Patent Publication Number: US-2012038982-A1

Title: Films enabling autostereoscopy

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Ser. No. 12/141,352, filed Jun. 18, 2008, now allowed, the disclosure of which is incorporated by reference in its entirety herein. 
    
    
     BACKGROUND 
     D/stereo is a technology that is growing rapidly. This technology is implemented in many ways. Stereoscopic solutions include shutter glasses, polarized glasses, and others requiring the user to wear additional equipment. Autostereoscopic solutions, which do not require additional equipment, are of increasing interest, but spatially multiplexed approaches can provide a poor viewing experience, and some techniques have been developed in an attempt to provide a good quality autostereoscopic display. 
     Some autostereoscopic solutions use a double sided film with contiguous features on both sides. However, this particular type of film can have some disadvantages. The thin land—either between the lenticular features and the substrate, or between the prism features and the substrate, or both—is set in thickness by the optics, but the sharp corners and the thinness of the land can cause delamination. In addition, differences in the volume and structure of the features on the double sided film can exacerbate film warping. From an optical perspective, the double sided film with contiguous features also has a broader horizontal viewing range than may be desirable. 
     SUMMARY 
     A stereoscopic 3D liquid crystal display module, consistent with the present invention, includes a liquid crystal display panel and a directional backlight positioned to provide light to the liquid crystal display panel. A double sided prism film is disposed between the liquid crystal display panel and the directional backlight. The prism film includes a first surface having a plurality of cylindrical lenses adjacent the liquid crystal display panel and a second surface, opposite the first surface, having a plurality of non-contiguous prisms adjacent the directional backlight. 
     A stereoscopic 3D liquid crystal display apparatus, consistent with the present invention, includes a liquid crystal display panel and a directional backlight positioned to provide light to the liquid crystal display panel. The directional backlight includes a light guide having a first side, a second side opposite the first side, a first surface extending between the first and second sides, and a second surface opposite the first surface. The first surface of the light guide substantially redirects light and the second surface substantially transmits light to the liquid crystal display panel. The directional backlight also includes a first light source disposed along the first side of the light guide and a second light source disposed along the second side the light guide. A synchronization driving element is electrically coupled to the first and second light sources, and the synchronization driving element synchronizes turning each of the first or second light sources on or off in an alternating order between the first and second sides. The apparatus also includes a double sided prism film disposed between the liquid crystal display panel and the directional backlight. The prism film includes a first surface having a plurality of cylindrical lenses adjacent the liquid crystal display panel and a second surface, opposite the first surface, having a plurality of non-contiguous prisms adjacent the directional backlight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic side view of an illustrative display apparatus; 
         FIG. 2A  and  FIG. 2B  are schematic side views of an illustrative display apparatus in operation; 
         FIG. 3A  is a diagram of tool used in a process to make a 3D film; 
         FIG. 3B  is a diagram illustrating coating black material on the tool; 
         FIG. 3C  is a diagram illustrating curing the black material; 
         FIG. 3D  is a diagram illustrating coating optical resin on the tool to form non-contiguous prisms; 
         FIG. 4  is a diagram illustrating curing the optical resin; 
         FIG. 5  is a diagram of the cured resin removed from the tool to form prisms in an optical film; 
         FIG. 6  is a diagram of lenses added to the optical film to form a 3D film with opaque sections between the non-contiguous prisms; and 
         FIG. 7  is a diagram of a 3D film with transmissive portions between the non-contiguous prisms. 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. 
     All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. 
     The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The term “autostereoscopic” refers to displaying three-dimensional images that can be viewed without the use of special headgear or glasses on the part of the user or viewer. These methods produce depth perception for the viewer even though the image is produced by a flat device. The term stereoscopic 3D incorporates the field of autostereoscopic devices but also includes the stereoscopic 3D display case in which special headgear, typically shutter glasses, are need to see stereoscopic 3D from a flat device. 
     The present disclosure relates to a backlit liquid crystal display apparatus and particularly to displaying stereo 3D images using liquid crystal display apparatus having a 3D film with non-contiguous prisms. Embodiments consistent with the present invention may be combined in a single display capable of providing a 3D visualization capability from a flat display either in a shutter glasses stereoscopic 3D display mode or in an autostereoscopic display mode. While the present invention is not so limited, an appreciation of various aspects of the invention will be gained through a discussion of the examples provided below. 
