Abstract:
A polarizing device contains a transparent plate and a birefringent material spread within the transparent plate. The birefringent material converts natural light propagating in the transparent plate into a first linearly polarized light and a second linearly polarized light, where the first and second linearly polarized lights are refracted toward different directions by the birefringent materials.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to flat display module, and more particularly, to flat display module with a single polarizer.  
         [0003]     2. Description of the Prior Art  
         [0004]     With the rapid development of technology, various kinds of intelligent informational products are available to people living in modern societies. For example, flat display modules, such as liquid crystal display modules, etc., have played quite an important role in informational products. Since a liquid crystal display (LCD) has the advantages of lightweight, low energy consumption, and free of radiation emission, the LCD is extensively applied in portable informational products, such as notebooks, personal digital assistants (PDAs), and cellular phones, etc. There is even a trend of gradually replacing the cathode ray tube (CRT) monitor of conventional personal computers and CRT TVs with flat display modules.  
         [0005]     Generally, a liquid crystal display module (LCM) is a key of the LCD, comprising an LCD panel and a back light module. The LCD panel is a liquid crystal molecular layer positioned in between two glass substrates. Each glass substrate is usually coated with an alignment layer for making the liquid crystal molecules align along a specific and parallel direction of a surface of the glass substrate. Transistors, electrodes, and other electrical devices on the glass substrate provide an electric field to the liquid crystal molecules that can be twisted by the magnitude of the electric field. The birefringent of the liquid crystal molecules can be changed by the direction of the liquid crystal molecules so that the direction of polarized light passing through the liquid crystal molecules is changed. Therefore, the display principle of the liquid crystal display panel is that polarizers are positioned on top and bottom surfaces of the liquid crystal display panel and the twist of the liquid crystal molecules is utilized to control the quantity of light exiting the panel to show images.  
         [0006]     Please refer to  FIG. 1  that is schematic diagram of display principles of a liquid crystal display panel according to prior art. The liquid crystal display panel includes two glass substrates  12  having electrodes, and liquid crystal molecules  14  positioned between the two glass substrates  12 . A first polarizer  16  and a second polarizer  18  are perpendicularly positioned with respect to each other&#39;s polarization on two sides of the glass substrates  12 . In the top-figure, no electric field is being applied and the natural light produced by a light source passes through the first polarizer  16  to form a linearly polarized light P″, and then the linearly polarized light “P” passes through the glass substrates  12  and a liquid crystal molecule layer  14 . It is noted that the liquid crystal molecule layer  14  has enough thickness to convert the linearly polarized light “P” 90 degrees into a linearly polarized light “S” for passage through the second polarizer  18 . On the other hand, exerting voltage can change the twist of the liquid crystal molecule layer  14  as is shown in the bottom-figure. For example, the twist of the liquid crystal molecule layer  14  parallels the electric field so that the linearly polarized light “P” passes through the liquid crystal molecule layer  14  without changing its polarization direction, resulting in not through the second polarizer  18 . As above-mentioned, the natural light is converted into linearly polarized light by the polarizer, and the linearly polarized light is converted into elliptically polarized light by exerting different electric field strengths to the liquid crystal molecules so that a gray image can be showed, so it is necessary that polarizers are positioned on two sides of the liquid crystal display plane in the LCM.  
         [0007]     However, the function of general polarizer allows specific directionally polarized light to pass through the polarizer, but absorbs light having polarizations perpendicular to the specific direction, meaning 50% of improperly polarized light is absorbed and causes a low utility rate of light. At the same time, the polarizers positioned on two sides of the liquid crystal display plane limit the size of the LCM so that the thickness of the LCM cannot decrease. Therefore, there are many problems that could be improved upon, such as the design of the LCM, the utility rate of light of the LCM, and the thickness of the LCM.  
       SUMMARY OF THE INVENTION  
       [0008]     It is therefore a primary objective of the claimed invention to provides a flat display module having a polarizing device to solve the above-mentioned problems.  
         [0009]     According to the claimed invention, the polarizing device includes a transparent plate having a light-incidence plane and a light-exiting plane, where natural light is capable of passing through the light-incidence plane into the transparent plate, and a birefringent material spread within the transparent plate. The birefringent material is capable of converting natural light propagating in the transparent plate into two perpendicular linearly polarized lights, and of scattering the two perpendicular linearly polarized lights with different refraction angles.  
