WO2000050953A1 - Transmission liquid crystal display - Google Patents

Abstract

A liquid crystal display with no color filter even when a linear or planar illumination light source is used. The liquid crystal display comprises a linear or planar light source, a wedgelike light guide to which a fraction of light radiated from the illumination light source is directed, wavelength separating means for separating light emerging from the wedgelike light guide obliquely and generally parallel into lights having wavelengths in a plurality of ranges, light focusing means for receiving lights separated by the separating means and focusing a light in a predetermined wavelength range on a predetermined sub-pixel, and a liquid crystal layer controllable for each sub-pixel. The light focusing means is desirably a cylindrical lens array. The wedgelike light guide specularly reflects light at the face opposed to the face from which light emerges, may have a metallic surface mirror, and preferably has a vertex angle of 0.1 to 3; more preferably 0.3 to 1.

Description

 Description Transmissive liquid crystal display Technical field

 The present invention relates to a transmissive liquid crystal display device capable of full-color display without using a color filter, and more particularly to a direct-view transmissive liquid crystal display device. Background art

 A color liquid crystal display device is composed of hundreds of thousands to hundreds of thousands of pixels, and each pixel is composed of RGB sub-pixels. An RGB color filter is used to display RGB for each sub-pixel, and a full-color image is obtained by combining the display of these sub-pixels. In this case, since 2Z3 of the light is absorbed by the color filter in each sub-pixel, only 1/3 of the light is theoretically used.

As a method of performing color display without using a color filter, a method of separating light into a plurality of wavelength regions and condensing the light for each wavelength region is known. For example, as a `` crystal projector, one microphone aperture lens is arranged for each pixel, that is, for every three sub-pixels, and the light separated by the microphone aperture lens is different using a color-selective mirror. A method has been proposed in which the light is reflected in the direction and the transmission or blocking of light is controlled by a liquid crystal layer for each sub-pixel corresponding to each color (SID Symposium 199, pp. 911, 911). Similarly, as a liquid crystal projector, the arc lamp light is reflected by the diffraction grating surface and separated into RGB light, which is condensed by a microlens array, and each subpixel is A method of controlling light transmission in a liquid crystal layer has been proposed (SID Symposium pp. 199, 199). In these projectors, it is relatively easy to separate light at the microphone aperture lens array. This is because a projector often uses a point light source such as a metal halide lamp with a high light intensity, but the point light source lamp has a high directivity of light itself. This is because it is easy to focus light on the pixels.

 However, when a linear or planar illumination light source is used, the directivity of the light is not sufficient, and the RGB light is difficult to completely separate. It has been difficult to obtain a liquid crystal display device using a suitable light separating means. As a result of intensive studies, the present applicant can make light of a predetermined wavelength incident on a predetermined sub-pixel by using the following method, even when a linear or planar illumination light source is used. A color liquid crystal display device that does not use a color filter has been completed. Disclosure of the invention

