Abstract:
A light illumination apparatus and method for providing a light source includes light emitting diodes (LEDs) ( 101, 102, 103 ) and optical waveguides ( 104, 105, 106 ) associated with the light sources for guiding the light to the nonpolarized dichroic combiner ( 107 ). The dichroic combiner ( 107 ) combines the light from the wave guides into a single light source. Lenses ( 207, 208, 209 ) may also be used to focus light from the waveguides to the dichroic combiner ( 107 ). The invention provides an efficient approach to provide a single source of light using LEDs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   Priority for this non-provisional application is based on provisional patent application entitled LED Polarizing Optics for Color illumination System, Ser. No. 60/646,775, filed Jan. 25, 2005; LED Color illumination Apparatus for Polarized Light Projection System, Ser. No. 60/646,777, filed Jan. 25, 2005; and RGB LED Illumination Apparatus for DLP Projection Applications, Ser. No. 60/646,778, filed Jan. 25, 2005, all owned by Jabil Circuit, Inc. 

   FIELD OF THE INVENTION 
   This invention generally relates to a polarized light illumination apparatus to provide illumination for a microdisplay projection-type display system. 
   BACKGROUND OF THE INVENTION 
   In recent years, digital projection systems using spatial light valve modulators, such as a digital micromirror device (hereafter “DMD”), transmissive liquid crystal display (hereafter “LCD”) and reflective liquid crystal on silicon (hereafter “LCoS”) have been receiving much attention as they provide a high standard of display performance. These displays offer advantages such as high resolution, a wide color gamut, high brightness and a high contrast ratio. 
   Color projection systems of the type based on either LCD or LCoS technology require linearly polarized light as the illumination light source; however, DMD systems do not require the use of polarized light. LCD and LCoS devices depend on either the polarization rotation effect or the birefringent effect of the liquid crystal to generate light. The light emitted from the light source must be converted into polarized light for illuminating an LCD or LCoS spatial light modulator. Those skilled in the art will recognize that the optical system contained within a commercial LCD or LCoS projector typically combines a fly&#39;s-eye lens array with a polarizing beam splitter array. Examples of such an arrangement can be found in U.S. Pat. Nos. 6,411,438, 6,776,489, 6,739,726 and 6,092,901 which are all incorporated by reference herein. Two drawbacks to using the fly&#39;s-eye type of optical system are that it is bulky and expensive to manufacture. 
   Most projection systems use short arc gaseous white lamps such as ultra-high pressure mercury, xenon or the like that can achieve a relatively high etendue efficiency required for panel illumination. Etendue refers specifically to the geometric capability of an optical system to transmit radiation such as its throughput. Currently, only a limited number of manufacturers are capable of producing high-quality short arc lamps. The typical operational lifetime of these types of lamps is about 2000 to 6000 hours. Moreover, there is a significant amount of ultraviolet (UV) and infrared (IR) light emitted from this type of lamp. 
   The unfiltered UV light reduces the lifetime of both the optical components and microdisplay panel within the system, while IR light requires additional cooling devices to maintain a desired operating temperature. 
   Significant efforts have been dedicated towards moving away from short arc lamps through the utilization of light emitting diodes (LED) in projection illumination systems. One apparent advantage is that LEDs using three primary colors can produce a wider color gamut than conventional white lamps. In addition, LEDs have a high light efficiency, i.e., the ratio of luminous output to the electrical power required, since all spectra of the red, green and blue light from LEDs can be utilized in a visual system. U.S. Pat. No. 6,224,216, which is incorporated by reference herein, describes a triple path projector employing three single-color LED arrays. The LEDs emit light propagating along separate paths through fiber bundles to respective waveguide integrators and thereafter to respective display devices. A problem exists in this type of system in view of the coupling between LEDs and fibers. In practice, due to coupling and transmission loss, it is difficult to efficiently couple light emitting from the LED arrays to the corresponding fiber bundles and waveguides. 
