Multi-clad black display panel

[0002] This application is a continuation-in-part of U.S patent application Ser. No. 09/116,230, filed Jul. 16, 1998 now abandoned, and entitled “MULTI-CLAD BLACK OPTIC DISPLAY”.

[0004] 1. Field of the Invention

[0005] The present invention is directed generally to a planar optical display, and, more particularly, to a multi-clad black display panel and a method of making a multi-clad black display panel.

[0006] 2. Description of the Background

[0007] Video display screens typically use cathode ray tubes (CRTs) for projecting an image onto the outlet face of the screen. A typical screen of this type has a width to height ratio of 4 with 525 vertical lines of resolution. An electron beam must be scanned both horizontally and vertically on the screen to form a number of pixels, which collectively form the image. Conventional cathode ray tubes have a practical limit in size and are relatively deep to accommodate the required electron gun. Larger screen televisions are available which typically include various forms of image projection for increasing the screen image size. However, such screens may experience limited viewing angle, limited resolution, decreased brightness, and decreased contrast. In order to improve brightness, more light must be incident to the viewer and less absorbed within the unit. In order to improve contrast, it is necessary that the viewing screen be as black as possible. It is not currently possible for direct view CRT's to be black because they utilize phosphors for forming the viewing image, and the phosphors are not black.

[0008] In U.S. Pat. No. 5,625,736, an optical panel having a plurality of stacked waveguides is rendered black using a black cladding layer between transparent cores of the waveguides. The cladding layers disclosed therein have a lower index of refraction than the waveguide cores for effectuating substantial internal reflection of the image light channeled through the cores, and thereby improve contrast. However, the dual function black cladding layer, because the layer is black in color and thus places black particles in direct contact with the core, creates a small amount of light absorption, thereby reducing the amount of total internal reflection. The maximum brightness of the image displayed on the screen is thereby reduced.

[0009] Therefore, the need exists for a display panel which provides substantially total internal reflection to improve brightness, while also providing a black screen to improve viewing contrast.

[0010] The present invention is directed to an optical display panel which provides improved viewing contrast and brightness by increasing the black area visible to a viewer, while minimizing light absorption within the panel by minimizing the exposure of black particles directly to the light. The multi-clad black display panel includes an inlet face at one end for receiving light, and an outlet screen at an opposite end for displaying the light. The inlet face is defined at one end of a transparent body formed by a plurality of waveguides, and the outlet screen is defined at an opposite end of the body and may be disposed obliquely with the inlet face. Each of the waveguides includes a core for channeling light, and the core is placed between an opposing pair of transparent cladding layers. The waveguides also have a black layer disposed between transparent cladding layers.

[0011] The present invention is also directed to a method of making a multi-clad black display panel. The method includes stacking a plurality of glass sheets, each having attached thereto opposed transparent cladding layers, with a black layer disposed between each sheet, and placing the stack against a saw and cutting the stack, using the saw, at two opposite ends at an angle to form a wedge-shaped panel having an inlet face and an outlet face.

[0012] The multi-clad black display panel solves problems experienced in the prior art by providing substantially total internal reflection, thereby improving screen brightness, while also providing a black screen to improve viewing contrast.

[0013] For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein:

[0014] FIG. 1 is an isometric view schematic illustrating a display panel; and

[0015] FIG. 2 is an isometric view illustrating a vertical cross section of a multi-clad black display panel.

[0016] 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.

[0017] FIG. 1 is an isometric view schematic illustrating a display panel 10. The display panel 10 may include a plurality of stacked optical waveguides 16a, an outlet face 16 at one end of a body 18 formed by the plurality of stacked waveguides 16a, an inlet face 12 at a second end of the body 18, and a light generator 21.

[0018] The body 18 is preferably solid and homogeneous, and receives light 14 along the surface of the inlet face 12. The light 14 is passed through the body 18 after entering the inlet face 12. In a preferred embodiment of the present invention, the body 18 is formed of the length, height, and width of the plurality of stacked waveguides 16a.

[0019] The plurality of stacked waveguides 16aforms the body 18 of the panel 10, forms at one end of the stack 16athe inlet face 12, and at a second end the outlet face 16. The waveguides 16amay be formed of any material known in the art to be suitable for passing electromagnetic waves therethrough, such as, but not limited to, plastics, or glass. The preferred embodiment of the present invention is implemented using individual glass sheets, which are typically approximately 0.004″ thick, and which may be of a manageable length and width. 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®.

