Fiber optic faceplate liquid crystal display

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention generally relates to a display, and more particularly to a display to which a special optical fiber face plate is added. This face plate is improved by providing a means for polarizing the ambient light that goes through the image forming portion such as an LCD or exits from the image forming portion.

【0002】

[Previous technology and its problems]

"Flat-Panel Displays Come on Strong in Speed, Resolution and Color" on February 1, 1989, Computer Design, pp. 65-82, describes a typical prior art flat-panel liquid crystal display (LCD) system. There is. May 1987 on the operation and performance of direct multiplexed LCDs, including twisted nematic (TN) displays, super twisted compound refraction effect (SBE) displays, and surface-stabilized ferroelectric liquid crystal (SSFLC) displays. Seminar 4 ociety for Information Display (SID) International Symposium Seminar Lecture Notes Volume 1 pp. 4.1-4.34 on the 11th, explained in "Direct-Multiplex Liquid-Crystal Displays" by Scheffer.

【0003】

U.S. Pat. Nos. 2,400,877, 2,481,380, and 2,544,659 issued to JFDreyer relate to the use of aligned organic dyes as polarizing bodies.

【0004】

In the present technology, it is known to combine an optical fiber faceplate with an LCD system. U.S. Pat. No. 4,349,817 (hereinafter referred to as the Hoffman patent) granted to Hoffman et al. Cited herein for reference provides examples of such combinations in the context of the present invention. The main advantages of LCDs are that they have a small and durable structure and that they are easy to carry as display screens for portable personal computers.

【0005】

In general, LCDs intended for use in portable systems are reflective because they utilize ambient light, which is useful for lighting, to avoid the inconvenient properties of being heavy, bulky, and power consuming in active or backlit systems. It has become. These displays include a liquid crystal layer sandwiched between transparent front and rear electrodes and a reflective or semi-reflective (ie, mirror-like) surface located behind the display to enhance reflection. .. The system has an off state, that is, a state in which no voltage is applied between the front electrode and the rear electrode, and an on state, that is, a state in which a voltage is applied between them.

【0006】

The Hoffman patent is exclusively related to dynamic scattering type LCDs. When this type of LCD is off, the liquid crystal is transparent and light passes through it and returns with reflection from the reflective rear electrode. When on, the liquid crystal scatters light in proportion to the increase in applied voltage. This mode, which controls the light transmittance of the liquid crystal material in response to the applied voltage, is the "dynamic scattering mode" (when light passes through the LCD) and the "reflective dynamic scattering mode" (light is reflected and incident on the LCD). If it comes out from the same side as you did).

【0007】

Reflective Dynamic Scattering Mode Contrast is a major issue when used in direct viewing applications for LCD devices. Here, the contrast is defined as the ratio of the brightness in the on state and the brightness in the off state. Therefore, the question with this technique is how to reduce the level of extra incident light emitted from unwanted light sources located outside the viewing angle of the LCD screen. If these unwanted light sources can be neutralized, the contrast will improve well.

【0008】

To solve this contrast problem resulting from stray light, the Hoffman patent combined a specially designed fiber optic faceplate with the LCD system. Figure 1 and Figure 2 are used to illustrate the Hoffman patented approach and the state of the prior art. In addition to these figures, the following description describes the disclosures surrounding each of FIGS. 3 and 2 of the Hoffman patent.

【0009】

FIG. 1 shows a direct-view liquid crystal image display system 20 viewed directly under ambient light from a light source 22 such as a sunny sky or a brightly lit room (not shown). Rays 24, 25, and 26 from light source 22 are permissible cones of face plate 28 Theta_max(Here, T_MAX) Corresponds to the optical fiber surface plate 28 at the angle of incidence. Rays 24, 25, and 26 reach the liquid crystal layer 30 of the LCD device 31 overlaid with the face plate 28.

【0010】

Allowable angle T_MAXThe definition and meaning of is shown in the discussion on equation (1) described later. T_MAXIs measured with respect to an axis 27 parallel to the horizontal optical propagation axis (no reference number) of the optical fiber constituting the optical fiber surface plate 28 and perpendicular to the optical fiber surface plate 28.