The present invention provides a linear or planar light source, a wedge-shaped light guide plate on which light emitted from the illumination light source is incident, and a light emitted from the wedge-shaped light guide plate obliquely and substantially parallel to a plurality of wavelengths. Wavelength separating means for separating the light into the light of the region, light collecting means for receiving the light separated by the wavelength separating means and collecting the light of the predetermined wavelength region to a predetermined sub-pixel, and controllable for each sub-pixel The present invention relates to a transmission type liquid crystal display device including a liquid crystal layer. The light source of the present invention is preferably a fluorescent lamp. The condensing means of the present invention is desirably a micro-lens array, for example, a cylindrical lens array. The wedge-shaped light guide of the present invention is one in which light is regularly reflected on the surface opposite to the emission surface, and may have a metal surface mirror. Has an apex angle of 3 to 1 degree. The wavelength separation means of the present invention is a diffraction grating. In the diffraction grating, a part of the incident light is specularly reflected on the incident surface, the emission surface has a saw shape, and the side farther from the illumination light source in the saw shape is in a direction perpendicular to the emission surface. It is desirable to form an angle of 5 to 20 degrees, more preferably 10 to 15 degrees. Further, in the transmission type liquid crystal display device of the present invention, a diffusion plate may be provided. BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a sectional view of a transmission type liquid crystal display device of the present invention. The liquid crystal display device of the present invention comprises a liquid crystal display unit 1 and a backlight unit 2. The liquid crystal display unit 1 is composed of two glass substrates 26 and a liquid crystal layer 30 inserted between them. Outside the lower glass substrate 26, a cylindrical lens array 20 is provided, and a polarizing plate 18 may be provided. Outside the upper glass substrate 26, a polarizing plate 18 and a diffuser plate 28 may be provided. The backlight unit 2 includes a fluorescent lamp 3, a light guide 4, and a diffraction grating 16. The light guide 4 may have a metal reflector 6. The light emitted from the linear fluorescent lamp 3 enters the light guide 4, and the light 12 gradually becomes steeper while repeatedly reflecting at the lower surface 8 and the upper surface 10 of the light guide. You. When the direction of the light 12 on the upper surface 10 exceeds the critical angle, the light 14 is emitted from the upper surface of the light guide. Since the light is emitted only after exceeding the critical angle, the light 14 is substantially parallel light. The light 14 is separated into RGB light at the diffraction grating 16. The separated RGB light enters the cylindrical lens array 20. The cylindrical lens array 20 includes a plurality of cylindrical lenses 22, 24, and the like. One cylindrical lens may be designed to correspond to one pixel, or one cylindrical lens may be designed to correspond to a plurality of pixels. The cylindrical lens 22 corresponds to the pixel 32, and the pixel 32 is composed of three sub-pixels of 32R, 32G, and 32B. For the light that has entered the cylindrical lens 22, R light enters the sub-pixel 32 R, G light enters the sub-pixel 32 G, and B light enters the sub-pixel 32 B. Light transmission or blocking is controlled. Any type of liquid crystal may be used as long as the transmittance can be controlled. In the case of a system in which the transmittance is controlled by changing the polarization state, it is necessary to arrange a polarizing plate as shown in FIG. 1, but in the case of using another system, the polarizing plate is used. Is not required. FIG. 2 shows a spectral characteristic of irradiation light of the fluorescent lamp 2 used in the present invention. In the present invention, it is necessary to separate light by a diffraction grating or the like, but since the exit angle of the diffracted light is affected by the wavelength of the incident light, it is better than that of light having a uniform and continuous light distribution characteristic. However, it is easier to separate light by using discontinuous light having some strong peaks. For example, typical blue, green, and red wavelengths are 445 nm, 530 nm, and 615 nm, which correspond to the fluorescent light peaks in Fig. 2. By separating the light in the specified wavelength region, blue, green, and red light can be separated. In the present invention, it is necessary to pass a predetermined light of the separated RGB through a predetermined sub-pixel of the liquid crystal layer. For example, in FIG. 1, red light 16R, green light 16G, and green light 16B need to pass through the sub-pixels 32R, 32G, and 32B, respectively. FIG. 3 schematically shows an enlarged area of the pixel 32. The figure shows a state in which red light 16R is incident on the sub-pixel 32R, and green light 16G is incident on the sub-pixel 32G. a indicates the distance from the point at which light enters the cylindrical lens 22 to the liquid crystal layer, and b indicates the pitch of the sub-pixels. The angle between the red light 16R and the green light 16G must be determined as follows. For example, a takes a slightly larger value because the thickness of widely used glass is 0.5 to 0.7 mm. b is 0.04 to 0.1 mm for a direct-view type, and 0.088 mm for a 13.3-inch diagonal XGA liquid crystal panel (resolution: 1,024 X 768). As a result, tan 0 = bZa is about 0.088 / 0.9 in a 13.3-inch XGA liquid crystal panel, and Θ is only about 5.5 degrees. Even if it is a very coarse old-fashioned LCD panel, Θ is only about 8 degrees. It can be seen that to achieve this, the directivity of the RGB light must be extremely high. For that purpose, the directivity of the light from the light source must be extremely high. FIG. 4 shows the diffraction phenomenon of light by the diffraction grating. Wavelength: Light power of L Incident light is incident on a transmission type diffraction grating made of a medium with a refractive index of n and having a grating interval of pitch d, emission angle Θ. Out. If the diffraction grating is in air, si η Θ o = sin Θ i— / d (m is an integer)

