Patent Publication Number: US-2007098326-A1

Title: Light guide screen with louver device

Description:
RELATED APPLICATIONS  
      This application is related to commonly owned U.S. patent application Ser. No. 10/698,829, filed on Oct. 31, 2003 by inventors Huei Pei Kuo, Lawrence M. Hubby, Jr. and Steven L. Naberhuis and entitled “Light Guide Apparatus For Use In Rear Projection Display Environments”, herein incorporated by reference. Further, this application is related to commonly owned U.S. patent application Ser. No. TBD, filed on TBD by inventors Huei Pei Kuo, Lawrence M. Hubby, Jr. and Steven L. Naberhuis and entitled “Holographic Louver Device for a Light Guide Screen”, herein incorporated by reference. 
    
    
     FIELD  
      This invention relates generally to the field of display devices, and more particularly to a light guide screen with a louver device.  
     BACKGROUND  
      Socially and professionally, most people rely upon video displays in one form or another for at least a portion of their work and/or recreation. With a growing demand for large screens, such as high definition television (HDTV), cathode ray tubes (CRTs) have largely given way to displays composed of liquid crystal devices (LCDs), plasma display panels (PDPs), or front or rear projection systems.  
      A CRT operates by scanning electron beam(s) that excite phosphor materials on the back side of a transparent screen, wherein the intensity of each pixel is commonly tied to the intensity of the electron beam. With a PDP, each pixel is an individual light-emitting device capable of generating its own light. With an LCD, each pixel is a back-lit, light modulating liquid crystal device.  
      As neither system utilizes a large tube, LCD and PDP screens may be quite thin and often are lighter than comparable CRT displays. However, the manufacturing process for LCDs, PDPs and most other flat panel displays is much more complex and intensive with respect to both equipment and materials than that of CRTs, typically resulting in higher selling prices.  
      Projection systems offer alternatives to PDP and LCD based systems. In many cases, projection display systems are less expensive than comparably sized PDP or LCD display systems. Rear projection display systems typically employ a wide angle projection lens (or multiple lenses), operating in connection with one or more reflective surfaces to direct light received from the projector through the lens(es) to the back of a screen. The lens and mirror arrangement typically enlarges the image as well.  
      To accommodate the projector, one or more lenses, and reflectors, rear projection displays are typically 18 to 20 inches deep and not suitable for on-wall mounting. A typical rear projection system offering a 55-inch HDTV screen may weigh less than a comparable CRT, but at 200+ pounds it may be difficult and awkward to install and support.  
      Often, rear projection display devices exhibit average or below average picture quality in certain environments. For example, rear projection displays may be difficult to see when viewed from particular angles within a room setting or when light varies within the environment. Light output and contrast are constant issues in most settings and viewing environments.  
      Despite advancements in projectors and enhanced lens elements, the lens and reflector design remains generally unchanged and tends to be a limiting factor in both picture quality and overall display system thickness.  
      A developing variation of rear projection displays utilizes light guides, such as optical fibers, to route an image from an input location to an output location and to magnify the image. Such displays may be referred to as light guide screens (LGSs).  
      The light guides, commonly glass or acrylic, are typically manufactured as individual fibers or layers of fibers. Typically, the orientation of input light may vary from the required orientation of the output light projected toward an observer. The light guide fibers, therefore, are flexible, and may be bent to accommodate design and manufacturing specifications.  
      Although flexible, there are limitations on the radius of curvature that may be imposed upon an optical fiber. If bent too sharply, the light may not properly propagate through the fiber. If bent too sharply the fibers may break. Accommodating the necessary radius of curvature for the optical fibers in a light guide screen, may impose limitations upon how thin the screen and the overall enclosing structure may be.  
      Weight, thickness, durability, cost, aesthetic appearance and quality are key considerations for rear projection display systems and display screens. Further, maintaining a required minimum bend radius for each light guide may be significant. From the manufacturing point of view, cost of production and increased yield are also important.  
