Patent Publication Number: US-2011063725-A1

Title: Lenticular Display

Description:
BACKGROUND OF THE INVENTION 
     Lenticular lens arrays may be used to construct stereoscopic liquid crystal displays (LCDs) that are viewable without wearing 3D glasses. A detailed description of such a display may be found in U.S. patent application Ser. No. 12/182,869, the complete disclosure of which is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, a display including a lenticular lens array and an immersing medium. The immersing medium covers the lenticular lens array. 
     Implementations may include one or more of the following features. There may be a flat front surface. There may be a flat sheet covering the immersing medium, and the flat sheet may form the flat front surface. There may be a conformal coating on the lenticular lens array. The lenticular lens array may include a convex lenticule. The lenticular lens array may include a concave lenticule. The lenticular lens array may have a back focal distance close to zero. The display may be a stereoscopic display. The display may include a liquid crystal display panel. The lenticular lens array may be bonded to the liquid crystal panel. There may be a spacer sheet behind the lenticular lens array. The spacer sheet may be bonded to the lenticular lens array. The lenticular lens array may have an index of refraction greater than 1.6. The immersing medium may have an index of refraction less than 1.45. The difference between the index of refraction of the lenticular lens array and the index of refraction of the immersing medium may be greater than 0.2. The immersing medium may include a fluorocarbon material, a silicone material, a fluid, or a gel. 
     In general, in one aspect, a stereoscopic display including a lenticular lens array with an index of refraction greater than 1.6, an immersing medium with an index of refraction less than 1.45, and a flat sheet that forms a flat front surface. The immersing medium fills the volume between the lenticular lens array and the flat sheet. 
     In general, in one aspect, a method of guiding light including the steps of generating a light beam from a pixel, guiding the light beam with an immersed lenticular lens array, and transmitting the light beam to an eye. 
     Implementations may include one or more of the following features. The additional steps of generating a second light beam from a second pixel, guiding the second light beam with the immersed lenticular lens array, and transmitting the second light beam to a second eye. The first light beam and the second light beam may form a stereoscopic image. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  is a top view of an immersed lenticular lens array; 
         FIG. 1B  is a front view of an immersed lenticular lens array; 
         FIG. 2  is a top view of an immersed lenticule and LCD panel showing light beams forming a stereoscopic image; 
         FIG. 3  is a top view of an immersed lenticular lens array with a flat sheet; 
         FIG. 4  is a top view of an immersed lenticular lens array with a spacer sheet; 
         FIG. 5  is a top view of an immersed lenticular lens array with a conformal coating; 
         FIG. 6  is a top view of an immersed lenticular lens array with concave lenticules; 
         FIG. 7  is a top view of a segment of immersed lenticular lens array showing dimensions and angles; 
         FIG. 8  is a top view of a segment of immersed lenticular lens array showing additional angles; and 
         FIG. 9  is a flowchart of a method of guiding light to form a stereoscopic image. 
     
    
    
