STACKED DISPLAY PANEL CONSTRUCTION AND METHOD OF MAKING SAME

Abstract: A stacked display panel construction (10) produces multishades of a single color, or a plurality of multiple colors (400, 500, 600). The system includes a nematic display panel (24) which, in one of its states, functions as a wave guide to rotate linearly polarized light from in a colored polarizer (23) to produce noncolored light (NC1) from an output polarizer (25). In its other state, the display panel (24) twists the linearly polarized light to emit therefrom predominantly linearly polarized light for enabling the output polarizer (25) to emit colored light (R2). The method of making the construction includes adjusting the angle of rotation in the wave guide state of the panel (24) until only noncolored light (NC1) is emitted from the output polarizer (25).

Description: Description STACKED DISPLAY PANEL CONSTRUCTION AND METHOD OF MAKING SAME Cross Reference to Related Applications This is a continuation-in-part of U.S. patent application Serial No. 07/506,429, filed April 9, 1990, entitled "STACKED DISPLAY PANEL CONSTRUCTION AND METHOD OF MAKING SAME" of U.S. patent application Serial No. 07/472,688, filed January 30, 1990, entitled "LIQUID CRYSTAL DISPLAY PANEL SYSTEM AND METHOD OF USING SAME," which is a continuation-in-part of U.S. patent application Serial No. 07/222,144, filed July 21, 1988, entitled "GRAY SCALE SYSTEM FOR VISUAL DISPLAYS." The foregoing patent applications are incorporated by reference. Technical Field The present invention relates, in general, to a display panel system, and a method of making it, to provide multiple colored images. More particularly, the present invention relates to a stacked liquid crystal display panel system, and a method of making it, to produce a multiple color display system. Background Art There have been many different types and kinds of multicolored liquid crystal display panel systems for producing multicolored display images. Such systems have been based on the three basic principles applicable to color liquid crystal displays, namely the principles of interference, dichroism and absorption. While such systems have been satisfactory for some application, all have exhibited certain limitations ranging from poor brightness to limited color producing capabilities. For example, as noted by Tatsuo Uchida in an article published in Vol. 23 No. 3 of Optical Engineering (1984) entitled "Multicolored liquid crystal displays," systems employing the interference principles have generally been limited to interference colors, and thus are unsatisfactory for producing full color displays. Attempts have been made to overcome the problems associated with interference type systems. For example, M.G. Clark and I.A. Shank in Proc. SID Symp Dig. 172 (1982) proposed a twisted nematic liquid crystal display device of the field sequential type, with a dichroic twisted nematic cell and monochrome cathode ray tube. In attempting to render this type of device suitable for multiplex addressing, it was found that the product of the thickness (d) of the liquid crystal layer and the birefringence (Δn) of the liquid crystal, had to be very small, typically in the range of 0.36 μm < d.Δn « 2.0 / x . The lowermost limit corresponds to the minimum value of the product d.Δn of the liquid crystal layer, at which linearly polarized light of a visible wavelength is rotated 90°. Because of the above mentioned limitation, it was found that when the product of d.Δn was larger than 2μm, light passing through the crystal layer tended to become predominantly linearly polarized, due to rotary dispersion. Consequently, when a pair of polarized light elements is utilized to pass selected light, an effect was produced giving an interference coloring. This interference coloring has been referred to as the "Mauguin effect," and tends to be enhanced when d.Δn « 2μm. This phenomenon is also ' responsible for the unwanted and undesired occurrence of coloring of inoperative elements of the display area, and results in a reduction in contrast relative to the operative elements of the same display area. Still other attempts have been made to overcome the aforementioned interference problems. For example, in U.S. patent 4,443,065, there is disclosed a double-layered structure having input and output polarizers with a first and second layer of liquid crystals disposed thereinbetween. The LCD devices have their longitudinal axes twisted in different directions so that the second layer serves to compensate for interference coloring. While such a structure may have reduced the interference coloring phenomenon, the patented structure exhibited parallax problems. Also, it is relatively expensive to manufacture, since each LCD panel in the system is multilayered. Therefore, it would be highly desirable to have a new and improved LCD display system which would utilize single layer LCD units in a stacked panel arrangement, and which would be relatively inexpensive to manufacture. Recent attempts have also been made in the field of liquid crystal displays employing the dichroism principle. For example, in U.S. patent 4,416,514 a liquid crystal color filter is disclosed and includes a set of differently colored dichroic polarizers interposed with an equal number of voltage responsive twisted nematic liquid crystal cells, and a plane polarizer. Each of the above described elements are arranged along an optical path in a predetermined manner for modifying the spectral content of visible light incident to the filter, to produce any one of a predetermined number of colors whose saturations and hue are related to the voltages applied to the liquid crystal cells. While such a system apparently is intended to produce a full color display, it generally exhibits poor transmittance for some applications, and should be precisely tuned to maintain an acceptable level of transmittance for certain applications, without introducing an unacceptable level of cross talk between energized and unenergized pixels. More particularly, because of inconsistency in the mass production manufacturing of twisted nematic liquid crystal display panels, it has been difficult, if not impossible, to obtain an acceptable level of transmittance, without introducing unwanted and undesired cross talk for certain applications. Therefore, it would be highly desirable to have a new and improved display panel construction, which does not require tight tuning and which would exhibit satisfactory transmittance for projection type displaying techniques. In this regard, such a display construction can be manufactured according to modern mass production techniques. Disclosure of Invention Therefore, it is the principal object of the present invention to provide a new and improved stacked color display panel construction, and a method of making it, without the need for precise tuning, and yet produce satisfactory transmittance. Another object of the present invention is to provide such a new and improved display construction, and method of making it, with substantial luminous transmittance characteristics and in a relatively inexpensive mass production manufacturing technique. Briefly, the above and further objects of the present invention are realized by providing a color display construction with a single dichroic assembly composed of a colored dichroic polarizer disposed in a common rectilinear optical path with a nematic display panel and polarizer. The dichroic polarizer is colored with a primary color dye for passing linearly polarized white light along its major polarization axis and linearly polarized colored light along an axis disposed orthogonally to the major polarization axis. In one of its states, the nematic display panel functions as a wave guide device for rotating the linearly polarized light through a predetermined angle for enabling the dichroic assembly to produce noncolored light from the output polarizer. In another one of its states, the display panel twists the linearly polarized light to