   Similarly, U.S. Pat. No. 6,220,714 discloses a projection system using LEDs for illumination, where light beams emitting from red, green and blue LED arrays are collimated by condenser lenses which pass through fly&#39;s-eye type of integrators for illuminating a single panel. Based on the geometry of the fly&#39;s-eye type integrator, only the surface area of light emitting region within a certain field of view can be effectively collected for illuminating a panel. A similar system can be found in U.S. Pat. No. 6,644,814, which describes an LED-illumination-type DMD projector with one panel. Generally, a common problem within these prior art systems is that some light from LEDs cannot enter the corresponding lens of the first and second fly&#39;s-eye lenses due to aberration and aperture limitation of the lens array. Therefore, a portion of the illumination light will fall outside of the panel area, resulting in low light efficiency and low contrast. 
   Thus, the need exists to provide a light illumination device for digital light processing (DLP) projection systems or the like which utilize non-polarized light with high efficiency and required brightness without the aforementioned problems and complicated or expensive components. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The above and other features and advantages of the present invention will be further understood from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. 
       FIG. 1  is a block diagram illustrating an LED color illumination assembly that includes three LEDs, three waveguides and a non-polarized cross-dichroic combiner in accordance with one embodiment of the invention. 
       FIG. 2  is a block diagram illustrating an LED color illumination assembly with lenses added to exit faces of the waveguides as shown in  FIG. 1 . 
       FIG. 3  is a block diagram illustrating the use of a non-polarized V-type dichroic combiner in accordance with an alternative embodiment of the invention. 
       FIG. 4  is a block diagram illustrating yet another alternative embodiment of the present invention with lenses added to exit faces of the waveguides shown in  FIG. 3 . 
       FIG. 5  is a block diagram illustrating yet another alternative embodiment of the present invention wherein the light-emitting devices shown in  FIG. 1  are arranged on the same plate. 
       FIG. 6  is a block diagram illustrating yet another alternative embodiment of the present invention with lenses added to exit faces of the waveguides shown in  FIG. 5 . 
       FIG. 7  is a block diagram illustrating yet another alternative embodiment of the present invention where a non-polarized V-type dichroic combiner is used with the system as shown in  FIG. 5 . 
       FIG. 8  is a block diagram illustrating an alternative embodiment of the present invention with lenses added to exit faces of the waveguides shown in  FIG. 7 . 
       FIGS. 9 ,  10  and  11  are block diagrams illustrating three different embodiments of a polarization converter system of the present invention. 
       FIG. 12  is a block diagram illustrating an LED color illumination system in accordance with the present invention, combining the assembly shown in  FIG. 2  with a polarization recovery system shown in  FIG. 9 . 
       FIG. 13  is a block diagram illustrating an alternative embodiment of an LED color illumination system combining the assembly shown in  FIG. 2  with the polarization recovery system shown in  FIG. 10 . 
       FIG. 14  is a block diagram illustrating an alternative embodiment of an LED color illumination system combining the assembly shown in  FIG. 2  with the polarization recovery system shown in  FIG. 11 . 
       FIG. 15  is a block diagram illustrating yet another alternative embodiment of an LED color illumination system combining the assembly shown in  FIG. 4  with the polarization recovery system showing in  FIG. 9 . 
       FIG. 16  is a block diagram illustrating yet another alternative embodiment of an LED color illumination system combining an assembly shown in  FIG. 4  with the polarization recovery system shown in  FIG. 10 . 
       FIG. 17  is a block diagram illustrating yet another alternative embodiment of an LED color illumination system combining an assembly shown in  FIG. 4  with the polarization recovery system shown in  FIG. 11 . 
       FIG. 18  is a block diagram illustrating yet another alternative embodiment of an LED color illumination system combining an assembly shown in  FIG. 6  with the polarization recovery system shown in  FIG. 10 . 
       FIG. 19  is a block diagram illustrating yet another alternative embodiment of an LED color illumination system using a polarizing cross-dichroic combiner for color combining. 
       FIGS. 20-23  are block diagrams illustrating light projection systems for projecting light from a dichroic combiner to a microdisplay panel. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present description is directed in particular to elements forming part of, or cooperating more directly with, the apparatus in accordance with the invention. 