     DETAILED DESCRIPTION 
     Conventional autostereoscopic displays with lenticular lenses on the front surface are subject to degradation from contamination, scratching, and other damage to the delicate lenticular surface. The crevices between the lenticules are also hard to clean. By attaching a flat sheet onto the front of the lenticular lens, these problems may be completely solved. An immersing medium with a low index of refraction is used to fill the space between the flat sheet and the lenticular lens. For the purposes of this disclosure, the locations of front, rear, and behind are defined relative to the viewer of the display. For example, in front of the lenticular lens array means closer to the viewer than the lenticular lens array and behind the lenticular lens array means farther from the viewer than the lenticular lens array. Covering means to place an object in front of another object. 
       FIGS. 1A and 1B  show an immersed lenticular lens array.  FIG. 1A  is a top view and  FIG. 1B  is a front view. In this example, there are five rows of cylindrical lenses  106 , but in many applications there are hundreds or thousands of rows. Each cylindrical lens  106  is called a lenticule. Lenticular lens array  100  is covered by immersing medium  102  to form a flat front surface  104 . 
       FIG. 2  shows a top view of one immersed lenticule and part of an LCD panel with light beams forming a stereoscopic image.  FIGS. 1A and 1B  include many lenticules which each act similarly to the one lenticule shown in  FIG. 2 . Left pixel  200  generates first beam segment  210  in lenticule  206 . First beam segment  210  is refracted at the interface between lenticule  206  and immersing medium  208  to form second beam segment  212 . Second beam segment  212  becomes third beam segment  234  as it passes into front sheet  230 . Third beam segment  234  exits front sheet  230  to form fourth beam segment  220 . Fourth beam segment  220  is viewed by left eye  224 . Right pixel  202  generates fifth beam segment  214  in lenticule  206 . Fifth beam segment  214  is refracted at the interface between lenticule  206  and immersing medium  208  to form sixth beam segment  216 . Sixth beam segment  216  becomes seventh beam segment  232  as it passes into front sheet  230 . Seventh beam segment  232  exits front sheet  230  to form eighth beam segment  218 . Eighth beam segment  218  is viewed by right eye  222 . Left pixel  200  and right pixel  202  are part of LCD panel  204 .  FIG. 2  shows a visible gap between lenticule  206  and LCD panel  204 , but this gap may be much smaller or it may be absent if lenticule  206  is bonded to LCD panel  204 . Actual beam paths and relative dimensions of the various parts are not shown exactly in  FIG. 2 . Beam reflections from surfaces and interfaces and some beam refractions may not be shown in  FIG. 2 . 
       FIG. 3  shows a top view of an immersed lenticular lens array with a flat sheet in front of the immersing medium. Lenticular lens array  300  is covered by immersing medium  302 . Immersing medium  302  is covered by flat sheet  306  to form flat front surface  304 . Flat sheet  306  may include a hard coating, antireflection coating, easily cleanable coating, or other coatings on its front face. Immersing medium  302  fills the volume between lenticular lens array  300  and flat sheet  306 . 
       FIG. 4  shows a top view of an immersed lenticular lens array with a spacer sheet behind the lenticular lens array. Spacer sheet  406  is covered by lenticular lens array  400 . Immersing medium  402  covers lenticular lens array  400  to form flat front surface  404 . Spacer sheet  406  may be bonded to lenticular lens array  400  so that there is no gap between the two. Spacer sheet  400  may have an index of refraction that matches lenticular lens array  400  or spacer sheet  400  may have an index of refraction that is chosen for convenience and low cost. 
       FIG. 5  shows a top view of an immersed lenticular lens array with a conformal coating on the lenticules. Lenticular lens array  500  is covered by conformal coating  506 . Conformal coating  506  conformally fits the shape of the lenticules in lenticular lens array  500  by having a constant thickness across the array. Immersing medium  502  covers conformal coating  506  to form flat front surface  504 . Conformal coating  506  may be made of a material with a high index of refraction. 
       FIG. 6  shows a top view of an immersed lenticular lens array with concave lenticules.  FIGS. 3 ,  4 , and  5  show convex lenticules.  FIG. 6  has lenticules curved the opposite direction as compared to  FIGS. 3 ,  4 , and  5  so that the lenticules in  FIG. 6  are convex with respect to the lenticule material. Immersing medium  602  covers convex lenticular lens array  600  to form flat front surface  604 . In the case of  FIG. 6 , the low and high indices of refraction may be reversed when compared to  FIGS. 3 ,  4 , and  5 . In other words, convex lenticular array  600  may be made of a material with a low index of refraction and immersing medium  602  may be made of a material with a high index of refraction. 
     The features shown in  FIGS. 3 ,  4 ,  5 , and  6  may be combined in various ways. For example, front sheet  306  in  FIG. 3  may be combined with spacer  406  in  FIG. 4  or front sheet  306  in  FIG. 3  may be combined with concave lenticular lens array  600  in  FIG. 6 . 
     The dimensions and material properties of the lenticular lens and immersing medium may be selected to enable effective stereoscopic viewing of the pixels in the LCD panel by using mathematical formulas based on Snell&#39;s law of refraction. The observation angle is chosen to obtain the number of desired stereoscopic viewing zones. Observation angles of 10 to 30 degrees are typical for stereoscopic applications with multiple viewing zones.  FIG. 7  shows a top view of a segment of immersed lenticular lens array showing various dimensions and angles. Lenticule  702  is covered by immersing medium  700 . First distance  710  is the radius of the lenticule lens. Second distance  708  is the pitch of the lenticule lens. Third distance  704  is the thickness of the lenticular lens. Fourth distance  706  is the thickness of the back of the lenticular lens. First angle  704  is an intermediate angle used for calculation, and second angle  712  is the angle of the extreme ray inside the lens. 
       FIG. 8  shows a top view of a segment of immersed lenticular lens array with additional angles that are not shown in  FIG. 7 . First angle  800  is the full observation angle. Second angle  802  is the angle of the extreme ray outside the lenticular lens. 
     In the thin lens approximation, the following formulas apply for an immersed lenticule: 
         R=A −arctan( p /( e−f ))
 
