Abstract:
Disclosed herein is an optical device with a function of homogenizing and color separation and an optical illumination system for a projector whose size can be reduced by use of the optical device.  
     The optical device with a function of homogenizing and color separation according to the present invention has a shape of rod, makes a distribution of light uniform by totally reflecting the incidence light at a boundary inside the device repeatedly, and separates the incidence light into light of different colors based on a wavelength band, the light of different colors outputted through different optical paths which are not overlaid one another.  
     The optical illumination system for the projector using the optical device with a function of homogenizing and color separation according to the present invention has remarkable advantages in that the miniaturization and lightweight of the projector can be accomplished and picture quality can be improved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to an optical illumination system for a projection system, and more particularly to an optical device with a function of homogenizing and color separation and an optical illumination system for a projector whose size can be reduced by use of the optical device.  
           [0003]    2. Description of the Prior Art  
           [0004]    Recently, as a kind of a flat display, which is thin in its thickness and can realize a large screen, substituted for a cathode ray tube display, which is limited in its screen size and large in its system size, projectors for projecting pictures of a small-sized screen on a large-sized screen with a magnification are coming into rapid and wide use.  
           [0005]    The projectors, which are display devices for realizing pictures on small-sized screen, can employ a cathode ray tube, an LCD (Liquid Crystal Display) or a DMD (Digital Micromirror Device), but use mainly the LCD or the DMD according to a trend of down-sizing in thickness.  
           [0006]    The LCD realizes pictures by changing an alignment state of liquid crystal molecules depending upon electrical variations from the external, and controlling an amount of light transmission based on the changed alignment state of liquid crystal molecules. The DMD realizes pictures by changing inclination angles of micromirrors between +10° and −10° depending upon electrical variations from the external, such that a reflection angle of light has two modes.  
           [0007]    Such projectors are currently developing with the most important point put on high brightness, miniaturization and lightweight.  
           [0008]    More particularly, the projectors are being improved to have a vivid screen even under bright surroundings by employing a lamp used as a source of light with a small magnitude of light emission, fly eye lenses for homogenizing an amount of light, polarization conversion devices for converting light emitted from the source of light into linear polarized light, etc., such that an efficiency of light is increased.  
           [0009]    In addition, for the miniaturization and lightweight, the projectors are developing from a three-plate system for realizing colors using three display elements to a single-plate system for realizing colors using one display element.  
           [0010]    The projectors employing the single-plate system using one display element use a method of color filters for realizing colors, a method of sequentially providing three primary colors for the display element, a method of separating and scrolling three primary colors, etc.  
           [0011]    Among these methods, an optical illumination system using three rotating prisms for changing a traveling direction of colored light and scrolling the colored light separated from dichroic mirrors for color separation can be representative of the method of separating and scrolling three-primary colors.  
           [0012]    [0012]FIG. 1 is a view showing a structure of a conventional optical illumination system of a projector employing a singleplate system using three rotating prisms.  
           [0013]    Referring to FIG. 1, the optical illumination system includes first and second fly eye lenses  4  and  6 , a polarizing beam split (referred to as PBS hereinafter) array  8 , first to fourth dichroic mirrors  12 ,  24 ,  32  and  44  for color separation, first and second total reflection mirrors  16  and  40  for totally reflecting incidence light, first to third rotating prisms  18 ,  26  and  28  for changing an optical path depending on their rotation angles, first to seventh condensing lenses  10 ,  14 ,  30 ,  36 ,  38  and  46  for condensing light, first and second relay lenses  34  and  42  for relaying an image formation point, and a PBS prism  50 , all of which are arranged on an optical path between a source of light  2  and a display device  52 .  
           [0014]    Now, an operation of the optical illumination system of the projector as shown in FIG. 1 will be described.  
           [0015]    The first and second fly eye lenses  4  and  6  make light distribution uniform by dividing white light from the source of light  2  by the unit of lens cell and outputting the divided light to the PBS array  8 .  
