Abstract:
Embodiments of the invention provide an image display device that is switchable between a two-dimensional display mode, a three-dimensional display mode enabling non-autostereoscopic image display, and a three-dimensional display mode enabling autostereoscopic image display. In one embodiment, the image display device comprises a display panel operable to transmit light corresponding to image data; a polarization state conversion section comprising a first polarization segment for converting light transmitted by the display device to a first polarization state, and a second polarization segment for converting light transmitted by the display device to a second polarization state; and an optical separation element that is placed, via application of a voltage, in an on state in which light transmitted by the display panel is refracted or an off state in which light transmitted by the display panel is not refracted.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a stereoscopic display unit for performing three-dimensional display by using binocular parallax. 
         [0003]    2. Description of the Related Art 
         [0004]    In the past, stereoscopic display units that realize stereoscopic vision by providing different images (parallax images) as a viewer left-eye image and a viewer right-eye image between which parallax exists. Examples of methods of such stereoscopic display units include eyeglass method and naked eye method. The eyeglass method realizes stereoscopic vision by wearing special eyeglasses for stereoscopic vision. In Japanese Patent No. 3767962, as eyeglasses for stereoscopic vision, a method using a polarization filter is disclosed. 
         [0005]    Meanwhile, in the naked eye method, stereoscopic vision is enabled with naked eyes without wearing the special eyeglasses. Examples of naked eye methods include parallax barrier method and lenticular method. In the parallax barrier method, a structure called a parallax barrier as a parallax separation means is arranged oppositely to a two-dimensional display panel. Right and left parallax images displayed on the two-dimensional display panel are parallax-separated in the horizontal direction by the parallax barrier, and therefore stereoscopic vision is realized. In the lenticular method, a lenticular lens as a parallax separation means is arranged oppositely to a two-dimensional display panel. Right and left parallax images displayed on the two-dimensional display panel are parallax-separated in the horizontal direction by the lenticular lens, and therefore stereoscopic vision is realized. Further, a display unit in which display is changeable between two-dimensional display and three-dimensional display by the lenticular method by using a variable lenticular lens composed of a liquid crystal lens or a liquid lens has been known (refer to Japanese Unexamined Patent Application Publication No. 2000-102038 and Japanese Unexamined Patent Application Publication No. 2005-517991). 
       SUMMARY OF THE INVENTION 
       [0006]    However, in the case of the parallax barrier method and the lenticular method, a stereoscopic range (visual region) is small. Thus, there is a disadvantage that viewing position and viewing distance are limited and many viewers are not able to view images at the same time. Meanwhile, in the case of the eyeglass method, limitation of viewing position and viewing distance is small, and many viewers are able to view images at the same time. However, there is a disadvantage that dedicated eyeglasses are necessitated. Thus, it is convenient if three-dimensional display method is switchable according to the number of viewers and audio-visual environment in one stereoscopic display unit. 
         [0007]    In view of the foregoing disadvantages, in the invention, it is desirable to provide a stereoscopic display unit with which display is switchable between two-dimensional display and three-dimensional display, and three-dimensional display methods are switchable between the naked eye method and the eyeglass method. 
         [0008]    One embodiment of the invention provides a stereoscopic display device, comprising: a display panel operable to transmit light corresponding to image data; a polarization state conversion section comprising a first polarization segment for converting light transmitted by the display device to a first polarization state, and a second polarization segment for converting light transmitted by the display device to a second polarization state; and an optical separation element that is placed, via application of a voltage, in an on state in which light transmitted by the display panel is refracted or an off state in which light transmitted by the display panel is not refracted. 
         [0009]    In some embodiments, the optical separation element may, for example, comprise a variable lens array, such as a variable lens array comprising a liquid lenticular lens. In some embodiments, the optical separation element may comprise a liquid crystal lens, and application of a voltage may place the liquid crystal lens in an on state by changing an alignment direction of liquid crystal molecules in the liquid crystal lens. 
         [0010]    Another embodiment of the invention provides an image display device comprising: a display that displays images in 2D and 3D, switchable between: a 2D display mode; a first 3D display mode enabling non-autostereoscopic image display; and a second 3D display mode enabling autostereoscopic image display. 
         [0011]    In some embodiments, the display may be switchable between the first 3D display mode and the second 3D display mode by applying a voltage to an optical separation element. 
         [0012]    According to embodiments of the invention, a stereoscopic display unit is provided in which a polarization state conversion section (the polarization section), variable lens array device, and polarized eyeglasses are appropriately combined, and the lens effect of the variable lens array device is variably switched between on-state and off-state according to the content of the image displayed on the two-dimensional display section. Thus, display is switchable between two-dimensional display and three-dimensional display, and three-dimensional display method is switchable between naked eye method and eyeglass method. Therefore, three-dimensional display suitable for audiovisual environment is enabled. For example, when the number of viewers is one or a small number such as two or more, three-dimensional display by naked eye method is able to be adopted. In this case, dedicated eyeglasses for three-dimensional display are not necessitated. Further, by performing three-dimensional display by eyeglass method, display images are able to be viewed by many persons, and a viewer is able to view display images by freely selecting the viewing position. 
