Abstract:
An optical panel having a small inlet, and a method of making a small inlet optical panel, are disclosed, which optical panel includes a individually coating, stacking, and cutting a first plurality of stacked optical waveguides to form an outlet face body with an outlet face, individually coating, stacking, and cutting a second plurality of stacked optical waveguides to form an inlet face body with an inlet face, and connecting an optical coupling element to the first plurality and second plurality of stacked optical waveguides, wherein the optical coupling element redirects light along a parallel axis of the inlet face to a parallel axis of the outlet face. In the preferred embodiment of the present invention, the inlet face is disposed obliquely with and askew from the outlet face.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/318,933, filed May 26, 1999, U.S. Pat. No. 6,222,971 and entitled “SMALL INLET OPTICAL PANEL AND A METHOD OF MAKING A SMALL INLET OPTICAL PANEL”, which is a continuation-in-part of U.S. patent application Ser. No. 09/118,270, filed Jul. 17, 1998, and entitled “SMALL INLET OPTICAL PANEL”, now abandoned. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under contract number DE-AC02-98CH10886, awarded by the U.S. Department of Energy. The Government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to a planar optical display, and, more particularly, to a small inlet optical panel and a method of making a small inlet optical panel. 
     2. Description of the Background 
     It is known in the art to form an optical panel from a plurality of stacked waveguides. The waveguides collectively define an inlet face at one end of the waveguides and an outlet face at an opposite end. The outlet face may be disposed obliquely with the inlet face. The outlet face may form an small acute face angle with the longitudinal axes of the waveguides, thus allowing the height of the screen to be substantially larger than the depth or thickness of the panel. The panel inlet face generally extends the fill width of the panel correspondent to the width of the outlet face, but is very narrow due to the thinness of the panel. For example, where an inlet face has a width of 133 cm, the corresponding length in the prior art would be 2.54 cm. 
     The narrow inlet face necessitates the use of a complex light projection system for distributing and focusing the image light across the full width and depth of the panel, thereby allowing for accurate display on the outlet face. This complex light projection system increases the complexity and cost of the overall system, and increases the space requirements of the display panel. 
     Therefore, the need exists for a waveguide optical panel having an aperture inlet which allows for simplification of light projection and focusing at the inlet, without a loss of image resolution at the outlet face. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to a small inlet optical panel, which includes a first plurality of stacked optical waveguides which forms an outlet face body with an outlet face, which includes a second plurality of stacked optical waveguides which forms an inlet face body with an inlet face, and an optical coupling element connected to the first plurality and to the second plurality, wherein the optical coupling element redirects light along a parallel axis of the inlet face to a parallel axis of the outlet face. In the preferred embodiment of the present invention, the inlet face is disposed obliquely with and askew from the outlet face. 
     The present invention is also directed to a method of making a small inlet optical panel which includes individually coating a plurality of glass sheets in a substance having an index of refraction lower than that of the glass sheets, stacking the plurality of coated glass sheets, wherein each coated glass sheet is fastened to an adjoining glass sheet using an adhesive, applying pressure to the stack, curing the adhesive, cutting the stack to form an outlet face body having a first wedge shape with an outlet face thereon, repeating the individually coating, the stacking, the applying and the curing to form a second stack, cutting the second stack to form an inlet face body having a second wedge shape correspondent to the first wedge shape and having an inlet face thereon, and joining together the inlet face body and the outlet face body at an optical coupling element, wherein the outlet face is disposed askew from the inlet face, for redirecting light incident into the inlet face body to a direction incident into the outlet face body. 
     The present invention solves difficulties encountered in the prior art by providing a waveguide optical panel having a small aperture inlet, which allows for simplification of light projection and focusing at the inlet, without a loss of image resolution at the outlet face. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein: 
     FIG. 1 is an isometric view schematic illustrating a small inlet optical panel; 
     FIG. 2 is an isometric view schematic illustrating a horizontal and vertical cross-section of a small inlet optical panel; 
     FIG. 3 is a schematic illustrating an exaggerated horizontal and vertical cross-section of the-small inlet optical panel; 
     FIG. 4 is a horizontal and vertical cross section of the small inlet optical panel illustrating an alternative embodiment of the panel using one plurality of waveguides; 
     FIG. 5 is an isometric view schematic illustrating an alternative embodiment of the small inlet optical panel which includes an optical coupler in the form of a holographic optical element; 
     FIG. 6 is an isometric view schematic illustrating an alternative embodiment of the small inlet optical panel wherein the inlet face is coplanar with the outlet face; and 
     FIG. 7 is an isometric view schematic illustrating an alternative embodiment of the small inlet optical panel wherein the inlet face is opposite the outlet face. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in a typical optical display panel. Those of ordinary skill in the art will recognize that other elements are desirable and/or required in order to implement the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
     FIG. 1 is an isometric view schematic illustrating a small inlet optical panel  10 . The display panel  10  includes an inlet face  12  for receiving light  14 , and an outlet face  16  disposed obliquely with and askew from the inlet face  12  for displaying light  14 . The light  14  is generated by a light generator  17 . The inlet face  12  and outlet face  16  are each formed by a plurality of waveguides  12   a ,  16   a , wherein one end of each waveguide  12   a ,  16   a  forms an inlet for that waveguide  12   a ,  16   a , and wherein the opposite end of each waveguide  12   a ,  16   a  forms an outlet for that waveguide  12   a ,  16   a.    
