Abstract:
A light recycler for use in color projection display systems. The light recycler redirects light reflected by a color wheel of the projection system to increase the light output of the projection system. The light recycler is capable of setting the desired numerical aperture of the light source beam, as well as providing the desired spatial distribution of light in terms of intensity and angle. This improves the light uniformity and brightness of the image displayed by the projection system, and improves the efficiency of the system. The light recycler includes at least one substantially planar optical element array receiving the non-uniform light from the light source. The optical element array includes an optically transmissive substrate and a plurality of optical micro-elements formed in the substrate. The micro-elements act together to produce an output light beam having a desired cross-sectional area and spatial distribution of light intensity and angle.

Description:
RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/458,390 filed on Jun. 10, 2003 now U.S. Pat. No. 7,306,344, titled “Light Guide Array, Fabrication Methods, and Optical System Employing Same”. This application also claims the benefit of U.S. Provisional Application Nos. 60/548,814, 60/548,293 and 60/548,619, all filed on Feb. 27, 2004. It is also related to U.S. patent application Ser. No. 11/066,616, titled “Compact Polarization Conversion System For Optical Displays” filed on Feb. 25, 2005 and U.S. patent application Ser. No. 11/066,605 titled “Compact Projection System Including A Light Guide Array”, filed on Feb. 25, 2005. The subject matter of the aforementioned applications is hereby incorporated by reference as though set forth in full. 

   TECHNICAL FIELD 
   The present invention relates generally to color projection systems utilizing one or more light modulators, and more particularly, to a color projection system that includes means for recycling light reflected from a color wheel. 
   BACKGROUND 
   Single-modulator and two-modulator sequential color display systems have been used as a cost effective alternative to three-modulator full color display systems. Such systems are described in published European Patent Application EP1,098,536 A2, to Duane Scott Dewald, which is hereby incorporated by reference. 
   As shown in  FIG. 1 , the brightness of the single-modulator  10  and two-modulator  25  sequential color display systems is improved through the use of a recycling solid light pipe  5  (or recycling light tunnel) coupled with a dynamic filter  7  and  14 , which provides one or more segments of each primary color filter to the light beam at all times. As shown in  FIGS. 1C-1E , the recycling pipe  5  consists of a light pipe  5   b  and a reflective plate  5   a  with an aperture  50   a  The exit aperture of the recycling pipe  5  typically has the same cross section aspect ratio as that of the modulator  9 ,  16  and  17  used by the display systems  10  and  25 . 
   In  FIGS. 1A-1B , the input light  3  and  13   a  is focused into the entrance aperture of a recycling pipe  5  through an aperture  50   a  in a reflective plate  5   a . Light beams  6  and  13   b  exit recycling pipe  5  more uniform and homogeneous and impinge on the color wheels  7  and  14  (i.e., dynamic filter). Some of the light beam impinging on the color wheels  7  and  14  passes through each of the three or more color segments illuminated by the beam. Each segment transmits some of the incident light and reflects the remainder, which reenters the recycling pipe  5  and travels toward the reflective plate Sa. Some of this light impinges on the reflective plate  5   a  and gets reflected back toward the color wheels  7  and  14  and the rest of it passes through the aperture  50   a  toward the lamp reflector  2  and  12 . Lens  8  focuses light transmitted by the color wheel  7  onto the spatial light modulator  9  as shown in  FIG. 1A . 
   As shown in  FIG. 1B , light beam  13   c  exiting the color wheel  14  enters a TIR (total internal reflection) prism assembly  15  which reflects the light beam to a color splitting prism assembly  18 . As a result, modulator  17  is always completely illuminated by one primary color (e.g., red), while the other two primary colors (e.g., blue and green) scroll across modulator  16 . The modulated light is focused by projection lens  19  onto a screen  20  to form an image. 
   Known single-modulator and two-modulator sequential color display systems suffer from low efficiency and lack of compactness. Therefore, there is a need for compact, light-weight, more efficient and cost-effective illumination systems to provide uniform light distribution over a certain area such as the active area of a modulator in sequential color display systems. 
   SUMMARY 
   It is an advantage of the present invention to provide a compact, light-weight, efficient and cost-effective color display system that utilizes an illumination system capable of producing a light beam of selected cross-section and selected spatial distribution in terms of intensity and angle. Such an illumination system enables color projection display systems with smaller modulators (≦0.5″), leading to more compact and less expensive color projection systems. 
   A novel aspect of the present invention is the use of one or more optical element arrays to form an illumination system which is capable of recycling light reflected by a color wheel, setting the numerical aperture of the light source beam, as well as providing the desired spatial distribution of light in terms of intensity and angle. 
   In accordance with an exemplary embodiment of the invention, a light recycler, includes of a light guide, a reflective plate with aperture and at least one optical element array. The optical element array splits a light beam into a large number of sub-beams, which mix in a superimposing manner within the light guide, leading to a uniform light distribution across the exit aperture of the light guide. When used in a color projector system, the reflective plate of light recycler causes light reflected by the color wheel to be reflected back toward the color wheel (recycled), increasing the output brightness of the projector. 
   In accordance with another exemplary embodiment of the invention, a recycler includes circulation, extraction and collimating optical element arrays. This recycler provides greater efficiency and compactness due to the use of highly compact and efficient array components. 