           [0016]    The PBS array  8  separates the incidence light into linear polarized light having one of optical axes, i.e., P polarized light and S polarized light. Here, the S polarized light is outputted as it is, and the P polarized light is converted and outputted into S polarized light by a ½ wavelength plate (not shown) partially attached on a back side of the PBS array  8 , such that a state of polarization becomes uniform. The first condensing lens  10  condenses the light outputted from the PBS array  8  into the first dichroic mirror  12 .  
           [0017]    The dichroic mirror  12  is made of a blue reflection coating for reflecting blue light, and green and red transmission coatings for transmitting green and red light, respectively. The first total reflection mirror  16  totally reflects blue light, which is reflected by the first dichroic mirror  12  and inputted through the second condensing lens  14 , into the first rotating prism  18 .  
           [0018]    The second dichroic mirror  24  made of a green reflection coating and a red transmission coating reflects green light into the second rotating prism  26  and transmits red light into the third rotating prism  28 , both of green and red light being incidence light transmitted by the first dichroic mirror  24  and inputted through the third condensing lens  20 .  
           [0019]    The first to third rotating prisms  18 ,  26  and  28  change traveling directions of blue, green and red light depending on their rotation angles, respectively. More particularly, The first to third rotating prisms  18 ,  26  and  28  change image formation positions of blue, green and red light at which images are formed on the display device  52  depending on their rotation angles, respectively, and scroll the image formation positions of the three color light sequentially, while they are rotating independently.  
           [0020]    The blue light transmitted through the first rotation prism  18  is inputted to the fourth dichroic mirror  44  via the fourth condensing lens  30 , the third dichroic mirror  32 , and the first relay lens  34 . The green light transmitted through the second rotation prism  26  is inputted to the fourth dichroic mirror  44  via the fifth condensing lens  36 , the third dichroic mirror  32 , and the first relay lens  34 . The red light transmitted through the third rotation prism  28  is inputted to the fourth dichroic mirror  44  via the sixth condensing lens  38 , the second total reflection mirror  40 , and the second relay lens  42 .  
           [0021]    The third dichroic mirror  32  is made of a red reflection coating for totally reflect the red light from the second rotating prism  26  and a blue transmission coating for transmitting the blue light from the first rotating prism  18 . The fourth dichroic mirror  44  reflects the incidence blue light and green light and transmits the incidence red light.  
           [0022]    Each of the red, green and blue light transmitted or reflected by the first to fourth dichroic mirrors  12 ,  24 ,  32  and  44  has a S polarization component and is inputted to the PBS prism  50  via the seventh condensing lens  46  and a polarization plate  48 .  
           [0023]    The S polarized light inputted from the polarization plate  48  to the PBS prism  50  is reflected at a polarized light split surface  50 A into the display device  52 . In this case, based on different initially set rotation angles of the first to third rotating prism  18 ,  26  and  28 , the red, green and blue light form images on different portions of the display device  52 . The different image formation positions are scrolled in a specific direction when the first to third rotating prism  18 ,  26  and  28  are driven. The display device  52  scrolls red, green and blue signals in accordance with the red, green and blue light inputted while the different image formation positions are speedily scrolled.  
           [0024]    Accordingly, each of the three color signals is implemented in an according pixel of the display device  52  and the implemented three color signals are integrated with time for displaying a color picture. In case that the display device  52  is a reflection-typed liquid crystal display device, the S polarized light inputted from the PBS prism  50  is converted into P polarized light depending on video signals for implementing a color picture. The color picture with the P polarized light component implemented in the display device  52  is projected on a screen with a magnification via the PBS prism  50  and a projection lens (not shown).  
           [0025]    However, the projectors employing the single-plate system using the three rotating prisms as described above have a problem that it is difficult to accomplish a synchronization in time among the three rotating prisms.  
           [0026]    More particularly, although the synchronization in time among the three rotating prisms is initially accomplished, a difference in the synchronization in time among the three rotating prisms is increasingly generated by a variation among drivers of the rotating prisms as a period of time elapses after the optical illumination system is organized. Thus, when the synchronization in time among the three rotating prisms becomes different, it is impossible to implement a desired color on the screen.  