emit therefrom predominantly linearly polarized light for enabling the output polarizer to emit colored light therefrom. It will be understood that, at least a portion of the light emitted from the panel is predominantly linearly polarized. In the second state, the dichroic unit passes multishades of a single color which corresponds to the basic color of the dichroic dye utilized in the dichroic polarizer. In order to enhance the transmittance of the dichroic assembly, the dichroic and output polarizers are arranged so they are not crossed polarized. The method of making the display construction includes adjusting the angle of rotation in the wave guide state of the panel, until noncolored light is emitted from the output polarizer. Such a technique does not require precise tuning techniques due to the wide tolerances in the ability to pass the orthogonal polarized color light through the output polarizer, once the noncolored light is adjusted in the wave guide state. In another form of the invention, a color display panel construction includes of a pair of dichroic assemblies having a shared neutral polarizer. Each of the dichroic assemblies include a highly twisted nematic liquid crystal display panel aligned in a common rectilinear optical path with a colored dichroic polarizer for producing a multicolored liquid crystal display system. In order to enhance the transmittance of the dichroic assemblies, the polarizer elements are not cross polarized. Each of the highly twisted nematic liquid crystal display panels are controlled by separate electronic drive units, which enable each respective panel to pass noncolored light in a nonexcited state, and to pass colored light in an excited state. In still another form of the invention, a color liquid crystal display panel construction includes of a set of three dichroic assemblies with a single shared neutral polarizer. Each of the dichroic assemblies includes a highly twisted nematic liquid crystal display panel aligned in a common rectilinear optical path with a colored dichroic polarizer for producing a multicolored liquid crystal display system. Each of the highly twisted nematic liquid crystal display panels are controlled by separate electronic drive units which enables each respective panel to pass noncolored light in a nonexcited state, and to pass colored light in an excited state. In still yet another form of the invention, a display panel construction includes a single highly twisted nematic liquid crystal display panel sandwiched between a pair of dichroic assemblies. Each of the dichroic assemblies, as well as the highly twisted nematic liquid crystal panel, is driven by separate electronic drive units which bias the panels to pass white or noncolored light in an unexcited state, and to pass colored light in an excited state. Each of the dichroic assemblies include a highly twisted nematic liquid crystal display panel aligned in a common rectilinear optical path with a colored polarizer for producing a multicolored liquid crystal display system. Each of the dichroic assemblies are aligned in the common rectilinear optical path with a highly twisted nematic liquid crystal display panel. The highly twisted panels are controlled by separate electronic drive units which enable the system to pass noncolored light when the panels are in a nonexcited state, and to pass colored light when at least one of the panels is in an excited state. Each of the aforementioned forms of the invention also includes a collimation assembly for correcting parallax errors which are inherent in any stacked optical system. Brief Description of Drawings The above mentioned and other objects and features of this invention and the manner of attaining them will become apparent, and the invention itself will be best understood by reference to the following description of the embodiment of the invention in conjunction with the accompanying drawings, wherein: FIG. l is a diagrammatic block diagram of a stacked display panel construction, which is constructed in accordance with the present invention, and which is illustrated with a collimating assembly and overhead projector; FIG. 2 is a diagrammatic block diagram of a dichroic unit of the construction of FIG. 1, illustrating its polarization and rotation angles; FIG. 3 is a diagrammatic block diagram of another stacked display panel construction, which is also constructed in accordance with the present invention; FIG. 4 is a diagrammatic block diagram of another stacked display panel construction, which is also constructed in accordance with the present invention; FIG. 4A is a diagrammatic block diagram of the stacked construction of FIG. 4, illustrating its polarization and rotation angles; FIG. 5 is a diagrammatic block diagram of still another stacked display panel construction, which is also constructed in accordance with the present invention; FIG. 5A is a diagrammatic block diagram of the stacked construction of FIG. 5, illustrating its polarization and rotation angles; FIG. 6 is a diagrammatic block diagram of yet another stacked display panel construction, which is also constructed in accordance with the present invention; FIG. 6A is a diagrammatic block diagram of the stacked construction of FIG. 6, illustrating its polarization and rotation angles; FIG. 7 is a set of polarization phase graphs, illustrating the polarization phase of each of the liquid crystal display panels of the construction of FIG. 1, illustrating the polarization phases as a function of applied voltage. Best Mode for Carrying Out the Invention Referring now to FIG. 1 of the drawings there is shown a stacked color display panel construction system 10 which is constructed in accordance with the present invention. The system 10 generally comprises a liquid crystal display panel construction 11 and an associated electronic drive unit 27 (FIG. 2) , which is more fully described in the aforementioned copending U.S. patent application Serial No. 07/472,668. The electronic drive unit 27 causes light entering the construction 11 to be varied between noncolored and colored light as will be explained hereinafter in greater detail. The system 10 can be used in conjunction with suitable projection optics, such as an overhead projection 12 having a light source generally indicated at 14 as having a lamp and a reflector. While the system 10 is shown and described to be utilized with an overhead projector, it will become apparent to those skilled in the art the system 10 may also be employed in a front projector arrangement (not shown) , a rear projector arrangement (not shown) , and other similar type arrangements to display multishaded single color images on suitable viewing surfaces such as screens (not shown) . The liquid crystal display panel construction 11 generally comprises a single liquid crystal display dichroic assembly 22 for producing a simple matrix color display with large information content, having a relatively high contrast ratio. The dichroic assembly 22 generally includes a multiplexed highly twisted nematic liquid crystal display panel 24, which is disposed between an input two-state dichroic-polarizer 23 and an output neutral gray polarizer 25, along a common rectilinear optic path. While the display panel 24 is described as a multiplexed driven liquid crystal display panel. it will become apparent to those skilled in the art that the display panel 24 may also be an active matrix liquid crystal display panel. The liquid crystal display panel 24 is controlled by the electronic drive unit 27, which causes polarized light passing through the liquid crystal display panel 24 to vary. When the panel 24 is in its unexcited state, the applied bias voltage of the drive unit 27 causes the liquid crystal display panel 24 to function as a wave guide device for rotating linearly polarized light entering the panel 24, through a predetermined angle determined by the applied bias voltage. In its excited state, the applied actuating voltage causes the linearly polarized light entering