      Hence, there is a need for a rear projection display that overcomes one or more of the drawbacks identified above.  
     SUMMARY  
      This invention provides a light guide screen with louver device. In particular, and by way of example only, according to an embodiment, provided is a light guide screen with louver device including: a plurality of aligned light guides, each light guide having an input end and an output end, the light guides subdivided into an input group and an output group; and a louver device disposed between the input group and the output group, the louver device having a first surface interfacing with the output ends of the input group and a second surface interfacing with the input ends of the output group. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram of an embodiment of a rear projection display;  
       FIG. 2  is a plane view of an input group and an output group of a magnifying layer incorporated in the display of  FIG. 1 ;  
       FIG. 3  is a perspective view of a louver device disposed between a first and a second group of light guides, the light guides arranged into magnifying layers according to an embodiment;  
       FIG. 4  is a partially exploded, perspective view of the louver device and light guide layers of  FIG. 3 , the louver device disposed between a first and a second group of light guides, the light guides arranged into magnifying layers according to an embodiment;  
       FIG. 5  is a partially exploded, perspective view of the louver device of  FIGS. 3 and 4 , disposed between a first and a second group of light guides according to an embodiment;  
       FIG. 6 a  top view of an input group and an output group of light guides, with a louver device disposed therebetween, according to an embodiment;  
       FIG. 7  is a cross-sectional view of a single light guide in an input group, a single light guide in an output group, and a louver device disposed therebetween; and  
       FIG. 8 a  top view of an input group and an output group of light guides, with a louver device disposed therebetween, according to an embodiment. 
    
    
     DETAILED DESCRIPTION  
      Before proceeding with the detailed description, it is to be appreciated that the present teaching is by way of example, not by limitation. The concepts herein are not limited to use or application with a specific light guide screen with louver device. Thus, although the instrumentalities described herein are for the convenience of explanation, shown and described with respect to exemplary embodiments, it will be appreciated that the principles herein may be equally applied in other types of light guide screen display systems.  
       FIG. 1  conceptually illustrates a portion of a light guide screen (LGS)  100 . In at least one embodiment, LGS  100  includes a plurality of aligned magnifying layers, of which magnifying layer  102  is exemplary. Each magnifying layer, e.g. layer  102  has an input location or end  104 , an output location  106  and a midsection  108 . Generally, layer  102  is structured and arranged to enlarge an image provided at input location  104  and present the enlarged image via output location  106 . Output location  106  may therefore be referred to as a magnifying output location  106 .  
      Collectively input locations  104  of each layer  102  provide an input face  109 . Collectively, output locations  106  of each magnifying layer  102  provide an output face  110 . In addition, in at least one embodiment, midsection  108  is a flexible midsection  108 .  
      As shown, each magnifying layer  102  provides one vertical slice of the output face  110 . In an alternative embodiment, not shown, each magnifying layer  102  provides one horizontal slice of the output face  110 . A light (or image) source  112 , is optically coupled to the input end  104 . The light (or image) source  112  is positioned proximate to the input face  109 . Alternatively an optical system  114  with at least one lens is disposed between the light source  112  and the input face  109 . The optical system  114  projects a focused image of the light source  112  onto the input face  109 . The output face  110 , image source  112 , optical system  114 , etc. are contained within a case  115 . An image  116  provided by light source  112  (such as a projector), and focused by optical system  114  upon input face  109 , is conveyed by the light guides of each magnifying layer  102  to the output face  110 . In certain embodiments, optical system  114  may be an incorporated part of light source  112 .  
      Referring now to  FIG. 2 , each magnifying layer  102  ( FIG. 1 ) includes a plurality of light guides  200 , of which light guide  202  is exemplary. Each light guide has an input end  204  and an output end  206 . The light guides are subdivided into an input group  208  and an output group  210 . A louver device  212  is disposed between the input group  208  and the output group  210 . More specifically, louver device  212  has a first surface  214  interfacing with the output end  206 A of light guide  202  in the input group  208 . Louver device  212  has a second surface  216  interfacing with an input end  204 B of light guide  218  in the output group  210 .  
