Abstract:
A method is used to design an optical engine for increasing performance. The method is directed to positioning dichroic mirrors at proper locations, such as, on the light paths of red, green, and blue lights, or on the locations where the optical noises are to be filtered. In such manner, the dichroic mirrors can reflect the optical noises of the red, green, and blue lights generated by the optical engine into the space other than the optical engine. As a result, the red, green, and blue lights passing through the dichroic mirrors can each be a pure light.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims the priority benefit of Taiwan application serial no. 90100337, filed Jan. 8, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The present invention relates to an optical engine design. More particularly, the present invention relates to a method for improving performance of an optical engine design, where a dichroic mirror is properly positioned in an optical engine, so as to reduce optical noises in the system, and reduce the thermal effect from the optical beam. The contrast and the saturation of color coordinate of the optical engine can be effectively improved.  
           [0004]    2. Description of Related Art  
           [0005]    Recently, liquid crystal display (LCD) device has been widely applied in the daily life, such as liquid crystal TV, portable computer, or liquid crystal projector. Usually, a projecting system of a liquid crystal projector includes an optical engine system that is categorized into two types. One is an off axial type, and the other is an on-line type. The off axial type has a property that the incident light source and the outputting light source are not located on the same plane, while the on line type has a property that the incident light source and the outputting light source are located on the same plane. The current projecting manner of the liquid crystal projector can further be categorized into a front projecting manner and a back projecting manner. The current design of the liquid crystal projector more often takes the back projecting manner and on line type. In the technology field of liquid crystal projector, the projecting quality and the weight and dimension of the optical engine are the main concerned issues.  
           [0006]    [0006]FIG. 1 is system block diagram, schematically illustrating a conventional optical engine system of a liquid crystal projector with reflection type. In FIG. 1, the optical engine system  100  uses light source  102  that emits a white light W. The white light travels through a filter, such that the ultra-violet component and the infra-red component are filtered away. The light continuously transmits through an S-P converter, where S represents S-polarization and P represents P-polarization. As a result, a white light WS with S-polarization is obtained and is incident onto a reflection mirror  104 . After reflection, the white light WS is incident onto a dichroic mirror  106  that divides the incident white light WS into a BSGS mixed light and a RS red light.  
           [0007]    The BSGS mixed light is the component mixed by blue and green components and is reflected by the dichroic mirror  106 , while red light RS is the component transmitting through the dichroic mirror  106 . The red light RS continuously travels onto a reflection mirror  108  and then is reflected onto a polarization splitter  110 . The polarization splitter  110  reflects the S-polarization component of the red light RS onto a red liquid crystal panel  112 . The BSGS mixed light reflected by the dichroic mirror  106  travels through a dichroic mirror  114 , whereby the green component and the blue component are respectively split into a green light GS through reflection and a blue light BS through transmission. The green light GS travels onto a polarization splitter  116  that reflects the S-polarization component of the green light GS onto a green liquid crystal panel  118 . The transmitting blue light BS travels on to a polarization splitter  120  that reflects the S-polarization component of the blue light BS onto a blue liquid crystal panel  122 . Then, the red liquid crystal panel  112 , the green liquid crystal panel  118 , and the blue liquid crystal panel  122  respectively reflect the incident red light RS, the green light GS, and the blue light BS, and change the S-polarization into P-polarization, whereby a red light RP, a green light GP, and a blue light BP travel onto an X-cube dichroic prism  124  for recombination. After recombination, the lights travels to a projector lens  126  and then are projected onto a screen (not shown).  
           [0008]    [0008]FIG. 2 is system block diagram, schematically illustrating a conventional optical engine system of a liquid crystal projector with transmitting type. In FIG. 2, an optical engine system  200  has a light source  202  that emits a white light W. The white light W is converted by an S-P converter  203  into an S-polarization white light WS. The white light WS is reflected by a reflection mirror  204  onto a dichroic mirror  206 . The dichroic mirror  206  splits the white light WS into a mixed light through reflection and a red light through transmission. The mixed light includes a mix of blue and green components. The red light RS is reflected by a reflection mirror  208  onto a red liquid crystal panel  210  and reaches to an X-cube dichroic prism  212 . The blue component and the green component of the mixed light is split by a dichroic mirror  214  into a blue light BS through transmission and a green light GS through reflection. The green light GS is reflected onto a green liquid crystal panel  211 , and then reaches to the X-cube dichroic prism  212 . The transmitted blue light BS is then further reflected by a dichroic mirror  218 , and then the component of S-polarization travels onto a reflection mirror  220 . The reflection mirror  220  reflects the blue light onto a blue liquid crystal panel  222 . The blue light then enters the X-cube dichroic prism  212 . The red light RS, the green light GS, and the blue light BS are recombined by the X-cube dichroic prism  212 , and are projected onto a screen (not shown) by a projection lens  224 .  