the panel 24 to be twisted at about 90 degrees and thus converted into predominantly linearly polarized light emitted therefrom. As will be explained hereinafter in greater detail, in the first or unexcited state, the bias voltage supplied by the drive unit 27 is adjusted so the dichroic assembly 22 passes noncolored light when the panel 24 is in an unexcited state. Similarly, in the second or excited state, the dichroic assembly 22 is energized by the drive unit 27 to twist the linearly polarized light by about 90 degrees so that the light emitting from the neutral polarizer 25 is colored. The color of the light passed by the dichroic assembly 22 is determined by the dichroic dye utilized in the dichroic polarizer 23 and the duty cycle of each of the pixels (not shown) in the display panel 24. The use of varying duty cycles is disclosed in greater detail in the foregoing mentioned patent applications Serial No. 07/472,688 and Serial No. 07/222,144. In order to correct any parallax errors associated with the depth of the stacked polarizers and liquid crystal display dichroic assembly 22, the liquid crystal display panel construction 11 also includes a collimation assembly comprising a collimating lens unit 17 and a focusing lens unit 19 for correcting parallax errors. The collimation assembly is well known to those skilled in the art and will not be described hereinafter in greater detail. The construction 11 is assembled by aligning the dichroic polarizer 23, the liquid crystal display panel 24 and the neutral gray polarizer 25 along the common rectilinear optical path, with the collimating assembly, such that when the liquid crystal display panel 24 is properly biased by the drive unit 27 to the unexcited or first state, primarily noncolored light is transmitted by the output polarizer 25 of the construction 11. When the liquid crystal display panel 24 is driven by the drive unit 27 to a second state, primarily colored light is transmitted from the polarizer 25. The color of the transmitted light in the second state is a function of the type of dichroic dye utilized in the input polarizer 23, as well as by the biasing of the electronic drive unit 27. In this regard, it should be understood that the dichroic polarizer 23 employs a dichroic dye suspended and laminated in a plastic substrate such as acetate cellulose. In the plastic substrate, all of the dye molecules are oriented to a given direction. The dichroic dye includes dye molecules whose optical absorption spectrum is a strong function of polarization of the incident light with respect to the molecular orientation. Table 1 shows several dichroic dyes with large dichroic ratios and suitable colors, as follows: TABLE 1. Dj*e« with Isrje dichroic r»li«. The optimum alignment between the dichroic polarizer 23, the liquid crystal display panel 24 and the neutral grey polarizer 25 for transmission of noncolored light is a function of the physical and electrical characteristics of the liquid crystal display panel 24 and the particular drive voltage applied by the electronics drive unit 27. Accordingly, because of inherent manufacturing inconsistencies in the panel 24, according to the inventive method of manufacturing the construction 11, optimal rotational or alignment angles are determined iteratively by adjustments in the drive unit voltages, to achieve passage of noncolored polarized light. In operation, the method of the present invention includes applying an initial bias voltage to the panel 24 via the drive unit 27 to cause polarized light to pass through the dichroic assembly 22 for determining whether the output light is noncolored. If the output light is colored, the bias voltage applied by the drive unit 27 is adjusted, causing the rotational angle of the panel 24 to be varied until the output light is noncolored. Once the noncolored bias voltage has been established, the second stage or excited voltage level is applied to the liquid crystal display panel 24. The output light of the panel 24 is then observed as the applied voltage is adjusted, to provide the brightest colored light possible for the given panel, without cross talk or noise being introduced. It should therefore be understood that the adjustment process is an iterative process for permitting the dichroic unit to be adjusted to give the greatest contrast between colored and noncolored light. In operation of the construction 11, the collimating unit 17 directs the light emitted by the light source 14 into the input dichroic polarizer 23 of the dichroic assembly 22. In order to enable the dichroic assembly 22 to produce colored and noncolored light, the dichroic polarizer 23 has a major polarization angle of about 20 degrees (FIG. 2) and is colored with a dichroic dye, such as a red dichroic dye. In this regard, as shown in FIG. 2, the dichroic polarizer 23 passes polarized noncolored light with a polarization angle (20°) corresponding to the major axis of polarization and colored light, shown generally as R, on an axis orthogonal to the major axis (-70°) . The passed colored and noncolored polarized light is directed to the surface of the liquid crystal panel which rotates the light as it passes through the panel 24 in its unexcited state. As a result of this wave guide effect, the linearly polarized noncolored light (shown generally as NC 1 in FIG. 2) , emerges from the panel 24 with a polarization phase of about +50 degrees, while the colored light (shown generally as R,) emerges with a polarization phase of about at -40 degrees. The rotational angle of the polarized light as it passes through the panel 24 is determined by the bias voltage applied thereto, and the physical structure of the panel itself. As noted earlier, the bias voltage is established so that the dichroic assembly 22 passes noncolored when the panel 24 is in a nonexcited state. The polarized colored light R, and noncolored light NC, emerging from the panel 24, impinges upon the neutral gray polarizer 25. The neutral grey polarizer 25 is not cross polarized with the dichroic polarizer 23, and has a major polarization axis at an angle of about 60 degrees (FIG. 2) , which is sufficiently close (within about 10 degrees) to the polarized noncolored light, to allow a significant portion of the noncolored light to pass therethrough, but sufficiently cross polarized relative to the colored light R, polarized at about -40°, to prevent the colored light R, from passing therethrough, during the nonexcited wave guide state of the panel. As a result of this rotation, the dichroic assembly 22 produces noncolored light in a nonexcited state. When the liquid crystal display panel 24 is energized by the drive unit 27, the linearly polarized light impinging upon the panel 24 is twisted by about 90 degrees, so that the polarization phase of the noncolored light emerging from the panel 24, is at about 140 degrees, while the polarization phase of the colored light (shown generally as R g in FIG. 2) is at about 50 degrees. Thus, the red polarized light is able to pass through the output polarizer during the excited state of the panel. The predominantly linearly polarized colored light R 2 emerging from the panel 24 is directed toward the neutral grey polarizer 25, whose major polarization angle of 60 degrees, is sufficiently cross polarized from the polarization phase (140 degrees) of the noncolored light, to block it and sufficiently close (within 10 degrees) to the polarization phase of the colored light j to permit a significant portion of the colored light R j to pass therethrough. The different shades of color produced by the panel is achieved, not by varying the voltage applied to the liquid crystal display panel, but rather by the electronic drive unit 27 as more fully described in the aforementioned copending U.S. patent application. Serial No. filed concurrently herewith, and U.S. patent application Serial No. 07/472,668. Considering now the system 10 in greater detail with reference to FIG. 1, the liquid crystal display panel 24 is a multiplexed