         [0013]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a structural view illustrating a whole structure of a stereoscopic display unit according to a first embodiment of the invention. 
           [0015]      FIGS. 2A and 2B  are cross sectional views illustrating a structure of a variable lens array device.  FIG. 2A  illustrates a structure in a state that lens effect of the variable lens array device is off as a whole, and  FIG. 2B  illustrates a structure in a state that lens effect of the variable lens array device is on as a whole. 
           [0016]      FIGS. 3A and 3B  are cross sectional views illustrating an operation principle of an electro-wetting type liquid lens.  FIG. 3A  illustrates a state that lens effect is generated, and  FIG. 3B  illustrates a state that lens effect is not generated. 
           [0017]      FIG. 4  is a structural view in the case where three-dimensional display is performed by eyeglass method in the stereoscopic display unit illustrated in  FIG. 1 . 
           [0018]      FIG. 5  is a structural view in the case where three-dimensional display is performed by naked eye method in the stereoscopic display unit illustrated in  FIG. 1 . 
           [0019]      FIG. 6  is cross sectional view illustrating a structure of a variable lens array device in a stereoscopic display unit according to a second embodiment of the invention. 
           [0020]      FIG. 7A  is a perspective view illustrating a structural example in an electrode section of the variable lens array device illustrated in  FIG. 6 .  FIG. 7B  is a perspective view illustrating a lens shape formed by the variable lens array device illustrated in  FIG. 6  in an optically equivalent manner. 
           [0021]      FIGS. 8A and 8B  are views for explaining on/off state of lens effect in the variable lens array device illustrated in  FIG. 6 .  FIG. 8A  illustrates a state that lens effect does not exist (lens effect is off), and  FIG. 8B  illustrates a state that lens effect is generated (lens effect is on). 
           [0022]      FIG. 9  is a structural view illustrating a first modified example of the stereoscopic display unit illustrated in  FIG. 1 . 
           [0023]      FIG. 10  is a structural view illustrating a second modified example of the stereoscopic display unit illustrated in  FIG. 1 . 
           [0024]      FIG. 11  is a structural view illustrating a third modified example of the stereoscopic display unit illustrated in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Embodiments of the invention will be described in detail with reference to the drawings. 
       First Embodiment 
       [0026]    Basic Structure of a Stereoscopic Display Unit 
         [0027]      FIG. 1  illustrates a whole structure of a stereoscopic display unit according to a first embodiment of the invention. In the stereoscopic display unit, display mode is switchable between two-dimensional display mode and three-dimensional display mode, and three-dimensional display mode is switchable between naked eye method and eyeglass method.  FIG. 4  schematically illustrates a state that three-dimensional display is performed by eyeglass method in the stereoscopic display unit.  FIG. 5  schematically illustrates a state that three-dimensional display is performed by naked eye method. The stereoscopic display unit includes a display panel  2  as a two-dimensional display section, a polarization state conversion section  5  arranged oppositely to the display surface side of the display panel  2 , and a variable lens array device  1 . Further, as illustrated in  FIG. 4 , the stereoscopic display unit includes a polarized eyeglasses  40  used in viewing three-dimensional display by eyeglass method. 
         [0028]    In the display panel  2 , a plurality of pixels are arranged in a state of matrix. The display panel  2  is intended to perform two-dimensional image display. The display panel  2  is structured so that light originated in a displayed image is output in a state of linear polarized light that is polarized in a specific direction.  FIG. 1  and the like illustrate an example that the displayed image light is output in a state of being linearly polarized in the horizontal direction (X-axis direction of  FIG. 1 ) from the display panel  2 . The display panel  2  is composed of, for example, a transmissive liquid crystal display. In the case of the liquid crystal display, a liquid crystal panel main body is sandwiched between two polarization plates so that each polarization direction is in a state of, for example, crossed nicols. The displayed image light is polarized in a direction determined by polarization direction of the polarization plate on the output side. The display structure itself may not output linear polarized light. A display having other structure may be used if a polarization plate is arranged oppositely to the display surface. For example, as the display panel  2 , an organic EL (Electro-Luminescence) display, a plasma display panel or the like may be used in combination with a polarization plate. 