     The inlet face  12  is preferably disposed generally perpendicular to and askew from the outlet face  16  for receiving the light  14  from the modulator  20  and projector  22 . The horizontal extension of each waveguide  12   a  of the inlet face  12  is disposed below and substantially perpendicular to the horizontal extension of each waveguide  16   a  of the outlet face  16 . The plurality of stacked waveguides  12   a  of the inlet face  12  extends vertically. 
     Each waveguide  16   a  extends horizontally, and the plurality of stacked waveguides  16   a  extends vertically, along the outlet face  16 . The light  14  is displayed on the outlet face  16  in a form such as, but not limited to, a video image  14   a  The outlet face  16  may be generally formed into a triangular wedge having an acute face angle A between the bottom  30  of the body  32  of the outlet face  16  and the back  34  of the body  32  of the outlet face  16 . The acute face angle A may be in the range of about 5 to 10 degrees, for example, with the panel  10  increasing in thickness from a minimum at the top  36  of the body  32  of the outlet face  16 , to a maximum thickness at the bottom  30  of the body  32  of the outlet face  16 . The maximum thickness may be chosen as small as is practicable in a given application. The panel  10  has a height from the top to the bottom of the outlet face  16 , and a width from the left to the right of the outlet face  16 . The width and height may be selected to produce width to height aspect ratios of 4:3 or 16:9, for example, for uses such as a typical television application. In an exemplary embodiment of the outlet face  16  of the present invention, a maximum thickness in the range of about 8 cm may be chosen, in conjunction with a height of 100 cm and a width of 133 cm. The left to right width of the inlet face  12  is chosen to be the same as the maximum thickness T of the panel  10 . The inlet face  12  has a suitable vertical height h, which is a matter of design choice. The inlet face  12  has a width to height aspect ratio which, for the purpose of ease of interface with the outlet face  16 , is preferably also 4:3. Correspondingly, the panel  10  diverges in two wedge shapes, one from the bottom  30  to the top  36  of the outlet face body  32 , and the second at the bottom  30  of the outlet face body  32 , from the left of the interface  40  to the inlet face  12 . 
     The disposition of the inlet face  12  with the outlet face  16  necessitates the redirection of the light  14 , which light  14  is incident on the inlet face  12  in an approximately horizontal plane and must be redirected to a vertically upwardly direction through the waveguide  16   a  of the outlet face  16 . This periscopic optical path permits the use of a relatively small area modulator  20  at the bottom of the panel  10  to provide a small aperture light source which is expanded through the panel  10  for display on the outlet face  16  at a substantially increased viewing area. 
     The light generator  17  generates light  14  and passes the light  14  to inlet face  12 , and the surface area of light generation immediately adjacent to the inlet face  12  preferably is equivalent to the surface area of the inlet face  12 . The light generator  17  may include a light source  22 , a light modulator  20 , or imaging optics. The light  14  may be initially generated by the light source  22 . The light source  22  may be, for example, a bright incandescent bulb, a laser, a plurality of phosphors, at least one LED, at least one OLED, at least one FED, or a projector. The light  14  from the source  22  is preferably collimated. The light  14  may be modulated by the modulator  20  for defining individual picture elements, known in the art as pixels. The modulator  20  may take a form known in the art, such as, but not limited to, a liquid crystal display (LCD), a Digital Micromirror Device (DMD), a GLV, a raster scanner, a vector scanner, a PDLC, an LCOS, a MEMS, and a CRT. The imaging optics may include light folding mirrors or lenses. The imaging optics may be optically aligned between the inlet face  12  and the light modulator  20  for compressing or expanding and focusing the light  14  as required to fit the inlet face  12 . The modulated light  14  is generally incident on the inlet face  12  from the imaging optics as a compressed image which is transmitted horizontally through the inlet face  12 , turned for transmission vertically upwardly through the outlet face body  32  for display, and expands for suitable horizontal and vertical resolution and scale. 