     3D Display 
     A liquid crystal display is a sample and hold display device such that the image at any particular point is stable until that point or pixel is updated at the next image refresh time, typically within 1/60 of a second or faster. In such a sample and hold system, displaying different images, specifically alternating left and right images for a 3D display, during sequential refresh periods of the display requires careful sequencing of the backlight light sources so that, for example, the left eye light source is not on during the display of data for the right eye and vice versa. 
       FIG. 1  is a schematic side view of an illustrative display apparatus  10 . The display apparatus includes a liquid crystal display panel  20  and a directional backlight  30  positioned to provide light to the liquid crystal display panel  20 . The directional backlight  30  includes a right eye image solid state light source  32  or plurality of first light sources  32 , and a left eye image solid state light source  34  or plurality of second light sources  34 , capable of being modulated between the right eye image solid state light source  32  and the left eye image solid state light source  34  at a rate of, in many embodiments, at least 90 Hertz. A double sided prism film  40  is disposed between the liquid crystal display panel  20  and the directional backlight  30 . 
     The liquid crystal display panel  20  and/or directional backlight  30  can have any useful shape or configuration. In many embodiments, the liquid crystal display panel  20  and directional backlight  30  has a square or rectangular shape. However, in some embodiments, the liquid crystal display panel  20  and/or directional backlight  30  has more than four sides or is a curved shape. While the present disclosure is directed to any stereoscopic 3D backlight including those requiring shutter glasses or more than a single lightguide and associated liquid crystal display panel, the present disclosure is particularly useful for autostereoscopic displays. 
     A synchronization driving element  50  is electrically connected to the directional backlight  30 , the plurality of first and second light sources  32 ,  34 , and the liquid crystal display panel  20 . The synchronization driving element  50  synchronizes activation and deactivation (i.e., modulation) of the right eye image solid state light source  32  and the left eye image solid state light source  34  as image frames are provided at a rate of, in many embodiments, 90 frames per second or greater to the liquid crystal display panel  20  to produce a flicker-free still image sequence, video stream, or rendered computer graphics. An image (e.g., video or computer rendered graphics) source  60  is connected to the synchronization driving element  50  and provides the images frames (e.g., right eye images and left eye images) to the liquid crystal display panel  20 . 
     The liquid crystal display panel  20  can be any useful transmissive liquid crystal display panel. In many embodiments, liquid crystal display panel  20  has a frame response time of less than 16 milliseconds, or less than 10 milliseconds, or less than 5 milliseconds. Commercially available transmissive liquid crystal display panels having a frame response time of less than 10 milliseconds, or less than 5 milliseconds, or less than 3 milliseconds include, for example, the Toshiba Matsushita Display (TMD) optically compensated bend (OCB) mode panel LTA090A220F (Toshiba Matsushita Display Technology Co., Ltd., Japan). 
     The directional backlight  30  can be any useful directional backlight that can be modulated between a right eye image solid state light source  32  and left eye image solid state light source  34  at a rate of, in many embodiments, at least 90 Hertz, or 100 Hertz, or 110 Hertz, or 120 Hertz, or greater than 120 Hertz. 
     The illustrated directional backlight  30  includes a first side  31  or first light input surface  31  adjacent to the plurality of first light sources  32  or right eye image solid state light source  32  and an opposing second side  33  or second light input surface  33  adjacent to the plurality of second light sources  34  or left eye image solid state light source  34 . A first surface  36  extends between the first side  31  and second side  33 , and a second surface  35 , opposite the first surface  36 , extends between the first side  31  and second side  33 . The first surface  36  substantially re-directs (e.g., reflects, extracts, and the like) light and the second surface  35  substantially transmits light. In many embodiments, a highly reflective surface is on or adjacent to the first surface  36  to assist in re-directing light out through the second surface  35 . 
     In many embodiments, the first surface  36  includes a plurality of extraction elements such as, for example, linear prism or lenticular features as shown. In many embodiments, the linear prism or lenticular features can extend in a direction parallel to the first side  31  and second side  33  or parallel to the linear prism and lenticular features of the double sided prism film  40 . 
     The solid state light sources can be any useful solid state light source that can be modulated at a rate of, for example, at least 90 Hertz. In many embodiments, the solid state light source is a plurality of light emitting diodes such as, for example, Nichia NSSWO20B (Nichia Chemical Industries, Ltd., Japan). In other embodiments, the solid state light source is a plurality of laser diodes or organic light emitting diodes (i.e., OLEDs). The solid state light sources can emit any number of visible light wavelengths such as red, blue, and/or green, or range or combinations of wavelengths to produce, for example, white light. The directional backlight can be a single layer of optically clear material with light sources at both ends or two (or more) layers of optically clear material with a light source for each layer which preferentially extracts light in a desired direction for each layer. 
