Patent Publication Number: US-2013250192-A1

Title: 3d display devices

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a 3D display device, and in particular to a 3D display device with a reflective barrier. 
     2. Description of the Related Art 
     In recent years, continuous advancement of display technologies has resulted in an increasing demand for a higher quality of display, such as higher image resolution, brightness, and so on. For 3D image display, high image resolution and high brightness are priorities. 
     For current 3D image display technologies, a fixed barrier is mainly utilized for controlling images viewed by the respective eyes of an observer. According to the visual characteristics of human eyes, when two images with the same content but different parallaxes are respectively viewed by an observer&#39;s left eye and right eye, two images are overlapped and interpreted as a 3D image (stereoscopic image) by his brain. 
     It should be noted that a 3D image is produced by the fixed barrier in a spatial-multiplexed manner, such that the resolution is reduced in half at some axis and light will be absorbed by the barriers. Also, the 3D display with fixed barrier cannot display 2D images but 3D images. Thus, the 3D display with fixed barrier cannot be extensively applied. 
     To solve said issue, a switchable barrier has been proposed and applied. The display with switchable barrier (switchable 2D/3D display) is able to display 2D images when the switchable barrier is turned off and display 3D images when the switchable barrier is turned off Specifically, in a conventional switchable 2D/3D display, a normally white mode TN-LC cell is usually used as the switchable barrier. Nonetheless, the switchable 2D/3D display should improve quality, such as brightness, contrast, symmetrical viewing angles, and so on. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the invention provides a 3D display device, comprising: a backlight system with a reflector disposed thereunder; a reflective barrier disposed above the backlight system; and a liquid crystal display (LCD) panel disposed above the backlight system. 
     In an embodiment, the reflective barrier comprises a plurality of protrusions. The protrusion comprises an anti-reflective layer and a reflective layer disposed on the anti-reflective layer. 
     In an embodiment, the reflective barrier comprises a first polarizer, a switchable barrier panel and a second polarizer. The switchable barrier panel is disposed between the first polarizer and the second polarizer. The first polarizer has a transmission axis and an absorption axis. The switchable barrier panel comprises a first substrate, a twisted nematic (TN) liquid crystal layer and a second substrate. The twisted nematic (TN) liquid crystal layer is disposed between the first substrate and the second substrate. When the switchable barrier panel is turned on, the twisted nematic (TN) liquid crystal layer is divided into an on-state area and an off-state area in an alternate arrangement. In the on-state area, liquid crystals are vertically arranged. In the off-state area, liquid crystals are horizontally arranged. The second substrate has a thickness less than a distance between the two on-state areas or two off-state areas. The second polarizer comprises a high-refractive-index polymer layer and a low-refractive-index polymer layer in an alternate arrangement. The second polarizer has a transmission axis and a reflection axis. The transmission axis of the first polarizer and the transmission axis of the second polarizer are substantially perpendicular to each other. The reflection axis of the second polarizer and the transmission axis of the first polarizer are substantially parallel to each other. 
     In an embodiment, the reflective barrier comprises a first polarizer, a switchable barrier panel and a second polarizer. The second polarizer is inserted into the switchable barrier panel. The first polarizer has a transmission axis and an absorption axis. The switchable barrier panel comprises a first substrate, a twisted nematic (TN) liquid crystal layer and a second substrate. The twisted nematic (TN) liquid crystal layer is disposed between the first substrate and the second polarizer. When the switchable barrier panel is turned on, the twisted nematic (TN) liquid crystal layer is divided into an on-state area and an off-state area in an alternate arrangement. In the on-state area, liquid crystals are vertically arranged. In the off-state area, liquid crystals are horizontally arranged. The second polarizer comprises a high-refractive-index polymer layer and a low-refractive-index polymer layer in an alternate arrangement. The second polarizer has a transmission axis and a reflection axis. The transmission axis of the first polarizer and the transmission axis of the second polarizer are substantially perpendicular to each other. The reflection axis of the second polarizer and the transmission axis of the first polarizer are substantially parallel to each other. 
