Abstract:
A projection display system includes a light source for providing a white light; a light separating unit for separating the red (R), green (G) and blue (B) lights from the white light provided by the light source; a light deflecting unit for concurrently deflecting R, G and B lights without being mixed with each other and irradiating R, G and B lights toward a modulating unit; and the modulating unit for modulating R, G and B lights to form a color image.

Description:
CLAIM OF PRIORITY  
         [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for  Optical Apparatus of One Panel Projection System  earlier filed in the Korean Industrial Property Office on Mar. 28, 2001 and there duly assigned Serial No. 2001-16259.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a projection display device, and more particularly, to a single-panel projection display device having a high optical efficiency.  
           [0004]    2. Description of Related Art  
           [0005]    A liquid crystal (LC) projector includes an LC panel as a modulator for modulating light from a light source to form an image. The LC panel is divided into two types including a transmissive type and a reflective type. A poly-silicon liquid crystal display is mainly used as the transmissive LC panel, and a digital micromirror device (DMD) and a liquid crystal on silicon (LCOS) device are mainly used as the reflective LC panel.  
           [0006]    Of these, the LCOS display recently receives an attention due to a small size and a high resolution. In the LCOS display, a three-panel LC projector or a single-panel LC projector has been used to achieve a full color.  
           [0007]    The three-panel LC projector is one which light rays emitted from a light source are divided into R (red), G (green) and B (blue) light rays by R, G and B dichroic mirrors, travel through three R, G and B liquid crystal panels, and are combined by a dichroic prism, and a color picture is projected through a projection lens in an enlarged color picture on a screen.  
           [0008]    The single-panel LC projector is one which light rays emitted from a light source are divided into R, G, and B light rays by a color separating means, and travel through a single LC panel, and a color picture is projected through a projection lens in an enlarged color picture on a screen. The color separating means includes a color wheel, a color switch, a philips prism, or the like.  
           [0009]    [0009]FIG. 1 is a schematic view illustrating a color wheel for use in a conventional single-panel projection system. The color wheel of FIG. 1 includes R, G and B color regions. The color wheel of FIG. 1 is rotated by a driving means (not shown) so as to separate light rays emitted from a light source such as a lamp into R, G and B light rays and to direct R, G and B light rays toward a single LC panel in sequence.  
           [0010]    However, since the color wheel of FIG. 1 separates R, G and B light rays by R, G and B color regions and then directs R, G and B light rays toward the single LC panel in sequence, an optical efficiency is merely a maximum of ⅓. That is, just one of R, G and B light rays directs toward the LC panel, leading to an optical loss of ⅔.  
         SUMMARY OF THE INVENTION  
         [0011]    It is therefore an object of the present invention to provide a projection display device having a high optical efficiency.  
           [0012]    It is another object of the present invention to provide a projection display device having a high operating speed.  
           [0013]    In order to achieve the above and other objects, the preferred embodiments of the present invention provide a projection display system, including a light source for providing a white light; a light separating unit for separating R, G and B lights from the white light provided by the light source; a light deflecting unit for concurrently deflecting R, G and B lights not to be mixed with each other and irradiating R, G and B lights toward a modulating unit; and the modulating unit for modulating R, G and B lights to form a color image.  
           [0014]    The light separating unit includes an X-cube and first and second mirrors. The X-cube includes first and second reflecting surfaces crossed with each other and the first and second mirrors are arranged parallel to the first and second reflecting surfaces, respectively. The light deflecting unit includes three polygon mirrors, the polygon mirrors are rotatable by a motor and deflecting R, G and B lights, respectively. Rotation axes of the polygon mirrors are spaced apart from each other to prevent R, G and B lights from being mixed.  
           [0015]    The system further includes an optical path difference equalizing unit for equalizing an optical path difference between R, G and B lights and for condensing R, G and B lights onto an optical path. The optical path difference equalizing unit includes three relay lenses. The optical path difference equalizing unit is disposed between the light separating unit and the light deflecting unit. The modulating unit is a reflective liquid crystal panel.  
           [0016]    The system further includes a fly-eyes lens for making light emitted from the light source uniform, a polarizing converting unit and a polarizing beam splitter, the polarizing converting unit for converting light to a p-wave polarized light, the polarizing beam splitter for transmitting a p-wave polarizing light and reflecting an s-wave polarized light generated from the modulating unit, and a projecting unit for enlarging the color image generated from the modulating unit and projecting the color image to a screen. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0018]    [0018]FIG. 1 is a schematic view illustrating a color wheel for use in a conventional single-panel projection system; and  
         [0019]    [0019]FIG. 2 is a block diagram illustrating a projection display device according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    Turning now to the drawings, FIG. 2 is a block diagram illustrating a projection display device  5  according to a preferred embodiment of the present invention.  
         [0021]    The projection display device  5  of FIG. 2 includes a light source  10 , a fly-eyes lens  20 , a polarization converting unit  30 , a light separating unit  40 , an optical path difference equalizing unit  50 , a light deflecting unit  60 , a modulating unit  70 , a polarizing beam splitter  80 , and a projecting unit  90 .  
