Abstract:
Reflective polarization valve engine and projection display are disclosed. Instead of prism PBS, the projector applies wire-grid polarizers with advantages of higher heat-resistance, no limitation of the incident angle and no birefringence effects, to provide excellent contrast luminance. The light source in the projector utilizes an elliptical lamp under a telecentric optical system to achieve higher efficiency and avoid color gradient. In addition, the light paths are in special arrangement. The original beam is first splitted into RGB, and then proceeding with color-recombining right after being polarized via wire-grid polarizers and analyzed by reflective polarization valves. Hence, the analyzed beams finally are recombined images with superior performances.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates to a projection display and its optical engine with reflective polarization valves, and more particularly, to a projection device that utilizes a wire-grid polarizer, a telecentric optical system and specific arrangement of light path, which have the beams proceeding with color-recombining right after being analyzed by reflective polarization valves.  
         [0003]     2. Related Art  
         [0004]     In the prior art, a LCOS (Liquid Crystal on Silicon) projector that uses LCOS as reflective polarization valve, is similar to LCD projector in portions of light-guiding, light-splitting and color-combining. The only difference is that the LCOS projector further applies prism PBS (Polarization Beam Splitter). PBS is a binding prism of two 45° isosceles right angle prisms. PBS reflects the S-polarized light of an incident beam and allows the P-polarized light to pass through. In general, the original beam emitting from a light source is splitted into R, G and B beams via dichroic mirrors. S-polarized beams are reflected into LCOS panels when the R, G, and B beams penetrate through their PBSs respectively. If the LCOS is under light state, the S-polarized beams are transformed into P-polarized beams. Consequently, we can obtain images via combining the analyzed P-polarized beams and projecting onto a screen.  
         [0005]     However, the application of a PBS causes some defects.  
         [0006]     First, the PBS has low heat-resistance so that birefringence effect and decreasing of contrast luminance are formed due to heat-expansion of the PBS. Second, the PBS has limitation in incident angles of beams. It is necessary to apply parallel light sources to increase the efficiency while using the PBS. In consequence, the light path is longer and the total volume becomes larger. Moreover, in current design of the light path, beams analyzed by reflective light valves (e.g. LCOS panels) have to pass PBSs for polarizing transformation before proceeding with color recombining. Therefore, the light path becomes longer and causes energy loss. In addition, the PBS reduces the purity of polarized beams because of its unstability, which makes an unsatisfactory performance of image combination.  
         [0007]     Except the PBS, there are other substitute prisms in unique shapes in the prior art. However, they are expensive and have low heat-resistance.  
         [0008]     In some special projection systems, peculiar optical elements such as Color-Quad, Color-Corner or X-plate are applied. Comparatively, because these optical elements&#39; unique shapes are hard to manufacture and have a lack of general uses, they are difficult for mass production and thereby have higher costs.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of the foregoing, the invention wants to solve the problems of low image performance and high cost when using the PBS, prisms of unique shapes and peculiar optical elements.  
         [0010]     The above problems have been solved by the present invention via providing a reflective polarization valve engine and a projection display. The projection display comprises a light source, a dichroic mirror, a reflective polarization valve, a wire-grid polarizer, a color-recombining unit and a projecting unit. The light source provides a polarized white beam. The dichroic mirror splits the white beam into color beams with different colors. The reflective polarization valve receives the polarized color beams and selectively reflects the color beams. The wire-grid polarizer is located between the dichroic mirror and the reflective polarization valve. The wire-grid polarizer allows the polarized color beams of one specific polarity to pass through, and reflects the polarized color beams of another specific polarity. The polarized color beams reflected from the reflective polarization valve under light state are reflected via the wire-grid polarizer for color recombining. The color-recombining unit combines the color beams reflected from the wire-grid polarizer. The projecting unit projects the combined color beams to form images.  