     In an embodiment, the reflective barrier comprises a first polarizer, a switchable barrier panel, a second polarizer and a third polarizer. The switchable barrier panel is disposed between the first polarizer and the second polarizer. The third polarizer is disposed on the second polarizer. The first polarizer has a transmission axis and an absorption axis. The switchable barrier panel comprises a first substrate, a twisted nematic (TN) liquid crystal layer and a second substrate. The twisted nematic (TN) liquid crystal layer is disposed between the first substrate and the second substrate. When the switchable barrier panel is turned on, the twisted nematic (TN) liquid crystal layer is divided into an on-state area and an off-state area in an alternate arrangement. In the on-state area, liquid crystals are vertically arranged. In the off-state area, liquid crystals are horizontally arranged. The second substrate has a thickness less than a distance between the two on-state areas or two off-state areas. The second polarizer comprises a high-refractive-index polymer layer and a low-refractive-index polymer layer in an alternate arrangement. The second polarizer has a transmission axis and a reflection axis. The third polarizer has a transmission axis and an absorption axis. The transmission axis of the first polarizer and the transmission axis of the second polarizer are substantially perpendicular to each other. The reflection axis of the second polarizer and the transmission axis of the first polarizer are substantially parallel to each other. The transmission axis of the second polarizer and the transmission axis of the third polarizer are substantially parallel to each other. The absorption axis of the third polarizer and the reflection axis of the second polarizer are substantially parallel to each other. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawing, wherein: 
         FIG. 1A  shows a cross-section view of a 3D display device according to an embodiment of the invention; 
         FIG. 1B  shows light paths within a 3D display device according to an embodiment of the invention; 
         FIG. 2A  shows a cross-section view of a 3D display device according to an embodiment of the invention; 
         FIG. 2B  shows a light path within a 3D display device according to an embodiment of the invention; 
         FIG. 2C  shows a light path within a 3D display device according to an embodiment of the invention; 
         FIG. 3A  shows a cross-section view of a 3D display device according to an embodiment of the invention; 
         FIG. 3B  shows a light path within a 3D display device according to an embodiment of the invention; 
         FIG. 3C  shows a light path within a 3D display device according to an embodiment of the invention 
         FIG. 4A  shows a cross-section view of a 3D display device according to an embodiment of the invention; and 
         FIG. 4B  shows sunlight readability of a 3D display device according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to one embodiment of the invention, referring to  FIG. 1A , a 3D display device with fixed barrier is illustrated. The 3D display device  10  comprises a backlight system  12 , a reflective barrier  16  and a liquid crystal display (LCD) panel  18 . The liquid crystal display (LCD) panel  18  is disposed above the reflective barrier  16 . The liquid crystal display (LCD) panel  18  is a transmissive display panel for displaying images. The reflective barrier  16  is disposed between the liquid crystal display (LCD) panel  18  and the backlight system  12 . 
     In this embodiment, the backlight system  12  comprises at least one light source  20 , one light guide plate  22 , and one reflector  14 . The reflector  14  is disposed under the light guide plate  22 . Additionally, the reflector  14  may comprise metal such as aluminum (Al), silver (Ag) or chromium (Cr). 
     In this embodiment, the reflective barrier  16  comprises a plurality of protrusions  24  on a substrate  16 ′ as fixed barriers. The protrusion  24  comprises an anti-reflective layer  26  on the substrate  16 ′ and a reflective layer  28  disposed on the anti-reflective layer  26 . The anti-reflective layer  26  may comprise resin or metal oxide such as chromium oxide (CrO x ). The anti-reflective layer  26  can absorb the ambiance light and maintain the contrast ratio for outdoor readability. The reflective layer  28  may comprise metal such as aluminum (Al), silver (Ag) or chromium (Cr). In an embodiment, when metal is used as the reflective layer  28 , the corresponding metal oxide can be used as the anti-reflective layer  26 , for example when “chromium (Cr)” is used as the reflective layer  28 , the corresponding metal oxide “chromium oxide (CrO x )” is used as the anti-reflective layer  26 . 
     Referring to  FIG. 1B , in this embodiment, within the 3D display device  10 , a part of light  1  emitted from the light source  20  can be alternately reflected between the reflective layer  28  and the reflector  14  as finally passing through an window  2  between the protrusions  24 . The process of alternately reflection improves light recycling efficiency to enhance total brightness. 
