 , is correspondingly shaped. To the left of points  127  and  128  is a CEC (compound elliptical concentrator), while to their right is a CPC. The narrower-angle output of distribution-transforming element  120  serves as suitable input for further embodiments. The advantage of this device relative to a simple CPC with exit angle 2θ is that TIR is more easily achieved at the bottom edges  123  and  124 . 
   Equally important for building blocks of the optical manifolds of the optical transformer described herein are etendue-conserving ways to transport luminance at a high NA, which is typically around 1, while mixing it to achieve high uniformity and a constant color. The NA can be calculated using either of the following equations:
 
 NA=n  sin(π/2−θ C )= n √(1−1/ n   2 ),
     where θ C  is the critical angle of the material and n is the index of refraction of the material. This equation is useful for determining the NA of a system where the input ray bundle is already inside a dielectric media. In this instance the value n in the equation is greater than 1.0.   

   Prior art relating to transport of illumination is shown in U.S. Pat. No. 6,819,687 by Fein, particularly his  FIG. 1F . This corner-turning configuration is only possible with conventional reflectors, since TIR will fail for arbitrary rays coming in. For all-TIR operation Fein has a device in his  FIG. 3B  for a 45° turn. An optic with a similar geometry is redrawn here, in  FIG. 7A , to promote discernment of the distinction from it, and advantages over it, of the angle-rotator disclosed herein. 
     FIG. 7A  shows the construction of Fein&#39;s corner-turner  1350 , with ports  1351  and  1352  lying at a 45° mutual orientation. It uses a construction angle θ, which is the complement of the critical angle θ c =sin −1 (1/n), which for n=1.495 is θ=49°. This corresponds to the maximum angle of guided light, or approximately NA=1. Inside wall  1353  is a flat mirror for which TIR is operable, running from point F 1  on port  1351  to point F 2  on port  1352 . Outside wall  1354  comprises a parabolic arc running from point P 1  on port  1351  to point P 2 , with focus at point F 2  and axis making an angle θ to the normal to the entrance aperture  1351 , in the direction (clockwise direction as seen in  FIG. 7A ) more nearly perpendicular to the line F 2 -P 1 , an elliptical arc running from point P 2  to point P 3 , with foci F 1  and F 2 , and a parabolic arc running from point P 3  to point P 4  on port  1352  with focus at point F 1  and whose axis makes an angle θ to the normal to the exit aperture  1352 . Construction lines  1355  are reflected against outer wall  1354  in the same way as the limiting rays of light at approximately NA=1. 
   Although these construction lines are for NA approximately equal to one, the device of  FIG. 3B  of Fein cannot actually transport such radiation via only total internal reflection. This is shown in  FIG. 7B , which depicts a ray trace of corner turner  1310 . Edge rays  1357  in  FIG. 7B  make an angle θ to the normal to entrance aperture, which is the complement of critical angle θ c  for the material of this device. Only one of them, ray  1357   e , is reflected by TIR. All the rest, refractively transmitted rays  1357   r , constitute leakage and a partial device-failure. More complete ray traces show that 100% delivery is only obtained when the ray incidence angles are less than or equal to the angle between the line connecting points F 1  and P 4 , and the normal to entrance aperture in  FIG. 7A . In the example of  FIG. 7A  this angle is approximately 3 degrees. Some rays with incidence angles greater than 3 degrees for this device will leak out the side of the optic. If all the light is to be redirected by means of total internal reflection, it should be clear that the devices described in Fein, as illustrated by his  FIG. 3B , are only suitable for rotating highly collimated light sources. 
   The angle-rotators used in the optical manifold satisfy total internal reflection for all rays up to the highest possible NA.  FIG. 7C  is a cross-sectional view of an angle-rotator  130 , with a first port  131  and a second port  132 , which are in complete exchange for light of angular width  2 θ. This angle is twice the complement of the critical angle for the transparent material of rotator  130 . The second port  132  is at angle β from the plane of port  131 , generally at the convenient value of approximately 45°, enabling two angle rotators to transport luminance around a right-angle bend with substantially no losses, a situation that would cause inescapable losses for the simple round or square cross-sections of the prior art. 