           [0027]    Also, in addition to the three rotating prisms and a plurality of dichroic mirrors for color separation, since the conventional optical illumination system for the projector employing the single-plate system further requires motors for driving the three rotating prisms, it has problems that the optical illumination system becomes complicated in its structure and large in its volume due to a relatively more space occupied by them, resulting in a difficulty of miniaturization and down-sizing in thickness of the system.  
         SUMMARY OF THE INVENTION  
         [0028]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an optical device with a function of homogenizing and color separation and an optical illumination system for a projector whose size can be reduced by use of only the optical device and one prism.  
           [0029]    The optical illumination system for the projector employing a single-plate system according to the present invention has an advantage in that homogenization of optical distribution and improvement of optical efficiency can be accomplished and the volume of the optical illumination system can be reduced at its maximum, compared to the conventional optical illumination system using the fly eye lenses and the three rotating prisms, by use of only the optical device with the function of homogenizing and color separation and one prism.  
           [0030]    In addition, since three colors light is scrolled by use of only one prism, deterioration of picture quality due to a difference in the synchronization in time among the three rotating prisms can be prevented, unlike the conventional optical illumination system using the three rotating prisms.  
           [0031]    In the end, the optical illumination system for the projector employing a single-plate system according to the present invention has remarkable advantages in that the miniaturization and lightweight of the projector can be accomplished and picture quality can be improved. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0033]    [0033]FIG. 1 is a view showing a configuration of an conventional optical illumination system for a projector employing a single-plate system using three rotating prisms;  
         [0034]    [0034]FIG. 2 is a view showing a configuration of an optical illumination system for a projector employing a single-plate system using an optical device with a function of homogenizing and color separation according to an embodiment of the present invention;  
         [0035]    [0035]FIGS. 3 and 4 are views for explaining methods for scrolling colors in a display device according to the present invention;  
         [0036]    [0036]FIG. 5 is a view showing a configuration of an optical illumination system for a projector employing a single-plate system using an optical device with a function of homogenizing and color separation according to another embodiment of the present invention; and  
         [0037]    [0037]FIG. 6 is a view showing a detailed configuration of the optical device with a function of homogenizing and color separation in an optical illumination system for a projector employing a single-plate system according to still another embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.  
         [0039]    [0039]FIG. 2 is a view showing a configuration of a conventional optical illumination system for a projector employing a single-plate system using an optical device with a function of homogenizing and color separation according to an embodiment of the present invention.  
         [0040]    Referring to FIG. 2, a configuration and an operation of an optical illumination system for a projector using an optical device with a function of homogenizing and color separation according to an embodiment of the present invention will be described below.  
         [0041]    The optical illumination system for the projector according to the present invention as shown in FIG. 2 includes an optical device  54  with a function of homogenizing and color separation, an anamorphic optical system  70 , a rotating prism  72 , and a total internal reflection prism (referred to as TIR hereinafter)  76 , which are sequentially arranged on an optical path between the source of light  52  and the display device ( 48  in FIG. 1), and further includes first and second relay lenses  74  and  80 .  
         [0042]    In addition, the source of light  52  is composed of a lamp (not shown) for emitting light and a reflection mirror (not shown) for reflecting the light emitted from the lamp into the optical device  54  with the function of homogenizing and color separation.  
         [0043]    The light emitted from the lamp is reflected by the reflection mirror and then condensed on an incidence surface  50 ′ of the homogenizing and color separation optical device  54 . The homogenizing and color separation optical device  54  makes the distribution of light uniform by totally reflecting, in its internal, the incidence light condensed on the incidence surface  50 ′ repeatedly, and separates the incidence light into the red, green and blue light.  
         [0044]    For the purpose of accomplishing this, the homogenizing and color separation optical device  54  is of the form of a comparatively long rod and has first and second dichroic coating surfaces  56  and  58  for separating the three colors light and a total reflection coating surface  60  provided in parallel to the coating surfaces  56  and  58 .  
         [0045]    The first and second dichroic coating surfaces  56  and  58  and the total reflection coating surface  60  are arranged with an inclination within the homogenizing and color separation optical device  54  such that the light reflected by the surfaces  56 ,  58  and  60  travels along a direction of a Y axis perpendicular to an X axis being a traveling direction of the incidence light.  