[0020] The inlet face 12 and outlet face 16 are formed by the plurality of waveguides 16a, wherein one end of each waveguide 16aforms an inlet for that waveguide, and wherein the opposite end of each waveguide 16aforms an outlet for that waveguide 16a. Each waveguide 16aextends horizontally, and the plurality of stacked waveguides 16aextends vertically. The light 14 may be displayed on the outlet face in a form such as, but not limited to, a video image 14a. The focusing length of the panel 10 may increase from the outlet face 16 to the back face 19 where the panel 10 is formed in a wedge shape, which may result in an image 14ahaving slightly reduced resolution. A panel 10 having reduced resolution may be used in alternate applications, rather than video display screen applications. For example, the panel 10 may be used as an illuminated button whose screen requires a simple image communicated to the viewer.

[0021] The outlet face 16 is formed by the plurality of stacked optical waveguides 16a. The outlet face 16 is at one end of the body 18, and is disposed obliquely with the inlet face 12. The inlet face 12 is generally defined as the bottom of the body 18, and the outlet face 16 is defined as the front of the body 18. The outlet face 16 may be generally perpendicular to the inlet face 12, forming a triangular wedge having an acute face angle A between the inlet face 16 of the body 18 and the back end 19 of the body 18. The acute face angle A may be in the range of about 1 to about 10 degrees, and is preferably about 5 degrees, with the panel 10 increasing in thickness from a minimum at the top of the body 18, to a maximum thickness at the bottom of the body 18. 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 use in a typical television application. In an exemplary embodiment of the present invention, a maximum thickness in the range of about 5.0 to 8.0 cm may be chosen, in conduction with a height of 100 cm and a width of 133 cm.

[0022] The light generator 21 generates light 14 and passes the light to inlet face 12. The light generator may include a light source 22, a light modulator 24, and imaging optics 25. 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, an arc lamp, or an LED. The light 14 from the source 22 may then be modulated by the modulator 24 for defining individual picture elements, known in the art as pixels. The modulator 24 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 raster scanner, a vector scanner, a CRT, or an FED. The imaging optics 25 may include light folding mirrors or lenses. The imaging optics 25 are optically aligned between the inlet face 12 and the light modulator 24 for compressing or expanding and focusing the light 14 as required to fit the inlet face 12. The light 14, after entry into the inlet face 12, travels through the panel body 18 to the outlet face 16. The light 14 is projected from the image optics 25 over the inlet face 12, and is thus directed generally vertically upward for projection from the outlet face 16.

[0023] The display panel 10 of the present invention may include at least one light redirective element connected at the outlet face 16 in order to redirect the light 14, which is incident in a direction generally vertically upward from the inlet face 12, to a direction perpendicular to the outlet face 16. The light redirective element may be, but is not limited to, a mirrored serration, a plurality of serrations, a holographic coating, a lens or series of lenses, a micro-lens or series of micro-lenses, or a Fresnel prism.

[0024] FIG. 2 is an isometric view illustrating a vertical cross section of a multi-clad black display panel 10. The multi-clad black display panel 10 is a preferred embodiment of the panel 10 of FIG. 1. The multi-clad black display panel includes a body 18 formed of a plurality of stacked optical waveguides 16a, extending from the inlet face 12 to the outlet face 16, for independently channeling and confining the light 14 therethrough.

[0025] The waveguides 16aare in the form of sheets or ribbons extending the full width of the outlet face 16 and are stacked to collectively form at their upper ends the height of the outlet face 16. The waveguides 16aare disposed along their longitudinal light transmitting axes at an acute face angle A with the outlet face, which angle is defined by the acutely beveled upper ends of the waveguides 16adisposed coplanar in the vertical plane. The number of waveguides 16amay be selected for providing a corresponding vertical resolution of the outlet face 16. For example, 525 of the waveguides 16amay be stacked to produce 525 lines of vertical resolution in the outlet face 16. Since the waveguides 16aextend the full width of the outlet face 16, horizontal resolution is controlled by horizontal modulation of the image light 14.

[0026] Each of the plurality of waveguides includes a central core 26 for channeling the image light 14 through the waveguides, and each core 26 is disposed between an opposing pair of cladding layers 28. In a preferred embodiment of the present invention, the cladding layers 28 extend completely from the inlet face 12 to the outlet face 16 along the entire width of the outlet face 16. A black layer 30 is disposed between adjoining cladding layers 28 for absorbing ambient light 32 at the outlet face 16. 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 black layer 30 is only necessary within the viewable region of the outlet face, but, in a preferred embodiment of the present invention, the black layer 30 extends completely from the inlet face 12 to the outlet face 16 along the entire width of the outlet face 16.