   In  FIG. 7C , a flat sidewall  133  extends between foci F 1  and F 2  of elliptical segment  134 , which is in turn flanked by flat sidewalls  135  and  136 . Sidewall  135  is oriented perpendicular to entrance aperture  131 , while sidewall  136  is oriented perpendicular to exit aperture  132 . Rays  137  run from focus F 1  to focus F 2  via a single total internal reflection, while ray  138  runs via a single total internal reflection from the opposite side of port  131  from point F 1  to the opposite side of port  132  from point F 2 . This shows how angle rotator  130  transfers all rays within ±θ from first port  131  to second port  132 , with none escaping. This nonimaging optical configuration tends to smear out any luminance non-uniformities it receives. This smearing is because each point on the second port  132  receives light from the entirety of port  131  as well as from reflections from the walls of angle rotator  130 . Since an image is just another type of luminance-nonuniformity, this is why this and other embodiments herein are termed ‘non-imaging’. 
     FIG. 7D  is a cross-sectional view of an angle-rotator  1300  similar to that in  FIG. 7C , comprising outer arc  1301  with center of curvature at point C and inner arc  1302  also centered on point C. Tailored curves  1303  terminate both ends of arc  1302 , as do tailored curves  1304  for arc  1301 . Curves  1303  and  1304  jointly define end ports  1305  and  1306 . Their two-way nature is shown by oppositely directed rays  1307  and  1308 , totally internally reflecting at outer incidence angle α and inner angle β, respectively against arcs  1301  and  1302 . The end-ports are not shown refracting the rays since they are expected to be joined to other optical manifolds such as disclosed herein. 
     FIG. 7E  also shows an angle-rotator  1300 , but with complete sets  1309  and  1310  of parallel paths of edge-rays, which define the angular limits within which rotator  1300  will convey all luminosity through large arcs via total internal reflection. 
     FIG. 8  is a cross-section of an optical shifter  140 , comprising first angle rotator  141  and oppositely oriented second angle rotator  142 . To fit together, both rotators have been modified by removal of segments analogous to flat segment  135  of  FIG. 7C . Thus interface F 1 -F 3  is wider than the input light. The net effect of shifter  140  is, in this example, a lateral shift of 1.5 widths of an input luminance distribution, which of course is confined to the critical angle of the transparent material composing it. The multiple internal reflections within shifter  140  tend to smooth out any luminance non-uniformities entering it. 
     FIG. 9A  is a cross-section of optical shifter  150 , also for lateral luminance shifting with no angle rotation. First port  151  spans points F 1 ′ and F 2 . Second port  152  spans points F 1  and F 2 ′ and is shifted a half width from port  151 , as shown by dotted line  150 L. When either port is a boundary with air, light entering it must be within the critical angle θ of the transparent material of  150 . Straight-line segment F 1 ′P 1  is perpendicular to port  152 , and straight-line segment F 2 ′P 2  is perpendicular to port  151 . Parabola F 1 P 1  has focus at F 2  and axis parallel to ray r 1 . Parabola F 2 P 2  has focus at F 1  and axis parallel to ray r 2 , which is parallel to ray r 1 . As a non-imaging optical device, element  150  tends to smear out, as previously discussed regarding  FIG. 7C , non-uniformities of the luminance distributions entering it. 
     FIG. 9B  is a cross-section of optical shifter  155 , for lateral luminance shifting by its full width, as shown by line  155 L. A first port  156  spans from point F 1  to point F 2 . A second port  157  spans from point F 3  to point F 4 . As previously, light is confined to the critical angle .theta. of the transparent material composing shifter  155 . This is shown in the  FIG. 15B  as the acute angle formed between the line defined by the ray from points F 3  to P 2  and the axis  155 L. Most of the perimeter of shifter  155  is straight lines, from point F 4  to Point P 2 , from point F 2  to point P 1 , from point F 1  to point P 3 , and from point F 3  to point P 4 . Parabolic segment  158  runs from point P 1  to point P 2 , and has its focus at point F 1  and its axis parallel to ray F 2 -P 3 . Parabolic segment  158 ′ runs from point P 3  to point P 4 , and has its focus at point F 4  and its axis parallel to ray F 3 -P 2 . 
     FIGS. 9A and 9B  show two variations along a continuum of possible values of lateral shift of luminance. Greater shifts merely require a longer shifter than  155  of  FIG. 9B . 
   Another advantage of various of the optical manifolds described herein is their ability to alter not only the limiting angle of light entering the manifold, but also the spatial shape of the luminance entering it, particularly from square to rectangular. The luminance shifters of  FIGS. 9A and 9B  can be adapted for this purpose, enabling elongated luminance distributions to be produced. 
     FIG. 10  is a perspective view of a luminance shifter  300 , formed from profile  301  of width w (at port  302 ), by an orthogonal sweep by w/2, so that first port  302  is a 2:1 rectangle. Second port  303  is shifted by w/4, rather than the w/2 shown in  FIG. 9A . 