         [0046]    In the embodiment of the present invention as shown in FIG. 2, the first and second dichroic coating surfaces  56  and  58  and the total reflection coating surface  60  are provided in the homogenizing and color separation optical device  54  by using a plurality of triangular prisms  62 .  
         [0047]    More particularly, of five triangular prisms  62  having same medium as a rod lens  51  of rectangular hexahedron shape, the first and second dichroic coating surfaces  56  and  58  are formed on inclined surfaces of two triangular prisms  62  by dichroic coating, and the total reflection coating surface  60  is formed on an inclined surface of one triangular prism  62  by total reflection coating.  
         [0048]    Next, two remaining triangular prism  62  are attached on the dichroic-coated inclined surfaces of the triangular prisms such that the first and second dichroic coating surfaces  56  and  58  and the total reflection coating surface  60  are arranged in parallel to each other. Finally, such a combination of the five triangular prisms  62  is integrally attached to the rod lens  51  of rectangular hexahedron shape, so that the homogenizing and color separation optical device  54  is completed.  
         [0049]    The homogenizing and color separation optical device  54  consists of a medium having a refractive index (n&gt;1) larger than that of the external, i.e., air, for internal total reflection. When the light inputted to the homogenizing and color separation optical device  54  travels inside the device  54  and then is inputted above a prescribed critical angle to a boundary between the homogenizing and color separation optical device  54  and the air, the light is totally reflected at the boundary. Thus, the light inputted to the homogenizing and color separation optical device  54  is inputted to the first dichroic coating surface  56  after totally reflected inside the device repeatedly.  
         [0050]    The first dichroic coating surface  56  reflects light having a desired wavelength band, for example, blue light, to be outputted to the external through a first output surface  53  and transmits the remaining red and green light to the second dichroic coating surface  58 . The second dichroic coating surface  58  reflects light having a desired wavelength band, for example, the red light, of the red and green light transmitted through the first dichroic coating surface  56 , to be outputted to the external through a second output surface  55  adjacent to the first output surface  53  and transmits the remaining green light to the total reflection coating surface  60 . The total reflection coating surface  60  outputs the green light transmitted through the second dichroic coating surface  58  to the external through a third output surface  57  adjacent to the second output surface.  
         [0051]    Thus, the blue, red and green light is in parallel outputted with an uniform distribution of light through the first to third output surfaces  53 ,  55  and  57 , which are not overlapped one another, of the homogenizing and color separation optical device  54 .  
         [0052]    First to third color filters  64 ,  66  and  68  for enhancing color purity are further provided on their respective paths of the three colors light corresponding to the first to third output surfaces  53 ,  55  and  57 , each filter being apart from a corresponding one of the output surfaces by a specific distance. When the blue, red and green light is outputted from the first to third output surfaces  53 ,  55  and  57 , blue, red and green color filters are respectively provided corresponding to the output surfaces in order to enhance the color purity.  
         [0053]    For the purpose of improving an optical efficiency of the three colors light outputted from the first to third output surfaces  53 ,  55  and  57  of the homogenizing and color separation optical device  54 , a display device  78  and each of the first to third output surfaces  53 ,  55  and  57  are set to have same aspect ratio. However, since the blue, red and green light separated in the homogenizing and color separation optical device  54  travels in parallel to the Y axis, an optical width in the direction of the Y axis is relatively increasing.  
         [0054]    For preventing this increase of the optical width, the anamorphic optical system  70  for reducing the optical width in the direction of the Y axis by ⅓ is provided, by which an aspect ratio of the optical path (a ratio of an optical width in the direction of the Y axis to that of a Z axis) along which the red, green and blue light travel becomes equal to an aspect ratio of the display device  78 . Such an anamorphic optical system  70  consists of a cylindrical lens and the like.  
         [0055]    The rotating prism  72  refracts the three colors light inputted to respective positions on the rotating prism  72  without any overlay via the anamorphic optical system  70  such that the three colors light is outputted in parallel along different optical paths, and scrolls the outputted three colors light in a specific direction by rotating by a driving motor (not shown).  