   Turning now to the figures,  FIG. 1  is a block diagram depicting a polarized light illumination assembly in accordance with the present invention which includes a red LED  101 , a green LED  102 , a blue LED  103 , three tapered waveguides  104 ,  105 ,  106 , and a cross-dichroic combiner  107 . The light beams emitting from the red LED  101 , green LED  102  and blue LED  103  are homogenized and guided by tapered waveguides  104 ,  105  and  106 , respectively. The light exit faces of the waveguides are connected to three entrance surfaces of the non-polarized cross-dichroic combiner  107 . The green light transmits through the dichroic combiner  107  while the red and blue light beams are reflected from the dichroic combiner  107 . As will be evident to those skilled in the art, the tapered waveguides  104 ,  105  and  106  are structures that “guide” the respective RGB light waves by tapering the beam to travel along a certain desired path to the dichroic combiner  107 . In this embodiment, the design of the tapered waveguide will act to guide cone light from a 60-degree diverge LED light to the input non-polarizing dichroic combiner. 
   With regard to the dichroic combiner which is sometimes referred to as an “x cube”, this device consists of two dichroic coating filters that combine or separate beams of three different colors, namely, red (r), green (g), and blue (b). One dichroic coating filter reflects blue light by transmitting green and red lights while another dichroic coating filter reflects red light by transmitting green and blue lights, where the RGB light from three input directions can be combined into one output light path, the dichroic combiner can be either a cross type, V-type or similar configuration. The non-polarizing dichroic combiner can be used to combine both P and S polarization input light at high efficiency. 
   In the invention, a tapered hollow pipe or a tapered integrator rod is used as a waveguide to achieve multifunctional objectives. A novel tapered waveguide is then used to collimate, homogenize and shape the light beam. The tapered waveguide can reduce the angle of the input cone at the tapered ratio due to etendue preservation which is the product of the illuminated area and the illumination solid angle at the output face of the waveguide is equal to the etendue at the input face of the waveguide. 
   As shown in  FIG. 1 , the area of the output face of the waveguides  104 ,  105 ,  106  is greater than that of its input face, thus the cone angle of the output beam is smaller than that of the input beam. Consequently, a collimation function is achieved. The second function of the tapered waveguides  104 ,  105 ,  106  is that of a light homogenizer that works to change the spatially, non-uniform distributed light on the input face of the waveguide to output light that has essentially uniform intensity. The third function of waveguides  104 ,  105 ,  106  is beam shaping where the aspect ratio of the output surface of the tapered waveguide will be different from that of the input surface. This is essential in the invention since the shape of the light source must be proportional to that of the panel that is illuminated. Compared with most collimation lenses or lens array based illumination systems, a tapered waveguide based system is highly efficient, relatively compact in size, simple in structure, and inexpensive in manufacturing cost. The embodiment shown in  FIG. 1  shows an intentional gap between the red waveguide  104  and the upper side surface of the non-polarized cross-dichroic combiner  107  as well as between the blue waveguide  106  and lower side surface of the non-polarized dichroic combiner  107 . Thus, light that exits from the green waveguide  105  reflects internally on both side surfaces of the dichroic combiner  107  and green light bleeding into the red and blue waveguides  105 ,  106  can be prevented. 
     FIG. 2  shows an alternative embodiment of the illumination assembly shown in  FIG. 1  where lenses  207 ,  208 ,  209  can be attached to the exit surfaces of the respective waveguides, allowing the light beams exiting from three waveguides to become further converged. The light emitting from red LED  201 , green LED  202  and blue LED  203  are homogenized and guided by tapered waveguides  204 ,  205  and  206 , respectively. The light beams exiting from three waveguides  204 ,  205  and  206  are further converged by three lenses  207 ,  208  and  209  and thereafter enter the three entrance surfaces of the non-polarized cross-dichroic combiner  207 . If the waveguide  204 ,  205 ,  206  is manufactured of solid glass rod, the lens and corresponding rod can be integrated into a one-piece optical component. Moreover, lenses may be added on top of the LEDs at the front end of the tapered waveguides to further collimate the LED light. 