         A =arcsin( p/ 2 r ) 
         f=r −sqrt( r   2 −( p/ 2) 2 )
 
         O= 2( A−I ) 
         I =arcsin( n   1 *sin( R )/ n   2 ) 
         F =( r*n   2 )/( n   1   −n   2 ) and 
     
       
      
       B=F−e/n 
       1  
      
     
     where p is the pitch of the lenticular lens, r is the radius of the lenticular lens, e is the thickness of the lenticular lens, n 1  is the index of refraction of the lenticular lens, n 2  is the index of refraction of the immersing medium, f is the thickness of the lenticule, h is the thickness of the back of the lens array, A is the intermediate angle, R is the angle of the extreme ray inside the lens, I is the angle of the extreme ray outside the lens, F is the focal length, O is the full angle of observation, and B is the back focal distance. 
     TABLE 1 shows the calculated full angle of observation and back focal distance for three examples of lenticular lens arrays. When the LCD panel is against the back of the lenticular lens array, the back focal distance should be zero or as close to zero as possible to properly image the pixels of the LCD panel through the lenticular lens array. Example 1 in TABLE 1 is a baseline case without an immersed lenticular lens. The pitch, radius and thickness are chosen to represent a typical lenticular lens array for a 119 cm (47 inch) diagonal stereoscopic LCD panel. The index of the lenticular lens material is 1.540 which is typical for plastics that are commonly used to construct lenticular lenses. The incident medium is air with an index of refraction equal to 1.000. The resultant observation angle is 14.4 degrees with a back focal distance of zero. 
     Example 2 in TABLE 1 is the same as example 1 except that the immersing medium has been replaced by silicone adhesive with an index of refraction equal to 1.406. The resultant observation angle is 18.1 degrees with a back focal distance of 28.54 mm. This back focal distance is much larger than the desired back focal distance of zero. In order to reduce the back focal distance, a larger difference in the index of refraction of the lenticular lens and the immersing medium is desirable. 
     Example 3 in TABLE 1 replaces the lenticular lens material with a high index plastic that has an index of refraction equal to 1.740 and replaces the immersing medium with a low index of refraction material that has an index of refraction equal to 1.330. By also changing the radius and thickness of the lenticular lens, a resultant observation angle of 8.2 degrees is obtained with a back focal distance of zero. This observation angle is sufficiently high for many stereoscopic applications. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Item 
                 Units 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Lenticular lens pitch 
                 mm 
                 1.55 
                 1.55 
                 1.55 
               
               
                 Lenticular lens radius 
                 mm 
                 3.30 
                 3.30 
                 1.27 
               
               
                 Lenticular lens thickness 
                 mm 
                 9.41 
                 9.40 
                 7.16 
               