     FIG. 2 is an isometric view schematic illustrating a horizontal and vertical cross-section of a small inlet optical panel  10  of FIG.  1 . The panel  10  includes a first, or top, plurality of stacked optical waveguides  16   a  forming an outlet face  16 , a second, or bottom, plurality of stacked waveguides  12   a  stacked perpendicularly to the outlet face  16  to form an inlet face  12  below the bottom  30  of the body  32  of the outlet face  16 , and a light redirection element  50  disposed inside the panel  10  at the interface  40  between the inlet face waveguides  12   a  and the outlet face waveguides  16   a  for redirecting the light  14  for periscopic transmission through the waveguides  12   a ,  16   a.    
     The waveguides  12   a ,  16   a  are configured in two independent groups with the first plurality of waveguides  16   a  forming a wedge defining the outlet face  16  and the interface  40 . The second plurality of waveguides  12   a  are disposed below the light redirection element  50  at the interface  40 , and forms a wedge defining the inlet face  12 . The second plurality of waveguides  12   a  are configured in a wedge correspondent to the wedge shape of the outlet face body  32 . The body  32  of the outlet face  16  wedge receives the light  14  for transmission vertically upwardly to the outlet face  16 . The body  32  of the outlet face  16  receives light  14  to along the surface of the bottom  30  of the body  32 , adjacent the light redirection element  50 . The light  14  received at the bottom  30  of the body  32  is passed through the body  32 , and is displayed on the outlet face  16 . The body  60  of the inlet face  12  wedge receives the light  12  at its vertical inlet face  12  for transmission substantially horizontally to emission at the light redirection element  50 . The inlet face  12  may be sized to match the area of the modulator  20  for receiving the light  14 , and the inlet face  12  is also substantially smaller in area than the interface  40  at the light redirection element  50 . The angle A of the outlet face  16  wedge may be about 5 to 10 degrees, and the second angle B of the inlet face  12  wedge is then be suitably smaller. 
     The plurality of stacked waveguides  12   a ,  16   a  used to form the inlet face  12  and the outlet face  16  may be formed of any material known in the art to be suitable for passing electromagnetic waves therethrough, such as, but not limited to, glass, plastics, polymers. The preferred embodiment of the present invention is implemented using individual glass sheets, which are typically approximately 2-40 microns thick. Two different thicknesses of glass sheet may be used simultaneously in a given application of the present invention, one to form the outlet face  16 , and one to form the inlet face  12 . In the preferred embodiment of the present invention, the glass sheets used within the inlet face  12  are approximately the same thickness, and the glass sheets used within the outlet face  16  are approximately the same thickness. The glass used may be of a type such as, but not limited to, glass type BK-7, or may be a suitable plastic laminate, such as Lexan®, commercially available from the General Electric Company®. The waveguides  12   a ,  16   a  are discussed with more particularity with respect to FIG.  3 . 
     The light redirection element  50  is disposed between the body  60  of the inlet face  12  and the body  32  of the outlet face  16 . The light redirection element  50  may be, for example, an optical coupling element, and may be fastened to each plurality of waveguides  12   a ,  16   a  using methods known in the art, such as an optically transparent epoxy. The function of the coupler  50  is to redirect the initially horizontally directed light  14  from the bottom plurality of waveguides  12   a  vertically upwardly into the top plurality of waveguides  16   a . Both the waveguides  12   a ,  16   a  and the coupler  50  of the present invention are passive optical devices. The light redirection element  50  is discussed with more particularity with respect to FIG.  3 . 
     FIG. 3 is a schematic illustrating an exaggerated horizontal and vertical cross section of the small inlet optical panel  10  embodied in FIG.  2 . The light redirection element  50  redirects the light  14  flowing into the inlet face  12 , which then flows through the bottom plurality of waveguides  12   a  and is thereby incident on the light redirection element SO, to flow into the top plurality of waveguides  16   a , and thereby be incident on the outlet face  16 . The light redirection element  50  preferably includes a plurality of fresnel prismatic grooves  50   a  which are straight along the width of the bottom waveguides  12   a  in the direction of the panel thickness T for redirecting the image light  14  vertically upwardly into the top plurality of waveguides  16   a . In a preferred embodiment, the light redirection element  50  is an optical coupler  50  in the form of a Transmissive Right Angle Film (TRAF) II, which is commercially available from the 3M Company of St. Paul, Minn. The TRAF II coupler  50  is effective for turning the image light at an angle of up to approximately 90°. In an alternative embodiment of the present invention, the light redirection element  50  may be in the form of a diffractive grating  50 , which diffractive grating  50  includes an extremely small series of straight gratings configured for optically diffracting the light  14  in order to turn the light flowing substantially horizontally through the bottom plurality of waveguides  12   a  vertically upwardly into the top plurality of waveguides  16   a . The diffractive grating  50  has a lower turning angle capability than the TRAF II embodiment. 