driven highly twisted negative nematic liquid crystal device capable of rotating light at least 90 degrees, but less than 180 degrees. A suitable panel is the one identified as model KL7248ASTPS C-9Z-24 panel, manufactured by Kyocera Corporation, located at 5-22 Kitainoue-cho, Higashiro Yamashira-ka Kyoto 607, Japan. Although the panel 24 is capable of twisting light at angles greater than 90 degrees in the preferred form of the present invention, the range of the twist angle is preferably between about 90 degrees and about 135 degrees, with the most preferred angle of rotation being at about 90 degrees, for producing the highest contrast with the least amount of electrical noise or cross talk. Figure 7 shows the response of three typical liquid crystal display panels, manufactured by Kyocera Corporation, as a function of voltage, where the phase information on the polarization data illustrates the 90 degree rotation utilized. The panel 24 is assembled with an interelectrode gap of about 10-15 microns. In order to encourage the liquid crystal display molecules to align with parallel orientation to the electrode surfaces, the electrode surfaces are lightly rubbed with a plastic material disposed on their surface. The rubbing for the different surfaces is done approximately 90 degrees apart, permitting the molecules to orient in a rotation angle from at least about 90 degrees, but less than about 180 degrees, in relation to each surface, depending upon the material physical properties of the liquid crystal display panel. Considering now the dichroic polarizer 23 in greater detail with reference to FIG. 1, the dichroic polarizer 23 is a commercially available dichroic polarizer, such as the one manufactured by Nitto Denko America under part numbers NPF-Q10R for red, NPF-Q10B for blue and NPF-Q10G for green. These polarizers have optimum transmission of greater than 50% for photopic polarized light, with about 50-70% polarizing efficiencies. Considering now the neutral gray polarizer 25 in greater detail with reference to FIG. 1, the neutral polarizer 25 is a commercially available polarizer, such as the one manufactured by Sauritsu Electric Co., located at 1-30-13 Narimasu, Itabashi-ku, Tokyo 175, Japan, under part number L C2-92-185. These polarizers have optimum transmission for polarized light at 43-44% and 99% polarizing efficiencies. Although in the preferred form of the present invention, the input polarizer 23 is a dichroic colored polarizer, it will be understood by those skilled in the art that the neutral and dichroic polarizers may be reversed as shown in the form of the invention as illustrated in FIG. 3, so that the liquid crystal display panel can twist the polarized light emitting from the neutral grey polarizer through approximately 90 degrees, to enable the light coming into the two-state dichroic polarizer to be oriented in orthogonal directions to the suspended dichroic dye molecules thus, changing its absorption spectrum from one state to the other or any intermediate state. Referring now to FIG. 3, a dichroic assembly 32 is shown, which generally comprises a highly twisted liquid crystal display panel 34 disposed between a neutral gray input polarizer 33 and a colored dichroic output polarizer 35. The liquid crystal display panel 34 is controlled by a electronic drive unit 37. In operation, the input polarizer 33 has a major axis of polarization of about 70 degrees (FIG. 3) for polarizing noncolored light. The polarized noncolored light shown generally at NC, impinges upon the face of the liquid crystal display panel 34 which rotates the light NC so that its polarization phase is at about 20 degrees (FIG. 3) when the panel is in an unexcited state. In this regard, it should be understood the panel rotates the noncolored light NC at about - 50 degrees, so the noncolored polarized light shown generally at NC,, emerges from the panel 34 with a polarization phase of at about 20 degrees. In the excited state, the polarized light NC, passing through the panel 34, is twisted at about 90 degrees, so the polarized light NC 2 emerging from the panel 34 in an excited state has a polarization angle at about 110 degrees and -70 degrees along the major polarization axis. In the unexcited state the polarization phase of the light NC 1 emerging from the panel 34 corresponds with the major polarization axis of the dichroic polarizer 35 thus, enabling the dichroic assembly 32 to produce noncolored light. In the excited state, the polarization phase of the light NC 2 emerging from the panel 34 is orthogonal to the major polarization axis of the dichroic polarizer 35 so the dichroic assembly 32 produces colored light. It should be understood that the colored light will correspond to the color of the dichroic dye utilized in the dichroic polarizer 35 and that different shades of the primary color will be determined by the duty cycle of the individual pixels within the panel as they are energized from an on to an off state by the electronic drive unit 37 as more fully described in copending U.S. patent application Serial No. 07/472,668. From the foregoing, it should be understood that the operation of the dichroic assembly 32 is substantially similar to the dichroic assembly 22 in that the bias voltage applied by the drive unit 37 in the unexcited state of the panel is adjusted to permit the dichroic assembly 32 to pass noncolored light. Regardless of the order of the polarizers, the basic combination of a dichroic polarizer, liquid crystal display panel and neutral polarizer functions as a switchable filter, transmitting either primarily noncolored light or primarily colored light, depending upon the dichroic dye utilized and the various voltage settings of the electronic drive units. Referring now to FIG. 4 there is shown another multicolored liquid crystal display panel system 400, which is constructed in accordance with the present invention. The system 400 can be utilized in conjunction with a conventional overhead projector 412 having a light source 414 and projection optics (not shown) . While the system 400 is shown and described to be utilized with an overhead projector, it will become apparent to those skilled in the art that the system 400 may also be employed in front projection arrangement, rear projection arrangement and other similar type arrangements to display multicolored images on an appropriate viewing surface. The system 400 generally comprises a liquid crystal display panel and an associated pair of drive electronics unit 428 and 429, which are substantially identical and more fully described in the foregoing mentioned copending U.S. patent application Serial No. , filed concurrently herewith, and Serial No. 07/472,668. The liquid crystal display panel construction 411 generally comprises a pair of liquid crystal display dichroic assemblies 422 and 432 for producing a simple matrix multicolored display with large information content having a relatively high contrast ratio. The dichroic unit 422 includes an input dichroic polarizer 423 and a liquid crystal display panel 424, which is aligned with and disposed behind the input dichroic polarizer 423. Panel 424 is controlled by the drive unit 428. The dichroic unit 432 is similar to dichroic unit 422, and includes of a liquid crystal display panel 426 and an output dichroic polarizer 427. The liquid crystal display panel 426 is controlled by the electronic drive unit 429, which is substantially similar to drive unit 428. Each of the dichroic assemblies 422 and 432 share a common neutral gray polarizer 425 which is sandwiched between panels 425 and 426. In this regard, the neutral polarizer 426 serves as an output polarizer for assembly 422 so that the dichroic assembly 422 is substantially similar to the dichroic assembly 22. With respect to assembly 432 the neutral gray polarizer 425 serves as an input polarizer, so that the dichroic assembly 432 is substantially similar to the dichroic assembly 32. The neutral gray polarizer 425 is shared between the two