           [0009]    [0009]FIG. 3 is a system block diagram, schematically illustrating another conventional optical engine system of a liquid crystal projector with reflection type. In FIG. 3, an optical engine system  300  has a light source  302  that emits white light W. The white light W is converted into a white light WS with S-polarization through an S-P converter. Three components R, G, B of the white light WS are properly reflected onto red, green, blue liquid crystal panels  308 ,  310 ,  312 , respectively, through a polarization splitter  304  and a dichroic mirror  306 . The red, green, blue liquid crystal panels  308 ,  310 ,  312  then reflect back the lights through the same light path. As a result, the red light, the green light, and the blue light are recombined and projected onto a screen through a projection lens.  
           [0010]    In the above conventional liquid crystal projectors, no matter whether the reflection type or the transmission type is used, three components of red, green, and blue of the lights travelling through the dichroic mirror or polarization splitter are not purely monochromatic. This results in optical noise. The optical noise cannot be controlled and reduced by liquid crystal panel, and aggravates the thermal effect for each optical path. As a result, when the liquid crystal panel is at a dark state, the optical noise causes a stronger contrast of the optical noise. When it is at a bright state, the phenomenon of color impurity may occur, and even results in an issue of thermal effect that affects the transmission rate, and then affects the projection quality of the optical engine system.  
         SUMMARY OF THE INVENTION  
         [0011]    One object of the invention is to introduce a method for effective improving performance of a system of the liquid crystal projector by properly positioning the dichroic mirror in the optical engine system, so that the optical noise would be reflected away from the optical engine system.  
           [0012]    As embodied and broadly described herein, the invention provides a method for assembling an optical engine with improved performance. The method includes positioning dichroic mirrors at proper locations, such as, on the light paths of red, green, and blue lights, or on the locations where the optical noises are to be filtered. In such manner, the dichroic mirrors can reflect the optical noises of the red, green, and blue lights generated by the optical engine into the space other than the optical engine. As a result, the red, green, and blue lights passing through the dichroic mirrors can each be a pure light. This can improve the light contrast in the optical engine and the saturation level of color coordinate. The performance can be effectively improved.  
           [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
         [0015]    [0015]FIG. 1 is system block diagram, schematically illustrating a conventional optical engine system of a liquid crystal projector with reflection type;  
         [0016]    [0016]FIG. 2 is system block diagram, schematically illustrating a conventional optical engine system of a liquid crystal projector with transmitting type;  
         [0017]    [0017]FIG. 3 is a system block diagram, schematically illustrating another conventional optical engine system of a liquid crystal projector with reflection type;  
         [0018]    [0018]FIG. 4 is a system block diagram, schematically illustrating an optical engine system of a liquid crystal projector with reflection type, according to one preferred embodiment of this invention;  
         [0019]    [0019]FIG. 5 is a system block diagram, schematically illustrating an optical engine system of a liquid crystal projector with transmission type, according to one preferred embodiment of this invention; and  
         [0020]    [0020]FIG. 6 is a system block diagram, schematically illustrating another optical engine system of a liquid crystal projector with reflection type, according to one preferred embodiment of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    In the invention, the dichroic mirrors are positioned at the proper locations in the optical engine, such as on the light path of each the red, green, and blue lights, just in front of liquid crystal panel. This arrangement can reduce the optical noise of the optical engine, the thermal effect due to the light beam, and improve the light contrast in the optical engine and the saturation level of color coordinate.  
         [0022]    [0022]FIG. 4 is a system block diagram, schematically illustrating an optical engine system of a liquid crystal projector with reflection type, according to one preferred embodiment of this invention. In FIG. 4, the optical engine  400  includes a light source  402  that can emit white light W. The white light W travels through an S-P converter, whereby a white light with S-polarization WS is generated. The white light WS is incident onto a reflection mirror  404 , which then reflects the white light WS onto a dichroic mirror  406 . The dichroic mirror  406  splits the white light WS into a mixed light BSGS of blue component and green component through reflection, and a red light RS through direct transmission. The transmitted red light RS is then incident onto a reflection mirror  408  and then is reflected onto a dichroic mirror  428 , and continuously travels to a polarization splitter  410 . The polarization splitter  410  then reflects the S-polarization component of the red light RS onto a red liquid crystal panel  412 . Returning to the dichroic mirror  406 , the mixed light BSGS travels onto a dichroic mirror  414 , which split the mixed light BSGS into a green light GS through reflection and a blue light BS through transmission. The reflected green light GS travels through a dichroic mirror  430  and enters a polarization splitter  416 . The polarization splitter  416  then reflects the S-polarization component of the green light GS onto a green liquid crystal panel  418 . The blue light BS travels through a dichroic mirror  432  and enters onto a polarization splitter  420 . The polarization splitter  420  then reflects the S-polarization component of the blue light BS onto a blue liquid crystal panel  422 .  
