Abstract:
The present invention discloses a 2D/3D switchable liquid crystal lens assembly. The liquid crystal lens assembly from an emitting surface to an incident surface sequentially includes a plurality of adjacently arranged elongated convex lenses, a first transparent substrate, a second transparent substrate, a plurality of electrodes disposed on the second transparent substrate, and a liquid crystal layer sandwiched between the first and second transparent substrates. The plurality of electrodes are used for controlling an alignment of liquid crystal molecules inside the liquid crystal layer so as to adjust a refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to at least one pixel. The refractive index progressively increase or progressively decrease from a center toward both sides to control a propagation direction of incident light and guide the passed incident light to one of the convex lenses.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a liquid crystal lens assembly, more particularly, to a two dimension/three dimension (2D/3D) switchable liquid crystal lens assembly having high lens power. 
         [0003]    2. Description of the Related Art 
         [0004]    Real-world images are perceived by the human eyes, and further, so-called three-dimensional (3D) images are perceived by the human brain depending on an apparent displacement of an object viewed along two different lines of sight. Such a displacement or a spatial difference is called parallax. A so-called 3D display device, simulating human vision to form different viewing angles, is capable of conveying 3D images to the viewer. The 3D display device produces two different 2D images with parallax, one for the viewer&#39;s right eye and the other for the left eye. Afterwards, the viewer&#39;s brain perceives these two different 2D images as a 3D image. 
         [0005]    Nowadays, there are two types of 3D display devices in general, auto-stereoscopic displays and stereoscopic displays. A user of an auto-stereoscopic display can see 3D images without wearing special type glasses. As for a user of a stereoscopic display, he/she has to wear special type glasses to see 3D images. A commonly seen auto-stereoscopic display is divided into two types: parallax barrier auto-stereoscopic displays and lenticular lenses auto-stereoscopic displays. The theorem of parallax barrier auto-stereoscopic displays lies on that a user sees parallax images through both eyes by controlling light propagation direction with an opaque parallax barrier, and the parallax images is perceived as stereoscopic view in the brain. 
         [0006]    As for lenticular lenses auto-stereoscopic displays, light propagation direction is controlled by varying the refractive index, which can be realized by different methods. One of them is to make a liquid crystal layer function as a physical lens. With the specially patterned indium tin oxide electrodes on top and bottom substrates, the unevenly distributed electric field lines are generated. The alignment of the liquid crystal molecules is thus changed to result in their different refractive indexes. Hence, the whole liquid crystal layer will behave like a lenticular lens to control the refraction direction of the incident light if a proper design is implemented. 
         [0007]    Please refer to  FIG. 1   a  and  FIG. 1   b ,  FIG. 1   a  is a schematic diagram showing a conventional GRIN lens without being applied with a voltage according to the prior art.  FIG. 1   b  is a schematic diagram showing the conventional GRIN lens being applied with a voltage. The GRIN lens (gradient index lens) is characterized by its refractive index distribution that varies with the distance to the axis. When no voltage is applied on the GRID lens, liquid crystal molecules will align in a manner as shown in  FIG. 1   a . Owing to the existence of the above-mentioned indium tin oxide electrode pattern (not indicated), the liquid crystal molecules will align in another manner, as shown in  FIG. 1   b , when a voltage is applied on the GRIN lens. The electric field to be generated will cause the liquid crystal molecules at the center of the lens have the highest refractive index (ne), and decreases gradually from the center to both edges of the lens until the lowest refractive index (no). When light propagates into the GRIN lens, the light travels through both edges of the lens will have a highest speed because of the lowest refractive index of the liquid crystal molecules near the edges. While the light travels through the center of the lens will have a lowest speed because of the highest refractive index of the liquid crystal molecules near the center. For an incident plane wave, the wavefront is thus curved. The curved wavefront, similar to a convex lens, is what focus the light on a focus point F. The equation for focal length is derived as follows: 
         [0000]    
       
         
           
             
               
                 f 
                 GRIN 
               
               = 
               
                 
                   r 
                   2 
                 
                 
                   2 
                    
                   
                     d 
                      
                     
                       [ 
                       
                         
                           n 
                           max 
                         
                         - 
                         
                           n 
                            
                           
                             ( 
                             r 
                             ) 
                           
                         
                       
                       ] 
                     