     The double sided prism film  40  can be any useful prism film having a lenticular structure on a first side and a prismatic structure on an opposing side. The double sided prism film  40  transmits light from the directional backlight to the liquid crystal display panel  20  at the proper angles such that a viewer perceives depth in the displayed image. Useful double sided prism films are described in U.S. Pat. Nos. 7,224,529 and 7,210,836, both of which are incorporated herein by reference as if fully set forth. 
     The image source  60  can be any useful image source capable of providing images frames (e.g., right eye images and left eye images) such as, for example, a video source or a computer rendered graphic source. In many embodiments, the video source can provide image frames from 50 to 60 Hertz or greater. In many embodiments, the computer rendered graphic source can provide image frames from 100 to 120 Hertz or greater. 
     The computer rendered graphic source can provide gaming content, medical imaging content, computer aided design content, and the like. The computer rendered graphic source can include a graphics processing unit such as, for example, an Nvidia FX5200 graphics card, a Nvidia GeForce 9750 GTX graphics card or, for mobile solutions such as laptop computers, an Nvidia GeForce GO 7900 GS graphics card. The computer rendered graphic source can also incorporate appropriate stereo driver software such as, for example, OpenGL, DirectX, or Nvidia proprietary 3D stereo drivers. 
     The video source can provide video content. The video source can include a graphics processing unit such as, for example, an Nvidia Quadro FX1400 graphics card. The video source can also incorporate appropriate stereo driver software such as, for example, OpenGL, DirectX, or Nvidia proprietary 3D stereo drivers. 
     The synchronization driving element  50  can include any useful driving element providing synchronizing activation and deactivation (i.e., modulation) of the right eye image solid state light source  32  and the left eye image solid state light source  34  with image frames provided at a rate of, for example, 90 frames per second or greater to the liquid crystal display panel  20  to produce a flicker-free video or rendered computer graphics. The synchronization driving element  50  can include a video interface such as, for example, a Westar VP-7 video adaptor (Westar Display Technologies, Inc., St. Charles, Mo.) coupled to custom solid state light source drive electronics. 
       FIG. 2A  and  FIG. 2B  are schematic side views of an illustrative display apparatus  10  in operation. In  FIG. 2A  the left eye image solid state light source  34  (i.e., plurality of second light sources  34 ) is illuminated and the right eye image solid state light source  32  (i.e., plurality of first light sources  32 ) is not illuminated. In this state, the light emitted from the left eye image solid state light source  34  transmits through the directional backlight  30 , through the double sided prism sheet  40 , and liquid crystal panel  20  providing a left eye image directed toward the left eye  1   a  of an viewer or observer. In  FIG. 2B  the right eye image solid state light source  32  is illuminated and the left eye image solid state light source  34  is not illuminated. In this state, the light emitted from the right eye solid state light source  32  transmits through the directional backlight  30 , through the double sided prism sheet  40 , and liquid crystal panel  20  providing a right eye image directed toward the right eye  1   b  of an viewer or observer. It is understood that while the right eye solid state light source  32  is located on the right side of the light guide and the left eye image solid state light source  34  is located on the left side of the light guide, is some embodiments, the right eye solid state light source  32  is located on the left side of the light guide and the left eye image solid state light source  34  is located on the right side of the light guide. 
     The light sources  32 ,  34  can be air coupled or index matched to the backlight light guide. For example, a packaged light source device (e.g., LED) can be edge-coupled without index matching material into the light guide. Alternatively, packaged or bare die LEDs can be index matched and/or encapsulated in the edge of the light guide for increased efficiency. This feature may include additional optical features, e.g., injection wedge shapes, on the ends of the light guide to efficiently transport the input light. The LEDs can be alternatively embedded in the edge or side  31 ,  33  of the light guide with appropriate features to efficiently collect and collimate the LED light into total internal reflection (TIR) modes of the light guide. 
     Liquid crystal display panels  20  have a refresh or image update rate that is variable, but for the purposes of this example, a 60 Hz refresh rate is presumed. This means that a new image is presented to the viewer every 1/60 second or 16.67 milliseconds (msec). In the 3D system this means that at time t=0 (zero) the right image of frame one is presented. At time t=16.67 msec the left image of frame one is presented. At time t=2*16.67 msec the right image of frame two is presented. At time t=3*16.67 msec the left image of frame two is presented, and this process is thus repeated. The effective frame rate is half that of a normal imaging system because for each image a left eye and right eye view of that image is presented. 