liquid crystal display panels 424 and 426 in order to minimize or prevent any unnecessary loss of light that could otherwise result from using more than one neutral polarizers in the system. The panel construction 411 also includes a collimation assembly for correcting any parallax errors associated with the depth of the stacked multiple liquid crystal display panels 424 and 426 and polarizers 423, 425 and 427. The conventional collimation assembly includes a collimating unit 417 and a focusing unit 419 for correcting parallax errors. The input polarizer 423 and the output polarizer 427 are both two-state dichroic polarizers which are substantially similar to the dichroic polarizer 23. The color produced by the system 400 depends upon the dichroic dye used in each of the dichroic polarizers 423 an 425 respectively and the voltage applied to the liquid crystal display panels 424 and 426 by their respective electronics drives 428 and 429 respectively. The liquid crystal panels 424 and 426 thus rotate polarized light through approximately 90 degrees in their excited states letting light from one dichroic state or the other dichroic state or any intermediate state to pass through the subsequent neutral grey polarizer 425 for producing a colored display. The dichroic assemblies 422 and 432 are aligned in a common optical path such that when the liquid crystal display panels 424 and 426 are properly biased by their respective electronic drive units 428 and 429 to their unexcited states, the system 400 passes noncolored light. Similarly, when the panels 424 and 426 are biased to their excited states the system 400 pass colored light. The color of the transmitted light in the second or excited state is a function of the color of the dichroic polarizers 423 and 427 and the bias voltages applied by the drive units 428 and 429 respectively. In operation, each of the liquid crystal display panels 423 and 425 permit color shades of their associated colored dichroic polarizers 423 and 427 respectively to pass in conjunction with noncolored light. For example, if the input polarizer is a dichroic red polarizer and the output polarizer is a dichroic yellow polarizer, the first liquid crystal display panel 424 in conjunction with the neutral polarizer 425 either passes linearly polarized noncolored light, or linearly polarized red light, to the second liquid crystal display panel 426 depending upon the voltage setting of the electronics drive 428. In a similar manner ,assuming the first panel 424 is in an unexcited state, the second liquid crystal display panel 426 in conjunction with the output polarizer 427 either passes linearly polarized noncolored or linearly polarized yellow light depending upon the voltage setting of the electronics drive associated with panel 124. Table II shows the basic colors produced by the two panel system with a red dichroic unit polarizer, a neutral polarizer and a yellow dichroic output polarizer. Table II COLOR OUT OF OUTPUT COLOR OUT OF DICHROIC FIRST PANEL NEUTRAL POLARIZER SECOND PANEL POLARIZER OFF WHITE OFF WHITE OFF WHITE ON YELLOW ON RED OFF RED ON RED ON ORANGE Considering now the operation of the system 400 in greater detail with reference to FIGS. 4 and 4A, the collimating unit 417 directs collimated light into the dichroic input polarizer 423. The input dichroic polarizer is a two state polarizer so that it passes noncolored light on its major polarization axis of 20 degrees (FIG. 4A) and red light on the orthogonal axis. The passed colored light R and noncolored light NC is directed to the surface of the liquid crystal display panel 424 which rotates the polarized light when the panel is in an unexcited state at about 50 degrees so the polarized light exciting from the panel 424 exit with a polarization phase angles of at about 70 degrees for the noncolored light (shown generally at NC, in FIG. 4A) and at about -20 degrees for the colored light (shown generally at R, in FIG. 4A) . The linearly polarized light NC, in an excited state is twisted at about 90 degrees, and exits the panel 424 with a polarization phase angle of at about 160 degrees for the noncolored light NC 2 and at about 70 degrees for the colored light R 2 . The linearly polarized light exiting from the panel 424 is nonexcited state impinged upon the neutral polarizer 425 which has a major polarization axis of at about 60 degrees which is substantially close to the phase angle of the noncolored light NC, to permit the noncolored light to pass therethrough, but sufficiently polarized from the colored light (R, at about -20 degrees) to block the colored light R,, from passing. Conversely, in the excited state, the predominantly linearly polarized colored light R 2 exiting from the panel 424, is disposed at about 70 degrees which is sufficiently close to the polarization angle (60 degrees) of the neutral polarizer 425 to permit the colored light R 2 to pass but sufficiently polarized from the polarization angle (160 degrees) of the noncolored light NC 2 to block the noncolored light NC 2 . Thus, in an excited state the dichroic assembly 422 passes colored light and in an unexcited state the dichroic assembly 422 passes noncolored light. The polarized light passed by the neutral polarizer 425 is impinged upon the light crystal panel 426. In the unexcited state the panel 426 rotates the linearly polarized light at about -30 degrees so that the linearly polarized light exiting the panel 426 has a polarization phase angle of about 30 degrees. In this regard, it should be understood that the linearly polarized light entering panel 426 will either be noncolored or colored depending upon the state of excitement of the panel 424. Accordingly, the linearly polarized light exiting the panel 426 will either be colored or noncolored corresponding to the polarized light entering the panel 426. The linearly polarized light exiting from the panel 426 is impinged upon the output dichroic polarizer 427 which has a major polarization axis of 30 degrees for passing noncolored light and a 120 degree (or -70 degree) orthogonal axis for passing colored light. As the linearly polarized light (NC,) exiting from the unexcited panel 426 has a polarization angle of at about 30 degrees the polarizer 427 permits the noncolored light to pass. In a similar manner when panel 426 is actuated by drive unit 429 to its excited state, the linearly polarized light entering the panel 426 is rotated about at 90 degrees to exit panel 426 at a polarization angle of at about 120 degrees (-60 degrees) which corresponds to the orthogonal axis of the output polarizer 427 thus permitting the dichroic unit 432 to produce colored light (AC) . It should be understood that if the linearly polarized light entering the panel 426 is colored polarized light and panel 426 is excited the colored polarized light will also be rotated at about 90 degrees so that the polarization phase angle of the colored light existing panel 426 will correspond to the orthogonal axis of the colored dichroic polarizer 427. Thus if the input colored light to panel 426 is red for example, the colored light out of output polarizer 427 (if it is dyed yellow) will be orange. The system 400 is adjusted to pass noncolored light substantially in the same iterative process as system 11. In this regard, collimated light is passed through the dichroic assemblies 422 and 432 which are aligned in a common rectilinear optical path and a first bias voltage is applied to each of the panels 424 and 426 by their respective drive units 428 and 429. The bias voltage of the drive units 428 and 429 are thus adjusted so that the dichroic assembly 432 passes noncolored light when panels 424 and 426 are bias in their unexcited states. After the assemblies 422 and 432 have been adjusted to pass noncolored light, the electronic drive unit 428 is readjusted to cause the panels 424 to be energized into its excited states. The voltage of drive unit 428 is then adjusted for the maximum color contrast. After the drive unit 428 has been adjusted