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where ‘f GRIN ’ is the focal length of the GRIN lens  10 ; “d” is the cell thickness; “r” is the radius of the GRIN lens  10 ; n max  is the extraordinary refractive index n e  of the liquid crystal molecules; “n(r)” means that refractive index is a function of r. When a design goal of 4 mm focal length is implanted, the cell thickness d must be maintained at approximately 30 μm if the refractive index difference Δn is 0.21. Therefore, in order to realize a small focal length, the only choice is to increase the cell thickness if the radius of the GRIN lens  10  cannot be reduced and the type of the liquid crystal molecules cannot be changed. However, the increased cell thickness not only increases the cell gap, but also increases the cost. It is therefore very important to provide a 2D/3D switchable liquid crystal lens assembly to improve the focus ability without increasing the cost resulted from the increased cell thickness. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a 2D/3D switchable liquid crystal lens assembly comprising an external set of fixed lenses to improve the lens power so as to resolve the problems of the prior art. 
         [0009]    The present invention provides a liquid crystal lens assembly. The liquid crystal lens assembly from an emitting surface to an incident surface sequentially comprises a plurality of adjacently arranged elongated convex lenses, a first transparent substrate, a second transparent substrate, a plurality of electrodes disposed on the second transparent substrate, and a liquid crystal layer sandwiched between the first transparent substrate and the second transparent substrate. The plurality of electrodes are used for controlling an alignment of liquid crystal molecules inside the liquid crystal layer so as to adjust a refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to at least one pixel. The refractive index progressively increase or progressively decrease from a center of the liquid crystal layer corresponding to the pixel toward both sides to control a propagation direction of incident light and guide the passed incident light to one of the convex lenses. 
         [0010]    In one aspect of the present invention, the electrode is an elongated electrode, the electrode extends along a direction parallel to an extending direction of the elongated convex lens. 
         [0011]    In another aspect of the present invention, the liquid crystal lens assembly cooperates with linear polarized light, the plurality of elongated convex lenses extend along a first direction and arrange in a second direction perpendicular to the first direction, the polarized direction is parallel to the second direction. 
         [0012]    In still another aspect of the present invention, the plurality of electrodes adjust the refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to the pixel to decrease from the center toward both of the sides to form 3D mode. 
         [0013]    In yet another aspect of the present invention, the plurality of electrodes adjust the refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to the pixel to increase from the center toward both of the sides to form 2D mode. 
         [0014]    The present invention provides another liquid crystal lens assembly. The liquid crystal lens assembly from an emitting surface to an incident surface sequentially comprises a first transparent substrate, a plurality of adjacently arranged elongated convex lenses, a second transparent substrate, a plurality of electrodes disposed on the second transparent substrate, and a liquid crystal layer sandwiched between the plurality of elongated convex lenses and the second transparent substrate. The plurality of electrodes are used for controlling an alignment of liquid crystal molecules inside the liquid crystal layer so as to adjust a refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to at least one pixel, the refractive index progressively increase or progressively decrease from a center of the liquid crystal layer corresponding to the pixel toward both sides to control a propagation direction of incident light and guide the passed incident light to one of the convex lenses. 
         [0015]    In one aspect of the present invention, the electrode is an elongated electrode, the electrode extends along a direction parallel to an extending direction of the elongated convex lens. 
         [0016]    In another aspect of the present invention, the liquid crystal lens assembly cooperates with linear polarized light, the plurality of elongated convex lenses extend along a first direction and arrange in a second direction perpendicular to the first direction, the polarized direction is parallel to the second direction. 
         [0017]    In still another aspect of the present invention, the plurality of electrodes adjust the refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to the pixel to decrease from the center toward both of the sides to form 3D mode. 
         [0018]    In yet another aspect of the present invention, the plurality of electrodes adjust the refractive index of the liquid crystal molecules inside the liquid crystal layer corresponding to the pixel to increase from the center toward both of the sides to form 2D mode. 
