Abstract:
The present invention relates to a projection system that can be applied to a projection TV or a projection monitor, and more particularly, to a projection system that can improve a contrast while maintaining a proper brightness of a set where the projection system is applied.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a projection system that can be applied to a projection TV or a projection monitor, and more particularly, to a projection system that can improve a contrast while maintaining a proper brightness of a set to which the projection system is applied.  
           [0003]    2. Description of the Related Art  
           [0004]    An optical system that is employed to a projection TV or a projection monitor is generally comprised of a polarization converting part for converting light that is irradiated from a light source lamp and has an irregular polarization direction (the light source will be referred as “irregular polarization light flux” hereinafter) into a plurality of polarization light fluxes having an identical single polarization direction, and a color separating part for separating the polarization light fluxes, which are irradiated from the polarization converting part with the single polarization direction, by colors.  
           [0005]    [0005]FIG. 1 shows a detailed view of a polarization converting part of a conventional optical system.  
           [0006]    As shown in FIG. 1, a polarization converting part includes a light source part  10  comprised of a light source lamp  11  and a parabolic reflector  12  and a polarization generating part  20  comprised of a first optical element  30  and a second optical element  40 .  
           [0007]    In addition, the first optical element  30  includes a plurality of light flux dividing lenses  31  shaped in a rectangular are arranged in a matrix configuration, and the second optical element  40  is formed in a complex member comprised of a condenser lens array  41 , a light shielding plate  44 , a polarization separating unit array  43 , a selective phase difference plate  45 , and a coupling lens  46 .  
           [0008]    The coupling lens  46  can be separated for convenience.  
           [0009]    In the polarization converting part constructed as above, the irregular polarization light flux that is incident from the light source part  10  to the first optical element  30  is divided into a plurality of intermediate light fluxes by the light flux dividing lenses  31 .  
           [0010]    The divided intermediate light fluxes are spatially separated in a P-polarization light flux space and an S-polarization space by the polarization separating unit array  43 . And then, the spatially separated polarization directions are coincided in an identical single polarization direction by the selective phase difference plate  45 . The coincided polarization light fluxes are induced toward a panel  50  through the coupling lens  46 .  
           [0011]    The coincided polarization light fluxes generated from the polarization converting part is separated by colors while passing through a reflection or transmission filter of the color separation part.  
           [0012]    [0012]FIGS. 2 and 3 show a detailed view of a conventional color separation part.  
           [0013]    [0013]FIG. 2 illustrates a transmissive LCD. As light flux emitted from the polarization generating part  20  is incident into a red light reflection mirror  71  of the color and light separation means, blue and green lights are transmitted but red light is reflected on the red light reflection mirror  71 . The reflected red light is reflected by a downstream reflection mirror  72  to reach a red light liquid crystal part  51 .  
           [0014]    Meanwhile, as the blue and green lights transmitted through the red light reflection mirror  71  are again incident into a green light reflection mirror  73 , the green light is reflected and the blue light is transmitted.  
           [0015]    The reflected green light reaches the green light liquid crystal part  52 , and the blue light transmitted through the green light reflection mirror  73  is reflected by a downstream blue light reflection mirror  74 .  
           [0016]    The reflected blue light is reflected by the downstream reflection mirror  75  to reach the blue light liquid crystal part  53 .  
           [0017]    The three liquid crystal parts  51 ,  52  and  53  modulate each of the color lights. The modulated color lights containing image information corresponding to the color lights is incident to color lights synthesizing means such as a cross dichroic prism  60 . The cross-dichroic prism  60  forms a color image by synthesizing the modulated fluxes to form a color image. The color image is projected to a screen  80  by a projection lens  70  defining a projection optical system, thereby forming a projected color image.  
           [0018]    [0018]FIG. 3 illustrates a reflective LCD. As light flux emitted from the polarization generating part  20  is incident into a blue light reflection mirror  76  of the color and light separation means, red and green lights are transmitted but blue light is reflected by the blue light reflection mirror  76 .  
           [0019]    The reflected blue light is reflected by a downstream reflection mirror  78  and then reflected by a downstream blue light filter  94  to reach a blue light liquid crystal part  56 , and is then shifted in its phase by 90°. After that, the phase-shifted light is incident into a cross dichroic prism  60  through the blue light filter  94 .  
           [0020]    Meanwhile, as the red and green lights transmitted through the green light reflection mirror  77  are incident into the green light reflection mirror  77  of the color and light separating means, the green light is reflected by the green light reflection mirror  77  and the red light is transmitted.  
           [0021]    The reflected green light is reflected by the green light filter  92  to reach a green light liquid crystal part  55 , and is then phase-shifted by 90°. After that, the phase-shifted light is incident to the cross dichroic prism  60  through the green light filter  92 .  
           [0022]    The red light transmitted through the green light reflection mirror  77  is reflected by a red light filter  90  to reach a red light liquid crystal part  54 , and is then phase-shifted by 90° through the red light liquid crystal part. After that, the phase-shifted light is incident to the diachronic prism  60  via the red light filter  90 .  