to enable the system to produce a first colored light, the drive unit 428 is readjusted to place the panel 424 in an unexcited state. Drive unit 429 is then energized to place panel 426 in an excited state. Drive unit 429 is then adjusted to cause the maximum color contrast from the dichroic unit 432. This iterative process of adjustment is accomplished easily allowing the system to be adjusted for inconsistencies in panel manufactures. Referring now to FIG. 5 there is shown another multicolored liquid crystal display panel system 500 which is also constructed in accordance with the present invention. System 500 generally comprises a panel construction 511 and a set of associated drive units 544, 545, and 546 which are substantially the same and are more fully described in U.S. patent application Serial No. filed concurrently herewith, and in the foregoing mentioned U.S. patent application Serial No. 07/472,668. The panel construction 511 is similar to construction 411 except that it includes an additional dichroic unit 542. Panel construction 511 generally consists of a stacked arrangement of a first dichroic assembly 522 having an input dichroic polarizer 523, a highly twisted liquid crystal display panel 524, an output dichroic polarizer 525, a second dichroic assembly 532 having a highly twisted liquid crystal display panel 526, and a neutral grey polarizer 527. The second dichroic assembly 532 also shares the dichroic polarizer 525 with the first dichroic assembly 522. In the second dichroic assembly 532 the dichroic polarizer 575 serves as an input polarizer for the assembly 532. The construction 511 also includes the third dichroic unit 542 having includes a highly twisted nematic liquid crystal display panel 528 and an output dichroic polarizer 529. The third dichroic unit 542 also shares the output polarizer 527 of the second dichroic unit 532. The polarizer 527 serves as an input polarizer for the third dichroic unit 542 and is a neutral grey polarizer. Each of the panels 524, 526 and 528 and controlled by the electronic drive units 544, 545 and 546 respectively. Considering now the operation of system 500 in greater detail with reference to FIGS. 5 and 5A, system 500 is adjusted substantially in the same manner as system 400 except that all three dichroic assemblies 522, 532, and 542 are first adjusted to pass noncolored light. Each assembly is then individually adjusted to pass colored light with each of the other assemblies being maintained in an unexcited state so as to pass noncolored light. Referring now to FIG. 5A, the collimating unit 517 directs light emitted by the light source 514 into the input dichroic polarizer 523 of the first dichroic assembly 522. In order to enable the dichroic assembly 522 to produce colored and noncolored light the dichroic polarizer 523 is a two state polarizer with a major polarization axis of at about 30 degrees for passing noncolored light and an orthogonal axis at about 120 degrees for passing colored light. For the purpose of explanation it will be assumed the polarizer is colored red. The passed colored and noncolored light exiting from the input polarizer 523 is impinged upon the liquid crystal panel 524 which in its unexcited state rotates the polarized light at about 20 degrees so that the linearly polarized light NC, exiting from the panel 524 exits with a polarization phase angle of at about 50 degrees for noncolored light and at about 150 degrees for colored light R 1 . In the excited state the liquid crystal panel 524 rotates the input light at about 90 degrees so that the light exiting the panel 524 is predominantly linearly polarized light with the polarization angle of the non colored light NC 2 at about 140 degrees and the polarized angle of the colored light C 2 at about 240 degrees. The linearly polarized light exiting panel 524 is impinged upon the dichroic polarizer 525 whose major polarization axis is at about 50 degrees for passing noncolored light and whose orthogonal axis is at about 140 degrees for passing colored (yellow) light. When panel 524 is unexcited the non color light exits panel 524 with a polarization phase angle (50 degrees) that corresponds to the major polarization areas of polarizer 525. Accordingly, noncolored light is passed to panel 526. As the linearly polarized color light exiting from panel 524 is orthogonal to the noncolored light, the polarizer 525 block the colored light from passing. When panel 524 is in an excited state the noncolored light exits panel 524 with a polarization phase angle of about 140 degrees which is sufficiently polarized from the polarization angles of the polarizer 525 to be blocked. Conversely, the linearly polarized color light exiting the panel 524 has a polarization angle at about 240 degrees which is sufficiently close to the polarization axis (+50 degrees and +140 degrees) of the polarizer 525 to pass colored light but sufficiently polarized from the noncolored light to block its passage. The polarized light exiting from the polarizer 525 is impinged upon the panel 526 which in its unexcited state rotates the linearly polarized light at about 40 degrees in an unexcited state and at about 90 degrees in an excited state. Therefore, in the unexcited state the noncolored light NC 1 exits panel 526 with a polarization phase angle at about 90 degrees while the colored light C 1 exits panel 526 with a polarization phase angle at about 0 degree. In a similar manner when the panel 526 is excited the noncolored predominantly linearly polarized light NC 2 exits the panel 526 with a polarization phase angle of at about 180 degrees while the colored predominantly linearly polarized light C 2 exits with a polarization phase angle of at about 90 degrees. The neutral grey polarizer 527 has a polarization angle of 90 degrees. Accordingly, it should be understood that the polarizer 527 will pass both the noncolored linearly polarized light (90 degree polarization phase angle) and the colored predominantly linearly polarized light (90 degree polarization phase angle) . The linearly polarized light passed by the neutral polarizer 527 is impinged upon the panel 528 which rotates the light at about -70 degree when panel 528 is in an unexcited state and at about -90 degrees when the panel is in an excited state. The linearly polarized light NC, exiting panel 528 in an unexcited state will have a polarization phase angle of at about 20 degrees. Similarly the predominantly linearly polarized light exiting panel 528 in an excited state will have a polarization angle of at about 0 degrees. As the output dichroic polarizer has a major polarization axis of at about 20 degrees for passing noncolored light and an orthogonal axis of at about (110 degrees and -70 degrees) the noncolored light NC, in the unexcited state of panel 528 will be able to be passed by polarizer 529. However, the colored light will not. In the excited state of panel 528, the colored light C will be sufficiently close to the polarization axis to be passed by the polarizer 529. Referring now to FIG. 6 and 6A, there is shown another multicolored display panel system 600, which is constructed in accordance with the present invention. The system 600 can be utilized in conjunction with a conventional overhead projection having a light source 614 and projection optics (not shown) . While the system 600 is shown and described to be utilized with an overhead projector, it will become apparent to those skilled in the art that system 600 may also be employed in front projector arrangement, rear projector arrangement, and other similar type arrangements to display multicolored images on an appropriate viewing surface. The system 600 generally comprises a panel construction 611 and a set of drive units 644, 645, and 646 respectively which are substantially identified to drive units 544, 545, and 546. The drive units 544, 545, and 546 are more fully described in copending U.S. patent application Serial No. filed concurrently herewith, and foregoing mentioned U.S. patent