     In this example, turning the first plurality of light sources on to light the right (or left) image at time t=0 provides light to the right (or left) image, respectively. At time t=16.67 msec the second image left or right, starts to be put in place. This image replaces the “time t=0 image” from the top of the LCD panel to the bottom of the LCD, which takes 16.67 msec to complete in this example. Non-scanned solutions turn off all the first plurality of light sources and then turns on all the second plurality of light sources sometime during this transition, typically resulting in a display with low brightness because the image data must be stable or reasonably so over the entire image if the sequential left and right images are not to be illuminated with the incorrect light source which will lead to 3D cross talk and a poor 3D viewing experience. 
     Providing at least 45 left eye images and at least 45 right eye images (alternating between right eye and left eye images and the images are possibly a repeat of the previous image pair) to a viewer per second provides a flicker-free 3D image to the viewer. Accordingly, displaying different right and left viewpoint image pairs from computer rendered images or images acquired from still image cameras or video image cameras, when displayed in synchronization with the switching of the light sources  32  and  34 , enables the viewer to visually fuse the two different images, creating the perception of depth from the flat panel display. A limitation of this visually flicker-free operation is that, as discussed above, the backlight should not be on until the new image that is being displayed on the liquid crystal display panel has stabilized; otherwise, cross-talk and a poor stereoscopic image will be perceived. 
     The directional backlight  30  and associated light sources  32 ,  34  described herein can be very thin (thickness or diameter) such as, for example, less then 5 millimeters, or from 0.25 to 5 millimeters, or from 0.5 to 4 millimeters, or from 0.5 to 2 millimeters. 
     3D Films 
     Embodiments of the present invention help reduce the disadvantages, identified above, of the particular type of two sided film having contiguous prisms. Since the peaks of the prisms are essential elements for defining good autostereoscopic optical effects, embodiments of the present invention provide for flats or spaces between the bases of the prisms making them non-contiguous. This feature increases the land thickness and can be tailored to reduce the sharpness of the features near the film substrate, in particular providing a curvature rather than a sharp transition between the prism and the land, which improves the mechanical stability of the film and prevents cracking and delamination and reduces film warping. An additional embodiment involves placing black or opaque (light absorbing) features into the structure between the non-contiguous prisms, which can reduce off-axis light. 
       FIGS. 3A-3B  and  FIG. 4  illustrate a process for making a doubled sided 3D prism film with non-contiguous prisms.  FIG. 3A  is a diagram of a portion of a tool used in a process to make a 3D film. The tool includes a series of non-contiguous truncated prisms  41 . Only one prism is shown for illustrative purposes; the tool has as many non-contiguous prism features as necessary or desired to make the 3D film. The truncated portion of the prisms  41  may form a well  42  or a flat, or the process used to cut the prisms may leave the original tool surface, typically flat, between prisms. The tool can be made using, for example, general diamond turning techniques as described in PCT Published Application WO 00/48037, incorporated herein by reference as if fully set forth. 
       FIG. 3B  is a diagram illustrating coating an opaque material, one type of secondary material, on the tool  41 . An opaque material  43  is applied onto the truncated portion  42  of each prism  41  in a kiss coating process. An example of opaque materials to use in the 3D film include the following: black pigment filled curable binder with preferably carbon black as the pigment and an optically curable acrylate as the binder; ink including black or any absorptive color of the desired wavelength; pigment filled resin; and UV curable acrylate loaded with carbon black. In the opaque material, it may be desirable that the binder refractive index match that of the layer to which it is adhered in order to minimize interfacial reflections. In other embodiments, it may be desirable that the binder refractive index be different than that of the layer to which it is adhered in order to achieve other desired optical effects. 
     The coated opaque material  43  is then cured, as illustrated in  FIG. 3C .  FIG. 3D  is a diagram illustrating coating optical resin on the tool. After the opaque material  43  is cured, an optical resin material  44  is coated onto the tool covering the prisms  41 . After coating, the optical resin material is cured, as illustrated in  FIG. 4 , and then removed from tool  41 . 