【0011】

First, considering the situation in the off state, the light ray 24 that hits the local region 32 of the liquid crystal in the off state is specularly reflected and reaches the observer's (not shown) eye 36 along the optical path 34. As a result, the observer sees a bright display area.

【0012】

On the contrary, when considering the situation of the on state, the above-mentioned ray 26 hits the local region 38 in the on state of the liquid crystal, and as a result, the ray 26 is scattered and only a part of the ray 26 is reflected. .. That is, the reflected portion of the scattered light follows the optical paths 40, 42, 44, 46, and 48 and returns to the observer's eye 36. Therefore, a relatively dark display area (ie, the on-state area 38) is visible.

【0013】

In order to treat stray light from other light sources located at light sources 50, 52, and 54 (sun), the prior art has a well-defined permissible angle T for the face plate 28._MAXThe system 20 is configured so that light can enter and exit the surface plate 28 only within the range of. By this approach, stray light is absorbed by the face plate 28.

【0014】

That is, the permissible cone T of the surface plate 28, such as the rays 56 from the light source (sun) 54 and the rays 58 from the light source 52._MAXBy absorbing light from an external light source, the faceplate 28 prevents unwanted degradation of the image contrast of the LCD image caused by ambient light caused by light sources such as light sources 22, 50, 52, 54. To do.

【0015】

FIG. 2 shows a cross-sectional view of one optical fiber 60 of the type that bundles to form the surface plate 28 shown in FIG. The face plate 28 is formed by many parallel optical fibers 60 that are integrated with each other. Each optical fiber 60 has a translucent core 62 having a refractive index of n. The core 62 is covered with a translucent sheath 64 having an index of refraction of n, which is less than n. Sheath 64 is further covered with absorptive material 66.

【0016】

Surface plate 28 has an allowable cone angle T_MAXThat is, it has an angle related to the index of refraction of the core 62 = n with respect to the index of refraction of the sheath 64 = n. These attributes are associated based on the well-known relationship expressed in Eq. (1) below: sinT_max= [(N)-(n)]^1/2= NA ...... (1) Here, NA is the numerical aperture of the optical fiber.

【0017】

Allowable angle T with respect to the axis 27 of the optical fiber_MAXThe incident ray 25 inside propagates through the core 62 by the well-known phenomenon of multiple internal total internal reflection from the boundary 70 between the core 62 and the sheath 64. On the contrary, the incident angle is T_MAXThe incident light 58 outside of is not totally reflected, but propagates through the boundary 70 into the transparent sheath 64, and is finally absorbed by the light-absorbing layer, that is, the light-absorbing material 66.

【0018】

More simply, the function of the fiber optic faceplate in the Hoffman patented LCD absorbs all light that hits the display outside the display's viewing angle (which defines the angle at which the display provides an acceptable contrast image). , Thereby reducing stray light and increasing the contrast of the display. However, despite this improvement, the dynamic scattering type LCD has not become an important device on the market due to its relatively limited viewing angle and low contrast.

【0019】

Twisted nematic (TN) LCDs and super twisted nematic (STN) LCDs, on the other hand, have improved contrast and viewing angles compared to earlier types such as dynamic scattering LCDs, with or without improvements to the Hoffman patent. As a result, it has become significantly more important in the market over the last decade or so.

【0020】

However, poor contrast and viewing angles, although improved, remain the most serious drawbacks for TN and STN LCDs. In fact, the LCD industry continues to seek displays that can provide an overall look, such as letters printed on paper.

【0021】

Applying the teachings of the Hoffman patent does not improve the contrast of TN and STN LCDs, but actually significantly degrades them. This is due to two reasons: [0022]

First, TN and STN displays are relative to the surface of the display, as they rely on the effect of the polarizer on the polarized light propagating within the display, rather than creating bright and dark areas of the image due to scattering. Even if the light that hits the display is removed at an angle larger than the visual value of the display, the contrast does not increase.