         [0029]    The display panel  2  is intended to perform two-dimensional image display and three-dimensional image display. In two-dimensional image display, two-dimensional matrix display is performed based on general two-dimensional image data. In three-dimensional display, display is performed based on three-dimensional image data. The three-dimensional image data is data including a plurality of parallax images corresponding to a plurality of view angle directions in three-dimensional image display. In this embodiment, as the three-dimensional image data, parallax image data including a left-eye image L and a right-eye image R between which parallax exists is used. When three-dimensional image display is performed, in the display panel  2 , the left-eye image L and the right-eye image R between which parallax exists are spatially separated, synthesized in one screen, and displayed. When three-dimensional image display by naked eye method is performed, as illustrated in  FIG. 5 , in the display panel  2 , image display is performed so that a left-eye pixel segment that configures the left-eye image and a right-eye pixel that configures the right-eye image are alternately arranged along the horizontal direction. In the case where three-dimensional display by eyeglass method is performed, as illustrated in  FIG. 4 , image display is performed so that the left-eye image L and the right-eye image R are alternately arranged along the vertical direction. 
         [0030]    The polarization state conversion section  5  converts light originated in an image displayed on the display panel  2  is converted to light in a first polarization state and light in a second polarization state with each polarization state different from each other for every given image region. The polarization state conversion section  5  alternately converts polarization state in the vertical direction for every region corresponding to the left-eye image L and the right-eye image R when three-dimensional display by eyeglass method is performed. 
         [0031]    The polarization state conversion section  5  has a first phase difference plate  5 A as a first polarization segment and a second phase difference plate  5 B as a second polarization segment. The first phase difference plate  5 A and the second phase difference plate  5 B are strip-shaped phase difference plates extended in the horizontal direction. A plurality of first phase difference plates  5 A and a plurality of second phase difference plates  5 B are alternately arranged in the vertical direction. The first phase difference plate  5 A is provided in a position corresponding to a display region of the left-eye image L displayed when three-dimensional display by eyeglass method is performed on the display panel  2 . The second phase difference plate  5 B is provided in a position corresponding to a display region of the right-eye image R displayed when three-dimensional display by eyeglass method is performed on the display panel  2 . 
         [0032]    The first phase difference plate  5 A converts the linear polarized light output from the display panel  2  to a first circular polarized light, and outputs the first circular polarized light in the first polarization state. The second phase difference plate  5 B converts the linear polarized light to a second circular polarized light with its rotation direction different from that of the first circular polarized light, and outputs the second circular polarized light in the second polarization state. More specifically, the first phase difference plate  5 A and the second phase difference plate  5 B are composed of a ¼ wave plate. A slow axis A 1  of the first phase difference plate  5 A and a slow axis B 1  of the second phase difference plate  5 B are tilted 45 deg in a direction different from each other in relation to the direction (X-axis direction) of the linear polarized light output from the display panel  2 . For example, the slow axis A 1  of the first phase difference plate  5 A is tilted 45 deg upper leftward, and the slow axis B 1  of the second phase difference plate  5 B is tilted 45 deg upper rightward. Therefore, in the first phase difference plate  5 A, the linear polarized light output from the display panel  2  is converted to circular polarized light counterclockwise, while in the second phase difference plate  5 B, the linear polarized light output from the display panel  2  is converted to circular polarized light clockwise. The first phase difference plate  5 A and the second phase difference plate  5 B are provided in the region corresponding to the left-eye image L and the right-eye image R that are displayed when three-dimensional display by eyeglass method is performed. In the result, the left-eye image L is converted to circular polarized light counterclockwise, and the right-eye image R is converted to circular polarized light clockwise. 
         [0033]    The polarized eyeglasses  40  have a first polarization filter  41 L for a left-eye  9 L and a second polarization filter  41 R for a right-eye  9 R. The first polarization filter  41 L transmits only light in the first polarization state converted by the first phase difference plate  5 A of the polarization state conversion section  5 . The second polarization filter  41 R transmits only light in the second polarization state converted by the second phase difference plate  5 B. 
         [0034]    Whole Structure of the Variable Lens Array Device  1   
         [0035]      FIGS. 2A and 2B  illustrate a structure of the variable lens array device  1 . The variable lens array device  1  is intended to selectively change passing state of light ray from the display panel  2  by electrically on/off controlling lens effect according to the display mode.  FIG. 2A  illustrates a structure in a state that lens effect of the variable lens array device  1  is off as a whole, and  FIG. 2B  illustrates a structure in a state that lens effect of the variable lens array device  1  is on as a whole. The variable lens array device  1  includes a liquid lenticular lens  3  and a fixed lenticular lens  4  sequentially from the side opposed to the display panel  2 . The liquid lenticular lens  3  has a plurality of variable lenses capable of electrically on/off controlling lens effect. 
