AU4504299A

AU4504299A - Flat display screen

Info

Publication number: AU4504299A
Application number: AU45042/99A
Authority: AU
Inventors: Maik Glatzer; Rainer Glatzer
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-06-02
Filing date: 1999-06-01
Publication date: 1999-12-20
Anticipated expiration: 2019-06-01
Also published as: CA2334403A1; ES2160433T3; CN1306656A; EP1018101B1; WO1999063508A1; ATE200588T1; EP1018101A1; JP2002517788A; AU754347B2; DK1018101T3

Abstract

The invention relates to a flat display screen for displaying an image using a plurality of pixels which are arranged in a matrix-shaped manner and which are supplied with light from semiconductor light sources (12, 13, 14) via optical waveguides (4, 16), whereby the light can be modulated between the light sources (12, 13, 14) and the pixels (1) for generating an image. In order to provide such a flat display screen whose construction is versatile and variable, the invention provides that the end viewing surface of the display screen is comprised of a plurality of display modules (6) which are similar to one another. A group of pixels (1) is combined in each of said display modules. The display modules (6) are each separately connected to semiconductor light sources (12, 13, 14), said sources separately belonging to each display module (6), via flexible or partially flexible light waveguides (4, 16). In addition, a light modulator device (17) is connected in the light waveguides (4, 16) which lead to each display module (6).

Description

FLAT DISPLAY SCREEN The invention relates to a flat display screen for displaying an image by means of a plurality of pixels which are arranged in the form of a matrix, in which groups of pixels are combined in display modules that are similar among each other. Said display modules jointly form the flat display screen and each are connected via flexible or partially flexible light wave guides to a light source belonging to each display module, whereby an arrangement of light modulators is interconnected in the light wave guides leading to each display module. Such a flat display screen is known, for example from US-4,747,648 A. In connection with said known flat display screen, which is primarily conceived for large sized display boards for sports facilities, hotels or gas stations, the pixels combined in display modules, on the one hand, and the display modules on the other hand form a relatively rough matrix. This means that the individual pixels have a relatively large spacing from each other, so that said flat display screen is primarily suitable for the display of alphanumerical information and less so for the displaying images. A further drawback is that incandescent lamps are used as light sources, which have to be cooled. Furthermore, high losses occur in connection with the modulation of the continuous flux of the light coming from the incandescent lamps especially when said flux of light frequently has to be wholly or partly interrupted, for example moving images. For said reason, it is possible only in a poor way in connection with said known flat display screen to make high light intensity available on each pixel. However, high light intensity per pixel is required if a largely flat image has to be produced with high contrasts and with a screen pattern that is hardly noticeable by the viewer. Obtaining high contrast is particularly important in a bright environment, for example at daylight. Another flay display screen is known from DE-PS 195 40 363. With this known flat display screen, the optical wave guides are arranged in the form of a grid on the back side of the flat display screen, and have decoupling points arranged with uniform distribution along their longitudinal expanse. The decoupling points thus form a matrix-shaped array of pixels. One end of each wave guide is connected to a semiconductor light source. The light sources or the decoupling points can be controlled in such a way that they reflect light in one color or light in different colors. By rapidly lining up the light proportions in terms of time, said light components having different intensities that successively exit from the decoupling points into the viewing space, the impression of an image is created in the eye which, in case of color modulation, is varicolored. The required 2 modulation of the light takes place either in the semiconductor light sources themselves or by means of modulators that are associated with the individual decoupling points, i.e. which are therefore arranged distributed in the form of a matrix as well. An important drawback of said known flat display screen lies in the fact that the optical wave guides are arranged in a stationary way in relation to each other and in relation to the display screen, so that the flat display screen necessaVily has and must retain a fixed outer form that is not variable. A further important drawback lies in the fact that the multitude of decoupling points are arranged in series one after the other along each wave guide, so that either only a small fraction of the full amount of the incoming light can be reflected, or the reflection of the full amount of light is possible only at larger time intervals. Finally, another drawback consists in that the modulators modulating the light exiting from the decoupling sites have to arranged in a narrow pattern in accordance with the narrow grid of the matrix, which ensues problems in view of the narrow arrangement of the control lines and in view of the dissipation of lost heat. Finally, a flat display screen is known from EP-0 422 777 Al in connection with which semiconductor light sources (LED's) are employed as the light sources. The 3