【0023】

Second, as in the teaching of the Hoffman patent, if the optical fiber surface plate is provided in a state where it is in almost contact with the liquid crystal layer itself, the image contrast is significantly reduced. This is because the light passing through such an optical fiber surface plate is greatly reduced in the degree of polarization, and thus the difference between the bright region and the dark region of the image is greatly weakened.

【0024】

In addition, it is neither necessary nor desirable to incorporate a means, such as a Hoffman patented fiber optic faceplate, that absorbs all light entering the TN or STN LCD from outside the nominal viewing angle of the display.

【0025】

The black interstitial material in the Hoffman patented fiber optic faceplate can plague observers of TN or STN type LCDs, making the display perfect from what a normal display looks like when increasing the viewing angle. There is a sudden change to a state that looks black. LCD observers may suffer from this phenomenon for the following reasons: The contrast of TN type LCD and STN type LCD decreases slowly with angle. At higher angles, the apparent contrast is not completely satisfactory, but even when the observer looks at the display at a larger angle, it still shows the general nature of what is being displayed, or just something. It is possible to determine that.

【0026】

This information is often important or desirable to the observer, so the Hoffman patented form of fiber optic faceplates is not adopted for improvements to many modern LCDs.

【0027】

The teaching of the Hoffman patent is to use fiber optic faceplates, each consisting of fiber optics with as small a numerical aperture as possible and limiting the viewing angle by using as much black interstitial material as possible to eliminate as much stray light as possible. On the other hand, the teaching of the present invention is to use an optical fiber surface plate having as large a numerical aperture as possible and allowing as wide a viewing angle as possible in order to collect as much ambient light as possible to illuminate the display.

【0028】

Figure 3 shows a typical reflective LCD with prior art using a polarizing device. The LCD 300 includes a layer of liquid crystal material 301 sandwiched between drive matrices 302a and 302b for applying an electric field at appropriate positions within the layer of liquid crystal material (L / C) 301. For example, within the layer of liquid crystal material 301, selected pixels 304 (shown as dark areas, but in reality may appear dark or bright depending on the orientation of the polarizer) are shown. .. Pixels are generated by the appropriate electric field that the drive matrices 302a and 302b apply to the portion through the liquid crystal material 301.

【0029】

The glass plates 303a and 303b serve as supports for the drive matrices 302a and 302b. Polarizers 305a and 305b are formed on the other side of the glass plates 303a and 303b, respectively. The polarizing device 305a acts as a surface exposed to the light of the LCD 300. The polarizing device 305b faces a semi-diffused mirror 307 separated from the polarizing device 305b by a gap 306, which may be convenient to fill with a glass plate. If desired, the semi-diffusive mirror 307 is formed with an aluminum coating on the surface of the polarizer 305b that is not in contact with the glass plate 303b.

【0030】

One of the drawbacks of the prior art LCD300 in Figure 3 is that the glass plate 303b is generally considerably thicker than the pixel-to-pixel spacing and the semi-diffusing mirror 307 is reflective or semi-reflective, so it is below the actual pixel 304. Is to form a ghost image or "shadow" 310. It is easy to see that such a problem actually occurs by just writing the optical paths of two rays based on the well-known principle of geometrical optics. Consider a ray 308-1, which enters the display from the upper left, passes through the display cell, is reflected by the semi-diffusing mirror 307, and is sent back out of the display as the ray 308-2. We will also consider the ray 309-1, which enters from the upper right and is also sent out as the ray 309-2. The extensions of rays 308-2 and 309-2 intersect shadow 310, so it appears to the observer as coming out of shadow 310. Also, since both rays pass through the position of the selected pixel 304, the intensity of both rays is modulated by the action of the display to be the same as the selected pixel 304. Therefore, boost image or shadow 310 Is a virtual image of pixel 304 located behind the selected pixel 304 in the geometrical optics sense, and may appear to be laterally displaced from pixel 304 by parallax, depending on the viewer's viewing position.