     FIG. 11A  is an exploded, perspective view of another embodiment. Upper half-width shifter  300 U is contiguous across line  300 Ud with orthogonal shifter  305 U, with downward shift of w/4. Nearly identical but inverted lower shifter  300 L is contiguous with shifter  305 L, to provide a side shift of w/2 and an upward shift w/4. 
     FIG. 11B  is a perspective view of the monolithic etendue-squeezer  310  shown in exploded view in  FIG. 11A . In  FIG. 11B , a square input face  311  is split into a top duct  311 U and a lower duct  311 L, also diverging to form a 4:1 rectangular output face (not shown). As previously, this device operates on light within the critical angle of its transparent material. 
     FIG. 11C  is another perspective view of the etendue-squeezer  310  shown in  FIG. 11B , showing a 4:1 rectangular output face  312 , and also showing its width  2   w  and height w/2. 
     FIG. 12  is a perspective view of a monolithic 9:1 etendue-squeezer  320 , comprising: an upper-to-left light-duct  321 , a central rectangular duct  322 , and a lower-to-right light-duct  323 . These light-ducts divide square-face port  324  into three parts, each having a 3:1 ratio, which are displaced and rejoined as 9:1 elongated rectangular duct  325 . The shape of rectangle  325  can be useful both as a fan-out for nine small light-ducts or as a synthetic light source for luminaries, particularly when phosphor-coated. 
   A practical issue with many embodiments of the optical manifold described herein is where to put attachment points for mounting a manifold in its proper position. When a surface is optically active, placing a mounting fixture thereupon will result in optical losses through diversion of light from its intended destination. Accordingly, it is often desirable to arrange for some optically inactive surfaces to be part of a manifold. 
     FIG. 13A  is a cross-sectional view of a light duct  330  having an input port  331  and an output port  332 , with limiting incidence angle θ upon both. The bottom side of duct  330  comprises flat mirror  333  perpendicular to face  332 , elliptical arc E 45  with foci at points F 4  and F 5 , elliptical arc E 24  with foci at points F 2  and F 4 , parabolic arc P 21  with focus at point F 2  and axis parallel to line r 1 , elliptical arc E 23  with foci at points F 2  and F 3 , and parabolic arc P 22  with focus at point F 2  with axis parallel to line r 2 . The upper surface of duct  330  comprises parabolic arc P 53  with focus at point F 5  and axis parallel to line r 3 , inactive surface  334 , parabolic arc P 11  with focus at point F 1  and axis parallel to line r 1 , and flat mirror  335 . It can be seen that no light touches surface  334 , in that the line joining points F 2  and F 4  represents an extreme ray. 
     FIG. 13E , is a cross-sectional view of an angle-rotating luminance duct  3300 , resembling that of  FIG. 7D , with a full 90° circular-arc outer profile  3301 , but without a corresponding inner circular arc. Instead, inactive optical profile  3302  lies inside arcuate caustic  3303  formed by ray-paths  3304 , propagating within  3300  with directions spanning total angle Θ. End-sections  3305  through  3308  are shaped to cause the formation of caustic  3303 , dispensing with any active inner wall. 
     FIG. 14  is a cross-sectional view of a light duct  340 , which has symmetrically placed ports  341  and  342 . Its upper surface comprises on the left flat mirror segment  343  and parabolic arc  344  having focus at F 2  and axis parallel to line r 1 . At upper center is optically inactive surface  345 . On the upper right are corresponding parabolic arc  346  and flat mirror  347 . The lower surface comprises parabolic arc  348  with focus at F 1  and axis parallel to line r 1 , and its mirror image arc  349 . 
     FIG. 15  is a cross-sectional view of a light duct  350  that has plurality of input ports  351  and an exit port  352 . A central optically inactive surface  353  is flanked by a parabolic segment  354  that defines a focus at F 4  with an axis parallel to line r 2 , and by flat mirror  355 . The bottom surface of light duct  350  comprises a flat mirror M, a parabolic arc P 1  with focus at F 2  and an axis parallel to line r 1 ; an elliptical arc E 12  with foci F 1  and F 2 , a parabolic arc P 2  with focus at F 1  and an axis parallel to line r 2 , an elliptical arc E 13  with foci at F 1  and F 3 , and a parabolic arc P 3  with focus at F 1  and an axis parallel to line r 3 . 