         [0019]    In contrast to the prior art, with the support of a set of external lenses and the proper electrode design on the transparent substrate, the present invention only needs to apply predetermined voltages on the electrodes to make the liquid crystal layer function as a convex lens. The incident light, refracted by the convex lens of the liquid crystal layer and then refracted by the external lens, will be focused on the human eyes to form 3D images at the emitting surface. Since the incident light is refracted twice, the overall focus ability is improved. As a result, not only is the lens power improved, but also the cell gap is decreased. Furthermore, when switched to the 2D mode, only applying different voltages on the electrodes the location of the convex lens of the liquid crystal layer is shifted. The effect of the external lens is thus canceled out to allow 2D images to be formed at the emitting surface. The present invention liquid crystal lens assembly has the advantages of simple switching, decreased cell thickness, and reduced cost. 
         [0020]    These and other features, aspects and advantages of the present disclosure will become understood with reference to the following description, appended claims and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0022]      FIG. 1   a  is a schematic diagram showing a conventional GRIN lens without being applied with a voltage. 
           [0023]      FIG. 1   b  is a schematic diagram showing the conventional GRIN lens being applied with a voltage. 
           [0024]      FIG. 2  is a cross-sectional view showing a present invention liquid crystal lens assembly and alignment of liquid crystal molecules in 3D mode according to a first embodiment of the present invention. 
           [0025]      FIG. 3  is a cross-sectional view showing the liquid crystal lens assembly of  FIG. 2  and alignment of liquid crystal molecules in 2D mode. 
           [0026]      FIG. 4  is a cross-sectional view showing a present invention liquid crystal lens assembly and alignment of liquid crystal molecules in 3D mode according to a second embodiment of the present invention. 
           [0027]      FIG. 5  is a cross-sectional view showing the liquid crystal lens assembly of  FIG. 4  and alignment of liquid crystal molecules in 2D mode. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. 
         [0029]    Please refer to  FIG. 2 ,  FIG. 2  is a cross-sectional view showing a present invention liquid crystal lens assembly and alignment of liquid crystal molecules in 3D mode according to a first embodiment of the present invention. As shown in  FIG. 2 , the liquid crystal lens assembly LCD  100  comprises a plurality of external lenses  102 , a transparent substrate  101   a , a liquid crystal layer  104 , a transparent substrate  101   b , and a plurality of electrodes  106  disposed on the transparent substrate  101   b  sequentially from a light emitting surface  112  to a light incident surface  110 . The plurality of external lenses  102  and the plurality of electrodes  106  are elongated along a direction A perpendicular to the paper surface. In the present embodiment, electrode  106   a , electrode  106   b , and electrode  106   c  disposed respectively corresponding to subpixel  108   a , subpixel  108   b , and subpixel  108   c  are illustrated as an example. Polarized light is provided to the liquid crystal lens assembly  100  by a polarizer (not indicated) disposed between the liquid crystal lens assembly  100  and the subpixels  108   a ,  108   b ,  108   c . The polarized light propagates along the direction indicated by an arrow shown in  FIG. 2 . The subpixel  108   a , subpixel  108   b , and subpixel  108   c  are a red subpixel, a green subpixel, and a blue subpixel, respectively. The subpixel  108   a , subpixel  108   b , and subpixel  108   c  constitute a pixel  108 . In the present embodiment, the polarized direction of the polarized light emitted from the polarizer (not indicated) being perpendicular to the direction A and the light propagation direction is illustrated as an example. However, the present invention is not limited to this. 
         [0030]    When voltages are applied on the electrodes  106   a ,  106   b ,  106   c , the electric field as generated will make the liquid crystal molecules inside the liquid crystal layer  104  rotate. The liquid crystal molecules near the electrodes  106   a ,  106   c  will align so that their optical axes are parallel to the propagation direction of the polarized light, while the liquid crystal molecules near the electrode  106   b  will align so that their optical axes are parallel to the polarized direction of the incident light. Owing to the birefringence property of the liquid crystal molecules inside the liquid crystal layer  104 , the liquid crystal molecules will have an ordinary refractive index n o  when the polarized light incident onto the liquid crystal lens assembly  100  has a polarized direction perpendicular to the optical axes of the liquid crystal molecules, and the liquid crystal molecules will have an extraordinary refractive index n e  when the polarized light incident onto the liquid crystal lens assembly  100  has a polarized direction in parallel with the optical axes of the liquid crystal molecules. The extraordinary refractive index is greater than the ordinary refractive index. 