               
                 Index of lenticular lens 
                 none 
                 1.540 
                 1.540 
                 1.740 
               
               
                 Index of incident medium 
                 none 
                 1.000 
                 1.406 
                 1.330 
               
               
                 Thickness of lenticule 
                 mm 
                 0.09 
                 0.09 
                 0.26 
               
               
                 Thickness of back of lens 
                 mm 
                 9.32 
                 9.31 
                 6.90 
               
               
                 array 
               
               
                 Intermediate angle 
                 degrees 
                 13.6 
                 13.6 
                 37.6 
               
               
                 Extreme ray inside lens 
                 degrees 
                 4.1 
                 4.1 
                 24.9 
               
               
                 Extreme ray outside lens 
                 degrees 
                 6.4 
                 4.5 
                 33.5 
               
               
                 Focal length 
                 mm 
                 6.11 
                 34.65 
                 4.12 
               
               
                 Full angle of observation 
                 degrees 
                 14.4 
                 18.1 
                 8.2 
               
               
                 Back focal distance 
                 mm 
                 0.00 
                 28.54 
                 0.00 
               
               
                   
               
            
           
         
       
     
     TABLE 2 shows three more examples of lenticular lens arrays. Example 4 in TABLE 2 replaces the lenticular lens material in example 3 with a high-index plastic that has an index of refraction equal to 1.650 and replaces the immersing medium in example 3 with a low-index material that has in index of refraction equal to 1.406. By changing the radius and thickness of the lenticular lens, a resultant observation angle of 3.2 degrees is obtained with a back focal distance of zero. This observation angle is too low for many stereoscopic applications, but may be appropriate for some applications such as those that have many stereoscopic viewing zones or are viewed from far away. 
     Example 5 in TABLE 2 is similar to Example 2 in TABLE 1 except that the radius has been decreased from 3.30 mm to 1.52 mm and the thickness has been adjusted to bring the back focal distance to zero. The resultant observation angle is only 1.6 degrees. This observation angle is too low for most stereoscopic applications. A larger gap in the index of refraction is desirable. In general, if the gap is at least 0.2, other parameters such as the radius and thickness of the lenticular lens may be adjusted within a practical range to find a useful combination of observation angle that is reasonably high and back focal distance which is sufficiently low. 
     Example 6 in TABLE 2 is similar to Example 4 in TABLE 2 except that the immersing medium has been replaced by one with a lower index of refraction which is equal to 1.330. The thickness of the lens is adjusted in example 6 to bring the back focal distance to 1.3 mm rather than zero. Even in cases where the lenticular lens array is bonded to the display, the back focal distance does not have to be exactly zero. As long as the back focal distance is close enough to zero, the pixels may be imaged into the proper viewing zones without an objectionable amount of ghosting from adjacent pixels. In this example, the resultant observation angle is 11.6 degrees. This observation angle is sufficiently high for many stereoscopic applications. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Item 
                 Units 
                 Example 4 
                 Example 5 
                 Example 6 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Lenticular lens pitch 
                 mm 
                 1.55 
                 1.55 
                 1.55 
               
               
                 Lenticular lens radius 
                 mm 
                 1.52 
                 1.52 
                 1.52 
               
               
                 Lenticular lens thickness 
                 mm 
                 14.49 
                 24.63 
                 8.31 
               
               
                 Index of lenticular lens 
                 none 
                 1.650 
                 1.540 
                 1.650 
               
               
                 Index of incident medium 
                 none 
                 1.406 
                 1.406 
                 1.330 
               
               
                 Thickness of lenticule 
                 mm 
                 0.21 
                 0.21 
                 0.21 
               
               
                 Thickness of back of lens 
                 mm 
                 14.28 
                 24.42 
                 8.10 
               
               
                 array 
               
               
                 Intermediate angle 
                 degrees 
                 30.6 
                 30.6 
                 30.6 
               
               
                 Extreme ray inside lens 
                 degrees 
                 24.4 
                 26.9 
                 19.7 
               