   In accordance with a further exemplary embodiment of the invention, a recycler includes a single optical element array, thus, providing an even more compact illumination. 
   Other embodiments, features, aspects, advantages, systems and methods of the invention will be or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional embodiments, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     It is to be understood that the drawings are solely for purposes of illustration and not as a definition of the limits of the invention. Furthermore, it is to be understood that the drawings are not necessarily drawn to scale and that, unless otherwise stated, they are merely intended to conceptually illustrate the systems, structures and methods described herein. In the figures, like reference numerals designate corresponding parts throughout the different views. 
       FIG. 1A  shows a cross-sectional view of a prior art single-modulator sequential full color projection system, which utilizes a recycler to provide uniform light distribution. 
       FIG. 1B  shows a cross-sectional view of a prior art two-modulator sequential full color projection system, which utilizes a recycler to provide uniform light distribution. 
       FIG. 1C  shows a perspective view of a prior art recycler used in projection system of  FIG. 1A . 
       FIG. 1D  shows a perspective view of a prior art light pipe or tunnel of  FIG. 1C . 
       FIG. 1E  shows a front plan view of a prior reflective aperture of  FIG. 1C . 
       FIG. 2A  shows a cross-sectional view of a single-modulator sequential full color projection system utilizing a compact recycler, in accordance with an exemplary embodiment of the present invention. 
       FIG. 2B  shows a cross-sectional view of a two-modulator sequential full color projection system utilizing a compact recycler, in accordance with another exemplary embodiment of the present invention. 
       FIG. 2C  shows a perspective view of a compact recycler used in the projection systems of  FIGS. 2A-2B , in accordance with a further exemplary embodiment of the present invention. 
       FIG. 2D  shows a front plan view of an optical element array used at the entrance aperture of compact recycler of  FIG. 2C . 
       FIG. 2E  shows a cross-sectional view of an optical element array of  FIG. 2D . 
       FIG. 2F  shows a front plan view of another optical element array that can be used at the entrance aperture of compact recycler of  FIG. 2C . 
       FIG. 2G  shows cross-sectional view of an optical element array of  FIG. 2F  using non-collimating tapered optical elements. 
       FIG. 2H  shows cross-sectional view of an optical element array of  FIG. 2F  using collimating tapered optical elements. 
       FIG. 2I  shows perspective view of a straight optical element. 
       FIG. 2J  shows perspective view of a tapered optical element. 
       FIG. 2K  shows perspective view of asymmetrical optical element. 
       FIG. 2L  shows a front plan view of a reflective plate with an optical element array bonded to its solid aperture. 
       FIG. 2M  shows a cross-sectional view of a reflective plate of  FIG. 2L . 
       FIG. 2N  shows a front plan view of another reflective plate with an optical element array bonded to its hollow aperture. 
       FIG. 2O  shows a cross-sectional view of a reflective plate of  FIG. 2N . 
       FIG. 2P  shows a front plan view of an optical element array used at the exit aperture of compact recycler of  FIG. 2C . 
       FIG. 2Q  shows a cross-sectional view of an optical element array of  FIG. 2P . 
       FIG. 2R  shows a cross-sectional view of two optical element arrays bonded together. 
       FIG. 2S  shows a cross-sectional view of an optical element array of  FIG. 2P  with collimating optical elements on both sides of the array. 
       FIG. 3A  shows a front plan view of a solid optical element array that can be used at the entrance aperture of compact recycler of  FIG. 2C . 
       FIG. 3B  shows a cross-sectional view of an optical element array of  FIG. 3A . 
       FIG. 3C  shows a cross-sectional view of an optical element array of  FIG. 3A  with a flat reflective layer. 
       FIG. 3D  shows a front plan view of a hollow optical element array that can be used at the entrance aperture of compact recycler of  FIG. 2C . 
       FIG. 3E  shows a cross-sectional view of an optical element array of  FIG. 3D  using shallow micro-tunnels. 
       FIG. 3F  shows a cross-sectional view of an optical element array of  FIG. 3D  using deep micro-tunnels. 
       FIG. 4A  shows a front plan view of a circulation array. 
       FIG. 4B  shows a cross-sectional view of the circulation array of  FIG. 4A . 
       FIG. 4C  shows a back plan view of an extraction array with circulation micro-elements on its back side. 
       FIG. 4D  shows a cross-sectional view of extraction array of  FIG. 4C . 
       FIG. 4E  shows a front plan view of an extraction array with circulation micro-elements on its front side. 
       FIG. 4F  shows a cross-sectional view of extraction array of  FIG. 4E . 
       FIG. 4G  shows a front plan view of a collimation array using micro-prisms. 
       FIG. 4H  shows a cross-sectional view of collimation array of  FIG. 4G . 
       FIG. 4I  shows a perspective view of a compact recycler with a collimation array, in accordance with another exemplary embodiment of the invention. 
       FIG. 4J  shows a cross-sectional view of compact recycler of  FIG. 41 . 
       FIG. 4K  shows a perspective view of a compact recycler without a collimation array, in accordance with another exemplary embodiment of the invention. 