There is a relationship. According to this equation, when θί is sufficiently large (close to 90 degrees), the change in the value of sin 0 i is small even if the value of 0 i varies somewhat, so the change in θο is not so large. You can see that. In other words, the more the light incident on the diffraction grating is incident on the diffraction grating at an angle close to parallel, the more the light emitted from the diffraction grating is directed It turns out that becomes high. When 6i is the incident light at 80 degrees and the value of d is determined so that the wavelength component of the green light (530 nm) is emitted right above, d = 530 / sin 80. = 5 38 nm. FIG. 8 shows the emission angle θο when the incident angle θί is 70 degrees, 80 degrees, and 90 degrees. From this figure, it can be seen that if the incident light with a central incident angle of 80 degrees and a spread of ± 10 degrees is used and green light is emitted directly above, emitted light with a directivity of less than 4 degrees can be obtained. I understand. In Fig. 8, the calculation is performed using the value of d = 548.5 nm. FIG. 9 similarly shows the calculation results at a central incident angle of 60 degrees and d = 612 nm, and FIG. 10 shows the calculation results at a central incident angle of 50 degrees and d == 691 nm. It can be seen that the smaller the central incident angle, the lower the directivity of the emitted light. On the other hand, when the incident angle is further increased to approach 90 degrees, the reflectance of the incident light on the surface of the diffraction grating becomes too high, and a problem arises that the light beam of the incident light is not introduced into the diffraction grating. FIG. 11 shows the transmittance when the incident angle 0 i was increased. The refractive index of the diffraction grating is 1.5. It can be seen that even with polarized light having a higher transmittance, there is only a transmittance of 76% at 80 ° incidence and 50% at 85 ° incidence. The light that does not pass through is hit by various components and is irregularly reflected, resulting in so-called stray light, which degrades the color separation characteristics. From the above, it can be seen that the transmission type liquid crystal display device of the present invention can be obtained by irradiating the diffraction grating with light having a spread of about 10 degrees at an incident angle of about 80 degrees. FIG. 5 is an example of a light guide useful in the present invention. The total reflection type light guide is a wedge-shaped transparent light guide having a very small apex angle of 0.1 to 3 degrees, more preferably 0.3 to 1 degrees. Preferably, the light guide has a metal reflector 6 on the back surface. It is sufficient that the angle formed between the upper surface and the lower surface of the light guide is such an angle, and the light guide may have a triangular cross-section as shown in FIG. 5, or a quadrangular cross-section as shown in FIG. You may have. When light from a fluorescent lamp is guided to such a light guide, the light is first totally reflected by the surface and returned inside the light guide. At each such total reflection, the incident light is reduced by the magnitude of the apex angle, and eventually the incident light does not satisfy the condition of total reflection, and some light is emitted to the outside. On the lower surface, the light is totally reflected by the metal reflector 6. The component not emitted from the upper surface returns to the inside of the light guide and is totally reflected by the lower surface. The incident angle is reduced by twice the apex angle, and is incident again on the boundary surface of the upper surface. Since the transmittance increases as the incident angle decreases, a part of the light is emitted and the rest is returned to the inside of the light guide again. Thereafter, the same operation is repeated. The intensity of the remaining light is low every time it is emitted In reality, most of the light power is emitted by repeating 4 to 5 times. FIG. 10 shows the intensity distribution with respect to the emission angle when a wedge-shaped light guide plate having a vertical angle of 0.5 degrees and a refractive index of 1.5 was obtained by simulation. It can be seen that the emitted light has a high directivity and a sufficient intensity at a center emission angle of about 80 degrees. By making the highly directional light incident on the diffraction grating at a large angle of 80 degrees, extremely separated directional light can be obtained.

If it is only to increase the angle of incidence on the diffraction grating, use a light guide whose emission angle from the light guide is smaller than that of the present invention, and arrange the upper surface of the light guide and the lower surface of the diffraction grating at an angle, It is not impossible that the angle of incidence on the diffraction grating is, for example, about 80 degrees. However, when the light guide and the diffraction grating are arranged in parallel, the light reflected by the lower surface of the diffraction grating and returned to the upper surface of the light guide can be reused, which is advantageous. FIG. 6 shows how the reflected light 42 that has been reflected by the lower surface of the diffraction grating 16 and returned to the upper surface of the light guide 4 is reused. In the present invention, since the incident light 40 on the diffraction grating 16 has a large incident angle Θ, the reflected light 42 reflected on the lower surface of the diffraction grating 16 and not separated by the diffraction grating occurs. There are many. When the upper surface of the light guide and the diffraction grating sheet are parallel, the reflected light 42 is totally reflected on the surface of the light guide 4 to become the re-incident light 44. The re-incident light 44 enters the diffraction grating 16 at the same incident angle Θ and is reused. The light guide 4 and the diffraction grating 16 are placed at an appropriate distance, for example, 1 μπ! Place at ~ 2 mm intervals. Effectively use the reflected light from the diffraction grating surface For use, it is desirable that the upper surface of the light guide 4 and the lower surface of the diffraction grating 16 are smooth surfaces. FIG. 7 is a cross-sectional view showing an example of the diffraction grating 16 of the present invention. The lower surface 52 of the diffraction grating 16 is a smooth surface, and the upper surface has a saw shape. The saw shape on the upper surface is an optical refractive index modulation structure, and is composed of stripe-shaped triangular protrusions 50 having a constant pitch and a cross section of a triangle ABC shape. The period of such a refractive index modulation structure is preferably 0.2 to 2 μπ, more preferably 0.4 / m to 0.7 Aim or 0.9 to 1.3 μm. Maseru. Adjacent triangular projections may be formed continuously, and there may be a plane parallel to the lower surface 52 between the adjacent triangular projections as shown in FIG. What is important in the structure of the diffraction grating 16 is the surface of the triangular projection on the side farther from the illumination light source, that is, the corner formed by AB in FIG. However, here, it is assumed that the illumination light source is located on the right side of the drawing as shown in FIG. Most of the light incident on the diffraction grating exits from the AB plane as RGB light. In the design of the liquid crystal display device, it is preferable to design so that the green light is almost directly above, and in consideration of the wavelength characteristics of the fluorescent lamp, the green light is inclined about 1 to 4 degrees toward the red side. Is also good. Desirable angle α for keeping the emission angle of green light in such a range is 5 degrees to 20 degrees, and more preferably 10 degrees to 15 degrees. Since the BC plane does not contribute much to the separation of light, it can take various other structures than the structure shown in Fig. 7. In the present invention, since the directivity of light is extremely high for each RG, there is a drawback peculiar to a direct-view type liquid crystal device that a color changes depending on a viewing direction and is seen. There is also. Therefore, in the present invention, a diffusion plate 28 may be provided as shown in FIG. As long as the diffusion plate 28 changes the polarization characteristics, it is desirable to place the diffusion plate outside the polarizing plate as shown in FIG. However, if it is located outside, the path of RGB light becomes longer, and the definition is reduced accordingly. If the diffusion plate does not change the polarization characteristics, it can be placed inside the polarization plate. Although the contents of the present invention have been described based on the specific examples, the contents of the present invention are not limited to these examples, and any changes and modifications may be made within the scope of the present invention. . Industrial applicability

