METHODS FOR MANUFACTURING

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U S Provisional Applicatio No 60/008,812, filed Decemnber 18, 1995 Technical Field This invention relates generally to viewing displays, front and rear projection screens, and flat panel electronic displays and, more particularly, it relates to the manufacture of the viewing screens for such displays

Background Art The performance of a viewing screen for a flat panel electronic display can be enhanced by incorporating tapered optical waveguides in the screen structure Relying in part on the phenomenon of total internal reflection or "TER," the waveguides focus and direct the light waves passing through the screen, enhancing the brightness of the image, while avoiding "hot spots " Such waveguides are discussed at length in pending U S. patent application serial no. 08/086,414, filed

July 1, 1993 for a "Direct View Display with Array of Tapered Waveguide," by Zimmerman et al , U S patent application serial no. 08/371,648, filed January 12, 1995 for a "Display Screen Device with Array of Tapered Waveguides," by Zimmerman et al., U S patent application serial no 08/390,603, filed February 17,

1995, for an "Optical Waveguide having Two or More Refractive Indices and Method of Manufacturing Same," by Zimmerman et al. and U.S. patent application and U.S. Patent No 5,462,700 for a "Process for Making an Array of Tapered Photopolymerized Waveguides," by Beeson et al., all assigned to the

same assignee as the present application and incorporated herein by reference

Currently, tapered optical waveguides are fabricated using photolithographic techniques using a removable mask. Among the drawbacks of a photolithographic process are the tooling expenses for the mask, the limited life of the mask, and the labor or automation required to attach and then remove the mask after photolithography. If the screen could be made without a mask, the tooling and attachment and removal efforts could be avoided.

Disclosure of Invention

This and other objects may be achieved by fabricating a viewing screen using a photochemical process that utilizes a textured or embossed surface or a gradient index-lens array substrate in place of a reusable mask. When fabricated in this manner, the textured or embossed or gradient index-lens-array substrate can remain as part of the final viewing screen structure and enhance the optical properties of the structure. One method of producing such a screen consists of embossing or cutting light-directing features such as grooves into one surface of a transparent film substrate, applying a monomer mixture layer to the film substrate, directing ultraviolet light through the substrate and through the monomer mixture layer, exposing only selected portions of the monomer mixture layer, and then removing

the unexposed portions of the monomer mixture layer, leaving tapered optical waveguides As a result of TIR occurπng at the faces of the "grooved" portions of the substrate, the ultraviolet light does not pass out of the substrate in the 'grooved" regions, as those faces are nearly parallel with respect to the rays of

ultraviolet light Rather, the ultraviolet light is redirected by the grooves to pass only through the film substrate surface between the grooves that are perpendicular or nearly perpendicular to the rays

In a vaπant of this method, lenses are cut or embossed into the surface of the film substrate When ultraviolet light is directed through the structure, the tenses focus the light through the central regions of the lenses

With either of the methods descπbed above, the grooves or lenses may be located on the surface to which the monomer mixture layer is applied or they may be located on the opposite surface

The light-directing feature can also be accomplished with an array of gradient index lenses in a film substrate Here, selected regions of the film are polymerized to change the refractive index of the selected regions and form gradient-index lenses Ultraviolet light is directed through the film containing the array of gradient-index lenses and then through a monomer mixture layer to create the tapered optical waveguides

Bπef Description of Drawings

A more complete understanding of the present invention, as well as other objects and advantages thereof not enumerated herein, will become apparent upon

consideration of the following detailed descπption and the accompanying drawings, wherein

Figure 1 is a cross-sectional diagram of a film substrate for a viewing screen having grooves embossed or cut into one surface of the film substrate;

Figure 2 is a cross-sectional diagram of the film substrate of Figure 1, with

a partially-exposed monomer mixture layer situated on the substrate;

Figure 3 is a cross-sectional diagram of the film substrate of Figure 2, where the unexposed monomer mixture has been removed,

Figure 4 is a cross-sectional diagram of a film substrate for a viewing screen, having lenses cut or embossed into one surface of the film substrate.