       FIG. 4L  shows a cross-sectional view of compact recycler of  FIG. 4K . 
       FIG. 5A  shows a front plan view of a recycler consisting of a single array, in accordance with another exemplary embodiment of the present invention. 
       FIG. 5B  shows a cross-sectional view of an exemplary structure of the recycler of  FIG. 5A . 
       FIG. 6A  shows a perspective view of a compact recycler in accordance with another exemplary embodiment of the present invention. 
       FIG. 6B  shows a perspective view of a compact recycler with a light guide, in accordance with further exemplary embodiment of the present invention. 
       FIG. 6C  shows a front plan view of the first array of  FIGS. 6A-6B . 
       FIG. 6D  shows a back plan view of the first array of  FIGS. 6A-6B . 
       FIG. 6E  shows a cross-sectional view of the array of  FIGS. 6A-6B . 
       FIG. 6F  shows a front plan view of the second array of  FIGS. 6A-6B . 
       FIG. 6G  shows a cross-sectional view of the array of  FIG. 6F . 
       FIG. 6H  shows a cross-sectional view of a compact recycler of  FIG. 6A . 
       FIG. 6I  shows a cross-sectional view of a compact recycler of  FIG. 6B . 
   

   DETAILED DESCRIPTION 
   Described herein are single-modulator and two-modulator sequential full color projection systems utilizing compact and efficient recyclers. 
     FIG. 2A  shows a cross-sectional view of a single-modulator sequential color display system  38 , which utilizes a compact light recycler  34 , according to one embodiment of the present invention. The projection system  38  includes light source  30  housed in an elliptical mirror  31 , reflective aperture  33 , recycler  34 , color wheel  35 , focusing lens  36  and display panel (i.e. modulator)  37 . 
     FIG. 2B  shows a cross-sectional view of a two-modulator sequential color display system  48 , which utilizes a compact light recycler  34  according to another embodiment of the invention. The projection system  48  includes light source  39  housed in an elliptical mirror  40 , recycler  34 , color wheel  41 , TIR (total internal reflection) prism assembly  42 , color splitting prism assembly  45 , two modulators  43  and  44 , projection lens  46  and screen  47 . 
   The single-modulator and two-modulator sequential full color projection systems  38  and  48  of  FIGS. 2A and 2B  are more efficient in terms of light utilization and provide more compactness when compared to known single-modulator and two-modulator sequential full color projection systems  10  and  25  of  FIGS. 1A-1B . The higher efficiency and compactness are due to the use of recyclers  34  which are highly compact and more efficient. The recyclers&#39;  34  higher efficiency enables the use of smaller modulators (modulator diagonal≦0.5″) and smaller projection components such as the projection lens, which in turn leads to projection systems  38  and  48  that are more compact and less expensive. 
   Other light recyclers having alternative optical structures, such as recyclers  1130 ,  1160 ,  1770 ,  1950  and  1970  described herein below, can be substituted for recycler  34  in the projection systems  10 ,  25 . 
   There are many variations of the recycler  34  and some of them are described in the various embodiments of this disclosure. The disclosed embodiments are examples only, illustrating the principles of the invention. The claimed invention extends to and covers other possible embodiments that are not fully described herein. 
   As used throughout the figures, the z-axis designates the primary optical axis of the light recyclers  34 ,  1130 ,  1160 ,  1770 ,  1950  and  1970 , and their respective components. 
   According to one embodiment,  FIG. 2C  shows a recycler  34  consisting of a solid light pipe (or hollow light tunnel with reflective sidewalls)  34   b , a reflective plate  34   a  with an aperture  137  and an optional optical element array  34   c . The transmissive aperture  137  can be circular, rectangular, square, oval, hexagonal or any other shape. The ratio R of the area A 1  of aperture  137  to the area A 2  of the reflective plate  34   a  is defined as R=A 1 /A 2 . For example, R=(d 1 ×d 2 )/(W 1 ×W 2 ) for reflective plate  34   a  of  FIG. 2D . The exit aperture of the recycling pipe  34   b  and the exit aperture of the optional optical element array  34   c  typically have the same cross section aspect ratio W 1 /W 2  as that of the modulators  37 ,  43  and  44  used by the display systems  38  and  48 . 
   According to another embodiment, reflective plate  34   a  is made as shown in  FIGS. 2D-2E .  FIG. 2D  shows a front plan view of reflective plate  34   a  where an optical element array  138  with a cross section d 1 ×d 2  is formed on the surface of the entrance aperture  137 .  FIG. 2E  shows a cross-sectional view of reflective plate  34   a  along line A of  FIG. 2D . Neighboring optical elements  134  of optical element array  138  are separated by air or material  135  with lower index of refraction than that of the optical elements  134 . Micro-guides  134  can be straight  134 , tapered  144  and asymmetrical  154  as shown in  FIG. 2I ,  FIG. 2J  and  FIG. 2K , respectively, and their density can be up to several millions per cm 2 . Design parameters of each optical element include size (C 1 , C 2 , C 3 , and C 4 ) and shape of cross-section, degree of taper, length, as well as angles θ 1 , θ 2 , θ 3 , and θ 4 . Design parameters of an optical element array include distribution of optical elements  134  within an optical element array  138 , which can be one dimensional, two dimensional, random, uniform or non-uniform. In addition to optical elements, other types of micro-elements such as micro-lenses and micro-prisms or combinations of different types can be fabricated within a single array. A reflective layer  136  is bonded or deposited on the backside of reflective plate  34   a  except for the entrance aperture  137  as shown in  FIG. 2E . 