         [0056]    The TIR prism  76  made from high polymer material totally reflects the three colors light inputted from the rotating prism  74  at a TIR surface  76 A into the display device  78  for picture implementation and transmits the picture implemented in the display device  78  to a projecting lens (not shown).  
         [0057]    The display device  78  implements the picture using the three colors light reflected by the TIR prism  76 .  
         [0058]    [0058]FIGS. 3 and 4 are views for explaining methods for scrolling colors in the display device  78  according to the present invention, where the three colors light inputted in parallel along the different optical paths via the rotating prism  72  forms images in color stripe regions R, G and B of the display device  78  as shown in FIG. 3.  
         [0059]    Simultaneously, as the rotating prism  72  is rotated, the color stripe regions R, G and B are scrolled with a lapse of time from t 1  to t 3 , as shown in FIG. 4.  
         [0060]    Also, in accordance with the red, green and blue light inputted while the color stripe regions R, G and B are scrolled, address lines RL, GL and BL for displaying red, green and blue light signals on the display device  78  are scrolled. Accordingly, the three colors light is sequentially implemented in each of pixels of the display device  78  and the implemented three colors light is integrated with time for the display of color picture.  
         [0061]    In case that the display device  78  is a DMD device, the picture is implemented by controlling an amount of reflection of the incidence light from the TIR prism  76  depending on a magnitude of electrical signal by using micromirrors.  
         [0062]    The color picture implemented in the display device  78  is projected with a magnification on the screen via the TIR prism  76 , and the projecting lens (not shown) and the first and second relay lenses  74  and  80  play a role of relaying image formation points of the traveling light without any loss.  
         [0063]    The optical illumination system according to the embodiment of the present invention as constructed above can be reduced at maximum in its size by using the homogenizing and color separation optical device  54  and one rotating prism  72 .  
         [0064]    Particularly, the size of the optical illumination system can be further reduced when optical parts are arranged such that an optical path from the source of light  52  to the projecting lens (not shown) has a “C” shape.  
         [0065]    [0065]FIG. 5 is a view showing a configuration of an optical illumination system for a projector employing a single-plate system using an optical device with a function of homogenizing and color separation according to another embodiment of the present invention.  
         [0066]    The optical illumination system as shown in FIG. 5 has same elements as in FIG. 2 except that a homogenizing and color separation optical device  82  of FIG. 5 is different in structure from that of FIG. 2, optical path change devices  86  and  88  are additionally provided in FIG. 5, and an entire arrangement of the optical parts in FIG. 5 is different from that in FIG. 2. Therefore, the detailed description for the same elements will be omitted for the purpose of simplification.  
         [0067]    In the optical illumination system as shown in FIG. 5, the source of light  52  consisting of a lamp (not shown) and a reflection mirror (not shown) condenses the light emitted from the lamp on an incidence surface  81 ′ of the homogenizing and color separation optical device  82 . The homogenizing and color separation optical device  82  makes the distribution of light uniform by totally reflecting, in its internal, the incidence light condensed on the incidence surface  81 ′ repeatedly, and separates the incidence light into the red, green and blue light.  
         [0068]    For the purpose of accomplishing this, the homogenizing and color separation optical device  82  is of the form of a comparatively long rod and has first and second dichroic coating surfaces  84 A and  84 B intersecting each other for separating the three colors light. The first and second dichroic coating surfaces  84 A and  84 B are respectively arranged such that the light reflected by the surfaces  84 A and  84 B travels along a +Y axis and a −Y axis, respectively, each axis perpendicular to an X axis being a traveling direction of the incidence light, and the light transmitted through the surfaces  84 A and  84 B travels along the X axis.  
         [0069]    In the optical illumination system as shown in FIG. 5, the first and second dichroic coating surfaces  84 A and  84 B are provided in the homogenizing and color separation optical device  82  by using a regular hexahedron prism  84  formed by four triangular prisms attached together.  