           [0023]    The cross-dichroic prism  60  synthesizes the modulated light fluxes to form a color image. The color image formed by the cross-dichroic prism  60  is projected onto a screen  80  by a projection lens  70 , which is a kind of a projection optical system, thereby forming a projected color image.  
           [0024]    The above-described optical system can be classified into a single plate type, a dual plate type, and a triple plate type depending on the number of the liquid crystal parts that are a display device. The optical systems depicted in FIGS. 2 and 3 are exampled as the triple optical system.  
           [0025]    However, the above-described optical system has a problem in that the brightness and the contrast are oppositely related with each other. That is, when the contrast is increased, the brightness is reduced, whereas when the brightness is increased, the contrast is reduced.  
         SUMMARY OF THE INVENTION  
         [0026]    Accordingly, the present invention is directed to a projection system that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
           [0027]    An object of the present invention is to provide a projection system that can improve a contrast while maintaining a proper brightness of a set to which the projection system is applied.  
           [0028]    Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0029]    To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a projection system comprising a polarization converting part for converting an incident polarization light flux into a polarization light flux having one direction, and a color separating part for color-separating the polarization light flux irradiated from the polarization converting part, the polarization converting part comprising: an FEL having a plurality of light flux dividing lenses shaped in a square and arranged in a matrix configuration, for dividing an incident light in a unit of cell; a condenser lens array for converting an incident light that is incident from the FEL, into a parallel light with respect to a specific portion; a green light filter for reflecting a part of green light of a plurality of intermediate light fluxes dividedly outputted from the FEL and passing remaining light; a polarization separating unit array for converting an incident light outputted from the condenser lens array into a linearly polarized light having a single optic axis; and a coupling lens for condensing an output light from the polarization separating unit array.  
           [0030]    Also, the green light filter is formed up and down so that a part of an upper portion and a lower portion of an incident green light among the plurality of intermediate light fluxes can be shielded.  
           [0031]    Further, the green light filter is formed left and right so that a part of a left portion and a right portion of an incident green light among the plurality of intermediate light fluxes can be shielded.  
           [0032]    Furthermore, the green light filter is formed up, down, left and right so that a part of an upper portion, a lower portion, a left portion and a right portion of an incident green light among the plurality of intermediate light fluxes can be shielded.  
           [0033]    Moreover, the green light filter is formed at a portion except for a circular central portion so that the portion except for the circular central portion of an incident green light among the plurality of intermediate light fluxes can be shielded.  
           [0034]    It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0036]    [0036]FIG. 1 shows a detailed view of a polarization converting part of a conventional optical system;  
         [0037]    [0037]FIGS. 2 and 3 show a detailed view of a conventional color separation part;  
         [0038]    [0038]FIG. 4 is a detailed view of a projection system according to the present invention;  
         [0039]    [0039]FIG. 5 is a view illustrating paths of the red light and the blue light in the polarization converting part of a projection system according to a preferred embodiment of the present invention;  
         [0040]    [0040]FIG. 6 is a view illustrating a path of the green light in the polarization converting part of a projection system according to a preferred embodiment of the present invention;  
         [0041]    [0041]FIGS. 7A, 7B,  7 C and  7 D are views illustrating structures of a green light filter according to the present invention;  
         [0042]    [0042]FIG. 8 is a view illustrating the position of the green light filter according to another embodiment of the present invention; and  
         [0043]    [0043]FIG. 9 is a view illustrating the position of the green light filter according to a further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0044]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0045]    [0045]FIG. 4 is a detailed view of a projection system according to the present invention.  
         [0046]    As shown in FIG. 4, a polarization converting part includes a light source part  10  comprised of a light source lamp  11  and a parabolic reflector  12 , and a polarization generating part  20  comprised of a first optical element  30  and a second optical element  40 .  
         [0047]    The first optical element  30  includes a plurality of light flux dividing lenses  31  arranged in a matrix configuration and called “FEL (Fly-Eye Lens).  
         [0048]    The second optical element  40  is made in a complex member, which includes a condenser lens array  41  for converting an incident light that is incident from the FEL  31 , into a parallel light with respect to a specific portion, a green light filter  42  formed at edges between the FEL  31  and the condenser lens array  41 , for reflecting only the green light of a plurality of intermediate light fluxes dividedly outputted from the FEL  31  and passing remaining light, a light shielding plate  44  for converting an incident light outputted from the condenser lens array  41  into a linearly polarized light, a polarization separating unit array  43 , a selective phase difference plate  45 , and a coupling lens  46  for condensing an output light from the polarization separating unit array  43 .  
         [0049]    The coupling lens  46  can be separated for convenience.  
         [0050]    The polarization converting part constructed as above divides an irregular polarization light flux that is incident from the light source part  10  to the first optical element  30 , into a plurality of intermediate light fluxes by the light flux dividing lenses  31 .  
         [0051]    After that, the divided intermediate light fluxes are incident into the polarization separating unit array  43  via the green light filter  42 .  