     FIGS. 2F-2H  show another form of a reflective plate  34   a .  FIG. 2F  shows a front plan view of a reflective plate  340   a  and  FIG. 2G  shows a cross-sectional view of  FIG. 2F  along line B. Two optical element arrays  339   a  and  339   b  are formed on the front and back sides of the entrance aperture of reflective plate  340   a . A reflective layer  336  is deposited on or bonded to one side of array  340   a  excluding arrays  339   a  and  339   b . Reflective plate  340   a  can be bonded to light pipe  34   b  so that array  339   b  faces the light pipe/tunnel  34   b  and array  339   a  faces the light source ( FIG. 2G ). In this case, optical element arrays  339   a  and  339   b  deliver a light beam with an increased cone angle to light pipe/tunnel  34   b  thus enhancing the light mixing within the light pipe/tunnel and providing high light uniformity at a reduced pipe/tunnel  34   b  length. On the other hand, it is possible to glue or bond reflective plate  340   a  to light guide  34   b  so that array  339   a  faces the light pipe/tunnel  34   b  and array  339   b  faces the light source ( FIG. 2H ). This arrangement decreases the cone angle of the received light beam and delivers more collimated light to the next stage. 
   According to another embodiment,  FIGS. 2L-2O  show an alternative approach to making reflective plate  34   a .  FIG. 2L  shows a front plan view of a reflective plate  50 .  FIG. 2M  shows a cross-sectional view of  FIG. 2L  along line C. In this case, optical element array  58  is bonded to a solid aperture in the reflective layer  56  of plate  50  rather than being an integral part of plate  50 .  FIGS. 2N and 2O  show a front plan view and a cross-sectional view along line C of a reflective plate  60 , respectively. In this case, optical element array  68  is bonded to a hollow aperture  64  in the reflective plate  60  rather than being an integral part of plate  60 . As shown in  FIGS. 2L-2O , reflective layers  56  and  66  are applied to plates  50  and  60 , respectively. This approach permits independent fabrications of reflective plates  50  and  60  and optical element arrays  58  and  68 , which in turn leads to making more optical element arrays  58  and  68  out of a certain plate or substrate, thus, lowering the cost of the optical element arrays  58  and  68  and recycler  34 . 
   According to one embodiment, optional optical element array  34   c  is shown in  FIGS. 2P-2S .  FIG. 2P  shows a front plan view of optical element array  34   c  and  FIG. 2Q  shows a cross-sectional view of  FIG. 2P  along line B. Micro-guide array  34   c  may consist of tapered optical elements  234  arranged in a two-dimensional array  238  on one side of the substrate as shown in  FIG. 2Q . The area  235  between adjacent optical elements  234  can be air or a material with an index of refraction lower than that of optical elements  234 . As shown in  FIG. 2R , two (or more) identical optical element arrays  238  and  239  can be arranged in tandem to perform the function of optical element array  34   c . Micro-guide arrays  238  and  239  can be different in terms of their design and can be fabricated on both sides of a single substrate as shown in  FIG. 2S . In this case, optical element array  34   c  receives light from light pipe/tunnel  34   b  and delivers a more collimated light beam to the next stage. 
   The operation of recycler  34  is explained as follows. As shown in  FIG. 2A , the input light  32   a  emitted from a light source  30  such as an arc lamp is focused into the entrance aperture  137  ( FIG. 2C ) of recycler  34  through an aperture in a reflective plate  33 . Micro-guide array  138  ( FIG. 2D ), which is located at the entrance aperture  137 , receives the input light, splits input light beam into a large number of sub-beams with selected cone angles and delivers them to the light pipe/tunnel  34   b . By splitting the light beam and increasing the cone angle of the sub-beams, required light uniformity can be achieved with shorter light pipe/tunnel  34   b  leading to a more compact recycler  34 . It is also possible to use a collimating optical element array at the entrance aperture  137 , which delivers a light beam with a smaller cone angle to the light pipe/tunnel  34   b . This leads to a higher degree of light coupling between the light source  30  combined with its reflector  31  and the display panel  37  at the expense of achieving the required light uniformity with a longer light pipe/tunnel  34   b . A light beam with the required uniformity is delivered to the optional optical element array  34   c , which in turn delivers a light beam with a lower cone angle when compared to the cone angle of light received from the light pipe/tunnel  34   b . In addition, optical element array  34   c  can be used to deliver light with a selected spatial distribution of cone angle to the next stage by controlling the design of the individual optical elements within optical element array  34   c . It is possible to have a recycler  34  with a single optical element array  34   a  and light pipe/tunnel  34   b  (i.e. without optical element array  34   c  at the exit aperture). The light beam  32   b  exits recycler  34  and impinges on the color wheel  35 . The color wheel  35  transmits part of the light  32   b  and reflects the rest of light beam  32   b  back to the recycler  34 . The reflected light travels toward the reflective plate  34   a  of the recycler  34  where part of it escapes toward lamp/reflector  30  and  31  through aperture  137  and the remainder gets reflected back toward the color wheel  35  by a reflective layer  136  and  336 . Light escaping to the lamp/reflector  30  and  31  may have a chance of being refocused back into the entrance aperture  137 . As the ratio R of reflective plate  34   a  is increased, more light enters from the light source into the light pipe/tunnel  34   b  and more of the light reflected by the color wheel  35  escapes toward the lamp/reflector  30  and  31 . Therefore, a balance between the area of aperture  137  and reflective area of the reflective plate  34   a  is required to obtain the optimum efficiency. Light transmitted by the color wheel  35  is imaged onto a display panel  37  (i.e. spatial light modulator) using lens  36 . The light beam which passes through the display panel  37  is focused by a field lens (not shown) into the aperture of a projection lens (not shown in  FIG. 2A ), which in turn projects the image displayed on the display panel  37  onto a screen (not shown in  FIG. 2A ). The exit aperture of recycler  34  is preferably positioned very close to the color wheel  35  so that light reflected by the color wheel enters the exit aperture of recycler  34 . 
