Display device employing ultraviolet-beam scanning and color separator

[0002] The present invention relates to a display device that scans a color phosphor screen with a laser beam.

[0003] Display devices of this type can display video and other color images similar to those displayed by a conventional cathode-ray tube. The advantage of scanning a color phosphor screen with a laser beam is that a laser beam does not require a large, evacuated glass tube for propagation. Issues must be addressed, however, in these display devices relating to modulating the laser beam and separating of the different colors in the display.

[0004] U.S. Pat. No. 5,003,179 describes a display device in which the intensities of three infrared laser beams are independently modulated, the intensity of each beam being selectively blanked to illuminate only phosphors which produce light of the desired color. Such a display device has drawbacks, however, because the need for selectively blanking light beams intensities is inconvenient.

[0005] Japanese Patent Kokai Publication No. 323686/1992 describes a display device that modulates the intensity of a single laser beam, which illuminates red, green, and blue phosphors. This system requires that the beam be modulated at three times the normal rate, and is inconsistent with conventional video signal processing.

[0006] Japanese Patent Kokai Publication No. 323686/1992 discloses a display device that scans a phosphor screen with a single ultraviolet beam, which is generated by converting the wavelength an infrared laser beam. This system is similarly inconsistent with conventional video signal processing.

[0007] It is accordingly an object of the present invention to display an image by scanning a screen with ultraviolet beams modulated by conventional red, green, and blue video signals.

[0008] Another object of the invention is to improve color separation in the displayed image.

[0009] A further object is to improve the brightness of the displayed image.

[0010] A still further object is to obviate the need for blanking of the ultraviolet beams.

[0011] The invented display device has a transparent screen coated with three types of phosphors. When illuminated by ultraviolet light, each type of phosphor emits visible light of a different color. The display device also has a light source for producing three beams of ultraviolet light, three modulating means for independently modulating the intensity of these three ultraviolet beams, a scanning means for scanning the three ultraviolet beams across the transparent screen in a two-dimensional pattern, and a color separator disposed between the scanning means and transparent screen, for directing the three ultraviolet beams onto phosphors of the respective types on the transparent screen.

[0012] The light source comprises, for example, three infrared lasers and a wavelength conversion means. The color separator comprises, for example, an aperture mask, or a lens array. The scanning means comprises, for example, a pair of movable mirrors, or a pair of acousto-optic elements.

[0013] A filter that transmits ultraviolet light but reflects visible light may be provided between the color separator and the transparent screen to improve the brightness of the display. A focusing lens may also be provided, to focus the three ultraviolet beams.

[0014] Two or more of the invented display devices can be combined to form a display apparatus with a larger screen size.

[0015] In the attached drawings:

[0016] FIG. 1 illustrates a display device according to a first embodiment of the invention;

[0017] FIG. 2 illustrates an acousto-optic element employed in the scanning means in FIG. 1;

[0018] FIG. 3 illustrates the aperture mask, phosphor coating, and transparent screen in FIG. 1;

[0019] FIG. 4 illustrates a lens array in a display device according to a second embodiment of the invention;

[0020] FIG. 5 illustrates the screen assembly in a display device according to a third embodiment of the invention;

[0021] FIG. 6 illustrates the screen assembly in a display device according to a fourth embodiment of the invention;

[0022] FIG. 7 illustrates a display device according to a fifth embodiment of the invention;

[0023] FIG. 8 illustrates the screen assembly in the fifth embodiment;

[0024] FIG. 9 illustrates a display device according to a sixth embodiment of the invention;

[0025] FIG. 10 illustrates a display device according to a seventh embodiment of the invention; and

[0026] FIG. 11 illustrates a display apparatus according to an eighth embodiment of the invention.

[0027] Embodiments of the invention will be described with reference to the attached illustrative drawings.

[0028] Referring to FIG. 1, a first embodiment of the invention is a display device 10 comprising three yttrium-aluminum-garnet (YAG) laser light sources 1, three non-linear optical elements 2 such as potassium-titanate-phosphate crystals serving as wavelength conversion means, three acousto-optic modulators 3, a scanning mechanism 4 having a horizontal scanning mirror 4aand a vertical scanning mirror 4b,an aperture mask 5 serving as a color separator, and a transparent screen 7 with a phosphor coating 6. The aperture mask 5, phosphor coating 6, and transparent screen 7 form a screen assembly 8. The scanning mechanism 4 and acousto-optic modulators 3 are controlled by a controller 9.