      It is understood and appreciated that light guides  200  and  210  as used herein may be cladded light guides. More specifically, each light guide, e.g. light guide  202 , may consist of a core that is substantially optically clear and a circumferential cladding, as discussed in detail below. The core may have an index of refraction, n 1 , and the clad has an index of refraction n 2 , wherein n 1 &gt;n 2 .  
      In at least one embodiment, the midsection  220  is a flexible midsection  220 . Each magnifying output end  206 A is configured to magnify an image presented to the input end  204 A. Further, in at least one embodiment, output end  206 B is also configured to magnify an image presented to end  204 B, as is further described with respect to  FIG. 3  below. In at least one embodiment, the plurality of magnifying output ends are aligned in substantially contiguous parallel contact.  
      More specifically, the magnifying output ends are in substantially contiguous intimate contact, without intervening spacers or material separating each individual output end, e.g.  206 A or  206 B, from its neighbors on either side. In other words, the magnifying output ends lie next to one another and are in actual contact, touching along their outer surfaces at a point.  
      Still referring to  FIG. 2 , a plurality of output ends such as output end  206 A, collectively form an output face  222 . As shown in  FIG. 2 , the magnification in this face or plane, M x , equals=sin(θ 2 )/sin(θ 1 ). In this instance, θ 1  may be defined as the angle between a longitudinal centerline of input group  208 , represented by arrow  224 , and the output face  222  (or input face  224 ). This angle can be either acute or obtuse. Similarly, θ 2  may be defined as the angle between a longitudinal centerline of output group  210 , represented by arrow  226 , and output face  222  (or input face  224 ). As discussed in greater detail below, the magnified image of output face  222  is transmitted to an output surface e.g. output surface  426  in  FIG. 4 , wherein it may be magnified yet again.  
      Considering now the structure of light guide screen  100  with louver device in greater detail,  FIG. 3  includes an input group  300  and an output group  302  of light guides having a louver device  304  disposed therebetween. In particular, input group  300  includes a plurality of light guides, of which light guides  306 ,  308 ,  310  and  312  are exemplary. Further, output group  302  includes a plurality of light guides, e.g. light guides  314 ,  316 ,  318  and  320 . The light guides  314 - 320  of output group  302  may be positioned transverse to the light guides  306 - 312  of input group  300 . In particular, in one embodiment, light guides  314 - 320  are positioned perpendicular to light guides  306 - 312 .  
      In at least one embodiment, the plurality of light guides of input group  300  and output group  302  are collectively arranged into a plurality of light guide layers, of which light guide layer  322  is exemplary. For example, light guide layer  322  includes light guides  306 - 312  from input group  300 , as well as light guides  314 - 320  from output group  302 . In an alternate embodiment, the plurality of light guides of input group  300  are arranged to form a plurality of light guide layers, such as light guide layer  324 . Similarly, the light guides of output group  302  form separate and distinct light guide layers, e.g. light guide layer  326 .  
      In at least one embodiment, each light guide layer, e.g. light guide layer  322 , has a thickness equal to approximately the width of one light guide of the input group  300 . The width of the light guides in the output group could vary from the same width of the light guides in the input group, up to that width times magnification, M x . As shown in  FIG. 3 , the collective height of the light guide layers of input group  300  is equal to “h 1 ”. In at least one embodiment, the individual light guide layers, e.g. layers  322  and  324 , have the same height.  
      Cross-referencing  FIGS. 3 and 4 , each light guide  306 - 312  of input group  300  has an input end, for example input end  400  of light guide  306 . The collection of input ends define an input plane or input face  402 , according to the coordinate system of  FIG. 3 . As shown, input face  402  is substantially perpendicular to a longitudinal center line  404 . Further, as disclosed above, the output ends of each light guide  306 - 312 , e.g. output ends  406 ,  408 ,  410  and  412 , may be beveled and oriented at an angle “θ 1 ” relative to center line  404 . The output ends  406 - 412  define an output plane or output face  414 . In at least one embodiment, output ends  406 - 412  may be in contiguous parallel contact. Also, beveled or tapered output ends  406 - 412  may magnify the imaged received at input face  402 .  