Figure 4a is an alternate embodiment of a lens shape cut or embossed into one surface of the film substrate;

Figure 5 is a cross-sectional diagram of the film substrate of Figure 4, with a partially-exposed monomer mixture layer situated on the substrate; Figure 6 is a cross-sectional diagram of the film substrate of Figure 5, where the unexposed monomer mixture has been removed;

Figure 7 is a cross-sectional diagram of a film substrate for a viewing screen having grooves on the undersurface of the film substrate;

Figure 8 is a cross-sectional diagram of the film substrate of Figure 7, with a partially-exposed monomer mixture layer situated on the substrate;

Figure 9 is a cross-sectional diagram of the film substrate of Figure 8, where the unexposed monomer mixture has been removed;

Figure 10 is a cross-sectional diagram of a film substrate for a viewing screen, having lenses cut or embossed into the undersurface of the film substrate,

Figure 1 1 is a cross-sectional diagram of the film substrate of Figure 10, with a partially-exposed monomer mixture layer situated on the substrate.

Figure 12 is a cross-sectional diagram of the film substrate of Figure 1 1, where the unexposed monomer mixture has been removed,

Figure 13 is a cross-sectional diagram of a mask and gradient index lenses created in a film by the mask,

Figure 14 is a cross-sectional diagram of the gradient index lens of Figure 13, with a partially-exposed monomer mixture layer situated on the substrate, and Figure 15 is a cross-sectional diagram of the gradient index lens of Figure 14, where the unexposed monomer mixture has been removed,

Best Mode for Carrying out the Invention

The screens discussed here are fabricated on a substrate 10 such as the film shown in Figure 1 The substrate may be a matenal such as polyethylene terephthalate (PET), or any other suitable material known to those skilled in the art In the embodiment of Figure 1, grooves 20 are cut or embossed on the top or front surface 12 of the substrate 10 The grooves 20 are cut or embossed as an array of parallel grooves or are cut or embossed in a grid pattern on surface 12 which divides surface 12 into an array of zones that may be tπangular, square, rectangular, hexagonal, or some other appropπate shape The grooves can be formed in substrate 10 by diamond machining or some other appropriate cutting method or formed from a master mold by techniques such as casting or embossing

The cross section of a groove can be in the shape of a "V" where the sides of the "V" can be straight or curved Alternatively, the cross section of a groove can be any curved or segmented surface Preferably the cross section of a groove is V-shaped where the sides of the "V" are straight The total included

angle, θ, of the '"V"' can range from about 1° to about 50° Preferably, θ ranges from about 5° to about 30°

As illustrated in Figure 2, a thin film of a photo-cross-linkable monomer mixture 30 is poured onto the grooved surface 40 of the substrate 10 The monomer mixture may include such materials as described in U S Patent 5,462,700 A covering film or plate 25 may be placed in contact with the top surface of the monomer mixture to prevent oxygen from diffusing into the monomer mixture during the subsequent exposure step.

Collimated or partially collimated ultraviolet light is then directed through the bottom surface 50 of the substrate 10. For the example illustrated in Figure 2, the index of refraction of the monomer mixture 30 must be less than the index of refraction of substrate 10. Then, by virtue of TIR, the walls 22 of the grooves 20 reflect the ultraviolet light rays so the light rays pass through the areas 24 between the grooves 20 and through the flat surfaces 26. When the ultraviolet light passes through the monomer mixture 30, the material is photopolymerized, forming tapered optical waveguides 60 on the flat regions 26. The unexposed portion 32 of the monomer mixture 30 is removed with a developer, leaving the tapered optical waveguides 60 and the underlying substrate 10, as shown in Figure 3

In an alternate embodiment, the ultraviolet light-focusing or concentrating effect can be achieved with optical lenses cut or embossed into the top surface of a

substrate An optical lens is meant to include any structure that refracts and concentrates light. Examples include curved lenses as shown in Fig. 4 or pyramidal-shaped as shown m Fig 4a