     FIG. 3  shows another embodiment of the invention where a V-type non-polarized dichroic combiner  308  or other shaped combiner can be employed to replace the cross-dichroic combiner shown in  FIG. 1  and  FIG. 2 . The main, advantages of the V-type non-polarized dichroic combiner  308  as compared to the non-polarized cross-dichroic combiner are in its low cost and ease of manufacture. Typically, the angular tolerance of a V-type dichroic prism is a few arc minutes while the angular tolerance of a cross-dichroic prism is a few arc seconds. The V-type dichroic combiner  308  includes two different dichroic coatings  310  and  311 . The coating  310  transmits green and red color and reflects blue color while the coating  311  transmits green and blue color and reflects red color. The light emitting from green LED  302 , guided by waveguide  305 , passes through the dichroic coatings  310  and  311 , while the light emitting from the blue LED  303 , guided by waveguide  306 , is reflected from the coating  310  and passes through the coating  311 . 
   An optional glass volume  307  is attached to the exit surface of the red waveguide  304  to adjust the optical path length of the red LED  301  to equal that of the green and blue LED  301 ,  303 . The light emitting from the red LED  301 , passing through the tapered waveguide  304  and glass volume  307 , is reflected from the coating  311 . On the exit face of the V-type dichroic combiner  308 , the optical axes of the red path, green path and blue path are coincident. The function of the gap between the blue waveguide  306  and dichroic combiner  308  and the gap between the glass volume  307  and dichroic combiner  308  is similar to that described in  FIG. 1 . The light exiting from the green waveguide  305  reflects internally on both side surfaces of the V-type dichroic combiner  308  and the escape of green light into the blue and red waveguides  306 ,  307  can be prevented. 
     FIG. 4  is another embodiment of the invention as shown in  FIG. 3 , where three lenses  407 ,  408  and  409  are attached to the red, green and blue waveguides  404 ,  405  and  406 , respectively. The light exiting from the three waveguides  404 ,  405  and  406  is further converged by three lenses  407 ,  408  and  409  and then enter to the V-type dichroic combiner  407  as described in  FIG. 3 . If the waveguide is made of solid glass rod, the lens and corresponding rod can be integrated into a one-piece optical component. 
     FIG. 5  shows yet another embodiment of the present invention where the system includes a red LED  501 , a green LED  502 , a blue LED  503 , three tapered waveguides  504 ,  505  and  506 , a cross-dichroic combiner  507  and two 45-degree prisms  508  and  509 . In contrast to the color illumination assembly shown in  FIG. 1 , three LEDs are configured to be on the same plate, enabling the system to be more compact in size for the LED driver circuits and cooling. Two 45-degree prisms  508  and  509  are arranged adjacent to two side surfaces of the non-polarized cross-dichroic combiner  507 . Gaps or spaces are included between both of the 45-degree prisms  508 ,  509  and the non-polarized cross-dichroic combiner  507 . The 45-degree prisms may include a high reflection coating at the reflecting surface to increase light efficiency. Consequently, the light from the red LED  501 , passing through the waveguide  504 , is reflected from the 45-degree prism  508  and then reflected from the cross-dichroic combiner  507 . Similarly, the light from the blue LED  503 , passing through the waveguide  506  is reflected from the 45-degree prism  509  and then reflected from cross-dichroic combiner  507 . The green light of LED  502 , passing through the waveguide  505 , transmits through the cross-dichroic combiner  507 . As a result, the red, green and blue optical axes are coincident on the exit face of the non-polarized dichroic combiner  507 . 
   As seen in  FIG. 6 , the embodiment shown in  FIG. 5  can be further improved by adding three lenses to the tapered waveguides. Three lenses  607 ,  608  and  609  are attached to the red, green and blue waveguides  604 ,  605  and  606 , respectively. The light beams exiting from three waveguides  604 ,  605  and  606  are further converged by three lenses  607 ,  608  and  609  and then enter the cross-dichroic combiner  610 . If the tapered waveguide is a solid glass rod, the lens and corresponding rod can be integrated to a one-piece optical component. Those skilled in the art will further recognize that  FIG. 6  may be further modified in the event that a collimating lens is required at the input of the waveguide. 