      With regard to output group  302 , each light guide  314 - 320  has an input end  415 , the plurality of which collectively define an input plane or input face  416 . Input face  416  is oriented toward louver device  304 . Cross-referencing for a moment with  FIG. 2 , it can be appreciated that input face  416  is oriented at an angle “θ 2 ” relative to a longitudinal centerline of the output group.  
      Still referring to  FIGS. 3 and 4 , each light guide  314 - 320  has a magnifying output end. More specifically, light guides  314 ,  316 ,  318  and  320  include magnifying output ends  418 ,  420 ,  422  and  424  respectively. The magnifying output ends  418 - 424  define an output plane or output face  426  which may be beveled relative to the light guide layers  322  and  326  at an angle θ 3  as shown in  FIG. 3 . Stated differently, output face  426  may slope away from louver device  304  at an angle θ 3  relative to the light guide layers  322  and  326 , as shown in  FIG. 3  and  FIG. 4 . In at least one embodiment, magnifying output ends  418 - 424  may be in contiguous parallel contact. As shown, the angled orientation of faces  414  and  416 , combined with beveled output face  426 , provide the magnification required (as represented by the numbers “1” and “2” in  FIG. 4 ) as an image is transmitted from input face  402  to output face  426 .  
      The magnification in the y direction is
 
 M   y =1/sin(θ 3 )
 
      where θ 3  is the bevel angle as shown in  FIG. 3 .  
      In practice it is desirable to design the imaging system with isotropic magnification, i.e. the magnification is the same independent of the orientation of an object. Isotropic magnification of the LGS is achieved by making magnification in the x direction, M x , equal to M y .(e.g. M x =M y ). This is accomplished by judiciously choosing the angles θ 1 , θ 2  and θ 3 , such that sin(θ 2 )/sin(θ 1 ).=1/sin(θ 3 ).  
      As shown in  FIG. 4 , louver device  304  is positioned to interface with input group  300  and output group  302 . In particular, surface  428  of louver device  304  interfaces with output face  414  of input group  300 . Likewise, surface  430  of louver device  304  interfaces with input face  416  of output group  302 . Louver device  304  may be joined to each face, i.e. output face  414  and input face  416 , by means well known in the art. In one embodiment, louver device  304  is joined to output face  414  and to input face  416  with a substantially boundaryless union at each interface using a glue that has an index of refraction substantially equal to that of the louver device  304  and the core material of the light guides.  
      In most environments, an observing party will most likely be viewing light emitting from output group  302  from a location substantially perpendicular to the output face  426 . The light input to LGS  100 , however, may be input along longitudinal centerline  404 , which is transverse to the light guides  314 - 320  of output group  302 . To reduce the loss of light, improve the viewing angle provided to an observer, and provide other advantages, louver device  304  is disposed between input group  300  and output group  302 , as discussed above. As further described below, louver device  304  receives light at acute angle of incidence and directs the light toward the output face  426  (output face  104  in  FIG. 1 ) at a near normal angle of incidence. In at least one embodiment, a louver film or device, such as that disclosed in U.S. patent application Ser. No. 11/052,605, entitled “Holographic Louver Device for a Light Guide Screen” and incorporated by reference herein, may also be attached to output face  426  to redirect or assist in redirecting the centroid of the output light toward an observer.  