【0031】

Another drawback of prior art LCDs such as the LCD 300 in Figure 3 is that the apparent illuminance of the display is significantly affected by the viewing angle. Furthermore, the display appears to be brightest illuminated by outside light when viewed at an angle close to the specular reflection of the light from the upper surface of the display (the upper surface of the polarizer 305a in FIG. 3). There is also a drawback. Therefore, observers are often motivated to look at the display in such a way that they have to deal with annoying glare.

【0032】

[Purpose of Invention]

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a bright display having high contrast.

【0033】

[Summary of Invention]

According to one embodiment of the present invention, a novel LCD comprising a layer of liquid crystal material, one or more polarizers, and a fiber optic faceplate is provided. Its fiber optic faceplate allows ambient light from a much wider range of incident angles to illuminate the LCD compared to prior art, and also prevents glare from appearing on the front of the display even under poor lighting conditions for the observer. And yet allow you to position yourself so that you can see the brightly lit display.

【0034】

[Examples of the invention]

The LCD with an optical fiber surface plate of the embodiment of the present invention is illuminated more brightly than a conventional reflective LCD under a wide range of ambient lighting conditions due to the excellent light diffusion characteristics of this optical fiber surface plate. appear. To understand that this is the case, consider the prior art reflective LCD shown in Figure 4a (for clarity, drive electrodes and alignment layers well known in the art are omitted).

【0035】

The apparent background lighting is the reflected ambient light. Let us consider the ambient rays that enter the conventional display from point A. After passing through the display cell, this ray exits point B and is reflected by the semidiffusive mirror at point C. The light contained in the original light rays spreads in a conical shape with a half-width of φ after reflection due to the diffusing action of the semi-diffusing mirror 307. This is shown in the two-dimensional pole figure for reflectance in Fig. 4b and the three-dimensional polar figure for reflectance in Fig. 4C. The axis of this cone coincides with the ray CD exiting the display at the same angle as the incident ray AC if the reflection is purely specular. That is, a cone that expresses the intensity of reflected illumination as a function of angle is a rotating body around the direction of specular reflection. This is a semi-diffusive mirror 307 due to reflection It shows that only the light source within the angle range that goes out from the upper surface of the polarizing device 305a, which is parallel to the parallel light source, and is directly visible to the observer, has a great influence on the apparent background illumination. Therefore, unless the angle φ is large, only a relatively small number of ordinary ambient light sources can contribute to illumination. However, due to the nature of the diffusion scattering process, light scattered at large angles tends to be depolarized. The light leaving the cell from point B is polarized by the action of the LC cell. When the polarized light is lost at the time of reflection at point C by the reflector that causes strong diffusion (necessary to increase the angle φ), up to half of the reflection is absorbed by the polarizers 305a and 305b of the LC cell. As a result, the apparent brightness of the display is reduced. Therefore, there is a trade-off between the large amount of diffusion and the overall brightness of the display. Therefore, in an actual display, the value of φ tends to be limited to a small value. As a result, traditional reflective LCDs The apparent brightness of is strongly dependent on the angle, and the light source that contributes to the brightness must be placed near a position where specular reflections (probably from the front of the display) are visible to the observer. Will not be. This limitation, combined with the fact that the LC cell itself can also severely limit the viewing angle at which it displays an image of reasonable contrast, can have catastrophic consequences for image quality.

【0036】

In order to understand the similar action to the above in the present invention using the optical fiber surface plate LCD, first, the behavior of one fiber with respect to the incident light as shown in FIG. 5 will be considered. Looking at FIG. 5a, which is a top view of the optical fiber, when the light 501 incident on the optical fiber descends in the optical fiber and exits from the bottom, the median surface (that is, the axis of the optical fiber) of the light is taken. You can see that only the part inside the containing surface, the light beam entering from point A, is in such a surface) stays in this surface. Other parts of the incident light, such as the light beam incident from point B, deviate in the directional direction each time it is reflected, and when it exits point C as the light beam 511, it has a certain net direction with respect to the original incident direction Ψ. Deviations are cumulative. All the light rays that are incident on the axis of the optical fiber at the same angle θ also exit at an angle θ with respect to the axis of the optical fiber.

