Providing optical elements over emissive displays

A display may be formed of a plurality of abutted tiles, each tile contributing a portion of the overall displayed image. Optical elements may be selectively situated between pixels to improve the optical performance of the display. In some embodiments, these optical elements may facilitate the use of relatively thicker cover glasses over the display tiles.

BACKGROUND

This invention relates generally to emissive displays including organic light emitting device (OLED) displays, light emitting diode (LED) displays and electro luminescence (EL) displays.

Emissive displays generally include a cover glass or transparent sheet over the light emissive elements. The transparent sheet generally is substantially transparent to light emissions. The thinner the glass sheet, normally the less its optical effects.

In displays made by combining a plurality of tiles, each including a cover glass, gaps may exist between adjacent tiles. The thicker the glass that is utilized, the more apparent are these gaps to viewers of such displays.

While the use of thin cover glasses has many advantages, it also has concomitant cost disadvantages. Thinner glass generally breaks more easily. In addition, manufacturing equipment is designed for certain minimum glass thicknesses. Using thinner glass may result in cost penalties or require the development of specialized equipment for handling glass processing.

Thus, the thicker the cover glass that is utilized, the more apparent are any gaps between adjacent tiles. The composite image of a large area display is the result of the images contributed by each of the tiles making up the large area display. To the extent that the individual tiles may be delineated because of the inter-tile gaps, the overall seamless effect of the display is lessened. Therefore, it is desirable to produce large area displays in which the individual tiles making up the displays are as invisible and undiscernible as possible.

Thus, while using thicker glass has many practical advantages, it may also increase the likelihood that seams between adjacent tiles become visible. Therefore, there is a need for a way to make the gaps between adjacent tiles less visible in large area displays.

State of the art tile displays, such as video walls, use mullions between individual tiles to hide the physical gap. However, if these mullions are discernible to the user, they are objectionable because they break the continuity of the image.

Another structure commonly found in non-tiled displays is a pattern of black lines. The black lines, like a mullion, produce inter-pixel black lines. A black line is put between the pixels to absorb ambient light in those areas in order to increase the display contrast. Black lines are found in non-modular displays such as cathode ray tubes and liquid crystal displays. With these displays, the black lines are smaller than the mullions. They are placed in the plane of the pixels, located between the pixels. Because the pattern of black lines is periodic and placed between pixels, it does not break the continuity of the image.

Thus, there is a need for ways to make the seams of large area displays less visible.

DETAILED DESCRIPTION

Referring toFIG. 1, a pair of adjacent display tiles10and12may combine to create a portion of an overall large area display made up of a plurality of tiles10and12. The region between display tiles10and12, indicated as A, is described herein as the gap. The gap A includes an upper surface which is closest to the viewer and a gap region that proceeds along the entire thickness of the tiles10and12. At the top of the gap A, differences in surface reflection, such as the angle of reflection and its intensity, are most important. Below the top of the gap surface in the gap region, the differences in refraction, reflection and absorption are important if they are different in the region of the tiles between the pixels that are not straddling a gap.

Two rays are shown emanating from the lower surface of the gap A and extending upwardly at an angle θccalled the critical angle. At the critical angle, a ray is refracted to an angle parallel to the top surface of each layer10or12. Light reaching the surface with angles less than the critical angle exits the layers10and12and light reaching the surface with angles larger than the critical angle is totally internally reflected.

Because of the critical angle, light emitted from a point within the layers10and12can escape from the panels by traveling at most a lateral distance of dcwhich is equal to the thickness of the layers10or12times the tangent of the critical angle. Therefore, light from any part of the gap A can be completely blocked by putting a black strip14of width Wmequal to 2dcover the gap A. Because of the symmetry of the relevant optics, this same black strip14also blocks any external rays (not shown) from detecting the gap A.