         [0031]    When light propagates, the light travelling in the vicinity of the electrodes  106   a ,  106   c  will have the highest speed because it encounters liquid crystal molecules having the lowest refractive index. Oppositely, the light travelling in the vicinity of the electrode  106   b  will have the lowest speed because it encounters liquid crystal molecules having the highest refractive index. By implementing a proper design, the different alignment of the liquid crystal molecules will result in the variation of the refractive index along the liquid crystal layer  104 . Hence, the liquid crystal layer  104  corresponding to the pixel  108  will behave like a convex lens to control the refraction direction of the incident light. 
         [0032]    After being refracted, the incident light propagates to the external lens  102 . Because the external lens  102  is also a convex lens, the incident light is refracted again and is focused on the human eyes. Therefore, the viewer is allowed to see 3D images at the emitting surface  112 . Since the incident light is refracted twice, the overall focus ability is improved. Hence, not only is the lens power improved, but also the cell gap is decreased. 
         [0033]    The liquid crystal lens assembly  100  is also adaptable to 2D mode. Please refer to  FIG. 3 ,  FIG. 3  is a cross-sectional view showing the liquid crystal lens assembly of  FIG. 2  and alignment of liquid crystal molecules in 2D mode. In 2D mode, the voltages applied on the electrodes  106   a ,  106   b ,  106   c  are changed. The electric field as generated will make the liquid crystal molecules inside the liquid crystal layer  104  rotate. The liquid crystal molecules near the electrodes  106   a ,  106   c  will align so that their optical axes are parallel to the polarized direction of the incident light, while the liquid crystal molecules near the electrode  106   b  will align so that their optical axes are parallel to the propagation direction of the polarized light. 
         [0034]    Due to the birefringence property of the liquid crystal molecules inside the liquid crystal layer  104 , by implementing a proper design, the different alignment of the liquid crystal molecules will result in the variation of the refractive index along the liquid crystal layer  104 . The liquid crystal layer  104  near the pixel  108  will thus behave like a convex lens, but however, the location of the convex lens is shifted when compared with that of the convex lens in 3D mode shown in  FIG. 2  to cancel out the effect of the external lens  102 . As a result, light travels along a straight line because there is no real effect of the lenses. The viewer is allowed to see 2D images at the emitting surface  112 . 
         [0035]    In the present invention, the 3D mode can be switched to the 2D mode by changing the voltages applied on the electrodes  106   a ,  106   b ,  106   c , or voltages can be applied on an extra set of electrodes to shift the location of the convex lens of the liquid crystal layer  104 . In this way, different set of electrodes is selected when switching to the 2D or 3D mode without the necessity of changing the voltages applied on the same set of electrodes. 
         [0036]    In  FIG. 2  and  FIG. 3 , the liquid crystal molecules inside the liquid crystal layer  104  are positive liquid crystal molecules whose optical axes are parallel to a direction of the electric field generated by applying voltages on the electrodes  106   a ,  106   b ,  106   c . In another embodiment, the liquid crystal molecules inside the liquid crystal layer  104  are negative liquid crystal molecules. Under the circumstances, the alignment direction and the elongation direction of the electrodes need to be changed so as to achieve a proper design. 
         [0037]    Please refer to  FIG. 4 ,  FIG. 4  is a cross-sectional view showing a present invention liquid crystal lens assembly and alignment of liquid crystal molecules in 3D mode according to a second embodiment of the present invention. The second embodiment differs from the first embodiment in that a plurality of external lenses  202  of a liquid crystal lens assembly  200  is disposed between a transparent substrate  201   a  and a transparent substrate  201   b  and adjacent to a liquid crystal layer  204 . The plurality of external lenses  202  and a plurality of electrodes  206  are elongated along a direction A perpendicular to the paper surface. In the present embodiment, electrode  206   a , electrode  206   b , and electrode  206   c  disposed respectively corresponding to subpixel  208   a , subpixel  208   b , and subpixel  208   c  are illustrated as an example. Polarized light is provided to the liquid crystal lens assembly  200  by a polarizer (not indicated) disposed between the liquid crystal lens assembly  200  and the subpixels  208   a ,  208   b ,  208   c . The polarized light propagates along the direction indicated by an arrow shown in  FIG. 4 . The subpixel  208   a , subpixel  208   b , and subpixel  208   c  are a red subpixel, a green subpixel, and a blue subpixel, respectively. The subpixel  208   a , subpixel  208   b , and subpixel  208   c  constitute a pixel  208 . In the present embodiment, the polarized direction of the polarized light emitted from the polarizer (not indicated) being perpendicular to the direction A and the light propagation direction is illustrated as an example. However, the present invention is not limited to this. 