   The operation of projection system  48  of  FIG. 2B  is described as follows. The input light is focused into the entrance aperture of a recycler  34  through an aperture  137  in a reflective plate  34   a  ( FIG. 2C ). The input light beam exits recycler  34  more uniform and homogeneous and impinges on the color wheel  41 . Some of the light beam passes through each of the three or more color segments of the color wheel and the remainder is reflected back toward the recycler  34 . Part of the reflected light impinges on the reflective plate  34   a  and gets reflected back toward the color wheel  41  and the rest of it passes through the aperture  137  toward the lamp/reflector  39  and  40 . Light beam exiting the color wheel  41  enters a TIR prism assembly  42  which reflects the light beam to a color splitting prism assembly  45 . As a result, modulator  44  is always completely illuminated by one primary color (e.g. red), while the other two primary colors (e.g. blue and green) scroll across modulator  43 . The modulated light is focused by projection lens  46  onto a screen  47  to form an image. 
   The recycler  34  of this disclosure ( FIG. 2 ) has six key advantages over known light recyclers  5  ( FIG. 1 ). First, the recycler  34  of this disclosure can use a larger reflective plate  34   a  while maintaining the etendue of the lamp/reflector. This leads to increasing the efficiency of the recycler  34  and display systems  38  and  48  either by increasing the size of the aperture  137  while maintaining the ratio R (i.e. increasing collection efficiency from light source/reflector while maintaining the recycling efficiency of light reflected by the color wheel) or by maintaining the size of the aperture  137  while decreasing the ratio R (i.e. maintaining collection efficiency from light source/reflector while increasing the recycling efficiency of light reflected by the color wheel). Second, higher coupling efficiency between the light source and the light valve (i.e. modulator) can be provided by the use of collimating optical element arrays  34   c  and/or  34   a  within the recycler  34 , which results in a more efficient use of light by the light valve, thus, reducing the required number of light sources and/or their power. In this case, collimating optical element arrays  34   c  and/or  34   a  do not increase the etendue of light beam delivered to the light valve thus enhancing coupling efficiency and increasing display brightness. Third, the recycler  34  of this disclosure provides higher level of light uniformity when compared to that of known recyclers  5  at an equivalent length. This high uniformity is due to the large number of additional virtual sources formed by optical element array  34   a . Images of these virtual sources are superimposed on top of each other forming an extremely uniform light distribution at the exit aperture of the recycler  34 . Fourth, the recycler  34  of this disclosure provides control over the spatial distribution of light in terms of its cone angle. This is done through the design of the individual optical elements of array  34   c . Fifth, the recycler  34  of this disclosure provides a superior level of compactness and light-weight. The length of the recycler  34  can be lower than the length of known recyclers  5  by up to three orders of magnitude resulting in very compact light-weight illumination systems. In addition, the high coupling efficiency enables the use of small size display panels (≦0.5″) which results in using smaller optical components such as the projection lens, thus, leading to very compact projection systems. Sixth, lower cost is achieved by using the optical element arrays of this disclosure due to the reduced size of the optical components used within the projection system. As the size of optical components is reduced, their cost is reduced and the cost of the overall system is reduced. 
     FIGS. 3A-3C  show a more effective reflective plate  434   a  according to another embodiment of the invention.  FIG. 3A  shows a front plan view of reflective plate  434   a , which has optical elements  434  arranged over the full surface of reflective plate  434   a  in a two dimensional optical element array  440 .  FIGS. 3B and 3C  show cross-sectional views of  FIG. 3A  along line C. As shown in  FIG. 3B , reflective layer  435  is deposited over the sidewalls of optical elements  434 . In  FIG. 3C , areas between sidewalls of optical elements  434  are filled with reflective layer  435 . A polishing step may be needed after the deposition of reflective layer  435  to obtain fillings with flat surface as shown in  FIG. 3C . Since input light beam enters plate  434   a  from the left and initially through side  438 , most of this light exits optical element array  440  with a higher cone angle, enters light pipe/tunnel and travels toward the color wheel ( FIGS. 2A-2B ). On the other hand, part of light traveling from right to left (i.e. light reflected by the color wheel) is reflected back toward the color wheel by reflective layer  435  and the remainder passes through the uncoated part of optical element array  440  toward the lamp/reflector ( FIGS. 2A-2B ).  FIGS. 3D-3F  show a reflective plate  534   a  that is similar to reflective plate  434   a  of  FIGS. 3A-3C  except for the use of micro-tunnels  534  rather than solid optical elements  434  to alter the cone angle of received light.  FIG. 3D  shows a front plan view of reflective plate  534   a  and  FIGS. 3E-3F  show cross-sectional views of  FIG. 3D  along line D. The depth d of micro-tunnels  534  of  FIG. 3E  is smaller than the substrate thickness t whereas micro-tunnels  534  of  FIG. 3F  have their depth extending across the substrate thickness t. The reflective layer  535  coats the sidewalls of micro-tunnels  534  as well as the area between them. 