         [0023]    The red liquid crystal panel  412 , the green liquid crystal panel  418 , and the blue liquid crystal panel  422  respectively reflect the incident red light RS, the green light GS, and the blue light BS, and change the S-polarization into P-polarization, whereby a red light RP, a green light GP, and a blue light BP travel onto an X-cube dichroic prism  424  for recombination. After recombination, the lights travels to a projector lens  426  and then are projected onto a screen (not shown).  
         [0024]    In the foregoing, the dichroic mirrors  428 ,  430 ,  432  can reflect optical noises of the red, green, and blue lights away from the optical engine  400 . In principle, the angle of the dichroic mirrors  428 ,  430 ,  432  can be set to any designed angle and any location on the light path, which can reflects the optical noises away from the optical engine  400 .  
         [0025]    [0025]FIG. 5 is a system block diagram, schematically illustrating an optical engine system of a liquid crystal projector with transmission type, according to one preferred embodiment of this invention. In FIG. 5, an optical engine system  500  has a light source  502  that emits a white light W. The white light W is converted by an S-P converter  503  into an S-polarization white light WS. The white light WS is reflected by a reflection mirror  504  onto a dichroic mirror  506 . The dichroic mirror  506  splits the white light WS into a mixed light through reflection and a red light through transmission. The mixed light includes a mix of blue and green components. The red light RS travels through a dichroic mirror  526  and reaches to a reflection mirror  508 . The reflection mirror  508  reflects the red light onto a red liquid crystal panel  510  and the red light reaches to an X-cube dichroic prism  512 . The blue component and the green component of the mixed light is split by a dichroic mirror  514  into a blue light BS through transmission and a green light GS through reflection. The green light GS is reflected onto a dichroic mirror  528  and enters a green liquid crystal panel  51   1 , and then reaches to the X-cube dichroic prism  512 . The transmitted blue light BS is then further reflected by a dichroic mirror  518 , and then the component of S-polarization travels through a dichroic mirror  530  and in incident onto a reflection mirror  520 . The reflection mirror  520  reflects the blue light onto a blue liquid crystal panel  522 . The blue light then enters the X-cube dichroic prism  512 . The red light RS, the green light GS, and the blue light BS are recombined by the X-cube dichroic prism  512 , and are projected onto a screen (not shown) by a projection lens  524 .  
         [0026]    In the foregoing, the dichroic mirrors  526 ,  528 ,  530  can reflect optical noises of the red, green, and blue lights away from the optical engine  500 . In principle, the angle of the dichroic mirrors  526 ,  528 ,  530  can be set to any designed angle and any location on the light path, which can reflects the optical noises away from the optical engine  500 .  
         [0027]    [0027]FIG. 6 is a system block diagram, schematically illustrating another optical engine system of a liquid crystal projector with reflection type, according to one preferred embodiment of this invention. In FIG. 6, an optical engine system  600  has a light source  602  that emits a white light W. The white light W is converted into a white light WS with S-polarization through an S-P converter (not shown). Three components R, G, B of the white light WS are properly reflected onto red, green, and blue liquid crystal panels  608 ,  610 ,  612 , respectively, through a polarization splitter  604  and a dichroic mirror  606 . Before the red, green, and blue lights enter the liquid crystal panels  608 ,  610 ,  612 , each the lights also additionally travel through the dichroic mirrors  614 ,  616 ,  618 , respectively. The red, green, blue liquid crystal panels  608 ,  610 ,  612  then reflect back the lights through the same light path. As a result, the red light, the green light, and the blue light are recombined and projected onto a screen through a projection lens.  
         [0028]    In the foregoing, the dichroic mirrors  614 ,  616 ,  618  can reflect optical noises of the red, green, and blue lights away from the optical engine  600 . In principle, the angle of the dichroic mirrors  614 ,  616 ,  618  can be set to any designed angle and any location on the light path, which can reflects the optical noises away from the optical engine  600 .  
         [0029]    In conclusion, the invention has at least the advantages as follows:  
         [0030]    1. The invention includes a few of dichroic mirrors, which are positioned at the proper locations in the optical engine, such as just in front of liquid crystal panel. This arrangement can reduce the optical noise of the optical engine, the thermal effect due to the light beam. The projection quality is effectively improved.  
         [0031]    2. The invention includes a few of dichroic mirrors, which are positioned at the proper locations in the optical engine, such as on the light path of each the red, green, and blue lights. This arrangement can improve the light contrast in the optical engine and the saturation level of color coordinate. The projection quality is effectively improved.  
         [0032]    3. The invention uses dichroic mirrors to achieve the filtering effect on the optical noises. The whole design principle of the optical engine is not necessary to be greatly modified, and the projection quality can be greatly improved. The fabricating cost still remains without raising.  
         [0033]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.