         [0070]    More particularly, of the four triangular prisms having same medium as a rod lens  81  of rectangular hexahedron shape, a first dichroic coating is applied on one surface of each of two triangular prisms and a second dichroic coating is applied on one surface of each of the remaining two triangular prisms. Next, the four triangular prisms are attached together such that the first and second dichroic coating surfaces  84 A and  84 B intersect each other. Finally, such a combination of the four triangular prisms is integrally attached to the rod lens  81  of rectangular hexahedron shape, so that the homogenizing and color separation optical device  82  is completed.  
         [0071]    The homogenizing and color separation optical device  82  consists of a medium having a refractive index (n&gt;l) larger than that of the external, i.e., air, for internal total reflection. When the light inputted to the homogenizing and color separation optical device  82  travels inside the device  54  and then is inputted above a prescribed critical angle to a boundary between the homogenizing and color separation optical device  82  and the air, the light is totally reflected at the boundary. Thus, the light inputted to the homogenizing and color separation optical device  82  is inputted to the first and second dichroic coating surfaces  84 A and  84 B after totally reflected inside the device repeatedly.  
         [0072]    The first dichroic coating surface  84 A reflects light having a desired wavelength band, for example, blue light, to be outputted to the external through a first output surface  83 . The second dichroic coating surface  84 B reflects light having a desired wavelength band, for example, the red light, to be outputted to the external through a second output surface  85  opposite to the first output surface  83 . The green light transmitted through the first and second dichroic coating surfaces  84 A and  84 B is outputted to the external through a third output surface  87  opposite to the incidence surface.  
         [0073]    In other words, the first to third output surfaces  83 ,  85  and  87  of the homogenizing and color separation optical device  82  are arranged into a “C” shape such that the blue, red and green light is outputted with a uniform distribution of light in three different directions (+Y axis, −Y axis and X axis directions) without any overlay.  
         [0074]    Each of first and second optical path change devices  86  and  88  changes traveling paths of the blue light from the first output surface  83  and the red light from the second output surface  85  such that the blue, red and green light having traveled in the three different directions (+Y axis, −Y axis and X axis directions) is in parallel traveled. For accomplishing this, the first and second optical path change devices  86  and  88  of a triangular prism shape have total reflection coating surfaces  86 A and  88 A on their inclined surfaces, respectively.  
         [0075]    The first optical path change device  86  provided with a prescribed air gap between the device  86  and the first output surface  83  of the homogenizing and color separation optical device  82  reflects at a right angle the blue light outputted from the first output surface  83  at a total reflection coating surface  86 A such that the blue light travels in parallel to the green light outputted from the third output surface  87 .  
         [0076]    The second optical path change device  88  provided with a prescribed air gap between the device  88  and the second output surface  85  of the homogenizing and color separation optical device  82  reflects at a right angle the red light outputted from the second output surface  85  at a total reflection coating surface  88 A such that the red light travels in parallel to the green light outputted from the third output surface  87 .  
         [0077]    The blue, red and green light outputted from the first and second optical path change devices  86  and  88  and the homogenizing and color separation optical device  82  has a uniform distribution of light. In addition, first to third color filters  90 ,  92  and  94  are further provided on the traveling paths of the three colors light for enhancing color purity.  
         [0078]    Other elements than the above-described elements in the optical illumination system of FIG. 5 are equal in structure and operation to those of FIG. 2 described earlier.  
         [0079]    In other words, the anamorphic optical system  70 , the rotating prism  72 , the TIR prism  76 , the display device  78 , and the first and second relay lenses  74  and  80  are equal in structure and operation to those of FIG. 2.  
         [0080]    The optical illumination system according to another embodiment of the present invention as constructed above can be also reduced at maximum in its size by using the homogenizing and color separation optical device  82  and one rotating prism  72 .  
         [0081]    Particularly, the optical parts are arranged such that an optical path from the source of light  52  to the projecting lens (not shown) has an “L” shape unlike FIG. 2.  
         [0082]    [0082]FIG. 6 is a view showing a detailed configuration of a homogenizing and color separation optical device in an optical illumination system according to still another embodiment of the present invention, which is also applicable to an arrangement of the optical path of the “L” shape as shown in FIG. 5.  