         [0022]    The light source  10  includes a lamp  10   a  and a parabolic reflector  10   b.  Light emitted from the lamp  10   a  is reflected by the parabolic reflector  10   b,  so that parallel light directs toward the fly-eyes lens  20 . The fly-eyes lens  20  is a light uniformization means which makes parallel light from the light source  10  uniform. The polarization converting unit (or polarizing conversion system)  30  is a light converting means which converts the uniformized light to a p-wave polarized light.  
         [0023]    The light separating unit  40  separates R, G and B light rays from the p-wave polarized light and irradiates R, G and B light rays to the optical path difference equalizing unit  50 . The light separating unit  40  includes an X-cube  42  and mirrors  44  and  46 . The X-cube  42  includes reflecting surfaces  42   a  and  42   b  which are crossed with each other. The reflecting surface  42   a  reflects the R light ray and directs the R light ray toward the mirror  46 , and the reflecting surface  42   b  reflects the B light ray and directs the B light ray toward the mirror  44 . The G light ray is transmitted through the X-cube  42  “as is” (without change).  
         [0024]    The optical path difference equalizing unit  50  includes relay lenses  50   a,    50   b  and  50   c,  and equalizes an optical path difference between R, G and B light rays. Such an optical path difference results from the fact that rotation axes  60   a ′ to  60   c ′ of polygon mirrors  60   a  to  60   c,  respectively, are spaced apart from each other. That is, the rotation axis  60   a ′ of the polygon mirror  60   a  is at a distance “d” from the rotation axis  60   b ′ of the polygon mirror  60   b,  and the rotation axis  60   b ′ of the polygon mirror  60   b  is at a distance “d” from the rotation axis  60   c ′ of the polygon mirror  60   c.    
         [0025]    The relay lenses  50   a  to  50   c  are designed in consideration of a wavelength characteristic and an optical path of R, G and B light rays. The relay lens  50   a  condenses the B light ray and directs the condensed B light ray to the polygon mirror  60   a.  The relay lens  50   b  condenses the G light ray and directs the condensed G light ray to the polygon mirror  60   b.  The relay lens  50   c  condenses the R light ray and directs the condensed R light ray to the polygon mirror  60   c.    
         [0026]    Meanwhile, the optical path difference equalizing unit  50  can be disposed at any location on an optical axis, and is preferably disposed between the light separating unit  40  and the light deflecting unit  60 .  
         [0027]    The light deflecting unit  60  includes the polygon mirrors  60   a  to  60   c.  The rotation axes  60   a ′ to  60   c ′ of the polygon mirrors  60   a  to  60   c  are spaced apart from each other so as to prevent R, G and B light rays from being mixed.  
         [0028]    By rotating the polygon mirrors  60   a  to  60   c  using a motor (not shown), the polygon mirrors  60   a  to  60   c  deflect R, G and B light rays so that R, G and B light rays can be irradiated toward the modulating unit  70 , respectively.  
         [0029]    Since the R, G and B light rays irradiated toward the modulating unit  70  are the p-wave polarized lights, the R, G and B light rays transmit through the polarizing beam splitter  80  and enter the modulating unit  70 .  
         [0030]    The modulating unit  70  is preferably a reflective liquid crystal (LC) panel. Pixels of the reflective LC panel  70  which are turned on, modulate the incident light thereto to s-wave polarized lights, and pixels of the reflective LC panel  70  which are turned off, modulate the incident light thereto to p-wave polarized lights.  
         [0031]    The polarizing beam splitter  80  reflects the s-wave polarized lights and transmits the p-wave polarized lights. The projecting unit  90  enlarges and projects the s-wave polarized lights, thereby forming a color image on a screen. That is, the polarizing beam splitter  80  irradiates only the lights selected to form a color image to a screen (not shown) through the projecting unit  90 .  
         [0032]    Operation of the projection display system is described below.  
         [0033]    Parallel light rays emitted from the light source  10  become uniform by the fly-eyes lens  20 . The uniformized light rays (light rays that are made uniform) are converted to p-wave polarized lights by the polarization converting unit  30 . The p-wave polarized lights are separated into R, G and B light rays by the light separating unit  40  and then direct toward the optical path difference equalizing unit  50 . The optical path difference equalizing unit  50  equalizes an optical path difference between R, G and B light rays. R, G and B light rays are deflected by the light deflecting unit  60  and are irradiated to the modulating unit  70 .  
         [0034]    The modulating unit  70  modulates the incident light thereto. The polarizing beam splitter  80  irradiates only the selected light to a screen (not shown) through the projection unit  90 , thereby forming a color image.  
         [0035]    Meanwhile, the polarization converting unit  30  can be designed to convert the uniformized light from the light source  10  to an s-wave polarized light. In this case, the polarizing beam splitter  80  is designed to transmit the s-wave polarized light and reflect the p-wave polarized light, and the LC panel  70  is designed such that pixels which are turned on modulate the incident light thereto to p-wave polarized lights, and pixels which are turned off modulate the incident light thereto to s-wave polarized lights.  
         [0036]    As described herein before, the projection display system according to the present invention irradiates R, G and B light rays to the LC panel concurrently and thus significantly improves the optical efficiency. Also, R, G and B light rays are concurrently irradiated to the LC panel, and therefore a response speed of the LC panel can be significantly improved, leading to a high operating speed.  
         [0037]    While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.