     In an embodiment, the brightness of the 3D display device  10  (with an aperture ratio of 30%) is improved from 30% (conventional fixed-barrier-type 3D display device) to about 69%. 
     In this embodiment, some structural features of the 3D display device  10  are: (1) the liquid crystal display panel  18  is a transmissive display panel for displaying images; (2) the reflector  14  is disposed under the light guide plate  22  of the backlight system  12 ; (3) the reflective barrier  16  is located between the liquid crystal display panel  18  and the backlight system  12 ; (4) the reflective barrier  16  is composed of high-reflective material; and (5) the 3D display device  10  is a fixed-barrier-type 3D display device. 
     According to another embodiment of the invention, referring to  FIG. 2A , a 3D display device with switchable barrier is illustrated. A 3D display device  50  comprises a backlight system  52 , a reflective barrier  56  and a liquid crystal display (LCD) panel  58 . The liquid crystal display (LCD) panel  58  is disposed above the reflective barrier  56 . The liquid crystal display (LCD) panel  58  is a transmissive display panel for displaying images. The reflective barrier  56  is disposed between the liquid crystal display (LCD) panel  58  and the backlight system  52 . In another embodiment, the liquid crystal display (LCD) panel  58  is disposed between the reflective barrier  56  and the backlight system  52  (not shown). 
     In this embodiment, the backlight system  52  comprises at least one light source  60 , one light guide plate  62  and one reflector  54 . The reflector  54  is disposed under the light guide plate  62 . Additionally, the reflector  54  may comprise metal such as aluminum (Al), silver (Ag) or chromium (Cr). 
     In this embodiment, the reflective barrier  56  comprises a first polarizer  64 , a switchable barrier panel  66  and a second polarizer  68 . The switchable barrier panel  66  is disposed between the first polarizer  64  and the second polarizer  68 . 
     The first polarizer  64  has a transmission axis  69  and an absorption axis  69 ′. The switchable barrier panel  66  comprises a first substrate  70 , a twisted nematic (TN) liquid crystal layer  72  and a second substrate  74 . The twisted nematic (TN) liquid crystal layer  72  is disposed between the first substrate  70  and the second substrate  74 . There are driving electrode patterns (not shown) on the first substrate  70  and the second substrate  74 . The liquid crystal layer  72  is between the driving electrode patterns of the first substrate  70  and the second substrate  74 . 
     The first substrate  70  and the second substrate  74  may be glass or transparent plastic film. As the switchable barrier panel  66  turned on, the twisted nematic (TN) liquid crystal layer  72  is divided into an on-state area  76  and an off-state area  78  in an alternate arrangement. As shown in  FIG. 2A , liquid crystals  80  are vertically arranged due to vertical electric field in the on-state area  76  and stay original arrangement in the off-state area  78 . Through the first polarizer  64  and the second polarizer  68 , the reflective barrier  56  becomes a barrier. At the time, the 3D display device  50  is able to display 3D images. By contrast, when the switchable barrier panel  66  is turned off (not shown), the 3D display device  50  is able to display 2D images. 
     In an embodiment, the second substrate  74  has a thickness less than a distance  82  between two the on-state areas ( 76 ,  76 ) or two off-state areas ( 78 ,  78 ). 
     In detail, the second polarizer  68  comprises a high-refractive-index polymer layer  84  and a low-refractive-index polymer layer  86  in an alternate arrangement, as shown in  FIG. 2A . Some of the light will be reflected by the low-refractive-index polymer layer  86 . The second polarizer  68  has both polarization function and reflection function. Additionally, the second polarizer  68  has a transmission axis  90  and a reflection axis  92 . 
     Still referring to  FIG. 2A , in this embodiment, specifically, the transmission axis  69  of the first polarizer  64  and the transmission axis  90  of the second polarizer  68  are substantially perpendicular to each other. The reflection axis  92  of the second polarizer  68  and the transmission axis  69  of the first polarizer  64  are substantially parallel to each other. The reflection axis  92  of the second polarizer  68  is perpendicular to the absorption axis  69 ′ of the first polarizer  64 . 