         [0036]    The fixed lenticular lens  4  has a plurality of fixed lenses provided correspondingly to the plurality of variable lenses. The plurality of fixed lenses respectively have refracting power to set off lens effect when the lens effect of respective corresponding variable lenses becomes in on-state. More specifically, the fixed lenticular lens  4  has a cylindrical lens array structure in which a plurality of cylindrical lenses  4 A as a fixed lens are arranged in parallel with each other. In the fixed lenticular lens  4 , the respective cylindrical lenses  4 A are arranged to be extended in the longitudinal direction in relation to the display surface of the display panel  2 , and to have positive refractive power in the right and left direction. The lens pitch in the lateral direction of the respective cylindrical lenses  4 A corresponds to the size of the pixel width (for example, two pixels) of one pair of the left-eye image L and the right-eye image R to be displayed on the display panel  2 . 
         [0037]    Structure of the Liquid Lenticular Lens  3   
         [0038]    The liquid lenticular lens  3  includes a first substrate  10  and a second substrate  20  that are oppositely arranged with a gap in between and a liquid layer arranged between the first substrate  10  and the second substrate  20 . The liquid layer is composed of a silicone oil (insulating oil)  15  and an electrolytic solution  16 . The first substrate  10  and the second substrate  20  are a transparent substrate made of, for example, a glass material or a resin material. In a peripheral section between the first substrate  10  and the second substrate  20 , a dividing wall  12  and a dividing wall  13  are formed. The dividing wall  12  is also formed in a position corresponding to the lens pitch of the cylindrical lens  4 A between the first substrate  10  and the second substrate  20 . For the dividing wall  12  in the position corresponding to the lens pitch, the length in the vertical direction is shorter than that of a gap between the first substrate  10  and the second substrate  20 , and a given gap exists between the dividing wall  12  in the position corresponding to the lens pitch and the first substrate  10 . A liquid layer between adjacent two dividing walls  12  forms one variable lens. Such one variable lens corresponds to one cylindrical lens  4 A of the fixed lenticular lens  4 . On the surface on the side contacted with the liquid layer of the first substrate  10 , a hydrophilic conducting film  11  is uniformly formed on almost whole area. On the surface of the dividing wall  12 , a conducting film  14 - 1  and an insulating water-shedding film  14 - 2  are formed sequentially from the dividing wall  12  side as described later. 
         [0039]    The liquid lenticular lens  3  is an electro-wetting type liquid lens array in which lens effect is on-off controlled according to an applied voltage. A description will be given of a basic structure and an operation principle of the liquid lenticular lens  3  with reference to  FIGS. 3A and 3B . In this case, for explaining the basic principle,  FIGS. 3A and 3B  illustrate a structure of one variable lens (liquid lens). For the sections corresponding to those of the structures illustrated in  FIGS. 2A and 2B , the same referential symbols are affixed thereto.  FIG. 3A  illustrates a state that lens effect of a liquid lens simple body is on (state that given negative refractive power is generated), and  FIG. 3B  illustrates a state that lens effect of a liquid lens simple body is off (state that refractive power is not generated). 
         [0040]    In the electro-wetting type variable lens, lens effect is controlled by changing interface shape of two types of liquids with each refractive index different from each other with the use of a fact that wetting characteristics between liquid and solid surface is changed according to an applied voltage. In the structure of the variable lens illustrated in  FIGS. 3A and 3B , the hydrophilic conducting film  11  is formed on the surface of the first substrate  10 , and the conducting film  14 - 1  and the insulating water-shedding film  14 - 2  are formed on the surface of the dividing wall  12 . The insulating water-shedding film  14 - 2  is made of, for example, a parylene film. The silicon oil  15  is injected to the second substrate  20  and the insulating water-shedding film  14 - 2  side, the electrolytic solution  16  is injected to the hydrophilic conducting film  11  side in the gap between the first substrate  10  and the second substrate  20 , and the gap is sealed. The hydrophilic conducting film  11  and the conducting film  14 - 1  are electrically connected to an electric power source  6 , and a voltage is applied thereto.  FIG. 3B  illustrates a state that a voltage is applied by the electric power source  6  (electrically on-state), and  FIG. 3A  illustrates a state that a voltage is not applied (electrically off-state). 
         [0041]    The electrolytic solution  16  has characteristics that wetting characteristics in relation to the surface of the dividing wall  12  (insulating water-shedding film  14 - 2 ) are improved in proportion as square of an applied voltage. Thus, where the contact angle with the surface of the dividing wall  12  when the applied voltage is 0 is θ 0  and the contact angle with the surface of the dividing wall  12  when the applied voltage is not 0 is θ v , relation of θ 0 &gt;θ v  is established. Further, a given applied voltage V 90  at which lens effect is zero (θ v =90 deg, the interface shape between the silicone oil  15  and the electrolytic solution  16  is flat) is able to be found. Accordingly, by switching the applied voltage between 0 and the given applied voltage V 90 , lens effect is able to be provided with on/off switch control. Where refractive index n 1  of the silicone oil  15  is higher than refractive index n 2  of the electrolytic solution  16 , negative refractive power lens effect is generated where the applied voltage is 0 as illustrated in  FIG. 3A . 