      In  FIG. 5 , an exploded view of louver device  304  is presented. In at least one embodiment, louver device  304  consists of a layer of transparent, optically clear material  500 , having an inner surface  502  and, parallel thereto, an outer surface  504 . The optically clear layer of material  500  may also be referred to as a sheet of optically clear material. In at least one embodiment, inner surface  502  and outer surface  504  are configured to join to input group  300  and output group  302  respectively, such as by a substantially transparent glue. In yet another embodiment, louver device  304  is configured to removably attach to input group  300  and output group  302 , such as by snaps, a tongue-and-groove system, Velcro™, screws, or other such appropriate non-permanent attachment devices.  
      A plurality of reflective angled surfaces or louver members  506  are disposed at least partially within the assembled louver device  304 . In at least one embodiment, louver members  506  are physical reflective surfaces disposed within optically clear layer  500 . Further, louver members  506  may be coated with a light-reflective coating  507  to reflect light entering louver device  304 . Also, louver members  506  are aligned to at least one predetermined angle. The members  506  may be similarly angled to define a plurality of light paths through transparent layer  500 .  
      In one embodiment of louver device  304 , louver members  506  are cylindrical mirror segments. In an alternative embodiment, louver members  506  are elliptical mirror segments. Moreover, the louver members  506  may be elliptical, cylindrical, or may have other geometric shapes. A method of providing such a louver device  304  is described in U.S. patent application Ser. No. 11/052,612 entitled “Method of Making a Louver Device for a Light Guide Screen” which is herein incorporated by reference. In at least one embodiment, louver device  304  incorporates holographic louvers. A holographic louver device is set forth and described in U.S. patent application Ser. No. 11/052,605 incorporated above.  
      Whether cylindrical, elliptical, or other geometric form, louver members  506  are provided with appropriate focusing power in the horizontal and vertical directions to spread and direct light emerging from output face  414  into input face  416 . As substantially all of the light is directed from the light guides, e.g. light guide  306 , out through output face  426  towards an observer  507 , louver device  304  incorporating louver members  506  advantageously enhances the image quality of LGS  100  and permits a wider range of predetermined viewing angles.  
      Still referring to  FIG. 5 , output face  414  comprises a plurality of output ends, e.g. output end  406 . The same may be said for input face  416  of output group  302 . The output end of each light guide, e.g. output end  406  of light guide  306 , may define in part the length, and/or height of the smallest pixel the LGS  100  can display. A pixel is understood to be the smallest complete element of a picture. The cross-sectional view provided in  FIG. 5  shows the horizontal width  508 , which is the center-to-center spacing of two adjoining output ends. This center-to-center spacing also may define the smallest pixel the LGS  100  can display.  
      It is understood and appreciated that the term pixel is highly context specific. Further, in certain instances a pixel may be formed from sub-pixel elements, such as red, green and blue elements. A typical standard TV display provides a vertical to horizontal resolution of 640:480 with about 307,200 pixels. A typical HDTV screen provides a vertical to horizontal resolution of 1920:1080 with about 2,116,800 pixels. Although capable of greater resolution a HDTV screen can display a typical TV picture either in a small portion of the usable display or by combining image elements to reduce resolution. With respect to LGS  100 , it can be appreciated that a pixel may be defined by several optical fibers or light guides, the output ends of which collectively define the pixel dimensions, or each output end may define a single pixel.  
      So as to effectively redirect light from output face  414  to input face  416 , louver members  506  are aligned to transversely cross output face  414 . The optimal angle of the louver is when the line  600  bisecting the angle between the longitudinal center lines  602 ,  604  of the light guides of the input and output group is perpendicular to the reflectors, as shown in  FIG. 6 . Under this condition, the angle, θ m  equals (θ 1 +θ 2 )/2. In the embodiment wherein the light guides are bent, the relationships stated above apply to the straight sections of the light guides immediately adjacent to the louver device  304 . Output ends, e.g. output end  406 , repeat with periodicity in creating output face  414 . The louver members  506  also repeat with periodicity. In at least one embodiment, louver members  506  are spaced at regular intervals and each louver member is substantially identical. In one embodiment, louver members  506  are arranged in parallel rows.  