         [0010]     Furthermore according to the claimed invention, the flat display module includes a backlight unit, a flat display panel positioned above the backlight unit, and a polarizer positioned on the display plane of the flat display panel. The backlight unit includes a transparent plate having a bottom surface and a top surface, the bottom surface having a plurality of diffusing patterns thereon for scattering light, and a light generator positioned at a side of the transparent plate for generating natural light that passes into the transparent plate. In addition, the backlight unit furthermore includes a plurality of birefringent particles distributed in the transparent plate, and the birefringent particles have a birefringence (double refraction, DR), air gap, or a material having one or more optical axes. The birefrigent particles are capable of converting natural light into two perpendicular linearly polarized lights, and of scattering the two perpendicular linearly polarized lights with different refraction angles.  
         [0011]     According to the claimed invention, a method of fabricating a flat display module provides a transparent plate including a light-exiting plane at a top surface of the transparent plate, and a plurality of diffusing patterns disposed on a bottom surface of the transparent plate. The transparent plate further includes a plurality of birefringent particles distributed therein and the birefringent particles are capable of converting light propagating in the transparent plate into two perpendicular linearly polarized lights. By adjusting the arrangement of angles and shapes of the birefringent particles in the transparent plate, the refracted two perpendicular linearly polarized lights can be made to propagate toward the light-exiting plane and a side surface or the bottom surface of the transparent plate respectively. Furthermore, by adjusting the shapes and the distribution densities of the diffusing patterns and the birefringent particles in the transparent plate, uniformed light leaves the transparent plate through the light-exiting plane. In addition, the method provides a flat display panel positioned above the light-exiting plane of the transparent plate, and a polarizer disposed on the display plane.  
         [0012]     The present invention&#39;s polarizing device utilizes a birefringent material spread within the transparent plate so that the natural light is converted into two perpendicular linearly polarized lights P and S. The linearly polarized lights P and S are scattered in different directions, so that only linearly polarized light P or linearly polarized light S is scattered out of the polarizing device and then into the flat display plane. The invention can replace a conventional first polarizer deposited under the flat display plane, and decrease the thickness and cost of the flat display plane.  
         [0013]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is schematic diagram of display principles of a liquid crystal display plane according to prior art.  
         [0015]      FIG. 2  is a cross-sectional view of the flat display module according to a first embodiment of the present invention.  
         [0016]      FIG. 3  is a magnified diagram of a part of the flat display module shown in  FIG. 2 .  
         [0017]      FIG. 4  is a cross-sectional view of the flat display module according to a second embodiment of the present invention.  
         [0018]      FIG. 5  is a cross-sectional view of the flat display module according to a third embodiment of the present invention.  
         [0019]      FIG. 6  is a cross-sectional view of the flat display module according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]     Please refer to  FIG. 2  and  FIG. 3 .  FIG. 2  is a cross-sectional view of a flat display module  50  according to a first embodiment of the present invention, and  FIG. 3  is a magnified diagram of a part of the flat display module  50  shown in  FIG. 2 . The flat display module  50  is a liquid crystal display module (LCM) that includes a back light module  52 , and a liquid crystal display plane  54  having a display plane  54   a  and positioned above the back light module  52 . In addition, the flat display module  50  has only one polarizer  60  positioned above the display plane  54   a  of the liquid crystal display module  54 .  
         [0021]     The back light module  52  includes a light generator  56  and a polarizing device  62 , and the light generator  56  is positioned at a side of the polarizing device  62 , for generating natural light into the polarizing device  62 . The polarizing device  62  includes a transparent plate  58  having a light-incidence plane  58   a  and a light-exiting plane  58   b . The light-incidence plane  58   a  is nearer the light generator  56 , for receiving the natural light generated by the light generator  56 , and the light-exiting plane  58   b  is a top surface of the transparent plate  58 , for allowing scattered light in the transparent plate  58  to pass through the light-exiting plane  58   b  into the liquid crystal display plane  54 . Furthermore, the function of the transparent plate  58  is for guiding the paths of scattering light and uniforming scattering light in the transparent plate  58 . The material of the transparent plate  58  can be a light guide acryl, or other light guide materials, such as a plastic material, polymethylmethacrylate (PMMA), polycarbonate (PC), ZEONOR®, and ARTON®, and can be made by injection-molding. A plurality of diffusing patterns  64  (preferably protruding dot patterns) is positioned on a bottom surface  58   c  of the transparent plate  58 , for breaking total reflecting light into scattering light, and changing the route of light to enhance the uniformitivity of the liquid crystal display plane  54 .  