         [0042]    In other words, in the variable lens composed of the liquid lenticular lens  3 , lens effect becomes in on-state ( FIG. 3A ) when it becomes in off-state electrically by setting the applied voltage to zero. Further, lens effect becomes off-state ( FIG. 3B ) when it becomes in on-state electrically by setting the applied voltage to the given voltage V 90 . Such a relation between electrically on/off state and on/off state of lens effect is specific to the electro-wetting type liquid lens. For example, by setting specific gravity of the silicone oil  15  to a value equal to that of the electrolytic solution  16 , gravity effect on two types of liquids is able to be equalized. Thus, in this case, it is regarded that the interface shape is determined by only wetting characteristics based on the applied voltage and gravity influence does not exist. 
         [0043]    Lens Action as the Whole Variable Lens Array Device  1   
         [0044]    In the variable lens array device  1 , in a state that a voltage is not applied to the liquid lenticular lens  3  by the electric power source  6  (electrically off-state) as illustrated in  FIG. 2A , lens effect of the plurality of variable lenses in the liquid lenticular lens  3  becomes in on-state. The lens effect of the respective variable lenses in the liquid lenticular lens  3  is set off by the corresponding fixed lens (cylindrical lens  4 A) in the fixed lenticular lens  4 . In other words, whole lens effect of a combination of the liquid lenticular lens  3  and the fixed lenticular lens  4  becomes in off-state. 
         [0045]    Meanwhile, in a state that a given voltage is applied to the liquid lenticular lens  3  by the electric power source  6  (electrically on-state) as illustrated in  FIG. 2B , lens effect of the plurality of variable lenses in the liquid lenticular lens  3  becomes in off-state. In this state, a voltage value is adjusted so that the interface shape between the silicone oil  15  and the electrolytic solution  16  composing the liquid layer in the liquid lenticular lens  3  becomes flat in the respective variable lens sections. In this state, lens effect of the liquid lenticular lens  3  is ineffective independently, and only lens effect by the fixed lenticular lens  4  is effective. In other words, whole lens effect of a combination of the liquid lenticular lens  3  and the fixed lenticular lens  4  becomes in on-state. 
         [0046]    As described above, the variable lens array device  1  includes the fixed lenticular lens  4  having refractive power to set off lens effect of the liquid lenticular lens  3 . Thus, electric on/off characteristics of lens effect of the liquid lenticular lens  3  are able to be reversed. In the variable lens array device  1 , whole lens effect of a combination of the liquid lenticular lens  3  and the fixed lenticular lens  4  becomes in off-state (state without refractive power) when lens effect of the liquid lenticular lens  3  becomes in on-state (state that given negative refractive power is generated). In addition, when lens effect of the liquid lenticular lens  3  becomes in off-state, whole lens effect becomes in on-state. In other words, electric on/off characteristics of lens effect of the whole variable lens array device  1  become in a state that is reversed in relation to characteristics of the liquid lenticular lens  3  as a simple body. 
         [0047]    Operation and Effect of the Stereoscopic Display Unit 
         [0048]    In the stereoscopic display unit, display is switched between display in two-dimensional display mode, display in three-dimensional display mode by eyeglass method (second three-dimensional display mode), and display in three-dimensional display mode by naked eye method (first three-dimensional display mode). 
         [0049]    (1) Two-Dimensional Display Mode 
         [0050]    In a state of performing two-dimensional image display (two-dimensional matrix display) on the display panel  2 , lens effect by the variable lens array device  1  is set to in off-state. By transmitting displayed image light from the display panel  2  without refracting the light by the variable lens array device  1 , two-dimensional display is directly performed. The light from the displayed image of the display panel  2  is converted to light in the first polarization state (circular polarized light counterclockwise) and light in the second polarization state (circular polarized light clockwise) for every pixel region corresponding to the region provided with the first phase difference plate  5 A and the second phase difference plate  5 B in the polarization state conversion section  5 . However, the foregoing polarization difference is not recognized with naked eyes, and thus observing two-dimensional display is not affected. 