AC

Owi g to the fact that each display module has its own semiconductor light source and that the full light output of said light source is available to each module\ at any time , an extraordinarily high power density is obtained over the entire flat display screen, which furthermore can be modulated at any time to the full extent for generating the image and/or the color. Due to the fact that the light modulate or device belonging to each display module is interconnected between each display module and the associated semiconductor light source, it is easily possible to position the light modulator device and its control in a suitable location in the space between the display field and the semiconductor light source. Therefore, in view of the arrangement of the modulators it is no longer necessary to depend on the narrow matrix of the end viewing surface of the display screen, but the light modulators and their control rather can be distributed in the space in a way such that both the control and, the dissipation of the lost heat can be manager without any problems. The modulator cells within the light modulator device do not even have o have the arrangement of a matrix, but can be arranged in any desired way, and even in an irregular manner, :.f need be. It is possible in this way to employ without loss of quality even those light modulator devices that have an irregular structure, -4for example because problems occurred during their manufacture. Furthermore, it is possible also without problems to make provision in a light modulator device for number of spare modulator cells which can be activated when required, for example when failures should occur within the area of the normal modulation cells. Similar considerations apply in view of thE arrangement of the semiconductor light sources. The latter, too, can be distributed in the space in a way required by the energy feed, the control and the dissipation of the lost energy. Preferably LCD's or diode-lasers are employed as semiconductor light sources, whereby the semiconductor light sources for each display/module at least have three LCD's or three diode lasers in the colors red, green and blue. Such semiconductor light-sources are chara terized by very high luminance and they can be controlled in a simple way. The semiconductor light sources preferably emit pulsed light. The light output can be substantially increased in this way without having to depend on any correspondingly increased continuous-wave light -5or 3 diode lasers in the colors red, green and blue. Such semiconductor light sources are characterized by very high luminous density and they can be controlled in a simple manner. Different modulator devices of the known type can be employed for modulating the flux of light, for example such as LCD's, electrostatic, electroacoustic or mechanical modulators. However, the invention makes it possible also to employ for said flat display screen for the first time optical ceramics as modulators, in connection with which the ratio between the active and the passive surfaces is poor because large spacings have to be maintained between the modulated surfaces. Therefore, provision is made according to a further development of the invention that the modulator devices each are realized in the form of a solid-state PLZT array with a multitude of modulation cells, and an ITO control. PLTZ is an electrooptical oxide ceramic material based on lead-lanthane-zirconate titanate whose active surfaces can be controlled by means of ITO-electrodes. An ITO is an oxide semiconductor based on indium oxide and tin oxide. Such a solid-state PLTZ array with ITO control operates with low loss, efficiently and practically free of wear. The drawback of such solid-state modulators, which substantially lies in the fact that large spacings have to be maintained 6 LLU )r, between the active switching surfaces, plays no role in conjunction with the flat display screen as defined by the invention because of the movable and optional arrangement of the light waveguides. If necessary, provision can be made for one solid state PLZT array per display module, with the bmodulation cells of said array switching the colors red, green and blue offset in terms of time. In such an arrangement it is possible to make do with one single solid-state PLZT array per display module. As an alternative, it -s possible also to make provision for three solid-state PLZT arrays per display module. Said arrays can be controlled in parallel andsof which each array switches a color red, green or blue. In such an arrangement', the required switching frequency is reduced by the factor-3. Furthermore, provision is usefully made that the display modules are arranged in a display screen frame that has a great number of module receptacles arranged in the form of a matrix. Such a display screen frame makes it possible to assemble the individual display modules to form a flat display screen in a quick and simple manner. The display modules usefully can be locked in the -7module receptacles of the display screen frame. The individual display modules can be quickly mounted in this way and, if need be, also dismantled again, for example in order to be replaced or in order to change their location in the arrangement. As an alternative, it is possible, of course, to join the display modules arranged in the display screen frame by gluing them together, and/or by gluing them to the display screen frame. In order to obtain defined viewing effects it may be useful under certain circumstances to cover the individual pixels with an optical foil by which the light is reflected in a defined direction or at a defined angle. According to a useful further development of the invention, provision is made that a multitude of pixels are glued next to each other to an optical foil made of deformable material in order to form a display module. In this way, the module remains deformable within itself, so that it is possible to produce flat display screens with surfaces shaped in any desired way. If need be, the pixels of the display modules also can be formed directly by the end surfaces of the light -8conducting fibers, which remain movable. A display screen surface that can be designed in any desired way and that takes into account all sorts of different aspects is obtained in this way as well. If necessary, the pixels also may consists of transparent solid bodies having the shape of a truncated pyramid, with the light waveguides feeding into said solid bodies from the one side, and with the opposite side being covered by a surface scattering the light. For the purpose of forming a display module under such aspects it is possible to assemble a great number of such solid bodies with the help of suitable auxiliary means. Finally, it is possible also to arrange the pixels of a display module next to each other on a transparent board, whereby light waveguides feed into said board from one side and separately for each pixel, whereas the board is provided with a light-scattering surface on the opposite side. Said board with the connected light waveguides then forms the display module. In order to make the flat display screen as defined by the invention additionally insensitive to mechanical damage or shocks, it is possible to wholly or partially embed the flexible or partially flexible light waveguides in a curing compound according to their association and -9