       FIG. 5  is a diagram of the cured optical resin removed from the tool to form one side of an optical film having non-contiguous prisms  44  separated by opaque material. To form the complete doubled sided prism film, cylindrical lenses  45  are added to the opposed surface of the optical film, as shown in  FIG. 6 . The lenses can be added using another tool having cylindrical grooves to be coated on the opposed side of the optical film and then cured and removed from the other tool. The lenses and prisms for the 3D film can be made using, for example, microreplication processes such as continuous cast and cure (3C). Examples of a 3C process are described in the following patents, all of which are incorporated herein by reference as if fully set forth: U.S. Pat. Nos. 4,374,077; 4,576,850; 5,175,030; 5,271,968; 5,558,740; and 5,995,690. The lenses can be registered with the prisms in the 3D film using methods to make optical films having microreplicated registered patterns on opposed surfaces as described in U.S. Pat. Nos. 7,165,959 and 7,224,529, both of which are incorporated herein by reference as if fully set forth. The liquid from which the microreplicated structures are created is typically a curable photopolymerizable material, such as acrylates curable by UV light. Other coating materials can be used, for example a polymerizable material, and selection of a material may depend upon the particular characteristics desired for the microreplicated structures. Examples of curing methods for use in the process include reactive curing, thermal curing, or radiation curing. Although the secondary material between the prisms can be opaque, as described above, useful optical effects may be obtained by adding a material between the prisms with other useful properties such as different indices of refraction, birefringence, mechanical elasticity, and the like. 
     The secondary material also need not be applied on the tool which forms the microreplicated features as described above. For example, the material can be loaded into an evaporative carrier, the carrier and material coated onto the desired side of the double sided film, and the carrier evaporated. This technique will leave a residue of the loaded material, which can form a deposit of secondary material as shown in  FIG. 5  and  FIG. 6 . 
       FIG. 6  is a diagram of lenses added to the optical film to form a double sided prism film with opaque sections between the non-contiguous prisms. As shown in  FIG. 6 , the 3D film includes a substrate portion  46 , a series of lenses  45  on one side of substrate  46 , and a series of non-contiguous prisms  44  separated by opaque portions  43  on the opposite side of substrate  46 . The land portion  55  on the lens side and the land portion  56  on the lenticular side can each be adjusted for mechanical and optical requirements. 
     The pitch of the lenses and prisms can be adjusted based upon a particular implementation. The term “pitch” with respect to the lenses refers to the distance between centers of adjacent lenses, as illustrated by distances  51  and  52 . The term “pitch” with respect to the prisms refers to the distance between centers of adjacent prisms, as illustrated by distances  53  and  54 . 
     An alternative embodiment includes a 3D film with transmissive portions between the non-contiguous prisms. As shown in  FIG. 7 , the double sided prism film in this alternative embodiment includes a substrate portion  46 , a series of lenses  45  on one side of substrate  46 , and a series of non-contiguous prisms  44  separated by transmissive portions  47  on the opposite side of substrate  46 . This film can be made in a manner similar to the film shown in  FIG. 6 , except that the steps shown in  FIG. 3B  and  FIG. 3C  can be eliminated such that the prisms are separated by portions of the cured optical resin without an opaque material. In addition, the tool to form the prisms can include a substantially flat top rather than the well  42  in order to form substantially flat transmissive portions between the non-contiguous prisms  44 . In the film shown in  FIG. 7 , The land portion  55  on the lens side and the land portion  56  on the lenticular side can each be adjusted for mechanical and optical requirements. Although the lenses are shown as contiguous in  FIG. 6  and  FIG. 7 , the lenses can alternatively be made non-contiguous. 
     In the 3D films of  FIG. 6  and  FIG. 7 , the lenses and prisms can have either a constant pitch or a differential pitch. The term “constant pitch” means that the pitch of the lenses is designed to be the same as the pitch of the prisms, for example distances  51  and  52  substantially equal distances  53  and  54  possibly within an acceptable margin based upon the manufacturing process. The term “differential pitch” means that the pitch of the lenses is designed to be different from the pitch of the prisms, for example distances  51  and  52  do not equal distances  53  and  54 . Also, based upon the pitch, it is possible to design the registration between the lenses and prisms such that the centers of the prisms are aligned with the centers of the lenses or, alternatively, the centers of the prisms are offset from the centers of the lenses. Either type of registration can be accomplished by the process to make films with microreplicated registered patterns in the patents identified above. 
     Preferred dimensions for the pitch of the lenses and prisms are usually determined, for example, by selecting a pitch that would result in the elimination or reduction of moire patterns in the LCD panel incorporating the 3D film. The pitches can also be determined based upon manufacturability. Exemplary pitch dimensions for a 3D film include the following: 26 microns; 29 microns; 29.5 microns; 70.5 microns; and 52 microns. As LCD panels are manufactured with different pixel pitches, it can be desired to change the pitch of the 3D film to accommodate the different pixel pitches. An example of a useful pitch range for a 3D film is 10 microns to 80 microns.