application Serial No. 07/472,668. The panel construction 611 general comprises a birefringent display unit 632 which is sandwiched between a pair of liquid crystal display dichroic assemblies 622 and 642 respectively, for producing a simple matrix multicolored display with large information content having a relatively high contrast ratio. The birefringent unit 632 shares polarizers with the two dichroic units 622 and 642 as will be explained hereinafter in greater detail. Considering now the panel construction 611 in greater detail with reference to FIGS 6 and 6A, the input dichroic assembly 622 includes an input dichroic polarizer 623 and a higher twisted liquid crystal display panel 624 which is aligned in a common rectilinear optical path with the input dichroic polarizer 624. The display panel 624 is controlled by the drive electronics unit 644. The dichroic unit 622 is similar to dichroic unit 22 and will not be described hereinafter in greater detail. The output dichroic unit 642 includes a liquid crystal display panel 628 which is aligned with an output dichroic polarizer 629. The liquid crystal display panel 628 is controlled by the drive electronic unit 646. The dichroic unit 642 is similar to dichroic unit 22 and will not be described hereinafter in greater detail. The birefringent unit 632 generally comprises a multiplexed driven highly twisted nematic birefringent nematic liquid crystal device 626 sandwiched between a pair of neutral grey polarizers 625 and 627 respectively which form part of dichroic units 622 and 624 respectively. The electronics drive unit 645 controls the color transmission states of the birefringent panel 626. In this regard, as the birefringent device can only provide color transmission states between a yellowish white, yellow and blue the electronics drive unit 645 is utilized to electrically switch the panel 626 between a relatively white state to a yellow state much like the dichroic liquid crystal unit 532 in the previously described system 500. However, because of the birefringent effect of the panel 626, it should be understood that the birefringent panel 626 should only be used with red and blue dichroic assemblies or red and yellow dichroic assemblies. When the orientation angles of an input polarizer, such as polarizer 323 and output polarizer, such as polarizer 325 are fixed the optimization of the birefringent color of nonexcited pixels in a birefringent cell have been shown by several researchers in a 1986 Japan Display article entitled "Effect of Various Parameters on Matrix Display Characteristics of SBE- Liquid Crystal Cells" to be determined by only Δnd.cos 2 <θ>, where (Δn) is birefringence, (d) is cell gap and <θ> is the average angle of molecular orientation of the liquid crystal molecules to the electrode surface, which is not depend upon any other parameters. More particularly, due to the low polarizing efficiency of the dichroic polarizers 623 and 629 optimal alignment is not critical; e.g. + 10 degrees in either direction will not effect the basic performance of the unit. It should be understood, however, the stacked system 600 as a whole must be adjusted electrically to give a reasonable performance in a manner similar to systems 400 and 500 where the system photopic light transmission is five to ten percent maximum white light as a reasonable (5 to 10) contrast ratio. Considering now the operation of the system 600 in greater detail with deference to FIGS. 6 and 6A, the collimating unit 617 directs the light emitted by the light source 614 into the input dichroic polarizer 623 of the dichroic assembly 622. The input polarizer 623 has a major polarization axis of 20 degrees for passing non-colored light and -20 degrees for passing colored light. Light passing through polarizer 623 impinges upon panel 624 which in an unexcited state rotates the polarized light at about 40 degrees so the linearly polarized noncolored light NC, exists panel 624 with a polarization phase angle at about .60 degrees while the linearly colored polarized light R, exist panel 624 with a polarization phase angle at about -30 degrees. Light passing through polarizer 623 impinged upon panel 624 in its excited state rotates the polarized light at about 90 degrees so the predominantly linearly noncolored polarized light NC 2 exits panel 624 with a polarization phase angle at about 150 degrees while the predominantly linearly polarized colored light R 2 exits panel 624 with a polarization angle at about 60 degrees. The light passing through panel 624 is impinged upon the neutral gray polarizer 625 which has a major polarization axis of 60 degrees. The neutral grey polarizer is not cross polarized with the dichroic polarizer 623 and has a polarization angle corresponding to the linearly polarized noncolored light NC t exiting panel 624 in its unexcited state. According noncolored light will be passed by the dichroic assembly 622 when the panel 624 is unexcited. As the predominantly linearly polarized colored light R 2 exiting from panel 624 has a polarization phase angle of 60 degrees, it also will be passed by the neutral gray polarizer 625 when the panel 624 is in an excited state. According colored light will be passed by the dichroic assembly 622 when the panel 624 is excited. The linearly polarized light exiting polarizer 625 is impinged upon the highly twisted birefringent panel 626 which rotates the light at about -10 degrees when the panel 626 is in an unexcited state and at about -90 degrees when the panel 626 is in an excited state. Therefore, depending upon the state of the panel 626, the light exiting panel 626 is either noncolored with a polarization phase angle of at about 50 degrees when the panel is in an unexcited state or colored light with a polarization phase angle of at about -40 degrees (+140 degrees) when the panel is in an excited state. The predominantly linearly polarized light passing through panel 626 is impinged upon a neutral grey polarizer 627 having a major polarization axis of 120 degrees. Accordingly, when the impinging light NC, has a polarization phase angle of at about 50 degrees, the polarizer 627 passes yellow light and when the impinging light NC 2 has a polarization phase angle of about -40 degrees the polarizer 627 passes primarily noncolored light. In this regard, it should be noted that the panel 626 was adjusted electrically to permit the assembly 632 to pass noncolored light when the panel 626 was in an unexcited (state based on the correct Δnd-cos 2 <θ> relationship) and yellow light when the panel was in an excited state. The light exiting the neutral grey polarizer 627 is impinged upon panel 628 which rotates the light at about 40 degrees in an unexcited state and at about 90 degrees in an excited state. The light exiting the panel 628 has a polarization phase angle of at about 160 degrees for noncolored light NC and at about 160 degrees for colored light C. Accordingly, as the output dichroic polarizer has a major polarization angle of at about 160 degrees, it will pass both colored and noncolored light exiting from the panel 628. Considering now the phase of polarized light as a function of voltage with respect to FIG. 7, the voltage range of the assemblies 532 and 542 is shown with reference to their phase curves 701, 702 and 703 and 704, respectively. Similarly the voltage range of assembly 522 is shown with reference to its phase curves 705 and 706 respectively. While particular embodiments of the present invention have been disclosed, it is to be understood that various different modifications are possible and are contemplated within the true spirit and scope of the appended claims. For example, it should be understood that while highly twisted nematic panels are preferred for the dichroic units, it will become apparent to those skilled in the art that super twisted (STN) , or regular twisted (TN) panels may also be employed for certain applications. There is no intention, therefore, of limitations to the exact abstract or disclosure herein presented.