         [0022]     The polarizing device  62  further includes a birefringent material  66  spreading in the transparent plate  58 . In the embodiment, the birefringent material  66  is a plurality of birefringent particles distributed in the transparent plate  58 , and the birefringent particles have a birefringence (double refraction, DR) and are capable of converting natural light into two perpendicularly linearly polarized lights, such as a linearly polarized light P and a linearly polarized light S, and of scattering the two perpendicular linearly polarized light with different refraction angles. As shown in  FIG. 3 , when the natural light passes through the light-incidence plane  58   a  into the transparent plate  58  and contacts the birefringent material  66 , the birefringent material  66  converts the natural light into the linearly polarized light P (shown as the solid line) and the linearly polarized light S (shown as the dotted line) which polarizes perpendicular to the linearly polarized light P, and scatters the two perpendicular linearly polarized lights P and S with different refraction angles. In this embodiment, any material that has the above-mentioned features can be applied in the present invention as the birefringent material  66  in the transparent plate  58 , such as quartz and liquid crystal material. Generally, the material having an air gap or one or more optic axes can be the birefringent material  66  in the present invention.  
         [0023]     It is noted that adjusting the arrangement of angles, positions, and shapes of the birefringent particles in the transparent plate  58  can control refraction angles of linearly polarized light P and S to scatter the linearly polarized light P toward the light-incidence plane  58   b  and the linearly polarized light S toward the bottom surface  58   c  of the transparent plate  58 , meaning the birefringent material  66  converts natural light into two perpendicular linearly polarized lights so that the linearly polarized light P always passes throughout the light-incidence plane  58   b . In this design, a polarizer does not need to be positioned between the liquid crystal display panel  54  and backlight module  52 , but linearly polarized light P scattered by the transparent plate  58  is directly utilized to coordinate with the polarizer  60  positioned above the liquid crystal display panel  54  to display image. In addition, for achieving the purpose of the above-mentioned and having better diffusion routing of light in the polarizing device  62 , the distribution densities of the birefrigent material  66  in the transparent plate may not be uniform. As shown in  FIG. 2 , the distribution density of the birefringent material  66  closer to the light-incidence plane  58   a  is less than the distribution density of the birefringent material  66  farther from the light-incidence plane  58   a  in the transparent plate  58 , to control the routes of light. According to the present invention, the birefringent particles of the birefringent material  66  in different places of the transparent plate  58  may have different arranging angles, or the shapes of birefringent particles are selectively changed to adjust the refracted paths of the linearly polarized lights P and S. Moreover, utilizing the optic axis or the air gaps of the birefringent particles can effectively separate the linearly polarized lights P and S.  
         [0024]     The polarizing device  62  of the present invention further includes a polarization conversion mechanism  74  having a quarter wave plate  70  and a bottom reflector  72  positioned at the bottom surface  58   c  of the transparent plate  58  respectively. As shown in  FIG. 3 , the linearly polarized light S scatted by the birefringent material  66  toward the bottom surface  58   c  of the transparent plate  58  passes through the quarter wave plate  70  and converts into a circularly polarized light C 1 , and then the circularly polarized light C 1  passes into the reflector  72  and is rebounded by the bottom reflector  72  to form a circularly polarized light C 2  whose rotational direction is opposite to the circularly polarized light&#39;s C 1 . The circularly polarized light C 2  passes through the quarter wave plate  70  and converts into the linearly polarized light P to pass through the light-exiting plane  58   b  into the liquid crystal display plane  54 . Therefore, the linearly polarized light S separated by the birefringent material  66  can be converted into the linearly polarized light P by the polarization conversion mechanism  74 , and the linearly polarized light P is re-used to enhance the whole brightness of the flat display module  50 .  
         [0025]     In order to improve brightness and utility rate of light, the back light module  52  of the present invention can selectively include a plurality of side reflectors  76  positioned on the surface of the transparent plate  58  except at the light-incidence plane  58   a  and the light-exiting plane  58   b , and can selectively comprise at least an optic film  68  on the polarizing device  62 . The optic film  68  can be a prism or a diffusion film.  
         [0026]     Therefore, as above-mentioned, the method of fabricating a flat display module  50  according to the present invention comprises:  
         [0027]     Step 1: providing a transparent plate  58 , a plurality of diffusion patterns  64  disposed on a bottom surface  58   c  of the transparent plate  58 , and the transparent plate  58  comprising a plurality of birefringent particles  66  formed with birefringent material distributed therein and the birefringent particles being capable of converting light propagating in the transparent plate  58  into two perpendicular linearly polarized lights P and S.  
         [0028]     Step 2: adjusting the arrangement of angles and shapes, optic axis, and/or air gap of the birefringent particles in the transparent plate to make the refracted linearly polarized lights P and s propagating toward the light-exiting plane  58   b  and a side surface or the bottom surface  58   c  of the transparent plate  58  respectively.  
         [0029]     Step 3: adjusting the distribution densities of the diffusing patterns  64  and the birefringent particles such that properly polarized light leaves the transparent plate  58  uniformly through the light-exiting plane  58   b.    