AL,

the three-dimensional arrangement. Furthermore, within the zone of the semiconductor light sources and the light modulator devices, the light waveguides each can be formed by a solid body that has a three-dimensional, light-conducting structure forming the light waveguides. Such solid bodies may consists of, for example transparent glass, a translucent polyester or similar materials, in whose volumes light-conducting structures serving as light waveguides are formed by a suitable physical treatment. If such solid bodies are employed, it is, of course, necessary to previously define the spatial position of the semiconductor light sources accordingly, on the one hand, and of the light modulator arrays on the other.- Exemplified embodiments of-the invention are explained in greater detail in ,the following with the help of the drawings, in which: FIG. 1 shows a highly enlarged vertical section through a pixel. FIG. 2 is a highly enlarged view of the end viewing surface of a display module, which is assembled from a multitude of pixels. -10- FIG. 3 is the same view as in FIG. 2, but shown in the original size. FIG. 4 shows by a perspective/schematic view a display module and its arrangement in a frame surrounding the flat display screen. FIG. 5 shows by a perspective/schematic view a first embodiment of the light supply and shape of a display module. FIG. 6 shows by a perspective/schematic view a second embodiment of the light supply and shape of a display module. FIG. 7 shows by a perspective/schematic view a third embodiment of the light supply and shape of a display module. FIG. 8 shows by a perspective/schematic view a fourth embodiment of the light supply and shape of a display module. FIG. 9 shows by a schematic sectional view a fifth embodiment of the shape and arrangement of a display module. -11- FIG. 10 shows by a schematic sectional view the shape of pixel in a modified form versus the one shown in FIG. 1; and FIG. 11 shows by a schematic sectional view the further modified form of a display module. In FIG. 1, the entity of as pixel is denoted by reference numeral 1. The pixel 1 has a pixel support body 2 which, on the sight side, is provided with a concave reflector 3. An optical waveguide in the form of a light conducting fiber 4 ends at and feeds into said reflector at its lowest point. On the sight side, the reflector 3 is covered by an optical foil 5, with the help of which the outlet end of the light-conducting fiber 4 is reproduced with uniform distribution over the viewing surface. The optical foil 5 may have preferred angles of reflection in this connection. The pixel support body 2 is designed tapering in the rearward direction in the form of a truncated pyramid, so that when the pixels are lined up next to each other and one on top of the other in the form of a matrix, free spaces remain available between the individual pixel support bodies 2. Said clear spaces widen in the rearward direction in the form of wedges and serve for receiving connecting means, for example in the form of a suitable -12adhesive. A large number, for example 400' of such pixels) 1/ arranged next to each and one on top of the other are assembled t form a display module 6 (see FIGS. 2 and 3-). The assembled pixels 1 are located on the front side of the display module 6 and jointly form there the square, edgeless end viewing surface of the-display module 6. Behind said end viewing surface 77 of the display module 6, the display module 6 has a module support body 8 that is tapering in the rearward direction in the form of a truncated pyramid, and which is provided in the zone of its side walls with the locking holes 9. For assembling a large number (e.g. 1200) of the display modules 6 to form a flat display screen, provision is made for a display screen frame 10 that is provided with a corresponding number of the module receptacles 11, which are arranged in the form of a matrix. The individual modules 6 can be inserted and fixed ir said module receptacles 11 directly bordering on each other, so that an uninterrupted end viewing surface is obtained on the sight side. The individual display modules 6 are fixed in the module receptacles 11 in that corresponding locking projections in the module receptacles 11 engage the wedge-shaped locking holes 9 of the module supports 8. Alternatively, the wedge-shaped -13intermediate spaces between the adjacent module bodies 8 can be filled with a suitable adhesive. Also, the individual module bodies 8 can be glued to the module receptacles 11 of the display screen frame 10. The pixels 1 are supplied with light by the semiconductor light sources 12 and 13 and 14 (see FIGS. 5 to 8). Said semiconductor light sources preferably are operated pulsed with a high frequency. FIG. 5 shows that the light emitted by the semiconductor light sources 12, 13 and 14 is first supplied to an optics 155 for homogenizing the flux of the light, and from there fed into a flexible or semi flexible light-conducting fiber bundle 16 with 400 individual fibers, and then supplied by the latter to a light modulator device 17. In all exemplified embodiments, said light modulator device 17 is realized in the form of a solid-state PLZT array with ITO control and has a total of 400 modulation cells. Each modulation cell of the light modulator device 17 is connected to a light-conducting fiber of the light-conducting fiber bundle 16. The light-conducting fibers 4 lead from each modulation cell of the light modulator device 17 to the individual pixels 1, whereby the individual light conducting fibers 4 can be combined also here to form a flexible or partially flexible bundle of light-conducting -14