     FIG. 7  and  FIG. 8  further illustrate a non-polarized V-type dichroic combiner  707 ,  810  that can replace the non-polarized cross-dichroic combiners in  FIG. 5  and  FIG. 6 . The system shown in  FIG. 7  includes a red LED  701 , a green LED  702 , a blue LED  703 , three tapered waveguides  704 ,  705  and  706 , a V-type dichroic combiner  707 , a glass volume  708  and two 45-degree prisms  709  and  710 . As noted in previous embodiments of the invention,  FIG. 8  illustrates the invention in  FIG. 7  further improved through the addition of three lenses to the waveguides. In this embodiment, three lenses  807 ,  808  and  809  are attached to the red, green and blue waveguides  804 ,  805  and  806 , respectively. The light beams emitting from red LED  801 , green LED  802  and blue LED  803  exit the three waveguides  804 ,  805  and  806  and are further converged by three lenses  807 ,  808  and  809 . The advantages of utilizing a V-type dichroic combiner as compared to the cross-dichroic combiner are those that have been already discussed herein. 
     FIGS. 9 ,  10  and  11  illustrate embodiments used for polarized light applications where polarization recovery and recirculation are included to improve overall polarization efficiency. The polarization recovery apparatus shown in  FIG. 9  includes a polarizing beam split (PBS)  901 , a 45-degree prism  902  and a half wave plate  903 . The light  904  entering the entrance surface (the left surface) of PBS  901  is split into the s-polarized light  906  and the p-polarized light  905 . The p-component  905  propagates through PBS  901  while the s-component  906  is reflected upwardly through the 45-degree prism  902  to the half wave plate  903 . The half wave plate  903  rotates the polarization state of the s-component  906  to p-polarized component  907  to propagate in a direction parallel to the direction of the p-component  905 . 
     FIG. 10  shows yet another embodiment of a polarization recovery apparatus of the present invention. The apparatus includes a PBS cube  911 , a 45-degree prism  912 , and a retro-reflective polarization rotator  913 . As will be recognized by those skilled in the art, a detailed description of a retro-reflective polarization rotator can be found in U.S. Patent Publication No. 2004/0090763 which is herein incorporated by reference. The principal advantage of this apparatus is that it is not sensitive to wavelength variations of the incoming light, temperature changes and polarization alignment errors. The incident light  914  entering the PBS  911  is split into the s-polarized light  916  and the p-polarized light  915 . The p-component  915  transmits through the PBS  911 . Unlike the embodiment shown in  FIG. 9 , a polarization rotator  913  is used to replace the half waveplate in order to rotate the polarization direction of the s-component  916  coming from the PBS  911  by rotating the polarization direction of the incoming beam by 90 degrees. After being reflected by the polarization rotator  913 , the otherwise unused s-component  916  becomes a p-polarized beam  917  and passes through the PBS cube  911  to the prism  912 . The 45-degree prism  912  thereafter redirects the p-polarized beam  917  in a propagation direction parallel to the direction of the p-component  915 . 
     FIG. 11  illustrates still yet another alternative embodiment of a polarization recovery apparatus that includes a PBS cube  922 , a 45-degree prism  921 , a quarter wave plate  923  and a mirror  924 . The light  925  entering the PBS  922  is split into s-polarized light  927  and p-polarized light  926 . The p-component  926  propagates through the PBS  922 . The s-component  927  propagates past the quarter wave plate  923  where it becomes circularly polarized. After being reflected from the mirror  924 , it again passes through the quarter wave plate  923  and becomes p-polarized light. The recovered p-component  928  passes through the PBS cube  922  to the prism  921 . The 45-degree prism  921  then redirects the beam  928  in a propagation direction parallel to the direction of p-component  926 . Each polarization recovery apparatus shown in  FIGS. 9 ,  10  and  11  can be combined with any LED assembly shown in  FIG. 1-FIG .  8  to provide an LED color illumination system for polarized light projection applications. Six exemplary embodiments are shown in  FIG. 12-FIG .  17 . 