     Referring to  FIG. 2B , in this embodiment, when light  3  emitted from the backlight system  52  passes through the first polarizer  64 , a first polarized light  4  with a polarization axis  4 ′ is formed (the polarization axis  4 ′ of the first polarized light  4  is parallel to the transmission axis  69  of the first polarizer  64 ). When the first polarized light  4  continuously passes through the off-state area  78  in the twisted nematic (TN) liquid crystal layer  72 , the first polarized light  4  is rotated 90° by liquid crystals (LC)  80  to form a second polarized light  5  with a polarization axis  5 ′. The second polarizer  68  allows the second polarized light  5  to pass through due to the polarization axis  5 ′ of the second polarized light  5  being parallel to the transmission axis  90  of the second polarizer  68  such that the off-state area  78  in the twisted nematic (TN) liquid crystal layer  72  corresponds to a bright area (not shown) of the liquid crystal display (LCD) panel  58 . 
     Further, referring to  FIG. 2C , another light path is illustrated. When light  3  emitted from the backlight system  52  passes through the first polarizer  64 , a polarized light  4  with a polarization axis  4 ′ is formed (the polarization axis  4 ′ of the polarized light  4  is parallel to the transmission axis  69  of the first polarizer  64 ). When the polarized light  4  continuously passes through the on-state area  76  in the twisted nematic (TN) liquid crystal layer  72 , the polarized light  4  is not modulated (rotated) by liquid crystals (LC)  80  so that the direction of the polarization axis  4 ′ thereof is preserved (see polarized light  4 - 1 ). The polarized light  4 - 1  with the polarization axis  4 ′ is then reflected by the second polarizer  68  (see polarized light  4 - 2 ) due to the polarization axis  4 ′ of the polarized light  4 - 1  being parallel to the reflection axis  92  of the second polarizer  68 . The reflected polarized light  4 - 2  then passes through the on-state area  76  in the twisted nematic (TN) liquid crystal layer  72  (the polarized light  4 - 2  is not modulated (rotated) by liquid crystals (LC)  80 )(see polarized light  4 - 3 ), passes through the first polarizer  64  and reaches the reflector  54  of the backlight system  52 . When the polarized light  4 - 3  is reflected by the reflector  54  again, an un-polarized light  3  is then formed and thus can be repeatedly used (improvement of brightness). Note that the on-state area  76  in the twisted nematic (TN) liquid crystal layer  72  corresponds to a dark area (not shown) of the liquid crystal display (LCD) panel  58 . 
     In an embodiment, the brightness of the 3D display device  50  is improved from 27% (conventional switchable-barrier-type 3D display device) to about 35%. 
     In this embodiment, some structural features of the 3D display device  50  are: (1) the second polarizer  68  is a reflective polarizer rather than an absorption polarizer; (2) the second substrate  74  with a thin thickness is preferable, for example less than the distance  82  between the two on-state areas ( 76 ,  76 ) or two off-state areas ( 78 ,  78 ) due to alteration of light path; and (3) the 3D display device  50  is a switchable-barrier-type 3D display device. 
     Still referring to  FIG. 2C , if the polarized light  4  passes through the on-state area  76  in the twisted nematic (TN) liquid crystal layer  72  but the reflected polarized light  4 - 2  passes through the off-state area  78  in the twisted nematic (TN) liquid crystal layer  72  (the polarized light  4 - 2  is rotated 90° by liquid crystals (LC)  80 )(not shown), then the passed through polarized light will be absorbed by the first polarizer  64  due to the polarization axis of the passed through polarized light being parallel to the absorption axis  69 ′ of the first polarizer  64 , resulting in an unwanted light path. However, in this embodiment, such an unwanted light path can be avoided by disposition of the thin second substrate  74 , for example having a thickness less than the distance  82  between the two on-state areas ( 76 ,  76 ) or two off-state areas ( 78 ,  78 ) of the second substrate  74 , to ensure that the polarized light  4  passes through the on-state area  76  in the twisted nematic (TN) liquid crystal layer  72  and the reflected polarized light  4 - 2  passes through the on-state area  76  in the twisted nematic (TN) liquid crystal layer  72 . 