         [0011]     In short, the invention achieves advantages as follows: 
        A. Provides higher contrast luminance of image.     B. By means of dichroic mirror, the light path is capable of change direction. Meanwhile, the entire light paths are highly concentrated and have more selectivity of arrangement, so as to achieve a projection system of smaller volume.     C. The wire-grid polarizer is produced via a semi-conductor producing procedures to provide an easier manufacturing process and lower costs.     D. Instead of drawbacks of color gradients, the invention achieves better color uniformity.     E. Specific arrangement of light paths provides better image performance.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will become more fully understood from the detailed description given herein below illustration only, and is thus not limitative of the present invention, and wherein:  
         [0018]      FIG. 1  is a structural diagram of a projection display provided by a preferred embodiment according to the invention;  
         [0019]      FIG. 2  is an explanation diagram of a wire-grid polarizer used in the preferred embodiment; and  
         [0020]      FIG. 3  is an energy-wavelength diagram of curves, showing a better performance in image luminance via combining red and blue beams under S-polarized state, and a green beam under P-polarized state. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Please refer to  FIG. 1 , which shows a structural diagram of a projection display provided by a preferred embodiment according to the invention. The projection display comprises light source  10 , dichroic mirror  20  and  21 , reflective polarization valve  30 ,  31  and  32 , wire-grid polarizer  40 ,  41  and  42 , color-recombining unit  61  and projecting unit  50 . The characteristic of the elements, their relations and the arrangement of light paths are illustrated in the following description.  
         [0022]     Light source  10  provides a polarized white beam. It is a telecentric optical system, which includes a white lamp  11 , a divergent lens  12 , a lens array  13 ,  14  and a P/S converter  15 . The white lamp  11  is an elliptical lamp of high efficiency. The white beam generated by the white lamp  11  first passes through the divergent lens  12  and then the lens array  13 ,  14 . Next, the white beam goes through the S-polarized transformation via the P/S converter  15 . After being splitted, the beams focus on the reflective polarization valve  30 ,  31 ,  32  via the focusing lens  16 ,  70  and  71 , to form parallel S-polarized beam. Reflector  17 ,  18 , and  19  modify the directions of the light paths.  
         [0023]     The dichroic mirror  20  and  21  split the white beam into color beams of three original colors, red, green and blue.  
         [0024]     The reflective polarization valve  30 ,  31  and  32  provided in the preferred embodiment are LCOS panels, but RLCD (reflective liquid crystal display) is practical as well. The reflective polarization valve  30 ,  31  and  32  receive the polarized color beams and selectively reflect the color beams.  
         [0025]     The wire-grid polarizer is a polarization-transforming element produced via processes of semiconductors, such as ProFlux™ provided by Moxtek Inc. The advantages include a higher heat-resistance, no limitation of the incident angle and no birefringence effects, to enhance the contrast luminance of the system. Moreover, because the wire-grid polarizer allows a larger incident angle, convergent light sources such as an elliptical lamp can be applied to shorten the light paths, achieve higher efficiency and a system of smaller volume. In consequence, the system is much easier to manufacture and has lower costs.  
         [0026]     The wire-grid polarizer  40 ,  41  and  42 , skew in angle 45° to the light axis  100 , are located between the dichroic mirror  20 ,  21  and the reflective polarization valve  30 ,  31 ,  32 . In detail, the wire-grid polarizer  40  is located between the dichroic mirror  20  and the reflective polarization valve  30 ; the wire-grid polarizer  41  is located between the dichroic mirror  21  and the reflective polarization valve  31 ; the wire-grid polarizer  42  is located between the dichroic mirror  21  and the reflective polarization valve  32 .  
         [0027]     With reference to  FIG. 2 , the wire-grid polarizer  40  ( 41 ,  42 ) has a polarizing surface  400  ( 410 ,  420 ). The polarizing surface  400  ( 410 ,  420 ) faces the reflective polarization valve  30  ( 31 ,  32 ). The opposite surface  402  ( 412 ,  422 ) of the wire-grid polarizer  40  ( 41 ,  42 ) allows the color beams mentioned above to pass through and project onto the reflective polarization valve  30  ( 31 ,  32 ). Furthermore, the polarizing surface  400  ( 410 ,  420 ) splits the beams reflected from the reflective polarization valve  30  ( 31 ,  32 ) according to their polarity. In short, the wire-grid polarizer  40  ( 41 ,  42 ) reflects P-polarized beams but allows S-polarized beams to pass through, or reflects S-polarized beams but allows P-polarized beams to pass through.  
         [0028]     When the pixels on the reflective polarization valve  30  ( 31 ,  32 ) are under light state, the reflective polarization valve  30  ( 31 ,  32 ) changes the polarity of the incident beams to P-polarized state. Meanwhile, instead of changing the polarity of the incident beams, the reflective polarization valve  30  ( 31 ,  32 ) reflects S-polarized beams back to the wire-grid polarizer  40  ( 41 ,  42 ) and passes through when the pixels are under dark state. The definition of the term ‘contract’ is the ratio of the largest luminance value and the smallest luminance value lightened on the pixels.  