     FIG. 12  illustrates an embodiment of a color illumination apparatus with a polarization recovery system in accordance with the present invention. The system includes a red LED  1001 , a green LED  1002 , a blue LED  1003 , three tapered waveguides  1004 ,  1005  and  1006 , three lenses  1007 ,  1008  and  1009 , a non-polarized cross-dichroic combiner  1010 , a PBS  1011 , a 45-degree prism  1012 , and a half wave plate  1013 . The light from the red LED  1001 , passing through the waveguide  1004 , is converged by lens  1007  and then reflected from the non-polarized cross-dichroic combiner  1010 . Similarly, the light from the blue LED  1003 , passing through the waveguide  1006 , is converged by lens  1009  and then reflected from cross-dichroic combiner  1010 . The green light of LED  1002 , passing through the waveguide  1005 , is converged by lens  1008  and then transmits through the non-polarized cross-dichroic combiner  1010 . The red, green and blue axes are coincident on the exit face of the non-polarized dichroic combiner  1010 . The light output from the non-polarized cross-dichroic combiner  1010  is split by PBS  1011  into s-polarized light  1022  and p-polarized light  1021 . The p-component  1021  transmits through the PBS  1011  while the s-component  1022  is reflected upwardly and is further reflected by the 45-degree prism  1012  to the half wave plate  1013 . The half wave plate  1013  rotates the polarization state of the s-component  1022  to p-polarized component  1023  that propagates in a direction parallel to the direction of the p-component  1021 . In fact, the color illumination system shown in  FIG. 10  is a combination of an LED assembly shown in  FIG. 2  with the polarization recovery apparatus shown in  FIG. 9 . 
   Similarly,  FIG. 13-FIG .  18  illustrate other exemplary embodiments of the color illumination system.  FIG. 13  illustrates the combination of the LED assembly shown in  FIG. 2  with a polarization recovery apparatus shown in  FIG. 10 . The embodiment in  FIG. 14  joins the LED assembly shown in  FIG. 2  and a polarization recovery apparatus shown in  FIG. 11 .  FIG. 15  is a combination of the LED assembly shown in  FIG. 4  and the polarization recovery apparatus shown in  FIG. 9 .  FIG. 16  is a combination of the LED assembly shown in  FIG. 4  and a polarization recovery apparatus shown in  FIG. 10 .  FIG. 17  is a combination of the LED assembly shown in  FIG. 4  and a polarization recovery apparatus shown in  FIG. 11 . Finally,  FIG. 18  is a combination of an LED assembly shown in  FIG. 6  and a polarization recovery apparatus shown in  FIG. 10 . As will be recognized by those skilled in the art, each of the individual components of these exemplary embodiments have been described herein and those descriptions should also be applied to the components shown in  FIGS. 13-18 . 
   The non-polarized cross-dichroic combiners or V-type combiners shown in  FIG. 1-FIG .  16  are all designed for non-polarized beams. Thus, the transmission properties of the coatings inside the dichroic combiners are very similar for both p-component and s-component. Alternatively, there is yet another type of dichroic combiner referred to as a “polarizing dichroic combiner.” A polarizing dichroic combiner is designed for combining polarized incoming color beams. It will be evident to those skilled in that art that most of the polarizing dichroic combiners on the market are the SPS-type. An SPS combiner reflects red and blue s-components of the light and transmits a green p-component. The main advantage of the polarizing dichroic combiner over the non-polarized dichroic combiner is that it has steeper transitional curves between the pass wavelength band and the stop wavelength band so that loss in the transitional band can be reduced. 
     FIG. 19  shows an embodiment of a light illumination apparatus of the present invention which utilizes a polarizing dichroic combiner. The apparatus as shown in  FIG. 19  includes a red LED  1701 , a green LED  1702 , a blue LED  1703 , three tapered waveguides  1704 ,  1705  and  1706 , three lenses  1707 ,  1708  and  1709 , three polarizing beam splitter (PBS) cubes  1710 ,  1711  and  1712 , three 45-degree prisms  1713 ,  1714  and  1715 , three half wave plates  1716 ,  1717  and  1718 , a polarizing cross-dichroic combiner  1719 , and a polarized-retarder-stack plate  1720 . The polarized-retarder-stack is known in the art and disclosed in U.S. Pat. No. 5,751,384 and is herein incorporated by reference. In operation, the light from the red LED  1701  passes through the waveguide  1704  and lens  1707  to the PBS cube  1710 . The s-component is reflected from the PBS cube  1710  while the p-component passes through  1710  to the 45-degree prism  1713 . The p-polarized light exiting from the prism  1713  goes through the half wave plate  1716  and becomes s-polarized beam. 