Claims: What is claimed is: Claims 1. A display apparatus comprising: voltage responsive display means for rotating polarized light in unexcited states and twisting light in excited states; said unexcited states and said excited states being determined by the voltage applied to said display means; polarizing means cooperating with said display means for passing noncolored light when said display means is in an unexcited state and for passing colored light when said display means is in an excited state; said display means including at least one highly twisted nematic liquid crystal display panel for twisting polarized light through about 90 degrees but less than at about 180 degrees, when said panel is excited; said polarizing means including at least one dichroic polarizer having a primary colored dichroic dye for producing colored light; and said liquid crystal display means and said polarizing means being aligned in a common rectilinear optical path for passing light along said path. 2. A display apparatus according to claim 1 further comprising: collimating means for correcting parallax error associated with said light passing along said optical path. 3. A method for displaying a colored image comprising: using a voltage responsive liquid crystal display means; applying a first voltage to said liquid crystal means to rotate polarized light entering said liquid crystal display means; applying a second voltage to said liquid crystal display means for rotating polarized light entering said liquid crystal display means; and passing said rotated and rotated light through polarizing means for transmitting selectively white light and color light to produce the colored image. 4. A display apparatus comprising: a dichroic polarizer for polarizing light, said polarizer having two states of light transmittance, wherein one of said states transmits linearly polarized noncolored light relative to a major polarization axis of said polarizer and the other one of said states transmits polarized colored light orthogonal to said major polarization axis; a voltage responsive highly twisted nematic liquid crystal display panel for rotating said polarized light in an unexcited state and twisting said polarized light in an excited state, said unexcited and excited states being determined by the voltage applied to said panel; and a neutral grey polarizer for passing a selective portion of the rotated polarized light and a selective portion of the rotated polarized light said neutral polarizer having a major polarization axis; said dichroic polarizer, said liquid crystal panel and said neutral gray polarizer being aligned in a common rectilinear optical path for passing light along said path. 5. A display apparatus according to claim 4, further comprising: collimating means for correcting parallax errors associated with said light passing along said optical path. 6. A display apparatus according to claim 4, wherein said dichroic polarizer is a colored dichroic polarizer. 7. A display apparatus according to claim 6, wherein said color is a primary color. 8. A display apparatus according to claim 4, wherein the major polarization axis of said dichroic polarizer is fixed relative to the horizontal plane of said dichroic polarizer. 9. A display apparatus according to claim 8, wherein said 5 fixed polarization axis is at about 20 degrees. 10. A display apparatus according to claim 4, wherein the major polarization axis of said neutral polarizer is fixed relative to the horizontal plane of said neutral polarizer. 11. A display apparatus according to claim 10, wherein said 10 fixed polarization axis differs from the polarization axis of said dichroic polarizer by less than 90 degrees. 12. A display apparatus according to claim 10, wherein said fixed polarization axis is at about 60 degrees. 13. A display apparatus according to claim 4, wherein said 15 voltage responsive panel rotates said polarized light of about 30 degrees in an unexcited state. 14. A display apparatus according to claim 4, wherein said voltage responsive panel rotates said polarized light in a preferred rotation at about 90 degrees but less than at about 20 180 degrees in an excited state. 15. A display apparatus according to claim 4, wherein said voltage responsive panel rotates said polarized light in a most preferred rotation at about 90 degrees. 16. A method for displaying an image comprising the steps 25 of: using a light source for generating light; directing said light into a dichroic polarizer to polarize said light, said polarizer having two states of transmittance wherein in one of said states linearly polarized 30 noncolored light is transmitted and in the other one of said « states linearly polarized colored light is transmitted, said noncolored light and said colored light being orthogonal to one another; using a voltage responsive highly twisted nematic liquid crystal display panel; applying a first voltage to said liquid crystal display panel for rotating polarized light passing therethrough; applying a second voltage to said liquid crystal display panel for twisting polarized light passing therethrough; using a neutral polarizer; passing a selected portion of the rotated polarized light through said neutral polarizer to produce noncolored light; and passing a selected portion of the rotated polarized light through said neutral polarizer to produce colored light. 17. A method of making a stacked display panel construction, comprising: aligning a display panel between an input polarizer and an output polarizer; and adjusting the angle of rotation in the wave guide state of the panel, until only noncolored light is emitted from the output polarizer.

Inventors: BOHANNON WILLIAM K, BOHANNON, WILLIAM, K.
Applicants: PROXIMA CORP, PROXIMA CORPORATION
Application year: 1991
Main classification: G02F1
IPC codes: G02F1, G09G3