     According to another embodiment of the invention, referring to  FIG. 3A , a 3D display device with switchable barrier is illustrated. A 3D display device  100  comprises a backlight system  102 , a reflective barrier  106  and a liquid crystal display (LCD) panel  108 . The liquid crystal display (LCD) panel  108  is disposed above the reflective barrier  106 . The liquid crystal display (LCD) panel  108  is a transmissive display panel for displaying images. The reflective barrier  106  is disposed between the liquid crystal display (LCD) panel  108  and the backlight system  102 . In another embodiment, the liquid crystal display (LCD) panel  108  is disposed between the reflective barrier  106  and the backlight system to  102  (not shown). 
     In this embodiment, the backlight system  102  comprises at least one light source  110 , one light guide plate  112 , and one reflector  104 . The reflector  104  is disposed under the light guide plate  112 . Additionally, the reflector  104  may comprise metal such as aluminum (Al), silver (Ag) or chromium (Cr). 
     In this embodiment, the reflective barrier  106  comprises a first polarizer  114 , a switchable barrier panel  116  and a second polarizer  118 . The switchable barrier panel  116  is disposed on the first polarizer  114 . Specifically, the second polarizer  118  is inserted into the switchable barrier panel  116 . 
     The first polarizer  114  has a transmission axis  119  and an absorption axis  119 ′. The switchable barrier panel  116  comprises a first substrate  120 , a twisted nematic (TN) liquid crystal layer  122  and a second substrate  124 . The twisted nematic (TN) liquid crystal layer  122  is disposed on the first substrate  120 . Specifically, the second polarizer  118  is disposed between the twisted nematic (TN) liquid crystal layer  122  and the second substrate  124 . There are driving electrode patterns (not shown) on the first substrate  120  and the second substrate  124 . The liquid crystal layer  122  is between the driving electrode patterns of the first substrate  120  and the second substrate  124 . 
     The first substrate  120  and the second substrate  124  may be glass or transparent plastic film. Additionally, when the switchable barrier panel  116  is turned on, the twisted nematic (TN) liquid crystal layer  122  is divided into an on-state area  126  and an off-state area  128  in an alternate arrangement. In detail, in the on-state area  126 , liquid crystals  130  are vertically arranged due to vertical electric field in the on-state area  126  and stay original arrangement in the off-state area  128 . Through the first polarizer  114  and the second polarizer  118 , the switchable barrier panel  116  becomes a barrier. At this time, the 3D display device  100  is able to display 3D images. By contrast, when the switchable barrier panel  116  is turned off (not shown), the 3D display device  100  is able to display 2D images. 
     In detail, the second polarizer  118  comprises a high-refractive-index polymer layer  134  and a low-refractive-index polymer layer  136  in an alternate arrangement, as shown in  FIG. 3A . Some of the light will be reflected by the low-refractive-index polymer layer  136 . The second polarizer  118  has both polarization function and reflection function. Additionally, the second polarizer  118  has a transmission axis  140  and a reflection axis  142 . 
     Still referring to  FIG. 3A , in this embodiment, specifically, the transmission axis  119  of the first polarizer  114  and the transmission axis  140  of the second polarizer  118  are substantially perpendicular to each other. However, the reflection axis  142  of the second polarizer  118  and the transmission axis  119  of the first polarizer  114  are substantially parallel to each other. The reflection axis  142  of the second polarizer  118  is perpendicular to the absorption axis  119 ′ of the first polarizer  114 . 
     Referring to  FIG. 3B , in this embodiment, when light  3  emitted from the backlight system  102  passes through the first polarizer  114 , a first polarized light  4  with a polarization axis  4 ′ is formed (the polarization axis  4 ′ of the first polarized light  4  is parallel to the transmission axis  119  of the first polarizer  114 ). When the first polarized light  4  continuously passes through the off-state area  128  in the twisted nematic (TN) liquid crystal layer  122 , the first polarized light  4  is rotated 90° by liquid crystals (LC)  130  to form a second polarized light  5  with a polarization axis  5 ′. The second polarizer  118  allows the second polarized light  5  to pass through due to the polarization axis  5 ′ of the second polarized light  5  being parallel to the transmission axis  140  of the second polarizer  118  such that the off-state area  128  in the twisted nematic (TN) liquid crystal layer  122  corresponds to a bright area (not shown) of the liquid crystal display (LCD) panel  108 . 