   Both s-components, i.e., the s-component directly reflected from the PBS  1710  and the s-component exiting from the half wave plate  1716 , are reflected by the polarizing cross-dichroic combiner  1719  and pass through the polarized-retarder-stack plate  1720 . Similarly, the light beam emitting from the blue LED  1703  and passing through the waveguide  1706  and lens  1709  is split by the PBS cube  1712 . The s-component is reflected from the PBS cube  1712  while the p-component passes through  1712  to the 45-degree prism  1715 . The p-polarized light exiting from the prism  1715  goes through the half wave plate  1718  and becomes s-polarized beam. Both s-components, namely, the s-component directly reflected from the PBS  1712  and the s-component exiting from the half wave plate  1718  are reflected by the polarizing cross-dichroic combiner  1719  and pass through the polarized-retarder-stack plate  1720 . Different from the red and blue LED light paths wherein the light entering the polarizing cross-dichroic combiner is s-polarized, the light along green LED path entering the polarizing cross-dichroic combiner  1719  is p-polarized. The light from the green LED  1702  passes through the waveguide  1705  and lens  1708  to the PBS cube  1711 . The p-component passes PBS  1711  while the s-component is reflected by the PBS  1711  and the 45-degree prism  1714 . The s-polarized light exiting from the prism  1714  goes through the half wave plate  1717  and becomes p-polarized. Both p-components, the p-component directly passing the PBS  1711  and the p-component exiting from the half wave plate  1717 , pass through the polarizing cross-dichroic combiner  1719  and the polarized-retarder-stack plate  1720 . Thus, the polarized-retarder-stack plate  1720  selectively changes the polarization direction of the green beam while maintaining the polarization direction of red and blue beams. It can also be designed to maintain the polarization direction of the green beam while changing the polarization directions of red and blue beams. 
     FIGS. 20-23  are diagrams illustrating light integrator and condenser lens systems. These systems are used for conveying non-polarized light from a dichroic combiner to a DMD panel.  FIG. 20  shows a condenser lens  2001  that is used to directly propagate a uniform output beam of light onto a DMD panel  2003 . In  FIG. 21 , a waveguide integrator  2101  and condenser lens  2103  are used to focus light onto a DMD panel  2103 . Those skilled in the art will recognize that the waveguide  2101  may be tapered or an additional condenser lens may be used to focus light into the entrance of the rectangular waveguide  2101 . The output of the waveguide  2101  is projected by the focusing lens  2103  on the DMD panel  2105  and can be a tapered light pipe or a tapered rod integrator with increasing taper, decreasing taper or straight shape. The shape of the exit surface of the waveguide  2101  should be proportional that of the DMD panel  2105 .  FIG. 22  shows yet another embodiment of a light integrator and condenser lens system where a collimation lens  2201 , a first lens array  2203 , second lens array  2205  and a focusing lens  2207  are used to project light onto a DMD panel  2209 . The first lens array  2203  works to separate and focus the light while the second lens array  2205  forms an image of the pupil of each corresponding lens in the first lens array  2201 . The focusing lens  2207  then operates overlapping the images of the pupil from each of the lenses in the second lens array  2203  to provide uniform illumination to the DMD panel  2205 . 
   Finally,  FIG. 23  illustrates yet another embodiment where a condenser lens  2301  is used to focus light into an integrator pipe  2303  where a focusing lens  2305  is used to focus the light onto a DMD panel  2307 . 
   Thus, the present invention is directed to a polarized light illumination source using light beams emitted from multicolor LEDs as used with non-polarized DMD projection applications. The invention offers an advantage by improving the color gamut of the imaging whereby unwanted UV or IR light is eliminated and the luminous efficiency of the light source is significantly increased. More specifically, the invention provides a polarized light illumination source that is comprised of at least one red, green and blue LED as the light source. A plurality of tapered waveguides are arranged so as to achieve light homogenization, collimation and a light guide for the light source. A non-polarized dichroic combiner is used for mixing incoming beams to form a combined color light flux while a polarizing beam splitter (PBS) separates the non-polarized beam into two linearly polarized components. A polarization converter converts the polarity of an unusable polarized component to the polarity of a usable polarized component and a 45-degree prism redirects the recovered polarized beam toward a direction of illuminating an image display panel. Finally, a number of light integrator and condenser lens systems are utilized to project non-polarized light from the dichroic combiner to the DMD panel. 
   As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the scope of the invention as a whole. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.