         [0051]    (2) Three-Dimensional Display Mode by Eyeglass Method ( FIG. 4 ) 
         [0052]    Display is performed so that the left-eye image L and the right-eye image R are alternately arranged along the vertical direction on the display panel  2 . Lens effect by the variable lens array device  1  is set to in off-state. In the polarization state conversion section  5 , light is output so that light originated in the left-eye image L is converted to light in the first polarization state (circular polarized light counterclockwise), and light originated in the right-eye image R is converted to light in the second polarization state (circular polarized light clockwise). In the variable lens array device  1 , converted first light ray originated in the left-eye image L and converted second light ray originated in the right-eye image R are transmitted without being refracted. The transmitted left-eye image L and the transmitted right-eye image R are observed through the polarized eyeglasses  40 , and therefore three-dimensional display by eyeglass method is performed. More specifically, in the first phase difference plate  5 A of the polarization state conversion section  5 , only light in the first polarization state is transmitted through the first polarization filter  41 L of the polarized eyeglasses  40 , and therefore only the left-eye image L is sensed by the left-eye  9 L of the observer. Further, in the second phase difference plate  5 B of the polarization state conversion section  5 , only light in the second polarization state is transmitted through the second polarization filter  41 R of the polarized eyeglasses  40 , and therefore only the right-eye image R is sensed by the right-eye  9 R of the observer. Therefore, binocular parallax stereoscopic vision is enabled. 
         [0053]    (3) Three-Dimensional Display Mode by Naked Eye Method ( FIG. 5 ) 
         [0054]    Display is performed so that the left-eye image L and the right-eye image R are alternately arranged along the horizontal direction on the display panel  2 . Lens effect by the variable lens array device  1  is set to in on-state. In the variable lens array device  1 , light ray originated in the left-eye image L and light ray originated in the right-eye image R displayed on the display panel  2  are refracted and optically separated so that stereoscopic vision by naked eyes is enabled. In other words, in the variable lens array device  1 , optical light ray separation is performed by refraction so that the left-eye image L and the right-eye image R selectively enter the left-eye  9 L and the right-eye  9 R of the observer  9  respectively and appropriately. Therefore, binocular parallax stereoscopic vision is enabled. In the three-dimensional display mode by naked eye method, the light from the display image of the display panel  2  is converted to light in the first polarization state and light in the second polarization state for every pixel region corresponding to the region provided with the first phase difference plate  5 A and the second phase difference plate  5 B in the polarization state conversion section  5 . However, the polarization difference is not recognized with naked eyes, and thus observing three-dimensional display by naked eye method is not affected. Further, if the polarized eyeglasses  40  are used, observation of the three-dimensional display is not affected. In this case, right and left parallax separation is already completed by the variable lens array device  1 . Thus, only the left-eye image L selectively enters the left-eye  9 L of the observer  9 , and the right-eye image R selectively enters the right-eye  9 R of the observer  9  through the polarized eyeglasses  40 , and therefore a stereoscopic image is sensed. 
         [0055]    As described above, in the three-dimensional display mode by naked eye method, the difference of the polarization states between the left-eye image L and the right-eye image R is not observed by naked eyes, and therefore the polarization state conversion section  5  is not limited to the structure illustrated in  FIG. 5 . For example, in  FIG. 5 , a left-eye polarization segment and a right-eye polarization segment may be alternately arranged along a horizontal direction (not illustrated) instead of a vertical direction. 
         [0056]    As described above, according to this embodiment, the polarization state conversion section  5 , the variable lens array device  1 , and the polarized eyeglasses  40  are appropriately combined, and the lens effect of the variable lens array device  1  is on-off controlled according to the content of the image displayed on the display panel  2 . Thus, display is switchable between two-dimensional display and three-dimensional display, and three-dimensional display method is switchable between naked eye method and eyeglass method. Therefore, three-dimensional display suitable for audiovisual environment is enabled. For example, when the number of viewers is one or a small number such as two or more, three-dimensional display by naked eye method is able to be adopted. In this case, dedicated eyeglasses for three-dimensional display are not necessitated. Further, by performing three-dimensional display by eyeglass method, display images are able to be viewed by many persons, and a viewer is able to view display images by freely selecting the viewing position. 
       Second Embodiment 
       [0057]    Next, a description will be given of a stereoscopic display unit according to a second embodiment of the invention. For the substantively same elements as those of the stereoscopic display unit according to the foregoing first embodiment, the same referential symbols are affixed thereto, and the description thereof will be omitted as appropriate. 
         [0058]      FIG. 6  illustrates a structure of a variable lens array device  1 A in the stereoscopic display unit according to the second embodiment. The stereoscopic display unit according to this embodiment includes the variable lens array device  1 A by liquid crystal lens method instead of the variable lens array device  1  using the liquid lens in  FIG. 1 . The structure of this embodiment is the same as that of the foregoing first embodiment, except that the structure of the variable lens array device  1 A is different. 