     FIG. 16  is a cross-sectional view of a luminance duct  360 , having a configuration that is bilaterally symmetrical about dotted line  360   d , and having ports  361 . Also shown are an optically inactive surface  362 , a parabolic arc  363  with focus at F 4  and axis parallel to line r 2 , a flat mirror  364 , a parabolic arc  365  with focus at F 1  and an axis parallel to line r 3 , an elliptical arc  366  with foci at F 1  and F 3 , a parabolic arc  367  with focus at F 1  and an axis parallel to line r 2 , an elliptical arc  368  with foci at F 1  and F 2 , and a parabolic arc  369  with focus at F 2  and an axis parallel to line r 1 . 
     FIG. 17A  is a cross-sectional view of an extended optical manifold comprising system  350  of  FIG. 15 , and a four-part manifold  371  fed by four LEDs  372 . The optical manifold  371  comprises the four sections  360  of  FIG. 16 , as well as angle rotators  374  and angle transformer  375 , which are shown joining to duct  350  by arrows  376 . Optically inactive surfaces  373  are available for mounting as well as for the location of injection gates and ejector pins in injection molding. 
     FIG. 17B  is a perspective view of another embodiment of an optical manifold. The optical manifold  3700  in  FIG. 17B  combines elements of previous Figures. In  FIG. 17B , an optical manifold  3700  comprises four input ports  3701  (each with CPC  3703 ) and a single output  3702  having only their combined etendue, so that all light entering the input ports will be conveyed out the exit port. Each input port  3701  feeds one of the angle-rotators  3704 , identical in profile to the embodiment of  FIG. 13A . The rotators feed combiner  3705 , which is identical to that of  FIG. 22 , and which in turn connects with large rotator  3706 . A structural beam  3707  connects with the optically inactive flanges of rotators  3704 , providing secure mounting in a different plane than that of flange  3708 . 
     FIG. 17C  is a cross-sectional view of yet a further combination, showing two individual dual-lens LEDs with remote phosphors  3750  including blue-pass dichroic filters  3755 , seen to be recycling rays  3756  of phosphor back emission. Each phosphor feeds angle rotator  3770 , their luminosity combined at output port  3780 . Brackets  3775  provide sturdy support so that phosphors  3760  receive no structural loads. 
     FIGS. 18A and 18B  are cross-sectional views of an alternative arrangement that includes dielectric CPCs. When a 90° turn is desired, the configuration of  FIG. 18A  shows why such a prism coupler may be necessary or useful. Dielectric CPCs  391  and  392  have orthogonal orientations, joining at diagonal  393 . Escaping rays r 1  and r 2  are exemplary of the optical losses incurred in this configuration.  FIG. 18B  shows separate dielectric CPCs  395  and  396 , coupled by diagonal prism  397  situated with air gaps  398  and  399 . Ray r 1  has been internally reflected by gap  398  and thus remains within CPC  396 . Similarly, ray r 2  has been internally reflected by gap  399 , onto the diagonal of  397  to be reflected therefrom into CPC  396 . 
   The method shown and discussed with reference to  FIG. 5  of recycling phosphor back-emission utilizes a blue-pass filter that returns this back-emission to the phosphor. This method utilizes low absorption in the phosphor. The configuration of  FIG. 19  can be utilized for a phosphor that does have significant absorption of its own emission wavelengths. Dielectric CPC  411  has blue LED  412  coupled to it, with its directed output shown as edge rays. This blue light passes unimpeded through diagonal blue-pass filter  413  and proceeds into dielectric CPC  415  to illuminate phosphor patch  416 . Phosphor back emission proceeds to filter  413  and is reflected into third dielectric CPC  417 , which has exit face  418 . An expanded section shows how flat section  417   f  acts to restrict incidence angles to less than the critical angle α C , given by α c =sin −1 (1/n) for refractive index n of the dielectric material comprising CPC  417 . 
   The CPC  411  has a diagonal exit face  413  with the blue-pass filter coated thereupon. Optically joined to face  413  is a diagonal prism  414 . Adjacent to the prism  414  is the dielectric CPC  415 , having the phosphor patch  416  on its exit face. Phosphor back-emission proceeds through prism  414 , reflects off diagonal exit face  413  into dielectric CPC  417 . This reflected back-emission forms a virtual source  418  at the exit face of CPC  417 . An expanded view shows how flat section  417   f  acts to restrict incidence angles on face  418  to the critical angle α c . 
   The description herein describes both individual optical elements and several embodiments that combine them as building blocks. One common theme of many of these elements and their combinations is preservation of source luminance through etendue preservation, using novel applications of the principles of non-imaging optics. 
   The preceding description of the presently contemplated best mode of practicing the optical transformer described herein is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined by reference to the claims. 
   It will be appreciated by those skilled in the art, in view of these teachings, that alternative embodiments may be implemented without deviating from the spirit or scope of the invention. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.