W

fibers at least over part of the length. With such an embodiment of the display module 6 and of the light supply, the colors red, green and blue are successively modulated in terms of time. The exemplified embodiment shown in FIG. 6 differs from the exemplified embodiment according to FIG. 5 in that a separate light modulator device 17 is used for each color. Accordingly, three light-conducting fiber bundles 16 are required in the present case. Furthermore, each pixel 1 is connected to three light-conducting fibers 4 which each are separately connected to the light modulator device 17 belonging to each color, namely extra for each color. It is possible in this way to control the three colors red, green and blue in a parallel manner, so that a switching frequency reduced by the factor three is required as compared to the embodiment according to FIG. 5. However, the present embodiment requires three times as many light-conducting fibers. The exemplified embodiment according to FIG. 7 is different from the exemplified embodiment according to Fig. 6 in that in the present case, each pixel 1 is subdivided in the sub-pixels la, lb and 1c, of which each one is responsible for a color red, blue or green, and is connected to the light modulator device 17 belonging to -15said color via the light-conducting fibers 4. The exemplified embodiment according to FIG. 8 corresponds with the exemplified embodiment according to the exemplified embodiment according to FIG. 5 with respect to the light supply; however, the individual pixels 1 are loosely arranged in the present case and are formed by the end surfaces of the individual light conducting fibers 4. With the present exemplified embodiment, the format of the display modules 6 can be varied at any time in any desired way. FIG. 9 shows that the individual pixels 1 can be glued also to an optical foil 18, if need be, said foil being elastically deformable. This results in a flexible viewing surface of the display module 6, which can be adapted to any desired spatial form. It is important in connection with all embodiments that the light-conducting fibers 4 and the light conducting fiber bundles 16 are designed flexible or partially flexible, so that the pixels 1 or the display modules 6 assembled from the pixels 1, and the modulator devices 17 or the semiconductor light sources 12, 13, 14 are decoupled from one another in terms of space. FIG. 10 shows that the pixel 1 may also consist of a -16transparent solid body 20 in the form of a truncated pyramid, if need be, into which the light waveguide coming from the one side feeds in the form of a light conducting fiber 4, and which is provided with a light scattering surface 21 on the other side. The transparent material of such a solid body has a higher refractive index than air, so that total reflection occurs on the sides. A great number of such solid bodies 20 can be combined to form a display module, using suitable auxiliary means. In connection with the display module shown in FIG. 11, the individual pixels 1 are located on a through extending board 23 consisting of transparent material. Light waveguides in the form of the light-conducting fibers 4 feed into said board from one side, namely separately for each pixel 1. On the opposite side, the transparent board 23 is provided with a transparent light-scattering surface 24 that is transparent as well and serves as the end viewing surface. In the present case, the board 23 provides for the cohesion of the display module. In connection with all exemplified embodiments, the flexible or partially flexible light waveguides 4, 16 can be wholly or partly embedded in a curing compound after they have been associated and arranged in the three :;,,LI-q-17 LU C) 1>Lu dimensional manner. In this way, the flat display screen as defined by the invention is rendered more insensitive to mechanical damage and shocks. Deviating from the exemplified embodiments shown, the light waveguides 16 each can be formed within the zone between the semiconductor light sources 12, 13, 14 and the light modulator devices 17 by a solid body having a three-dimensional, light-conducting structure that is forming the light waveguides. -18-