         [0059]    Whole Structure of the Variable Lens Array Device  1 A 
         [0060]    The variable lens array device  1 A is a variable lens array by liquid crystal lens method, and is able to electrically on/off control lens effect. The variable lens array device  1 A is intended to selectively change passing state of light ray from the display panel  2  by controlling lens effect according to the display mode. 
         [0061]    As illustrated in  FIG. 6 , the variable lens array device  1 A includes a first substrate  10 A and a second substrate  20 A that are oppositely arranged with a gap d in between and a liquid crystal layer  30  arranged between the first substrate  10 A and the second substrate  20 A. The first substrate  10 A and the second substrate  20 A are a transparent substrate made of, for example, a glass material or a resin material. On the side opposed to the second substrate  20 A on the first substrate  10 A, a first electrode  21  made of a transparent conductive film such as an ITO film is uniformly formed over almost all area. Further, a first alignment film  23  is formed over the first substrate  10 A with the first electrode  21  in between and is contacted with the liquid crystal layer  30 . On the side opposed to the first substrate  10 A on the second substrate  20 A, a second electrode  22 Y made of a transparent conductive film such as an ITO film is partially formed. Further, a second alignment film  24  is formed over the second substrate  20 A with the second electrode  22 Y in between and is contacted with the liquid crystal layer  30 . 
         [0062]      FIGS. 8A and 8B  illustrate the basic principle of lens effect generation in the variable lens array device  1 A. In  FIGS. 8A and 8B , for explaining the basic principle, the structure of the variable lens array device  1 A is illustrated simplistically. The liquid crystal layer  30  includes liquid crystal molecules  31 . Lens effect is controlled by changing alignment direction of the liquid crystal molecules  31  according to a voltage applied to the first electrode  21  and the second electrode  22 Y. The liquid crystal molecule  31  has refractive index anisotropy, and has a structure of, for example, a refractive index ellipsoidal body in which refractive index in relation to transmitted light ray in the longitudinal direction is different from that in the short direction. The state of the liquid crystal layer  30  is electrically switched between a state without lens effect and a state with generation of lens effect according to the state of a voltage applied to the first electrode  21  and the second electrode  22 Y. 
         [0063]    In the variable lens array device  1 A, as illustrated in  FIG. 8A , in a normal state that an applied voltage is 0 V, the liquid crystal molecules  31  are uniformly aligned in a given direction determined by the first alignment film  23  and the second alignment film  24 . Thus, a wave surface  201  of transmitted light ray becomes plane wave, and lens effect does not exist. Meanwhile, in the variable lens array device  1 A, the plurality of second electrodes  22 Y are estranged at given intervals. Thus, when a given drive voltage is applied between the first electrode  21  and the second electrode  22 Y, bias is generated in electric field distribution inside the liquid crystal layer  30 . In other words, electric field having the following characteristics is generated. In the section corresponding to the region where the second electrode  22 Y is formed, the electric field intensity is increased according to the drive voltage, while as location is close to the central section of each aperture between the plurality of second electrodes  22 Y, the electric field intensity is decreased. Thus, as illustrated in  FIG. 8B , alignment of the liquid crystal molecules  31  is changed according to the electric field intensity distribution. Therefore, a wave surface  202  of transmitted light ray is changed, and lens effect is generated. 
         [0064]    Electrode Structure of the Variable Lens Array Device  1 A 
         [0065]      FIG. 7A  illustrates a planar structure example of the electrode section of the variable lens array device  1 A.  FIG. 7B  illustrates a lens shape formed in the case of the electrode structure illustrated in  FIG. 7A  in an optically equivalent manner. The second electrode  22 Y has an electrode width Lx, and is extended in the vertical direction. As illustrated in  FIG. 7A , the plurality of second electrodes  22 Y are arranged in parallel with each other at intervals corresponding to lens pitch p in generating lens effect. In the case where lens effect is generated, a given electric potential difference at which alignment of the liquid crystal molecules  31  is able to be changed between the upper and lower electrodes sandwiching the liquid crystal layer  30  is given. The first electrode  21  is formed over the whole area of the first substrate  10 A, and the second electrodes  22 Y are partially arranged at certain intervals in the lateral direction. Thus, when a given drive voltage is applied to the second electrodes  22 Y, bias is generated in electric field distribution inside the liquid crystal layer  30  based on the principle illustrated in  FIG. 8B . In other words, electric field having the following characteristics is generated. In the section corresponding to the region where the second electrode  22 Y is formed, the electric field intensity is increased according to the drive voltage, while as location departs from the second electrode  22 Y in the lateral direction, the electric field intensity is decreased. In other words, electric field distribution is changed so that lens effect is generated in the lateral direction (X-axis direction). In other words, as illustrated in  FIG. 7B , a plurality of cylindrical lenses  31 Y that are extended in the Y-axis direction and have refractive power in the X-axis direction are arranged in parallel with each other in the X-axis direction in an equivalent manner. 