         [0052]    The green light filter  42  reflects the green light of the incident light fluxes and pass the red light and the blue light.  
         [0053]    Thus, the green light filter  42  is used to adjust the angle of the light that is incident into a panel through the coupling lens  46 .  
         [0054]    In other words, since the arc of a used lamp that is an optic system source is not a point source but a face source and thus light is irradiated dispersed with a predetermined angle, the angle of the light that is incident into the panel  50  through the coupling lens  46  has a close relationship with amount and contrast of the light.  
         [0055]    Accordingly, by making the angle of the output light from the light source part  10  large, the brightness of a set is increased and the contrast of the set is deteriorated. On the other hand, by making the angle of the output light small, the contrast of the light is enhanced and the brightness of the set is decreased.  
         [0056]    In the above, the green light influences the contrast and the red and blue lights influence the brightness.  
         [0057]    The contrast and the brightness of the set are pitted against each other. Reviewing the lamp of the present projection TV, since the green light is considerably larger than the blue light, the green light is cut away circuit-optically.  
         [0058]    However, if the green light is cut away circuit-optically, the contrast of the set is enhanced but the brightness of the set is decreased.  
         [0059]    Accordingly, the projection system of the present invention does not cut away the green light but makes the angle of the transmitted green light small to enhance the contrast with maintaining the brightness of the set.  
         [0060]    In other words, the angle of the incident green light is made small to enhance the contrast while the angles of the blue light and the red light are maintained so as not to influence the brightness of the set.  
         [0061]    For this purpose, the green light filter  42  is formed at a predetermined region on a path of the light that is incident into the second optical element  40 . Accordingly, the red light and the blue light maintain their brightness since a change in the angle is not given, while the contrast of the green light is changed by changing the angle of the green light.  
         [0062]    [0062]FIG. 5 is a view illustrating paths of the red light and the blue light in the polarization converting part of a projection system according to a preferred embodiment of the present invention, and FIG. 6 is a view illustrating a path of the green light in the polarization converting part of a projection system according to a preferred embodiment of the present invention.  
         [0063]    As shown in FIG. 5, since the red light and the blue light have the same light amount, the brightness of the set is maintained as it is.  
         [0064]    Further, as shown in FIG. 5, since the green light is reflected from the green light filters  42  positioned at both sides of the polarization converting part and condenser lens arrays  41  positioned at both sides of the polarization converting part is not used, the green light is incident into only a central condenser lens array part not having the green light filter  42  so that an incident angle of the light into a panel can be reduced and accordingly a contrast of the set can be improved.  
         [0065]    As described above, the contrast control using the green light is because the green light is relatively abundant than other colors of light and the contrast is greatly dependent on the green light, and the red light and the blue light are used as they are so as not to affect the brightness of the set.  
         [0066]    This is because the brightness of the set is dependent on the red light and the blue light and accordingly, even though the green light is controlled, a whole brightness of the set is not varied.  
         [0067]    [0067]FIGS. 7A, 7B and  7 C are views illustrating a structure of the green light filter  42  according to various embodiments of the present invention.  
         [0068]    [0068]FIG. 7A is a view illustrating an embodiment of a structure of the green light filter  42  for reducing, at both horizontal sides, the incident angle of the green light incident into a second optical element  40 .  
         [0069]    Further, FIG. 7B is a view illustrating another embodiment of a structure of the green light filter  42  for reducing, at both vertical sides, the incident angle of the green light incident into the second optical element  40 .  
         [0070]    Furthermore, FIG. 7C is a view illustrating yet another embodiment of a structure of the green light filter  42  for reducing, at an upper and lower side and at a left and right side, the incident angle of the green light incident into the second optical element  40 .  
         [0071]    Additionally, FIG. 7D is a still another embodiment of a structure of the green light filter  42  for circularly reducing the incident angle of the green light incident into the second optical element  40 .  
         [0072]    Through ways shown in FIGS. 7A, 7B,  7 C and  7 D, the incident angle of the green light can be optionally controlled vertically, horizontally or bi-directionally, etc. depending on a characteristic of the projection system.  
         [0073]    As mentioned above, the light incident into the second optical element  40  via the green light filter  42  is respectively spatially separated in a P-polarized light flux and an S-polarized light flux through a polarization separate unit array  43 .  
         [0074]    Additionally, a selective phase difference plate  45  unites spatially separated polarization directions into one, and introduces the united polarization light flux into a panel  50  through a coupling lens  46 .  
         [0075]    As described above, in this embodiment, the green light filter  42  is positioned between the FEL  31  and the condenser lens array  41 , but the green light filter  42  can be, as shown in FIG. 8, allowed to be positioned between the polarization separate unit array  43  and the coupling lens  46 , and can be, as shown in FIG. 9, allowed to be positioned on a surface of the coupling lens  46 .  
         [0076]    As described above, the projection system according to the present invention has an advantage in that the whole brightness of the projection set is maintained as it is while the contrast can be increased.  
         [0077]    It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.