         [0029]     The color-recombining unit  61  combines the color beams reflected from the reflective polarization valve  30  ( 31 ,  32 ) and the wire-grid polarizer  40  ( 41 ,  42 ). The projecting unit projects the combined color beams to form images. An X-cube is a practical color-recombining unit  61 . Polarizers  60 ,  62 ,  63  and half-wavelength lens  65 ,  66  are located between the color-recombining unit  61  and the wire-grid polarizer  40  ( 41 ,  42 ) respectively. The wire-grid polarizer can be practically used as the polarizer  60 ,  62 , and  63 . The half-wavelength lens  65 ,  66  are utilized for changing the directions of the color beams during the color-recombining procedure.  
         [0030]     The projecting unit  50  is a projecting lens, used for projecting the recombined color beams from the color-recombining unit  61  onto a screen  52  to form images. In accordance with the projecting direction and the position of the screen, we can group light projectors into types of front projection and rear projection. The front-projection light projector has a projector located at the same side of the audience, with its host system and the screen separated. The rear-projection light projector is also known as projection display, with its projector and the audience located at the opposite sides of the screen.  
         [heading-0031]     (1) Light Path of the Blue Beam  
         [0032]     The S-polarized white beam provided by light source  10  first passes through the dichroic mirror  20 , with the blue beam reflected and the rest passing through. The blue beam, maintaining S-polarized, goes through the wire-grid polarizer  40  and projects onto the reflective polarization valve  30 . Under light state, the reflective polarization valve  30  reflects P-polarized blue beam back to the wire-grid polarizer  40 . Next, the blue beam is reflected and passes through the polarizer  62  and half-wavelength lens  65 . The half-wavelength lens  65  transforms the P-polarized blue beam into the S-polarized state to ensure the blue beam entering the color-recombining unit  61  under S-polarized state.  
         [heading-0033]     (2) Light Path of the Green Beam  
         [0034]     The beam with the blue beam sieved out, goes through the dichroic mirror  21  for sieving out the red beam and allowing the green beam to pass through. The green beam, maintaining S-polarized, goes through the wire-grid polarizer  41  and projects onto the reflective polarization valve  31 . Under light state, the reflective polarization valve  31  reflects the P-polarized green beam back to the wire-grid polarizer  41 . Next, the green beam is reflected and passes through the polarizer  63  for transforming any possible S-polarized light into the P-polarized state, and then enters the color-recombining unit  61 .  
         [heading-0035]     (3) Light Path of the Red Beam  
         [0036]     The red beam, with the blue and green beams sieved out, passes in sequence of reflector  18 , focusing lens  70 , reflector  19  and focusing lens  71 . Next, the red beam, maintaining S-polarized, goes through the wire-grid polarizer  42  and projects onto the reflective polarization valve  32 . Under light state, the reflective polarization valve  32  reflects the P-polarized red beam back to the wire-grid polarizer  41 . Consequently, the red beam is reflected and passes through the polarizer  60  and half-wavelength lens  66 . The half-wavelength lens  66  transforms the P-polarized red beam into the S-polarized state, to ensure the red beam entering the color-recombining unit  61  under S-polarized state.  
         [0037]     In the foregoing embodiment, the S-polarized blue and red beams proceed with color recombining with the P-polarized green beam to differentiate from all the color beams recombining under S-polarized state in the prior art. The embodiment provides images with better luminance performance and lower contract. An energy-wavelength diagram of curves is shown in  FIG. 3 .  
         [0038]     The disclosed technique is suitable for any type of light projector, including front projection and rear projection without limitation in the projection display provided in the foregoing embodiment.  
         [0039]     In short, the invention achieves advantages as follows: 
        a. Use of the wire-grid polarizer provides advantages of higher heat-resistance, no limitation of the incident angle and no birefringence effects, to enhance the contrast luminance of the system. Moreover, because the wire-grid polarizer allows a larger incident angle, convergent light sources such as an elliptical lamp can be applied to shorten the light paths, achieve higher efficiency and a system of smaller volume. In consequence, the wire-grid polarizer is much easier to manufacture via processes of semiconductors and has lower cost.     b. Without using peculiar optical elements such as the Color-Quad, Color-Corner or X-plate, the entire system is easy to produce with lower costs.     c. The invention applies a telecentric optical system as a light source to overcome color gradients and provides better color uniformity.     d. The elliptical lamp used in the invention has a high efficiency, small volume but no need of peculiar optical elements, to achieve simplified light paths and easy production.     e. The polarized beams of high purity proceed with color recombining right after being transformed via the reflective polarizatioin valve to provide better image performance.        
 
         [0045]     Certain variations would be apparent to those skilled in the art, which variations are considered within the spirit and scope of the claimed invention.