[0029] FIG. 2 illustrates the structure of one of the acousto-optic modulators 3 in more detail. This acousto-optic modulator 3 comprises an acoustic medium 18 such as a crystal of tellurium oxide (TeO₂) or lead molybdenide (PbMo₄), or a glassy material such as fused quartz (SiO₂), tellurite glass, or chalcogenide glass, to which an ultrasonic resonator 19 is attached. The ultrasonic resonator 19 is linked to the controller 9 by a signal line 20, and generates ultrasonic waves 21 in the acoustic medium 18 with an intensity controlled by the controller 9. Incident light 22 is partially diffracted by the ultrasonic waves 21, so that a diffracted beam 23 and non-diffracted beam 23aemerge.

[0030] The operation of the display device 10 can be described as follows.

[0031] The three YAG laser light sources 1 emit three coherent beams 11a,11b,and 11cof infrared light with wavelengths of one thousand sixty-four nanometers (1064 nm). The three non-linear optical elements 2 convert these three coherent beams 11a,11b,and 11cto three ultraviolet beams 12a,12b,and 12cwith the fourth-harmonic wavelength of two hundred sixty-six nanometers (266 nm). The three acousto-optic modulators 3 independently modulate the intensity of these three ultraviolet beams 12a,12b,and 12caccording to red, green, and blue video signals received from the controller 9 to produce three modulated beams 13a,13b,and 13c.

[0032] In each acousto-optic modulator, the appropriate video signal is supplied through the signal line 20 to the resonator 19 in FIG. 2, and controls the intensity of the ultrasonic waves 21. The intensity of the ultrasonic waves 21 in turn controls the amount of ultraviolet light that is diffracted, thus determining the intensity of the diffracted beam 23. The diffracted beam 23 in FIG. 2 is one of the three modulated beams 13a,13b,and 13cin FIG. 1, while the incident beam 22 is one of the three ultraviolet beams 12a,12b,and 12c.

[0033] In the scanning mechanism 4, the horizontal scanning mirror 4adeflects the three modulated beams 13a,13b,and 13chorizontally in response to a horizontal drive signal from the controller 9. The resulting horizontally scanned beams 14a,14b,and 14care then scanned vertically by the vertical scanning mirror 4bin response to a vertical drive signal from the controller 9. The horizontal scanning mirror 4ais, for example, a polygon mirror. The vertical scanning mirror 4bis, for example, a galvano-mirror. The scanning mechanism 4 thus produces three ultraviolet beams 15a,15b,and 15cthat are scanned horizontally and vertically in a two-dimensional pattern. FIG. 1 shows these three ultraviolet beams 15a,15b,and 15cin three different scanning positions.

[0034] FIG. 3 illustrates the detailed structure and operation of the aperture mask 5 and the phosphor coating 6 on the transparent screen 7. The phosphor coating 6 comprises red phosphor dots 6a,green phosphor dots 6b,and blue phosphor dots 6cseparated by a black matrix 6d.The apertures in the aperture mask 5 are positioned so that ultraviolet beam 15ailluminates only red phosphor dots 6a,ultraviolet beam 15billuminates only green phosphor dots 6b,and ultraviolet beam 15cilluminates only blue phosphor dots 6c.When illuminated, a red phosphor dot 6aemits red light 16a,a green phosphor dot 6bemits green light 16b,and a blue phosphor dot 6cemits blue light 16c.

[0035] An ultraviolet sensor (not visible in FIG. 1) is disposed between the scanning mechanism 4 and the screen assembly 8, at a point that does not interfere with the display. When the ultraviolet beams 15a,15b,and 15cilluminate this sensor, a signal is returned to the controller 9, which thereby learns the position of the beams. This signal enables the controller 9 to synchronize the operation of the scanning mechanism 4 with the red, green, and blue video signals supplied to the acousto-optic modulators 3. This ultraviolet sensor is similar to a well-known sensor used for a similar purpose in laser printers.