【0037】

However, many rays representing the light that fills the fiber include rays that exit the fiber with that deviation for any possible deviation angle Ψ. Therefore, incident light from a single direction, that is, light rays incident on the fiber as a single line, is converted so that its apex angle spreads in the shape of the surface of a cone equal to the incident angle θ. FIG. 5b shows a side view of the optical fiber of FIG. 5a, and FIG. 5C shows the operation of the optical fiber of FIGS. 5a and 5b in three dimensions. These figures show that incident light from one direction is converted into a hollow cone of light with an apex angle equal to the incident angle.

【0038】

Next, consider an example of an LCD with an optical fiber faceplate graphically shown in FIG. 6a (again, the drive electrodes and alignment layer are omitted for clarity). Illumination incident from a single direction spreads in a hollow cone by the action of the individual fibers of the fiber optic faceplate 619, as just described. After passing through the LC cell, the incident light hits the specular reflector 607. The specular reflector 607 sends this light back through the cell without diminishing its degree of polarization or reducing its intensity. When this light passes through the fiber optic surface plate 619 for the second time, it produces a second azimuth diffusion and a far field pattern of the same hollow cone as described above.

【0039】

As shown in 2D in Figure 6b and 3D in Figure 6c, there are two important differences between this situation and the situation with traditional reflective LCDs. First, diffusion occurs completely before and completely after the light passes through the LC cell and its polarizers 605a, 605b twice, so there is no loss of light due to weakened polarization. .. Second, the volume representing the intensity of light scattered at a given angle is, in this case, a rotating body around the normal of the display surface, not around the direction of specular reflection.

【0040】

This means three things: (a) the light from a given ambient light source spreads over a much larger distant viewing angle than traditional displays, and (b) from the perspective of a given observer. Ambient light from a wider variety of directions contributes to the illuminance at that time compared to conventional displays. (C) Observers see specularly reflected light in order to see a brightly illuminated display. You don't have to get close to where you can get in.

【0041】

FIG. 7 shows one of the examples of an optical fiber surface plate LCD configured according to the teachings of the present invention. This shows how the ghost image is significantly removed.

【0042】

Let us consider a geometric configuration with two incident rays 701-1 and 702-1 similar to that shown in Figure 3. To pass through the selected pixel 304, the rays 701-1 and 702-1 are incident on the portion of the fiber optic faceplate located just above the pixel 304 due to the well-known optical properties of the individual fiber optics. Must. Rays 701-1 and 702-1 are reflected by mirror 607 as they pass through the display cell. The reflected rays 701-2 and 702-2 hit the optical fiber face plate again.

【0043】

Since the thickness of the lower half of the display is usually large compared to the distance between the fibers in the optical fiber surface plate, the rays 701-2 and 702-2 are the optical fibers struck by the rays 701-1 and 702-1. It hits a completely different optical fiber, and the ray 701-2 hits a completely different optical fiber from the optical fiber hit by the ray 702-2. Also, when the rays 701-2 and 702-2 hit the optical fiber, they pass through it, and according to the incident angle and azimuth of the rays 701-1 and 702-1 (parameters θ and Ψ in FIG. 5), the optical fiber The exiting rays 701-3 and 702-3 exit the display from random positions in the core, so the azimuths they exit are randomized, as already mentioned in the discussion in Figure 5. In general, it does not look like a ghost, as it emerges from a single area of space.

【0044】

The light, which is normally concentrated in the ghost image, is blurred by the diffusion effect when it passes through the fiber optic faceplate a second time, in which case it is much larger and more diffused than the conventional LCD in Figure 3. A shadow is formed around the selected pixel 304. This larger and more diffused shadow is not as clear to the observer as the ghost image in Figure 3 in two respects. First, shadows mix so much with light that has passed through the close area of the display, so its maximum brightness or darkness, whichever it is, depends on the optical state of the selected pixel 304. It's not much different from the area around the display. Second, shadows are so spatially diffused as out-of-focus images that, from the observer's point of view, shadows are not easily and clearly visible as containing any information.