 In the present invention, since RGB light having extremely high directivity can be made incident on the liquid crystal layer, it is possible to provide a direct-view transmission-type liquid crystal display device that does not use a color filter. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a sectional view showing an example of the liquid crystal display device of the present invention.

 FIG. 2 is a graph showing the wavelength characteristics of the fluorescent lamp used in the present invention.

 FIG. 3 is a cross-sectional view schematically showing a pixel in the liquid crystal display device of the present invention.

 FIG. 4 is a diagram showing the incidence and emission of light in the diffraction grating of the present invention.

FIG. 5 is a diagram showing a backlight unit of the present invention. FIG. 6 is a sectional view showing a liquid crystal display device according to the present invention. FIG. 7 is a diagram showing an example of the diffraction grating of the present invention.

Claims

The scope of the claims 1. A linear or planar light source, a wedge-shaped light guide plate on which light emitted from the illumination light source is incident, and light emitted obliquely and substantially parallel from the wedge-shaped light guide plate in a plurality of wavelength ranges. Wavelength separating means for receiving light separated by the wavelength separating means, and condensing means for collecting light in a predetermined wavelength region to predetermined sub-pixels; and controllable for each sub-pixel. A transmissive liquid crystal display device consisting of a liquid crystal layer.  2. The transmissive liquid crystal display device according to claim 1, wherein the light source is a fluorescent lamp. 3. The transmissive liquid crystal display device according to claim 1, wherein the light condensing means is a cylindrical lens array.  4. The transmissive liquid crystal display device according to claim 3, wherein the wedge-shaped light guide regularly reflects light on a surface opposite to an emission surface.  5. The transmissive liquid crystal display device according to claim 4, wherein the wedge-shaped light guide has an apex angle of 0.1 to 3 degrees.  6. The transmissive liquid crystal display device according to claim 4, wherein the wedge-shaped light guide has a vertex angle of 0.31 degrees.  7. The transmission type liquid crystal display device according to claim 4, wherein the wedge-shaped light guide has a metal surface mirror on a surface opposite to an emission surface.  8. The transmissive liquid crystal display device according to claim 3, wherein the wavelength separating means is a diffraction grating. 9. The transmissive liquid crystal display device according to claim 8, wherein the diffraction grating reflects part of incident light on an incident surface. 10. The diffraction grating has an emission surface having a saw-like shape, and a side of the sawtooth shape that is farther from the illumination light source forms an angle of 5 to 20 degrees with respect to a vertical direction of the emission surface. 9. The transmission type liquid crystal display device according to claim 8.  1 1. The diffraction grating has an emission surface having a sawtooth shape, and a side of the sawtooth shape that is farther from the illumination light source has an angle of 10 to 15 degrees with respect to a vertical direction of the emission surface. 9. The transmission type liquid crystal display device according to claim 8, wherein  1 2. The transmission type liquid crystal display device according to claim 3, wherein the transmission type liquid crystal display device further includes a diffusion plate.