     Further, referring to  FIG. 3C , another light path is illustrated. When light  3  emitted from the backlight system  102  passes through the first polarizer  114 , a polarized light  4  with a polarization axis  4 ′ is formed (the polarization axis  4 ′ of the polarized light  4  is parallel to the transmission axis  119  of the first polarizer  114 ). When the polarized light  4  continuously passes through the on-state area  126  in the twisted nematic (TN) liquid crystal layer  122 , the polarized light  4  is not modulated (rotated) by liquid crystals (LC)  130  so that the direction of the polarization axis  4 ′ thereof is preserved (see polarized light  4 - 1 ). The polarized light  4 - 1  with the polarization axis  4 ′ is then reflected by the second polarizer  118  (see polarized light  4 - 2 ) due to the polarization axis  4 ′ of the polarized light  4 - 1  being parallel to the reflection axis  142  of the second polarizer  118 . The reflected polarized light  4 - 2  then passes through the on-state area  126  in the twisted nematic (TN) liquid crystal layer  122  (the polarized light  4 - 2  is not modulated (rotated) by liquid crystals (LC)  130 )(see polarized light  4 - 3 ), passes through the first polarizer  114  and reaches the reflector  104  of the backlight system  102 . When the polarized light  4 - 3  is reflected by the reflector  104  again, an un-polarized light  3  is then formed and thus can be repeatedly used (improvement of brightness). Additionally, the on-state area  126  in the twisted nematic (TN) liquid crystal layer  122  corresponds to a dark area (not shown) of the liquid crystal display (LCD) panel  108 . 
     In an embodiment, the brightness of the 3D display device  100  is improved from 27% (conventional switchable-barrier-type 3D display device) to about 35%. 
     In this embodiment, some structural features of the 3D display device  100  are: (1) the second polarizer  118  is inserted into the switchable barrier panel  116 , for example, inserted between the twisted nematic (TN) liquid crystal layer  122  and the second substrate  124 ; and (2) the 3D display device  100  is a switchable-barrier-type 3D display device. 
     Still referring to  FIG. 3C , if the polarized light  4  passes through the on-state area  126  in the twisted nematic (TN) liquid crystal layer  122  but the reflected polarized light  4 - 2  passes through the off-state area  128  in the twisted nematic (TN) liquid crystal layer  122  (the polarized light  4 - 2  is rotated 90° by liquid crystals (LC)  130 )(not shown), then the passed through polarized light will be absorbed by the first polarizer  114  due to the polarization axis of the passed through polarized light being parallel to the absorption axis  119 ′ of the first polarizer  114 , resulting in an unwanted light path. However, in this embodiment, such an unwanted light path can be avoided by inserting the second polarizer  118  into the switchable barrier panel  116 , to ensure that the polarized light  4  passes through the on-state area  126  in the twisted nematic (TN) liquid crystal layer  122  and the reflected polarized light  4 - 2  passes through the on-state area  126  in the twisted nematic (TN) liquid crystal layer  122 . 
     According to another embodiment of the invention, referring to  FIG. 4A , a 3D display device with switchable barrier is illustrated. A 3D display device  150  comprises a backlight system  152  a reflective barrier  156  and a liquid crystal display (LCD) panel  158 . The liquid crystal display (LCD) panel  158  is disposed above the reflective barrier  156 . The liquid crystal display (LCD) panel  158  is a transmissive display panel for displaying images. The reflector  154  is disposed under the backlight system  152 . The reflective barrier  156  is disposed between the liquid crystal display (LCD) panel  158  and the backlight system  152 . In another embodiment, the liquid crystal display (LCD) panel  158  is disposed between the reflective barrier  156  and the backlight system  152  (not shown). 
     In this embodiment, the backlight system  152  comprises at least one light source  160 , one light guide plate  162  and one reflector  154 , such that the reflector  154  is disposed under the light guide plate  162 . Additionally, the reflector  154  may comprise metal such as aluminum (Al), silver (Ag) or chromium (Cr). 