   Reflective plates  434   a  and  534   a  of  FIGS. 3A-3F  have an additional advantage over reflective plates  34   a ,  340   a ,  50  and  60  of  FIGS. 2D-2O . Reflective plates  434   a  and  534   a  allow the use of larger light sources, which are typically cheaper and provide more light flux. By using the whole surface of the reflective plate  434   a  and  534   a  as an input aperture rather than using a small portion of it, larger light sources can be used and more light can be collected even when using smaller light sources. In this case, most or all of light received by reflective plates  434   a  and  534   a  from the light source is delivered to the next stage (i.e., light pipe/tunnel  34   b ) with a higher cone angle and a small fraction of this light is reflected back toward the light source. On the other hand, a substantial amount of the light traveling in the opposite direction (i.e., light reflected by color wheel toward the reflective plate) is reflected back toward the color wheel by the reflective coating  435  and  535 . In order to maintain lamp/reflector etendue, a collimating optical element array  34   c  is usually used at the exit aperture of the light pipe/tunnel  34   b . In reflective plates  34   a ,  340   a ,  50  and  60 , light is focused into the entrance aperture  137  ( FIG. 2C ), which forms a small portion of the surface area of reflective plate  34   a ,  340   a ,  50  and  60 , thus, collecting less light from the light source. In order to collect more light without increasing the etendue, smaller light sources such as lamps with small arc gaps (1 mm or lower) are usually used in the recyclers of known art. 
     FIGS. 4A-4L  show more compact and more efficient recyclers  1130  and  1160  when compared to the recycler  34  of  FIG. 2C . Recyclers  1130  and  1160  perform the function of recycler  34  with the added advantage of being more compact.  FIG. 4A  shows a plan view of a two-dimensional optical element array  1100 , which consists of circulation micro-elements  1102  arranged in two dimensions (x and y).  FIG. 4B  shows a cross-sectional view of optical element array  1100  along line C of  FIG. 4A  with an exploded three-dimensional view of micro-element  1102 . Each micro-element has four sidewalls  1103  as well as entrance  1104   a  and exit  1104   b  apertures. Reflective layer  1101   a  is bonded to or deposited on the four sidewalls of array  1100  while sidewalls of circulation micro-elements  1102  are coated with a reflective layer  1101   b .  FIGS. 4C and 4E  show plan views of two-dimensional optical element arrays  1120  and  1125 , which consist of extraction micro-elements  1122  and  1127  arranged in two dimensions (x and y).  FIGS. 4D and 4F  show cross-sectional views of optical element arrays  1120  and  1125  along line C of  FIGS. 4C and 4E . Exploded three-dimensional views of micro-element  1122  and  1127  are shown with their corresponding sidewalls  1123  and  1128  as well as entrance  1124   a  and  1129   a  and exit  1124   b  and  1129   b  apertures. Reflective layers  1121   a  and  1126   a  are bonded to or deposited on the four sidewalls of array  1120  and  1125 . In addition, reflective layers  1121   b  and  1126   b  are deposited on areas between extraction micro-elements  1122  and  1127  as well as on sidewalls of extraction micro-elements  1127 .  FIG. 4G  shows a plan view of micro-prisms  1202  arranged in a two-dimensional micro-prism array  1200 . Reflective layer  1201   a  is bonded to or deposited on the four sidewalls of array  1200 . 
     FIG. 4H  shows a cross-sectional view of micro-prism array  1200  along line C of  FIG. 4G  with an exploded three-dimensional view of micro-element  1202 . As shown in  FIG. 4H , each micro-prism  1202  has four sidewalls  1203  (two sidewalls are shown in the perspective view of the exploded micro-prism) as well as entrance  1203  and exit  1204  apertures. Micro-elements  1102 ,  1122 ,  1127 , and  1202  of arrays  1100 ,  1120 ,  1125  and  1200  can have any desired size and shape such as square, rectangular, circular, hexagonal and irregular. 
     FIGS. 4I and 4K  show perspective views of two recyclers  1130  and  1160  according to two embodiments, respectively.  FIGS. 4J and 4L  show the corresponding cross-sectional views of recyclers  1130  and  1160  along line D of  FIGS. 4I and 4K . Recycler  1130  consists of circulation optical element array  1100 , extraction optical element array  1120  and micro-prism array  1200 , which are attached or bonded together as shown in  FIGS. 4I-4J . As shown in  FIGS. 4K-4L , recycler  1160  consists of circulation optical element array  1100 , plain glass plate  1150  with reflective layer on its four sidewalls and extraction optical element array  1125 , which are attached or bonded together. 