         [0083]    The homogenizing and color separation optical device  100  as shown in FIG. 6 makes the distribution of light uniform by totally reflecting, in its internal, the incidence light condensed by the reflection mirror within the source of light ( 52  in FIGS. 2 and 5) repeatedly, and separates the incidence light into the red, green and blue light.  
         [0084]    For the purpose of accomplishing this, the homogenizing and color separation optical device  100  is of the form of a comparatively long rod and has a first dichroic coating surface  102  inside the device  100  for color separation. Outside the homogenizing and color separation optical device  100 , a second dichroic coating surface  104  for color separation and a total reflection coating surface  106  for optical path conversion are arranged in parallel to the first dichroic coating surface  102 .  
         [0085]    The first dichroic coating surface  102  is arranged with an inclination such that the light reflected by the surface  102  travels along the Y axis perpendicular to the X axis being the traveling direction of the incidence light.  
         [0086]    More particularly, of two triangular prisms  108  having same medium as a rod lens  101  of rectangular hexahedron shape, as shown in FIG. 6, the first dichroic coating surface  102  is formed by dichroic coating on an inclined surface of one triangular prism. Next, the other triangular prism is attached to the inclined surface of one triangular prism. Finally, such a combination of the two triangular prisms is integrally attached to the rod lens  101  of rectangular hexahedron shape, so that the homogenizing and color separation optical device  100  is completed.  
         [0087]    The homogenizing and color separation optical device  100  consists of a medium having a refractive index (n&gt;l) larger than that of the external, i.e., air, for internal total reflection. When the light inputted to the homogenizing and color separation optical device  100  travels inside the device  100  and then is inputted above a prescribed critical angle to a boundary between the optical device  100  and the air, the light is totally reflected at the boundary.  
         [0088]    Thus, the light inputted to the homogenizing and color separation optical device  100  is inputted to the first dichroic coating surface  102  after totally reflected inside the device repeatedly.  
         [0089]    The first dichroic coating surface  102  transmits light having a desired wavelength band, for example, green light, to be outputted to the external through a first output surface  103  opposite to the incidence surface, and reflects the remaining blue and red light to be outputted to the external through a second output surface  105  perpendicular to the incidence surface.  
         [0090]    The second dichroic coating surface  104  and the total reflection coating surface  106  are in parallel arranged by using three triangular prisms  108 . Of the three triangular prisms  108 , the second dichroic coating surface  104  and the total reflection coating surface  106  are respectively formed on each of inclined surfaces of two triangular prisms. Next, the coating surfaces  104  and  106  are attached to the triangular prisms  108  such that they are in parallel arranged.  
         [0091]    In addition, a prism complex in which the second dichroic coating surface  104  and the total reflection coating surface  106  are formed is arranged with a prescribed air gap between the prism complex and the second output surface  105  of the homogenizing and color separation optical device  100 .  
         [0092]    The second dichroic coating surface  104  reflects light having a desired wavelength band, for example, red light of the incidence light from the second output surface  105 , such that the red light travels in parallel to the green light outputted from the first output surface  103 .  
         [0093]    The total reflection coating surface  106  reflects at a right angle the blue light transmitted through the second dichroic coating surface  104  such that the blue light travels in parallel to the red light.  
         [0094]    The first to third color filters  90 ,  92  and  94  for enhancing color purity are further provided on the traveling paths of the three colors light which travels in parallel with the uniform distribution of light and the color separation achieved by the homogenizing and color separation optical device  100 , the second dichroic coating surface  104  and the total reflection coating surface  106 .  
         [0095]    By using the homogenizing and color separation optical device  100  having the structure as described above, the optical illumination system can accomplish the reduction of size in addition to the homogenized distribution of light and the improvement of optical efficiency.  
         [0096]    In addition, when a square PBS prism is used instead of the TIR prism, a reflection-typed LCD panel can be used as the display device.  
         [0097]    Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Therefore, it should be understood that this invention should not be limited to the detailed description, but should be limited only by the scope and spirit of the appended claims.