         [0038]    When voltages are applied on the electrodes  206   a ,  206   b ,  206   c , the electric field as generated will make the liquid crystal molecules inside the liquid crystal layer  204  rotate. The liquid crystal molecules near the electrodes  206   a ,  206   c  will align so that their optical axes are parallel to the propagation direction of the polarized light, while the liquid crystal molecules near the electrode  206   b  will align so that their optical axes are parallel to the polarized direction of the incident light. By implementing a proper design, the different alignment of the liquid crystal molecules will result in the variation of the refractive index along the liquid crystal layer  204 . Hence, the liquid crystal layer  204  corresponding to the pixel  208  will behave like a convex lens to control the refraction direction of the incident light. The incident light is therefore refracted and then propagates to the external lens  202 . Because the external lens  202  is also a convex lens, the incident light is refracted again and is focused on the human eyes. Therefore, the viewer is allowed to see 3D images at the emitting surface  212 . Since the incident light is refracted twice, the overall focus ability is improved. Hence, not only is the lens power improved, but also the cell gap is decreased. 
         [0039]    The liquid crystal lens assembly  200  is also adaptable to 2D mode. Please refer to  FIG. 5 ,  FIG. 5  is a cross-sectional view showing the liquid crystal lens assembly of  FIG. 4  and alignment of liquid crystal molecules in 2D mode. In 2D mode, the voltages applied on the electrodes  206   a ,  206   b ,  206   c  are changed. The electric field as generated will make the liquid crystal molecules inside the liquid crystal layer  204  rotate. The liquid crystal molecules near the electrodes  206   a ,  206   c  will align so that their optical axes are parallel to the polarized direction of the incident light, while the liquid crystal molecules near the electrode  206   b  will align so that their optical axes are parallel to the propagation direction of the polarized light. Due to the birefringence property of the liquid crystal molecules inside the liquid crystal layer  204 , by implementing a proper design, the different alignment of the liquid crystal molecules will result in the variation of the refractive index along the liquid crystal layer  204 . The liquid crystal layer  204  near the pixel  208  will thus behave like a convex lens, but however, the location of the convex lens is shifted when compared with that of the convex lens in 3D mode shown in  FIG. 4  to cancel out the effect of the external lens  202 . As a result, light travels along a straight line because there is no real effect of the lenses. The viewer is allowed to see 2D images at the emitting surface  212 . 
         [0040]    Similarly, the 3D mode can be switched to the 2D mode by changing the voltages applied on the electrodes  206   a ,  206   b ,  206   c , or voltages can be applied on an extra set of electrodes to shift the location of the convex lens of the liquid crystal layer  204 . In  FIG. 4  and  FIG. 5 , the liquid crystal molecules inside the liquid crystal layer  204  are positive liquid crystal molecules whose optical axes are parallel to a direction of the electric field generated by applying voltages on the electrodes  206   a ,  206   b ,  206   c . In another embodiment, the liquid crystal molecules inside the liquid crystal layer  204  are negative liquid crystal molecules. Under the circumstances, the alignment direction and the elongation direction of the electrodes need to be changed so as to achieve a proper design. 
         [0041]    In summary, with the support of a set of external lenses and the proper electrode design on the transparent substrate, the present invention only needs to apply predetermined voltages on the electrodes to make the liquid crystal layer function as a convex lens. The incident light, refracted by the convex lens of the liquid crystal layer and then refracted by the external lens, will be focused on the human eyes to form 3D images at the emitting surface. Since the incident light is refracted twice, the overall focus ability is improved. As a result, not only is the lens power improved, but also the cell gap is decreased. Furthermore, when switched to the 2D mode, only applying different voltages on the electrodes the location of the convex lens of the liquid crystal layer is shifted. The effect of the external lens is thus canceled out to allow 2D images to be formed at the emitting surface. The present invention liquid crystal lens assembly has the advantages of simple switching, decreased cell thickness, and reduced cost. 
         [0042]    While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements made without departing from the scope of the broadest interpretation of the appended claims.