【0045】

The only aspect in which the observer can clearly see the selected pixels is due to the image 720 located on the top surface of the fiber optic face plate due to the well-known optical properties of the individual fibers in the fiber optic face plate. .. In order for this image to be spatially sharp, the polarizing plate 605a must be thin compared to the pixel size of the display.

【0046】

In one embodiment of the invention, the polarizer 605a is thin layered (typically about 0.5-100) to produce a sharp looking image 720 when used at pixel spacing on a typical display of 100-400 microns. Formed in the micron range). The thin polarizing device 605a can be made using an aligned organic dye as described in the above Dryer patent. In one particular embodiment, the polarizing device 605a is manufactured using a 105MS polarizing coating available from Da-Lite Screen Corporation in Cincinnati, Ohio, USA. A topcoat layer, such as a special polymer topcoat from Da-Lite Corp or a thin topcoat with a suitable material such as silicon dioxide, may be required between the polarizing coating and the other functional layers of the liquid crystal cell. ..

【0047】

In an embodiment of the invention in which the polarizing device 605b is used, the polarizing device 605b is formed in the same manner as the polarizing device 605a. Individual fiber optics can be made in the range of 6 to 25 microns and the fiber optic faceplate 619 can be made to have a thickness in the range of about 0.7 to 1.1 millimeters. In one of the examples, the fiber optic faceplate 619 is made of approximately 0.66na fused glass fiber plate available from Incom, Inc., Southbridge, Massachusetts, United States.

【0048】

Therefore, according to the teaching of the present invention, (a) the visual sense, contrast, and other operating characteristics of the liquid crystal element itself are not deteriorated. (b) Widen the angular range of ambient light received for lighting. (c) A novel LCD structure is shown, including a fiber optic faceplate, that allows the observer to stay away from the specularly visible ambient light.

【0049】

The teachings of the present invention are valid not only for LCDs with polarizing plates on both sides of the liquid crystal, but also for LCDs with at least one polarizing plate, such as LCDs with polarizing plates only on the observer side of the liquid crystal. .. The teachings of the present invention can be applied to LCDs containing one or more birefringents that act to convert light between elliptically and linearly polarized light, in addition to one or more polarized lighters. ..

【0050】

All publications and patent applications cited herein are incorporated herein by reference as if each individual publication or patent application was specifically directed to be incorporated as a reference individually. There is.

【0051】

The above detailed description and drawings provide some specific examples of the best embodiments of the present invention. However, it is the claims that actually define the invention and set the scope of the invention.

【0052】

[Effect of the invention]

As described in detail above, according to the present invention, it is possible to obtain a display that is bright and has less reflection of the light source on the surface plate and less ghost image.

[Simple explanation of drawings]

[Figure 1]

The figure explaining the problem of the prior art.

[Figure 2]

The figure explaining the problem of the prior art.

[Fig. 3]

The figure explaining the problem of the prior art.

[Fig. 4]

The figure explaining the problem of the prior art.

[Fig. 5]

The figure explaining the operation of the optical fiber used for the surface plate of one Example of this invention.

[Fig. 6]

The figure explaining one Example of this invention.

[Fig. 7]

The figure explaining one Example of this invention.

[Explanation of symbols]

20: Display system 22, 24, 25, 26: Light source 27: Axis 28: Optical fiber surface plate 30: Liquid crystal plate 31: LCD device 34, 40, 42, 44, 46, 48: Optical path 36: Eyes 50, 52, 54: Light source 60: Optical fiber 62: Core 64: Sheath 66: Absorbent material 70: Boundary 300: LCD 301: Liquid crystal material 302a, 302b: Drive matrix 303a, 303b: Glass plate 304: Pixel 305a, 305b: Polarizer 306: Gap 307: Semi-diffusing sex mirror 310: Shadow 501: Light 511: Light beam 601: Liquid crystal material 603: Glass plate 605a, 605b: Polarizer 607: Specular reflector 619: Optical fiber surface plate 720: Image