   The operation of recycler  1130  and  1160  is based on circulating the input light within the body of an optical element array  1120  or glass plate  1150  using circulating optical element array  1100 . The circulated light is uniformly extracted out of the body of the optical element  1120  or glass plate  1150  using extraction micro-elements  1122  and  1127 . As shown in  FIG. 4J , the input light  1135  is focused onto the center of optical element array  1100  perpendicularly with a cone angle of a and impinges on the circulation micro-elements  1102  within the circulation array  1100  which increases the cone angle of preferably a substantial part of input light so that it is guided within the body of optical element array  1120  via total internal reflection (TIR) and reflection unless it is extracted by micro-elements  1122 . In other words, the function of circulation array  1100  is to deliver light to array  1120  with an angle θ&gt;θ c . Extraction micro-elements  1122  are distributed non-uniformly and may be randomly within extraction array  1120  so that their density is inversely proportional to the light density within the body of the optical element  1120 .  FIGS. 4C and 4E  show that the density of extraction micro-elements  1122  and  1127  increase from array  1120  and  1125  center toward its edges. As a result, the light delivered by extraction array  1120  and  1125  is highly uniform. Light extracted by micro-elements  1122  enters the micro-prism array  1200  with an angle β in  and exits with an angle β out , thus, a collimated and uniform light beam is delivered by recycler  1130 . On the other hand, light reflected back by the color wheel ( FIGS. 2A-2B ) toward recycler  1130  (i.e. light travels in the −Z direction) enters the micro-prism array  1200  and most of it gets refracted or reflected back toward the color wheel by the micro-prisms  1202  and/or reflective layer  1121   b , respectively. The remainder enters extraction optical elements  1122  toward the body of extraction array  1120  where it circulates until it gets extracted then directed toward the color wheel. 
   In recycler  1160  of  FIGS. 4K-4L , the input light is focused onto the center of optical element array  1100 , which in turn increases the angle of this light and delivers it to the body of glass plate  1150 . The function of array  1100  is the same in both recyclers  1130  and  1160 . The light travels within glass plate  1150  via total internal reflection (TIR) and reflection off of reflective sidewalls of glass plate unless it is extracted by micro-elements  1127  within extraction array  1125 . Extraction array  1125  is designed as described above to uniformly extract light from the glass plate  1150 . In recycler  1160 , light gets collimated within the tapered optical elements  1127 . In addition, it is possible to use a collimating optical element array or micro-prism array after array  1125  to provide more collimation to the color wheel ( FIGS. 2A-2B ). Light reflected back by the color wheel toward recycler  1160  enters the optical element array  1125  and most of it gets reflected back toward the color wheel by the reflective layer  1126   b  and the remainder enters the glass plate  1150  where it circulates then gets extracted and directed toward the color wheel. 
   Therefore, recyclers  1130  and  1160  provide more efficient recycling of light (reflected by the color wheel) since eventually all the light reflected by the color wheel gets redirected toward the color wheel. This means 100% theoretical recycling efficiency in comparison to 60% theoretical recycling efficiency of known recyclers. In addition, such recyclers  1130  and  1160  provide control over the spatial distribution of light in terms of intensity and cone angle. 
   Design parameters of each micro-element  1102 ,  1122 ,  1127 , and  1202  within an array  1100 ,  1120 ,  1125  and  1200  include shape and size of entrance and exit apertures, depth, sidewalls shape and taper, and orientation. Micro-elements  1102 ,  1122 ,  1127 , and  1202  within an array  1100 ,  1120 ,  1125  and  1200  can have uniform, non-uniform, random or non-random distributions and range from thousands to millions with each micro-element  1102 ,  1122 ,  1127 , and  1202  being distinct in its design parameters. The size of the entrance/exit aperture of each circulation micro-element is preferably ≧5 μm in case of visible light in order to avoid light diffraction phenomenon. However, it is possible to design micro-elements with sizes of entrance/exit aperture being &lt;5 μm. In such case, the design should consider the diffraction phenomenon and behavior of light at such scales to provide homogeneous light distributions in terms of intensity, viewing angle and color over a certain area. Micro-elements  1102 ,  1122 ,  1127 , and  1202  can be arranged as a one-dimensional array, two-dimensional array, circular arrays and can be aligned or oriented individually. 