               
                 Extreme ray outside lens 
                 degrees 
                 28.9 
                 29.7 
                 24.7 
               
               
                 Focal length 
                 mm 
                 8.78 
                 15.99 
                 6.33 
               
               
                 Full angle of observation 
                 degrees 
                 3.2 
                 1.6 
                 11.6 
               
               
                 Back focal distance 
                 mm 
                 0.00 
                 0.00 
                 1.30 
               
               
                   
               
            
           
         
       
     
       FIG. 9  shows a method of guiding light to form a stereoscopic image. In step  902 , light it generated by a left pixel. In step  904 , the left pixel light is guided with an immersed lenticular lens array. In step  906 , the left pixel light is transmitted to the left eye of a viewer. In step  908 , light it generated by a right pixel. In step  910 , the right pixel light is guided with the immersed lenticular lens array. In step  912 , the right pixel light is transmitted to the right eye of the viewer. In step  914 , a stereoscopic image is formed from the left pixel light and the right pixel light. 
     Various high-index-of-refraction and low-index-of-refraction materials may be used for the lenticular lens array and the immersing medium. In general, the largest possible gap between the two indices of refraction is desirable. For the purposes of this disclosure, high-index materials have an index greater than 1.6, and low-index materials have an index less than 1.45. Materials with an index between 1.6 and 1.45 are considered medium-index materials. High-index plastics for ophthalmic use have an index of refraction as high as 1.74. High-index glasses have an index of refraction in the range of 1.9 or higher. High-index thermoplastics that are easily extruded have an index of refraction in the range of 1.63. Low-index adhesives such as silicones go down to approximately 1.40. Other low index optical materials such as fluorocarbon-based coatings and gels can be as low as 1.33. Fluorocarbon-based fluids go down to 1.30. Any of these high-index and low-index materials may be matched to produce significant refraction at the interface between the lenticular lens array and the immersing medium. 
     The optimal design of a lenticular lens array for stereoscopic use may be achieved by selecting the radius and thickness of the lenticules so that the back focal distance is close to zero. In this case, the lenticular lens array may be bonded directly to the display. Alternatively, the back focal distance may be larger than zero and an air gap or spacer sheet made of transparent material may be inserted between the lenticular lens array and the front surface of the display. An air gap has the disadvantage of additional reflections and decrease in contrast. Even if an antireflection coating is used, the air gap tends to visibly degrade the image. If a spacer sheet is used, direct bonding of the spacer to both the lenticular lens and the display will avoid the problems of an air gap. 
     In the preceding analysis, the pixels are assumed to be formed at the front surface, or close to the front surface of the display. If the pixels are not formed at the front surface of the display, the back focal distance may be appropriately adjusted to image the pixels through the lenticular lens array without ghosting. This adjustment is simply a positive offset to the back focal distance by the amount of the optical distance between the pixel surface and the front surface of the display. 
     Cylindrical lenses are usually used for lenticular lens arrays, but lenses with non-cylindrical cross-sections may also be used. Aspheric lenses may be shaped such that lens aberrations are reduced, especially in the case of lenses with large curvature. The thin lens approximation may not hold for cylindrical lenses that have high curvature, but may be more accurate for aspheric lenses that are designed to minimize aberrations. 
     Some of the advantages of using a front sheet and an immersing medium in front of a lenticular lens are that the display becomes more rugged against hits and scratches, less susceptible to contamination, and easier to clean. A display with both a front sheet and immersing medium will have lower reflection of ambient light and higher contrast compared to a display that uses a front sheet but no immersing medium. 
     In addition to stereoscopic displays, other types of displays may benefit from using a front sheet and immersing medium. These include displays which use lenticular lens arrays to make still images become moving images depending on angle of view, and displays which change or morph one image into another image. These displays may be either electronic such as LCD panels, or non-electronic such as images printed on paper. 
     Other implementations are also within the scope of the following claims.