Claims

1. A flat display s c reen for displaying a display screen image by means of a multitude of pixels arranged in the form of a matrix, said pixels being supplied with light via optical waveguides of semiconductor light sources, whereby the light can-be modulated between the light sources and the pixels for generating the image, characterized in that the end viewing surface of the display screen is assembled from a multitude of display modules (67) of the same type among one another, with a group of pixels (1) being combined in each display module, whereby the display modules (6) each are separately connected via flexible or partially flexible light waveguides (4, 16) with semiconductor light sources (12, 13, 14) separately belonging to each display module (6), and a light modulator device (17) is interconnected in the light waveguides leading to each display module (6).

2. The flat display screen according to claim 1, characterized in that the semiconductor light sources (12, 13, 14) for each display module (6) have at least three LED's or diode lasers in the colors red, green and blue.

3. The flat display screen according to claim 2, -19- characterized in that the se iconductor light sources (12, 13, 14) emit pulsed light.

4. The flat display screen according to claim"1, characterized in that the modulator device (17) is realized in each case in the form of a solid-state PLZT array /with a multitude of modulation cells and an ITO control.

5. The flat display screen according to claim 4, characterized in that provision is made for one solid state PLZT array per display module (6), with the modulation cells of said arrays modulating the colors red, green and blue successively in term of time.

6. The flat display ,screen according to claim 4, characterized in that provision is made for three solid state PLZT arrays per display module (6), said arrays modulating th'e colors red, green and blue in parallel in terms of time.

7. The flat display screen according to claim 1, characterized in that the display modules (6) are arranged in a display screen frame having a multitude of module receptacles (11) arranged in the form of a matrix.

8. The flat display screen according to claim 7, -20- characterized in that the display modules (6)\can be locked in the module receptacles (11) of the display screen frame (10).

9. The flat display screen according to claim 7, characterized in that the display modules (i) inserted in the display screen frame (10) are glued with each other and/or glued to the module receptacles (11) of the display screen frame (10).

10. The flat display screen according to claim 1, characterized in that the individual pixels (1) are covered by an optical foil (5) from which the light is reflected in a defined dirmetion or at a defined angle.

11. The flat display screen according to claim 1, characterized in that for forming a display module, a multitude of pixels (1) are glued next to each other to an optical foil (18) made of deformable material.

12. The flat display screen according to claim 1, characterized in that the pixels (1) of the display module (6) are directly formed by the end surfaces of the movable light waveguides (4).

13. The flat display screen according to claim 1, -21- characterized in that the pixels (1) each consist of transparent, truncated pyramid-shaped solid bodies (120), into which the light waveguides (4) feed from the one side, and which are provided with a light-spattering surface (21) on the opposite side.

14. The flat display screen according to claim 1, characterized in that the pixels (1)of a display module are arranged on a transparent board (23) , whereby light waveguides (4) feed into said board (23) from one side and separately for each pixel (1), whereas the board (23) is provided on the opposite side with a light-scattering surface (24).

15. A method of producing a flat display screen according to claim 1, characterized in that the flexible or partially flexible light waveguides (4, 16) are wholly or partially embedded in a curing compound according to their association and three-dimensional arrangement.

16. The flat display screen according to claim 1, characterized in that the light waveguides (16) within the zone between the semiconductor light sources (12, 13, 14) and the light modulator devices (17) each are formed by a solid body having a three-dimensional, light conducting structure forming the light waveguides. -22-