   According to another embodiment of the invention,  FIGS. 5A-5B  show a recycler  1770  consisting of circulation  1777   a  and extraction  1778   a  and  1778   b  optical element arrays fabricated on a single optically transmissive substrate  1772 .  FIGS. 5A and 5B  show front plan view and cross-sectional view of a recycler  1770  of  FIG. 5A  along line B. Circulation array  1777   a  and extraction array  1778   a  are fabricated on the back side of substrate  1772 . Extraction array  1778   a  consists of extraction micro-elements  1773   a  and  1773   b  which overlap with circulation micro-elements  1774   b . On the front side of substrate  1772 , there are extraction array  1778   b  and an optional collimating array  1777   b . Collimating array  1777   b  can be eliminated or replaced by an optical element array of another type. Extraction array  1778   b  consists of one dimensional prisms, which extend in the x-direction and are coated with a reflective layer  1774   c  and collimate light impinging on them so that it exits the array  1770  surface perpendicularly (i.e. substantially parallel to the Z-axis). Extraction micro-elements within array  1778   b  may have other shapes such as micro-prisms or micro-lenses that are distributed in a two dimensional array. Micro-elements within extraction arrays  1778   a  and  1778   b  are distributed over the surface of the substrate  1772  so that light is extracted uniformly from the body of the substrate  1772 . It is possible to have a recycler  1770  with only one extraction array  1778   a  or  1778   b  rather than two arrays  1778   a  and  1778   b . For simplicity of illustration, the circulation array  1777   a  is shown to have one circulating micro-element  1771  as shown in  FIG. 5A . Number, size and shape of circulating micro-element  1771  are some of the design parameters of circulation array  1777   a . A reflective layer  1774   a  is bonded or deposited on the four edges of substrate  1772 . The operation of collimating  1777   b , circulation  1777   a  and extraction  1778   a  and  1778   b  optical element arrays is no different from the operation of the already discussed collimating, circulation and extraction arrays. Thus, recycler  1770  and recyclers  1130  and  1160  operate in a similar manner. The advantage of recycler  1770  over recyclers  1130  and  1160  is its high compactness. 
     FIGS. 6A-6B  show perspective views of two recyclers  1950  and  1970  according to two embodiments of the invention. Recycler  1950  uses two optical element arrays  1910  and  1925  in its structure, whereas, recycler  1970  uses in addition to that a light pipe/tunnel  1935 .  FIGS. 6C and 6D  show a top and bottom views of optical element array  1910  and  FIG. 6E  shows a cross-sectional view of  FIGS. 6C-6D  along line A. A collimating optical element array  1900 A is shown on the front surface of optical element array  1910 , which correspond to the location of the hot spot of the input light beam. On the back side of array  1910 , there are extraction optical elements  1900   b  arranged in an array in the xy-plane. Distribution of these extraction optical elements  1900   b  can be uniform ( FIG. 6D ), non-uniform or random. Non-uniform distribution is preferable since it allows uniform extraction of light over the recycler&#39;s exit aperture. Exploded perspective views of collimating optical elements  1900   a  and extraction optical elements  1900   b  are shown in  FIG. 6E . 
     FIGS. 6F and 6G  show a perspective view and cross-sectional view of collimating optical element array  1925  along line C of  FIG. 6F . As shown in  FIGS. 6F-6G , micro-prisms  1920  are distributed over the surface of array  1925  in areas that do not correspond to the input light (i.e. collimating array  1900 A). A perspective view of micro-prisms  1920  is shown in  FIG. 6G . Cross-sectional views of recyclers  1950  and  1970  are shown in  FIGS. 6H-6I  along plane B of  FIGS. 6A-6B . 
   The operation of recyclers  1950  and  1970  is based on collimating part of the input light that passes through the entrance apertures of the collimating optical elements  1900   a  of array  1900 A. The input light that passes through the sidewalls of optical elements  1900   a  is diverged (i.e. cone angle is increased) and gets spatially separated from the collimated light as it reaches the extraction optical elements  1900   b . For simplicity of illustration, rays A 1  and A 2  represent the input light that goes through the entrance apertures of the collimating optical elements  1900   a  and rays B 1  and B 2  represent the input light that goes through their sidewalls as shown in  FIG. 6H . Light extracted (i.e. diverged light) from the body of array  1910  is collimated by micro-prism array  1925  while light collimated by array  1900 A travels through plates  1910  and  1925  without encountering any micro-elements. Light exiting plate  1925  enters light pipe/tunnel  1935  for further homogenization then to next stage ( FIG. 61 ) or is delivered directly to the next stage ( FIG. 6H ). Recyclers  1950  and  1970  have the advantage over previous embodiments of providing a high level of collimation using a simpler fabrication and assembly process. 
   The specific shapes, sizes and arrangements of the optical element arrays described herein are only a small subset of the possible optical element arrays that can be used within the scope and spirit of the invention. Some of the other array types that are usable with the systems disclosed herein are described in the U.S. Patent Applications identified in the immediately following paragraph. 
   Techniques for manufacturing the optical element arrays disclosed herein are described in U.S. patent application Ser. No. 10/458,390, titled “Light Guide Array, Fabrication Methods and Optical System Employing Same” and U.S. patent application Ser. No. 11/066,605, titled “Compact Projection System Including A Light Guide Array”, filed on Feb. 25, 2005, both of which are incorporated herein by reference. 
   While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that more embodiments and implementations, other than those specifically described above, are possible that are within the scope of this invention. Further, the foregoing summary, detailed description, drawings and embodiments described above are considered as illustrative only of the principles of the invention and are not intended to limit the scope of the invention. Since other modifications and changes may be or become apparent to those skilled in the art, the invention is thus not limited the exact embodiments shown and described above, and accordingly, all suitable modifications and equivalents are deemed to fall within the scope of the invention, as it is defined by the claims below.