         [0066]    Switching operation between two-dimensional display and three-dimensional display and switching operation between naked eye method and eyeglass method of three-dimensional display are basically similar to those of the foregoing first embodiment. 
       Modified Example 
       [0067]    The invention is not limited to the foregoing respective embodiments, but various modifications may be made. For example, in the foregoing respective embodiments, the variable lens array device  1  or  1 A is arranged on the light exit side of the polarization state conversion section  5 . However, as illustrated in  FIG. 9 , the variable lens array device  1  or  1 A may be arranged between the display panel  2  and the polarization state conversion section  5 . 
         [0068]    Further, in the foregoing respective embodiments, in performing three-dimensional display by eyeglass method, display is performed so that the left-eye image L and the right-eye image R are alternately arranged along the vertical direction on the display panel  2 . However, display may be performed in the same manner as that in the three-dimensional display by naked eye method. In other words, display may be performed so that the left-eye image L and the right-eye image R are alternately arranged along the horizontal direction on the display panel  2 . In this case, as illustrated in  FIG. 10 , the first phase difference plate  5 A and the second phase difference plate  5 B in the polarization state conversion section  5  are alternately arranged in the horizontal direction correspondingly to the display regions of the left-eye image L and the right-eye image R. In this case, the light originated in the image displayed on the display panel  2  is alternately converted to light in the first polarization state and light in the second polarization state in the horizontal direction for every region corresponding to the left-eye image L and the right-eye image R. After that, as in the display example of  FIG. 4 , by observing through the polarized eyeglasses  40 , only the left-eye image L is sensed by the left-eye  9 L of the observer, only the right-eye image R is sensed by the right-eye  9 R of the observer, and therefore binocular parallax stereoscopic vision is enabled. 
         [0069]    Further, in the foregoing respective embodiments, in performing three-dimensional display by eyeglass method, the linear polarized light output from the display panel  2  is converted to respective circular polarized light with its rotation direction different from each other by the polarization state conversion section  5 . However, the respective light may be converted in a different manner. For example, the respective light may be converted to respective linear polarized light with its polarization direction different from each other.  FIG. 11  illustrates an example of such a modified example. In the modified example of  FIG. 11 , compared to the structure of  FIG. 4 , a polarization state conversion section  51  is included instead of the polarization state conversion section  5 , and polarized eyeglasses  40 A are included instead of the polarized eyeglasses  40 . 
         [0070]    The polarization state conversion section  51  has a transmission section  5 D and a phase difference plate  5 C. The transmission section  5 D and the phase difference plate  5 C are in the shape of a strip being extended in the horizontal direction. A plurality of transmission sections  5 D and a plurality of phase difference plates  5 C are alternately arranged in the vertical direction. The transmission section  5 D is provided in a position corresponding to a display region of the left-eye image L displayed when three-dimensional display by eyeglass method is performed in the display panel  2 . The phase difference plate  5 C is provided in a position corresponding to a display region of the right-eye image R displayed when three-dimensional display by eyeglass method is performed in the display panel  2 . Alternatively, the transmission section  5 D may be provided in the position corresponding to the display region of the right-eye image R, and the phase difference plate  5 C may be provided in the position corresponding to the display region of the left-eye image L. In this case, where light originated in the image displayed on the display panel  2  is linear polarized light that is polarized in the first polarization direction (X-axis direction), the transmission section  5 D outputs the linear polarized light in the first polarization direction output from the display panel  2  as light in the first polarization state without changing the polarization direction. The phase difference plate  5 C is made of a ½ wave plate. The phase difference plate  5 C converts the linear polarized light in the first polarization direction output from the display panel  2  to a linear polarized light in the second polarization direction (Y-axis direction) 90 deg different from the first polarization direction, and outputs the converted light in the second polarization state. Therefore, the left-eye image L is converted to linear polarized light in the first polarization direction by the transmission section  5 D, and the right-eye image R is converted to linear polarized light in the second polarization direction by the phase difference plate  5 C. To match therewith, the first polarization filter  41 L for the left-eye  9 L in the polarized eyeglasses  40 A is set to a filter that transmits only linear polarized light in the first polarization direction, and the second polarization filter  41 R for the right-eye  9 R in the polarized eyeglasses  40 A is set to a filter that transmits only linear polarized light in the second polarization direction. Therefore, only the left-eye image L selectively enters the left-eye  9 L of the observer  9 , and the right-eye image R selectively enters the right-eye  9 R of the observer  9  through the polarized eyeglasses  40 A, and therefore a stereoscopic image is sensed. 
         [0071]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-264985 filed in the Japan Patent Office on Nov. 20, 2009, the entire contents of which is hereby incorporated by reference. 
         [0072]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.