If the strip14width is less than 2dcbut wider than the width of the top of the gap A, then it will completely hide the top of the gap A and a portion of a gap region near the top of the gap A. Thus, the strip14makes the top of the gap A and part or all of the underlying gap region invisible to a user. In practice, the black strip14may be slightly wider to account for any finite width of the gap A and for any tolerance for the mis-positioning of the black strip14directly over the gap A.

Using a black strip14that is wide enough to hide the entire gap A top and gap region makes the gap A substantially invisible. If mullions (not shown) are used around the edges of the display, a visual discontinuity may result because of the difference in widths of the mullions versus the black strips14. Making the black strips14identical to the mullions may make this discontinuity less noticeable. Also the use of the strips14may increase the contrast of the displayed image. In some embodiments, the same techniques may be used over the regions between pixels that are used between the layers10and12to provide greater uniformity.

Referring toFIG. 2, a pair of transparent layers10and12may be abutted together to form part of an overall large area display. The gap A may be defined between the layers10and12. Each of the layers10and12may have coated on its lower surface one or more light emitting elements15. In the case shown inFIG. 2, a set of three light emitting elements15are provided, one for each color of a tricolor color space such as red, green, blue (RGB) color space.

Each of the light emitting elements15closest to the gap A emits light having a ray most adjacent to the gap A and indicated by the letters B and C. As a result, a space D may be defined over the strip14that is not impacted by any emitted light. In particular, the strip14may be sized so that it obscures the gap A while refraining from blocking substantial light emitted by the light emitting elements15.

In some embodiments of the present invention, the light emitting elements15may be any emissive elements including an organic light emitting device (OLED), a light emitting diode (LED), or an electroluminescent display (EL), to mention a few examples. However, the other display technologies may be utilized including liquid crystal display technologies in some embodiments.

InFIG. 3, each layer10and12is overlaid by a layer16. In some embodiments, the layers10and12may be formed of glass. In some embodiments, the layer16may be formed of glass or plastic that is, at least in part, transparent. In particular, the layer16may include transparent regions20positioned more directly over the light emitting elements15and non-transparent regions18intermediate between adjacent regions20. The layers10and12may be integrated to a layer16for example by conventional bonding techniques including heat welding and adhesive bonding as two examples.

In some embodiments, the non-transparent regions18may be rectangular or square and may be black in color throughout their thickness. The sides19of the region18may be coated to make them more reflective. This may be done by providing a mirrored or white surface as two examples. As a result, the rays B and C described in connection withFIG. 2may be reflected from the sides19as indicated at E and F. In this way, light may still not be blocked, as was the case inFIG. 2, but a gap blocking, non-transparent region18of greater vertical dimensions may be provided.

Because of the imposition of the region18close to the light emitting elements15, the gap A may be more effectively hidden. Also, in some cases the layers10and12, reinforced by the layer16, may be thinner.

In some cases, the layer16may be abutted against an adjacent layer16producing gaps between adjacent layers16. These gaps may be obscured in some cases by using an overlying sheet40. This overlying sheet40, which may be called an optical integrating plate, may be utilized to assemble the various tiles that include the layers10and12. The plate40may include mullions42to cover the gaps A. Those tiles together form the composite image of a large area display. In addition, an optical integrating plate may provide a diffusing effect to obscure any gaps between layers16in some cases.

The layer16may be formed in a variety of different fashions. It may be possible to diffuse a non-transparent material into the regions18while masking the transparent regions20. However, as another embodiment, a lithography process may be used to etch a plurality of holes in the layer16. The layer16may be transparent in general. Each of those holes may then be coated with a suitably reflective layer to form the sides19. The remaining holes may then be filled with a dark or black material to form the regions18.

Turning next toFIG. 4, in this case, black material22is formed in the layer16ain a triangular shape. The sides23of the black material22may be oriented at an angle so as not to block the emitted rays B and C. Thus, in some cases, the sides23need not be made reflective, as was the case in the embodiment shown in FIG.3.