Referring to Fig. 4, lenses 1 10 are embossed or cut into the top or front surface 102 of the film substrate 100 Monomer mixture 130, having an index of refraction preferably less than the index of refraction of the lenses 1 10, is then applied to the top surface 102 and collimated or partially collimated ultraviolet light is directed through the undersurface or back surface 150, as illustrated in Figure 5 The lenses 1 10 focus the ultraviolet light, causing it to pass through the monomer mixture 130 in a concentrated fashion. This results in photopolymerization in the monomer mixture 130 about the axes 112 of the lenses 1 10, to create tapered optical waveguides 160. A developer is then applied to remove the unexposed portion 132 of the monomer mixture 130, leaving the film substrate 100 and the tapered optical waveguides 160 of Figure 6. When the index of refraction of the tapered waveguide 160 is different from that of the film substrate 100, the junction 170 of each tapered waveguide 160 will function as an embedded lens. The embedded lens will reduce the undesirable effect of seeing directly through the screen structure to the light source (not shown) or other structure in the viewing device. The light-focusing or concentrating effect can also be achieved by placing grooves on the underside of the substrate. In Figure 7, grooves 220 are cut or embossed into the undersurface or back surface 250 of a film substrate 200 The grooves can be narrow and spatially separated as shown in Figure 7 or they can be wide and connected to form triangular or pyramidal-shaped structures. The cross

section of a groove can be in the shape of a "V" where the sides of the " \T can be straight or curved Alternatively, the cross section of a groove can be any curved or segmented surface Preferably, the cross section of a groove is V-

shaped where the sides of the "V" are straight The total included angle, θi.of the

"V" ^' can range from about 5° to about 89° Preferably, θ, ranges from about 40°

to about 80° Again, a monomer mixture 230 is placed on the top or front surface 202 of the film substrate 200, as shown in Figure 8 In this example, it is not necessary that the index of refraction of the monomer mixture be less than the index of refraction of the substrate 200 When collimated or partially collimated ultraviolet light is directed through the underside of substrate 200, the light refracts through the zones 224 between the grooves 220, causing the polymeπzation of the monomer mixture 230 to create tapered optical waveguides 260 above each zone 224 After removal of the unexposed monomer mixture 232. the film substrate 200 and optical waveguides 260 of Figure 9 remain. The grooved underside 250 of the film substrate 200 can also serve as part of the final optical structure Grooves 220 enhance the optical performance of the tapered optical waveguides 260 by increasing the amount of light which the viewing screen transmits and reduces the undesirable effect of seeing directly through the screen structure to the light source The waveguides of Figure 9 could also be created with lenses cut or embossed into the undersurface of the film substrate In Figure 10, lenses 310 have been cut or embossed into the underside 350 of a film substrate 300 In Figure 1 1 , the lenses 3 10 focus and direct collimated or partially collimated ultraviolet light through a monomer mixture layer 330 to form tapered optical

waveguides 360 When the unexposed monomer mixture 332 is removed, the film substrate 300 and the waveguides 360 remain, as shown in Figure 12 If the lenses 3 10 are not index-matched to another substrate, i e , a substrate adjoining the undersurface 350 of the substrate 300, the lenses 310 will work with the

waveguides 360 to focus and concentrate the light output of the waveguides 360

A tool for creating the tapered optical waveguides can also be fashioned using an array of gradient-index lenses The lenses can be made from a photosensitive film containing a monomer mixture such as a holographic film As illustrated in Figure 13, a mask 400 having multiple light-blocking blackened areas 410 is placed adjacent a sheet of photosensitive film 420 When collimated or partially collimated ultraviolet light is applied to the free surface 402 of the mask 400, the light will pass between the blackened areas 410, exposing the coincident regions 422 of the photosensitive film 420, to change the refractive index of the exposed regions to create a gradient-index lens array 430 The gradient-index lens array 430 is now used in the same fashion as the

"grooved" or "lensed" substrates of Figures 1, 4, 7, and 10. As shown in Figure 14, a monomer mixture layer 440 is applied to the surface of the gradient-index lens array 430. Collimated or partially collimated ultraviolet light is now applied to the undersurface 450 of the gradient-index lens 430, exposing portions of the monomer mixture layer 440 to create tapered optical waveguides 460. As shown in Figure 15, the tapered optical waveguides 460 and the underlying gradient index lens 430 remain after the unexposed portion 442 of the monomer mixture layer 440 is removed.

While there has been described what is believed to be the preferred embodiment of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such embodiments that fall within the true scope of the invention.