      When two periodic structures are close to the same periodicity or simple fractions thereof and disposed proximate to one another, visible fringe patterns may occur. In at least one embodiment, the potential for such fringe patterns on output face  104  ( FIG. 1 ) may be significantly reduced by spacing louver members  506  at intervals about one-third the size of each pixel, which interval is optimal for pixel resolution with reduction in fringing patterns. There is little change if the intervals are smaller. However, as intervals approach one-half or more of the pixel size, fringing patterns may become problematic and resolution can be degraded. In addition, the signal light of one pixel propagated through the light guides of an input group will be coupled to the neighboring pixels of the light guides in the corresponding output group. This causes degradation of the image resolution. In at least one embodiment, the dimensions of the light guides, e.g. light guide  306 , are defined to be less than one half of the size of the pixel. Light guides of this magnitude further reduce the fringing pattern on the output face  426  and the cross coupling of the light signal. Moreover, as shown in  FIGS. 3, 4  and  5 , louver members  506  may be appropriately spaced such that more than one louver member is provided across the length of output end  406 .  
      In at least one embodiment, the index of refraction for optically clear layer  500  will be substantially the same as the index of refraction of the light guide cores establishing the light guide screen. Typically the input group  300  and the output group  302  of the LGS  100  are joined through the louver device  500  via a glue of substantially the same index of refraction. Having substantially the same index of refraction the boundary between the output face  414  and inner surface  502  will not significantly reflect light. Similarly the interface between the outer surface  504  and the input face  416  will not significantly reflect light. In other words, light from a light guide will not be reflected out the back side of light guide  306 , i.e. back out through input end  400 .  
      Considering now the transmission of light through LGS  100 , with louver device  304 ,  FIG. 7  conceptually illustrates a cross section of a single light guide  700  from an input group, e.g. input group  300  ( FIG. 3 ), a single light guide  702  from an output group, e.g. output group  302  ( FIG. 3 ), and portion of louver device  304  as used in a light guide screen  100 . As shown, input end  704  may be substantially transverse to longitudinal centerline  706  for receiving an input image or light  708 . Further, output end  710  is at an angle relative to longitudinal centerline  706 , as is input end  712 . Output end  714 , which constitutes a portion of the output face  104  of LGS  100 , is substantially transverse to a longitudinal centerline  716 .  
      In at least one embodiment, light  708  is transmitted through light guides which are optical fibers, each having a longitudinal light guide core  718  and an external circumferential cladding  720 . It is, of course, realized that light guides  700  and  702  may bend, coil, or otherwise contour such that they may not always lie in a straight line. However, light guides  700  and  702  are shown as straight for ease of discussion and illustration, and as a representation of the preferred embodiment.  
      In at least one embodiment, light  708  is transmitted through a core  718  formed of a generally optically clear plastic or plastic-type material, including but not limited to a plastic such as acrylic, Plexiglas, polycarbonate material, and combinations thereof. In an alternative embodiment, core  718  is formed of a generally optically clear glass.  
      Light guides  700 ,  702  are preferably substantially totally internally reflecting such that the light  708  (further illustrated as lines  722 ,  724  and  726 ) received at the input end  704  from image source  112  ( FIG. 1 ) is substantially delivered to the magnifying output end  710  with minimal loss. The same may be said as light rays  722 - 726  travel from input end  712  to output end  714  and the output face  104  ( FIG. 1 ). Cladding  720  is a material having a refraction index lower then that of core  718 . Total internal reflection, or TIR, is the reflection of all incident light off a boundary between cladding  720  and core  718 . TIR only occurs when a light ray is both in a medium of higher index of refraction and approaches a medium of lower index of refraction, and the angle of incidence for the light ray is greater than the “critical angle.” In this example, core  718  has a higher index of refraction than cladding  720 .  