However, in some cases, it may still be possible for some light to impact the sides23of the triangular black material22. In such cases, it may still be desirable to make the sides23reflective. For example, as shown inFIG. 5, reflective sides26may be provided on a black triangular material24in a sheet16b. The resulting reflected rays E and F reduce the loss of light which might otherwise occur. The embodiment shown inFIG. 5may be advantageous, particularly in situations where relatively thick layers10and12are utilized. In the embodiments ofFIGS. 4 and 5, an optical integrating plate40may be used as described in connection with FIG.3.

In some cases, if the index of refraction of the material24is sufficiently lower than the index of refraction of the surrounding region20, it may not be necessary to make the sides26reflective. Instead, the rays may be reflected due to the differences in indices of refraction between the material24and the region20. In some cases, embodiments of the type shown inFIGS. 4 and 5may exhibit less contrast improvement for the overall display compared to those of the type shown inFIG. 7because of reflections off of the tapered sides26or23. Thus, in situations where high contrast is desired, embodiments of the type shown inFIG. 3may be preferable. In cases where the redistribution of the light may become a problem, embodiments of the type shown inFIG. 4may be preferable.

Referring next toFIG. 6, an optical structure may be provided that improves the optical separation between pixels. This structure may be made as a vertically laminated or multilayer structure, as shown inFIG. 6, or may be formed from a single layer. Each of the layers10and12may be associated with one or more hemispherical lenses20athat may be described as microlenses. The lenses20amay be formed of glass, plastic or other transparent materials.

The lenses20aprovide a means of concentrating emitted light from a pixel light emitting element15into the viewing space, providing a brighter display. Lenses20amay also reduce the internally reflected light by waveguiding the light outwardly from the display. This is because the lenses20amay increase the critical angle of the outbound light in some embodiments. Each lens20amay be either one or two dimensional. In the case of linear lenses or one dimensional lenses, the lens20amay be oriented horizontally so as to concentrate the light into a smaller vertical viewing zone.

Between each adjacent layer10or12, over the gap A, a dark region28may be formed for example by deposition. The dark region28obscures the underlying gap A as was the case in previously described embodiments. In this case, the lateral extension of the region28may avoid obscuring the outbound light from the light emitting elements15. The effect of the lenses20ais indicated by the rays B and C, which are the rays most adjacent to gap A. The rays B and C are refracted, as indicated at G and H, towards the center of each lens20a, effectively concentrating the resulting outbound light.

The use of lenses20b(with a greater aspect ratio than those shown inFIG. 6) is illustrated in FIG.7. In some cases, the lenses20bmay use refraction as well as internal reflection as indicated by the arrows E and F in FIG.7. In some cases, a reflective coating may be applied to the external sides30of the lenses20b. In other cases, total internal reflection may be utilized. A black matrix material28ais situated between adjacent lenses20b. In the embodiment shown inFIG. 7, the matrix material28amay cover the sides30of the lenses20bbecause of the use of internal reflection.

The use of a unitary cover plate32is shown in FIG.8. In this example, the plate32may replace both the layers10and12and any overlying layer such as the layer20. This may be possible because the plate32may be formed with integral optical elements38. The plate32may be molded to the shape that is desired using plastic as one example. In other cases, the desired shape may be formed by grinding, sawing, abrasive jets, etching or other formation techniques. The elements38defined in the plate32may be triangular in one embodiment of the present invention. The triangular elements38reflect incoming light and obscure underlying gaps.

The elements38may be coated or filled with black or reflective materials to make optics that isolate or concentrate light from the pixels defined by elements15. Thus, as shown inFIG. 9, a filler40is used in place of the open spaces (FIG. 8) that may make up part of the elements38.

Where a coating is utilized as indicated at38inFIG. 8, the remaining opening area34may be utilized to locate electrodes, connections and other features. Thus, a contact36may be provided to metal or other conductive lines to reach the light emitting layer15in one embodiment.

The elements38may be open spaces with air which has a relatively low index of refraction. This may create, in some embodiments, total internal reflection without the need for a coating. Gaps may be defined between adjacent plates32.