     An individual waveguide  12   a ,  16   a  used in the present invention typically includes a cental core  100  laminated between cladding layers  102 , a receiving end  104 , and an outlet end  106 . The central core  100  channels the image light  14  through the waveguide  12   a ,  16   a , is disposed between cladding layers  102 , and extends from the receiving end  104  to the outlet end  106 . The central core  100  is, in the preferred embodiment, a glass sheet of thickness T in the range between 2 and 40 microns, as discussed hereinabove. The central core  100  has a first index of refraction. The cladding layers  102  also extend from the receiving end  104  to the outlet end  106 . The cladding layers  102  may be black in color to improve contrast and brightness. Alternatively, a black layer maybe disposed between adjoining cladding layers  102  for absorbing ambient light at the outlet end  106 , where the adjoining cladding layers  102  are transparent. The term black is used herein to encompass not only pure black color but additionally, any functionally comparable dark color suitable for use in the present invention, such as dark blue. The cladding layers  102  have a second index of refraction, lower than that of the central core  100 , for ensuring total internal reflection of the image light  14  as it travels from the receiving end  104  to the outlet end  106 . 
     The top plurality  16   a  and the bottom plurality  12   a  of stacked waveguides may be made by several methods. A plurality of glass sheets may be individually coated with, or dipped within, a substance having an index of refraction lower than that of the glass, and a plurality of coated sheets may then be fastened together using glue or thermally curing epoxy. Alternatively, the glue or epoxy could form the cladding layers and be applied directly to the glass sheets. In one embodiment of the present invention, a first coated or uncoated glass sheet is placed in a trough sized slightly larger than the first coated glass sheet, the trough is filled with a thermally curing black epoxy, and the coated or uncoated glass sheets are repeatedly stacked at an angle, forming a layer of epoxy between each coated or uncoated glass sheet. The stacking is preferably repeated until between approximately 500 and 800 sheets have been stacked. The number of waveguides  16   a  which are stacked to form the outlet face  16  are selected for providing a corresponding vertical resolution of the outlet face  16 . For example,  525  of the waveguides  16   a  may be stacked in the outlet face  16  to produce 525 lines of vertical resolution in the outlet face  16 . Uniform pressure may then be applied to the stack, followed by a cure of the epoxy, and a sawing of the stack into a wedge shape of an angle dependant on the use of the stack as an outlet face  16  or an inlet face  12 . The wedge may be sawed curved or flat, and may be frosted or polished after sawing. 
     FIG. 4 is a horizontal and vertical cross section of the small inlet optical panel  10  illustrating an alternative embodiment of the panel  10 . In this alternative embodiment, the top plurality of waveguides  16   a  extend vertically, continuously from the outlet face  16  to the side inlet face  12 , with the interface  40  being horizontal and disposed at the bottom edge  30  of the outlet face  16 . 
     In this alternative embodiment, the light redirection element  50   c , is disposed at the bottom of the panel  10  and is inclined from the inlet face  12  at the right side of the outlet face  16  to the opposite side of the outlet face  16 . The bottom of the plurality of waveguides  16   a , as well as the element  50   c , are therefore inclined at the small acute angle B from the bottom of the panel  10 , thereby defining a bottom wedge portion. Also in this alternative embodiment, the element  50   c  includes a plurality of tilted reflective facets or mirrors  50   c  optically aligned between the inlet face  12  and the interface  40  for reflecting the substantially horizontally directed light  14  vertically upwardly to the outlet face  16 . 
     FIG. 5 is an isometric view schematic illustrating an alternative embodiment of the small inlet optical panel  10 , and includes a light redirection element  50   d  in the form of a holographic optical element  50   d  configured to reflect the image light  14  from the inlet face  12  across the interface  40  for display on the outlet face  16 . The holographic coupler  50   d  may take a conventional form known in the art for turning the light  14  from a substantially horizontal direction to the vertical direction required for internal transmission through the top plurality of waveguides  16   a  to the outlet face  16 . 
     FIG. 6 is an isometric view schematic illustrating an alternative embodiment of the small inlet optical panel  10 , including a top plurality of waveguides  16   a  configured as in the above embodiments. The alternative embodiment of FIG. 7 also includes a bottom plurality of waveguides  12   a  which are continuous along the full width W of the outlet face  16  and are stacked vertically. In this embodiment, the inlet face  12  extends the full width W of the outlet face  16  directly below the outlet face  16  at the front of the panel  10 . 
     FIG. 7 is an isometric view schematic illustrating an alternative embodiment of the small inlet optical panel  10 , wherein the inlet face  12  extends the full width W of the outlet face  16 , but is disposed at the back of the panel  10 . 
     Those of ordinary skill in the art will recognize that many modifications and variations of the present invention may be implemented. The foregoing description and the following claims are intended to cover all such modifications and variations.