[0027] Each central core 26 has a first index of refraction. The cladding layers 28 have a second index of refraction, lower than that of the central core 26, for ensuring total internal reflection of the image light 14 as it travels from the inlet face 12 to the outlet face 16. The core is preferably bidirectional. In a preferred embodiment of the present invention, the cladding layers 28 are transparent in order to effectuate total internal reflection of the image light 14, and thereby maximize the brightness of the light 14 at the outlet face 16. The black layers 30 may have any index of refraction. Due to the positioning of the waveguides 16aat the acute face angle A with the outlet face, the black layers 30 are exposed at the outlet face 16 and are viewable at the outlet face 16, thus absorbing ambient light 32 and thereby increasing viewing contrast of the outlet face 16. The black layers 30 are also viewable at the outlet face 16 through the transparent central cores 26 and transparent cladding layers 28, thereby further absorbing ambient light 32 and increasing viewing contrast. Because the black layers 30 are separate from the cladding layers, the black layer does not contact the glass directly, thus preventing the absorption of any portion of the light due to black particle. Therefore, because only lower refraction index particles are in direct contact with the glass, internal reflection is substantially improved.

[0028] The plurality of stacked waveguides 16amay be formed by several methods. A plurality of glass sheets, as described above, may be used as the central cores 26, and may be individually coated with, or dipped within, a clear substance having an index of refraction lower than that of the glass, such as, but not limited to, polyurethane, clear coat, silicons, cyanoacreylates, and low index refraction epoxys, thereby forming a coated glass sheet. This clear substance is the opposed cladding layers 28. Alternatively, two pieces of polymethylmethacrylate (plexiglass) could be fastened to each face of the glass sheet by methods known in the art, thereby forming the coated glass sheet. A first coated glass sheet is then placed in a trough sized slightly larger than the first coated glass sheet. The trough may then be filled with a thermally curing black epoxy. The black epoxy need not possess the properties of a suitable cladding layer. After filling of the trough, coated glass sheets are repeatedly stacked, and a layer of epoxy forms between each coated glass sheet, thereby forming the black layers 30. The sheets are preferably stacked at a slight angle, which angle must be less than 90 degrees. The stacking is preferably repeated until between approximately 500 and 800 sheets have been stacked. Uniform pressure may then be applied to the stack, thereby causing the epoxy to flow to a generally uniform level between coated glass sheets. The stack may then be baked to cure at 80 degrees Celsius for such time as is necessary to cure the epoxy, and the stack is then allowed to cool slowly in order to prevent cracking of the glass. After curing, the stack is placed against a saw, such as, but not limited to, a diamond saw, and cut at two opposite ends at an angle to form a wedge-shaped panel 10 having an inlet face 12 and an outlet face 16. The inlet face 12 and the outlet face 16 may be cut as planar or curved as desired. The cut portions of the panel 10 may then be polished with a diamond polisher to remove any saw marks. For example, the lower end of the stack may be polished for receiving the image light 14 over the inlet face 12. Furthermore, the exposed ends of the central cores 26 at the outlet face 16 may be frosted to diffuse the image light 14.

[0029] In a second embodiment of the present invention, the coated glass sheets may be coated with a black substance, such as spray paint. The coated blackened glass sheets may then be stacked within a trough containing clear or black epoxy, followed by the steps recited hereinabove.

[0030] In another embodiment of the present invention, the coated blackened glass sheets may be individually fastened using glue or epoxy, without the use of a filled trough or the equivalent, followed by the steps recited hereinabove.

[0031] In another embodiment of the present invention, the coated glass sheets preferably have a width in the range between 0.5″ and 1.0″, and are of a manageable length, such as 12″. The coated glass sheets are stacked, but need not be stacked at an angle, and a layer of black UV adhesive is placed between each sheet. Ultraviolet radiation is then used to cure each adhesive layer, and the stack may then be cut and/or polished and discussed hereinabove. The adhesive layers are preferably approximately 0.0002″ in depth.

[0032] In another embodiment of the present invention, the black layer 30 may be a black plastic laminate, or a black polyethylene, bonded between respective pairs of cladding layers 28 using glue or black or clear epoxy, which bonded stack may then be cut and/or polished as described hereinabove.

[0033] In another embodiment of the present invention, both the clear substance and the black layer could be formed of a suitable substance and placed, in turn, on the glass core using sputtering techniques known in the art, or deposition techniques known in the art. The steps are then followed as recited above.

[0034] Those of ordinary skill in the art will recognize that many modifications and variations of the present invention may be implemented. For example, different steps of the various methods of forming the multi-clad black display panel may be interchangeably combined, while still producing a substantively similar panel. The foregoing description and the following claims are intended to cover all such modifications and variations.