[0036] If necessary, a plurality of ultraviolet sensors can be provided. Separate sensors can be provided for horizontal scanning and vertical scanning, for example.

[0037] As the above description shows, the phosphor screen 6, like the screen of a conventional color television set, is scanned by three independently modulated beams. These three beams can be modulated by conventional red, green, and blue video signals, and a conventional scanning sequence can be employed. Because of the aperture mask 5, there is no need to blank the beams to avoid having them illuminate the wrong phosphor dots.

[0038] The apertures in the aperture mask 5 may be round, or may have the form of oblong slots. Similarly, the phosphor dots in the phosphor coating 6 may be either round or oblong in shape.

[0039] Next a second embodiment will be described. The second embodiment is identical to the first embodiment except that the color separation means is a lens array, instead of an aperture mask. The description of the second embodiment will be confined to the structure and operation of the lens array.

[0040] Referring to FIG. 4, the lens array 50 comprises a plurality of microlenses disposed in positions corresponding to the apertures in the aperture mask 5 of the first embodiment. As the drawing shows, these microlenses focus the ultraviolet beams 15a,15b,and 15conto phosphors of the respective types that emit red light 16a,green light 16b,and blue light 16c.The same color-separating effect is obtained as in the first embodiment, with the added advantage that all of the light in the ultraviolet beams 15a,15b,and 15cis directed onto the phosphor coating 6, so a brighter display is obtained.

[0041] The lenses in the lens array may be round, or may have an oblong shape or any other suitable shape.

[0042] Next a third embodiment will be described. The third embodiment differs from the first embodiment only in the structure of the screen assembly 8, so the description will be confined to this point.

[0043] Referring to FIG. 5, the screen assembly 8 in the third embodiment has the same aperture mask 5, transparent screen 7, and phosphor coating 6 as in the first embodiment, and also has a transparent plate 17 disposed between the aperture mask 5 and phosphor coating 6. The transparent plate 17 supports the aperture mask 5 and maintains an exact positional relationship between the aperture mask 5 and phosphor coating 6. This ensures accurate color separation.

[0044] The third embodiment can also simplify the fabrication of the aperture mask 5. The aperture mask 5 can be formed by evaporation deposition or printing of an opaque substance on the transparent plate 17.

[0045] Next a fourth embodiment will be briefly described. Referring to FIG. 6, the fourth embodiment combines the features of the second and third embodiments, having a lens array 50 supported on a transparent plate 17. The lens array 50 and transparent plate 17 may be combined into a single structure, by processing the surface of the transparent plate 17 to form an array of lenses.

[0046] Next, a fifth embodiment will be described.

[0047] FIG. 7 shows a display device 26 according to the fifth embodiment, using the same reference numerals as in FIG. 1 for elements that are the same as in the first embodiment. The fifth embodiment differs from the first embodiment only in the structure of the screen assembly 25. The fifth embodiment provides a filter 24 between the aperture mask 5 and phosphor coating 6. This filter 24 transmits ultraviolet light, but reflects visible light.

[0048] FIG. 8 illustrates the operation of the filter 24 in the fifth embodiment. Ultraviolet beam 15bpasses through an aperture in the aperture mask 5, passes through the filter 24, and illuminates a green phosphor dot 6b.The phosphor dot 6bemits green light, with an intensity responsive to the intensity of the ultraviolet beam 15b,but the light is emitted in all directions. Green light 27bemitted toward the filter 24 is reflected back, and the reflected green light 28bpasses through the transparent screen 7 to enhance the intensity of the light 16bemitted directly through the transparent screen 7.

[0049] Red and blue light are similarly reflected from the filter 24, which thus improves the overall brightness of the display.

[0050] For clarity, FIG. 8 shows a gap between the filter 24 and phosphor coating 26, but the filter 24 may be disposed in contact with the phosphor coating 6.

[0051] The fifth embodiment can be combined with the second, third, or fourth embodiment, by employing a lens array 50 instead of an aperture mask 5, and/or by adding a transparent plate between the filter 24 and the aperture array 5 or lens array 50.

[0052] Next a sixth embodiment will be described.