     In this embodiment, the reflective barrier  156  comprises a first polarizer  164 , a switchable barrier panel  166 , a second polarizer  168  and a third polarizer  171 . The switchable barrier panel  166  is disposed between the first polarizer  164  and the second polarizer  168 . The third polarizer  171  is disposed on the second polarizer  168 . 
     The first polarizer  164  has a transmission axis  169  and an absorption axis  169 ′. The switchable barrier panel  166  comprises a first substrate  170 , a twisted nematic (TN) liquid crystal layer  172  and a second substrate  174 . The twisted nematic (TN) liquid crystal layer  172  is disposed on the first substrate  170  and the second substrate  174 . There are driving electrode patterns (not shown) on the first substrate  170  and the second substrate  174 . The liquid crystal layer  172  is between the driving electrode patterns of the first substrate  170  and the second substrate  174 . 
     The first substrate  170  and the second substrate  174  may be glass or transparent plastic film. Additionally, when the switchable barrier panel  166  is turned on, the twisted nematic (TN) liquid crystal layer  172  is divided into an on-state area  176  and an off-state area  178  in an alternate arrangement. In detail, in the on-state area  176 , liquid crystals  180  are vertically arranged due to vertical electric field in the on-state area  176  and stay original arrangement in the off-state area  178 . Through the first polarizer  164  and the second polarizer  168  and the third polarizer  171 , the reflective barrier  156  becomes a barrier. At this time, the 3D display device  150  is able to display 3D images. By contrast, when the switchable barrier panel  166  is turned off (not shown), the 3D display device  150  is able to display 2D images. 
     In an embodiment, the second substrate  174  has a thickness less than a distance  182  between the two on-state areas ( 176 ,  176 ) or two off-state areas ( 178 ,  178 ). 
     In detail, the second polarizer  168  comprises a high-refractive-index polymer layer  184  and a low-refractive-index polymer layer  186  in an alternate arrangement, as shown in  FIG. 4A . The second polarizer  168  has a transmission axis  190  and a reflection axis  192 . Additionally, the third polarizer  171  comprises a first base film, a polarized film and a second base film (not shown). The third polarizer  171  has a transmission axis  194  and an absorption axis  196 . 
     Still referring to  FIG. 4A , in this embodiment, the transmission axis  169  of the first polarizer  164  and the transmission axis  190  of the second polarizer  168  are substantially perpendicular to each other. The reflection axis  192  of the second polarizer  168  and the transmission axis  169  of the first polarizer  164  are substantially parallel to each other. Specifically, with regard to the second polarizer  168  and the third polarizer  171 , the transmission axis  190  of the second polarizer  168  and the transmission axis  194  of the third polarizer  171  are substantially parallel to each other. The absorption axis  196  of the third polarizer  171  and the reflection axis  192  of the second polarizer  168  are substantially parallel to each other. 
     In this embodiment, the light paths within the 3D display device  150  are similar to  FIGS. 2B and 2C  and the brightness of the 3D display device  150  is also improved. 
     In an embodiment, the brightness of the 3D display device  150  is improved from  27 % (conventional switchable-barrier-type 3D display device) to about 35%. 
     In this embodiment, some structural features of the 3D display device  150  are: (1) a composite polarizer including the second polarizer  168  (reflective polarizer) and the third polarizer  171  (absorption polarizer) disposed thereon having transmission axes ( 190 ,  194 ) and being parallel to each other, is disposed on the switchable barrier panel  166 ; (2) the absorption axis  196  of the third polarizer  171  and the reflection axis  192  of the second polarizer  168  are parallel to each other; and (3) the 3D display device  150  is a switchable-barrier-type 3D display device. 
     Referring to  FIG. 4B , under sunlight  7 , a polarized light with a polarization axis  7 ′ parallel to the reflection axis  192  of the second polarizer  168  is absorbed by the third polarizer  171  due to the absorption axis  196  of the third polarizer  171  being parallel to the reflection axis  192  of the second polarizer  168 , improving sunlight readability (low surface reflection). 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.