      The critical angle is defined as the angle of incidence measured with respect to a line normal to the boundary between the two optical media for which light is refracted at an exit angle of 90 degrees—that is, the light propagates along the boundary—when the light impinges on the boundary from the side of the medium of higher index of refraction. For any angle of incidence greater than the critical angle, the light traveling through the medium with the higher index of refraction will undergo total internal refraction. The value of the critical angle depends upon the combination of materials present on each side of the boundary.  
      The delivered light  708  emerging from output end  710  passes through a substantially boundaryless interface or union between light guide  700  and louver device  304 . The index of refraction of the material of louver device  304  is substantially the same as the index of refraction of core  718 , hence little or no light is reflected or refracted as the light passes from light guide  700  to louver device  304 . The direction of propagation will, therefore, be substantially in line with longitudinal centerline  706  and will have an annular field of view, θ i , substantially defined by the equation n i  sin(θ i )=n o  sin(θ o ). Wherein θ o  is the angle of acceptance of the light guide  700  and n i  is the index of refraction of the core of the light guides. Of note, n o  is the index of refraction of the medium from where the image light impinges up the light guide. This medium is usually air or vacuum and n o  is substantially equal to 1. In at least one embodiment, the light emerges from the output end  714  into the same medium n o , and the divergence angle is substantially the same as the acceptance angle θ o . The output end  714  is usually beveled, as depicted in  FIG. 4 . In particular the beveled output ends  418 - 424  form a portion of the beveled output face  426 . In some instances, this may be an angular field of view that is both smaller than desired and oriented away from a normal viewing location.  
      To improve the viewing angle provided to an observer, and provide other advantages, a louver device  728  may be disposed on the output face defined by the output ends, e.g. output end  714 . This louver device  728  receives light from light guide  702  at acute angle of incidence to the output face and directs the light such that it emerges from the output end  714  of light guide  702  with an output cone centered at a near normal angle of exit. The exit cone angles are further customized as described in U.S. patent application to ______, Ser. No. ______, filed ______, titled “Louver Device for a Light Guide Screen” and incorporated by reference herein.  
      As shown in  FIG. 8 , the size or width (center-to-center spacing) of input group  800  may be smaller than the center-to-center spacing of output group  802 . More specifically, the center-to-center spacing, “w 1 ”, of pixels defined by input light guides, e.g. light guide  804  may be smaller than the center-to-center spacing, “w 2 ”, of pixels defined by output light guides, e.g. light guide  806 . This may be necessitated, in part, by the magnitude of angle “θ 2 ”, i.e. the acute angle of output face  808  ( FIG. 4 ) and louver device  810  relative to longitudinal centerline  812 . Moreover, the number of input group  800  light guides may not be equal to the number of output group  802  light guides. For example, in  FIG. 8 , ten (10) input light guides feed into 20 output light guides, through louver device  304 .  
      In at least one alternative embodiment, the number of the light guides in the input group  800  and the output group  802  is the same (as is shown in  FIG. 2  for input group  208  and output group  210 ). So as to accommodate the beveled output ends of the input group  802 , the width of the output group is selected to be larger. In an embodiment where there is a one to one relationship between the light guides of the input group  800  and the out put group  802 , each single input end of input group  800  may correspond to a single image pixel observed by an observer viewing the collective output ends of output group  802 . In an embodiment where there is a greater number of input group  800  light guides when compared to output group  802  light guides, generally multiple input ends will correspond to a single image pixel.  
      A benefit of employing a louver device  810  to redirect input images or light is clearly represented in  FIG. 8 . With a louver device  810  positioned between input group  800  and output group  802 , it is possible to “bend” or redirect light transverse to the orientation of the input light guides, without having to physically bend the light guides. The radius of the bend is usually made to be at least ten times bigger than the cross sectional dimension of the light guide. The output light guides are transverse to the input light guides, and may be normal thereto. In this manner, a LGS  100  with a reduced through-thickness may be manufactured.  
      Changes may be made in the above methods, systems and structures without departing from the scope thereof. It should thus be noted that the matter contained in the above description and/or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method, system and structure, which, as a matter of language, might be said to fall therebetween.