[0053] FIG. 9 illustrates the sixth embodiment, using the same reference numerals as in FIG. 1 for elements that are the same as in the first embodiment. To the structure of the first embodiment, the sixth embodiment adds a focusing lens 29 made, for example, of fused quartz. This focusing lens 29 focuses the ultraviolet beams 15a,15b,and 15cto points on the phosphor coating 6, thereby increasing the amount of light that gets through the aperture mask 5 and enhancing the brightness of the display.

[0054] The focusing lens 29 in FIG. 9 is shown as a simple meniscus lens, but a compound lens may be used instead. The lens material is not restricted to fused quartz; any material capable of focusing ultraviolet light may be used.

[0055] The focusing lens 29 need not be disposed between the scanning mechanism 4 and screen assembly 8; other locations are possible. For example, the focusing lens 29 may be disposed between the horizontal scanning mirror 4aand vertical scanning mirror 4b.Alternatively, a first focusing lens may be provided between the horizontal scanning mirror 4aand vertical scanning mirror 4b,and a second lens may be provided between the vertical scanning mirror 4band the screen assembly 8.

[0056] The sixth embodiment can be combined with the second, third, fourth, or fifth embodiment, by adding a similar focusing lines 29 to any of those embodiments.

[0057] Next, a seventh embodiment will be briefly described. Referring to FIG. 10, the seventh embodiment has infrared laser light sources 1, non-linear optical elements 2 for wavelength conversion, acousto-optic modulators 3, a scanning mechanism 4, and a screen assembly 8 as in the first embodiment, and a reflecting plate 30. The reflecting plate 30 reflects the ultraviolet beams output from the scanning means, thereby directing the ultraviolet beams onto the screen assembly 8. In this way, the back-to-front length of the display device is reduced, as compared with the preceding embodiments.

[0058] The seventh embodiment is not limited to a single reflecting plate 30. Two or more reflecting plates may be provided, allowing a long Light path to be obtained in a confined space.

[0059] The reflecting plate 30 of the seventh embodiment can be used in combination with any of the preceding six embodiments.

[0060] Next, an eighth embodiment will be briefly described. Referring to FIG. 11, the eighth embodiment is a display apparatus employing four of the display devices 10 of the first embodiment. Each of these display devices 10 has its own infrared laser light sources 1, non-linear optical elements 2, acousto-optic modulators 3, scanning mechanism 4, and screen assembly 8. Compared with the first embodiment, the eighth embodiment doubles the height, width, and resolution of the display.

[0061] The eighth embodiment is not limited to a combination of four display devices 10. Any number of display devices may be combined in a similar manner, to form a display screen of any desired size.

[0062] The screen assemblies 8 in FIG. 11 may abut directly against one another to form a large, continuous display area, an arrangement which would be impossible with conventional cathode-ray tubes. Alternatively, the screen assemblies 8 can be held in a supporting framework, like the panes of glass in a window. The display devices 10 may be housed in a single cabinet, or in separate cabinets.

[0063] The display devices are not restricted to the display devices 10 of the first embodiment. Display devices as described in any of the other preceding embodiments can be similarly combined.

[0064] The invention is not restricted to the embodiments above. Further variations are possible, such as the following.

[0065] The modulating means need not be acousto-optic modulators as described in the embodiments above. Optical intensity modulators employing electro-optic elements, for example, are well known, and may be used instead of acoustic modulators.

[0066] The scanning mechanism 4 may be replaced by an acousto-optic scanning means, employing acousto-optic elements of the same type as shown in FIG. 2. Scanning can be accomplished by varying the frequency at which the ultrasonic resonator 19 is driven, thus varying the angle at which the ultraviolet beams are diffracted. This acousto-optic scanning method has the advantage of eliminating moving mirrors and other moving parts.

[0067] The scanning mechanism 4 may also be replaced by an electro-optic scanning means using prisms with refractive indices that vary in response to an applied voltage.

[0068] The embodiments above produced ultraviolet beams by wavelength conversion of infrared light, but the invention can also be practiced with ultraviolet light sources, in which case wavelength conversion is unnecessary.

[0069] Those skilled in the art will recognize that still further variations are possible within the scope claimed below.