         [0030]     Step 4: providing a flat display panel  54  positioned above the light-exiting plane  58   b  of the transparent plate  58  and having a display plane  54   a.    
         [0031]     Step 5: providing a polarizer  60  disposed on the display plane  54   a.    
         [0032]     The polarizing device  62  is the combination of the transparent plate  58 , birefringent material  66 , and diffusion patterns  64 . A method of disposing the birefringent particles formed with birefringent material  66  into the transparent plate  58  is by doping, drawing, or pouring the birefringent particles into the materials of the transparent plate  58 . Also, the method of the present invention further comprises positioning a polarization conversion mechanism  74  under the transparent plate  58 , and the polarization conversion mechanism  74  has a quarter wave plate  70  and a bottom reflector  72  for improving the utility rate of light.  
         [0033]      FIG. 4  is a cross-sectional view of the flat display module  50  according to second embodiment of the present invention. For convenient illustration in  FIG. 4 , similar components retain the same label numbers that were used in  FIG. 2 . In this second embodiment, the bottom surface of the liquid crystal display plane  54  has a bottom polarizer  60 a for filtering light generated by the back light module  52  for allowing the linearly polarized light P to pass through the bottom polarizer  60 a but absorbing the linearly polarized light S. Therefore, the bottom polarizer  60 a can ensure that only the linearly polarized light P passes into the liquid crystal display panel  54  while blocking the linearly polarized light S so that the liquid crystal display plane  54  has the best image. The linearly polarized light S refracted from the birefringent material  66  to the bottom surface  58   c  passes through the quarter wave plate  70  and is rebounded by the bottom reflection layer  72 , and then passes through the quarter wave plate  70  again to convert to linearly polarized light P that can be transmitted to the liquid crystal display plane  54 .  
         [0034]     In addition, in this embodiment, a side of the polarizing device  62  further has a quarter wave plate  78  positioned between the transparent plate  58  and the side reflection layer  76 . When the light is refracted by the birefringent material  66 , most linearly polarized light P directly enters into liquid crystal display plane  54 , but the linearly polarized light S is converted to linearly polarized light P by the quarter wave plate  78  and the side reflection layer  76  on the side of the polarizing device  62  to improve the utility rate of light.  
         [0035]     The method of fabricating the polarizing device is not limited to application in edge-type backlight modules, but also is applicable to a direct-type backlight module by changing the location of the light generator to the bottom of polarizing device as shown in  FIG. 5 , which is a cross-sectional view of the flat display module  50  according to a third embodiment of the present invention. For convenient illustration in  FIG. 5 , similar components retain the same label numbers that were used in  FIG. 2 . In this embodiment, the flat display module  50  has a direct-type light source as shown in  FIG. 5 . A plurality of light generators  56  are positioned under the polarization conversion mechanism  74 , and the bottom reflection layer  72  includes a plurality of openings corresponding to the light generators  56  for letting the light from the light generators  56  enter into the polarizing device  62 .  
         [0036]     Shown in  FIG. 6  is a cross-sectional view of the flat display module  50  according to a fourth embodiment of the present invention. In this embodiment, the light generator  56  is positioned under the polarizing device  62  to form a direct-type backlight module. The bottom surface of the liquid crystal display plane includes a bottom polarizer  60   a  for filtering light to allow linearly polarized light P to pass through the bottom polarizer  60   a  but absorbing linearly polarized light S. Accordingly, the bottom polarizer  60   a  can further ensure that only the linearly polarized light P generated from the backlight module  52  passes into the liquid crystal display plane  54  while preventing linearly polarized light S so that the liquid crystal display plane  54  has the best image. In this embodiment, at least a polarization conversion mechanism can be selectively positioned on a side of the polarizing device  62 , which means the quarter wave plate  78  can be deposited between the side reflection layer  76  and the transparent plate  58  to change the linearly polarized light S propagating to a side of the polarizing device  62  into linearly polarized light P to improve the utility rate of light.  
         [0037]     Compared to prior art, the present invention provides a polarizing device in the back light module, and the polarizing device includes a birefringent material that can convert the natural light into two perpendicular linearly polarized lights and scatter the two perpendicular linearly polarized lights with different refraction angles. The present invention utilizes the polarizing device to substitute for a conventional polarizer in the flat display module that can effectively decrease the thickness and cost of the flat display module. Also, by adjusting the arrangement of angles and shapes of the birefringent material in the polarizing device and diffusing patterns of the bottom of the polarizing device can control the whole brightness and uniformity of the flat display module and improve the utility rate of the light.  
         [0038]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.