KR100429451B1 - Transmission liquid crystal display - Google Patents

Abstract

An object of the present invention is to provide a liquid crystal display device which does not use a color filter even when a linear or planar illumination light source is used.

The present invention provides a linear or planar light source, a wedge-shaped light guide to which light irradiated from the illumination light source is incident, and light emitted from the wedge-shaped light guide in substantially oblique directions and parallel to the light in a plurality of wavelength regions. A transmissive liquid crystal display comprising a wavelength separating means for separating, a light collecting means for receiving light separated by the wavelength separating means and condensing light of a predetermined wavelength region to a predetermined sub pixel, and a liquid crystal layer controllable for each sub pixel. It is about. As the light collecting means, a cylindrical lens array is preferable. In the wedge-shaped light guide of the present invention, light is reflected on the opposite side of the exit surface, and may have a metal reflector, and may be 0.1 ° to 3 °, more preferably 0.3 ° to 1 °. Have a vertex angle

Description

Transmissive liquid crystal display {TRANSMISSION LIQUID CRYSTAL DISPLAY}

The color liquid crystal display is composed of hundreds of thousands to hundreds of thousands of pixels, and each pixel is composed of RGB subpixels. RGB color filters are used to display RGB for each sub-pixel, and a full color image can be obtained by combining the display of these sub-pixels. In this case, since two thirds of the light is absorbed by the color filter in each sub-pixel, only one third of the light is theoretically used.

As a method of performing color display without using a color filter, a method of separating light into light of a plurality of wavelength regions and condensing light for each light of each wavelength region is known. For example, as a liquid crystal projector, one microlens is disposed for each pixel, that is, for every three subpixels, and the light separated from the microlens is reflected in a different direction by using a reflector having color selectivity, A method of controlling transmission or blocking of light by the liquid crystal layer for each sub pixel corresponding to each color has been proposed (SID Symposium 1996, p. 911). Similarly, as a liquid crystal projector, a method of reflecting arc lamp light on the diffraction grating surface, separating the light into RGB light, condensing it with a microlens array, and controlling the transmission of light in the liquid crystal layer for each subpixel has been proposed (SID Symposium). 1998, p. 199). In these projectors, separation of light in the microlens array is relatively easy. For this reason, a projector often uses a point light source such as a metal halide lamp having a high amount of light. Since the point light source lamp has a high directivity of light, the microlens array generates light in a predetermined wavelength region. This is because it is also easy to focus on the sub pixels.

However, in the case of using a linear or planar illumination light source, since the directivity of the light is not sufficient and the light of RGB is difficult to be completely separated, a liquid crystal display using an optical separation means such as a microlens array without using a color filter. It was difficult to get the device. As a result of full investigation, the present applicant finds that a color liquid crystal display device which does not use a color filter capable of injecting light of a predetermined wavelength into a predetermined sub-pixel even when a linear or planar illumination light source is used by the following method. To complete.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive liquid crystal display device capable of full color display, in particular a direct-view type transmissive liquid crystal display device without using a color filter.

1 is a cross-sectional view showing an example of a liquid crystal display device according to the present invention.

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

It is sectional drawing which shows typically the pixel in the liquid crystal display of this invention.

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

5 is a diagram illustrating a backlight unit of the present invention.

It is sectional drawing which shows the liquid crystal display device in this invention.

Fig. 7 is a diagram showing an example of the diffraction grating in the present invention. Fig. 8 is a diagram showing the exit angle θ _o when the incident angles θ _i are 70 °, 80 °, and 90 °. Fig. 9 is a diagram showing the calculation result at the center incident angle of 60 ° and d = 612 nm. Fig. 10 is a diagram showing the calculation result at the center incident angle of 50 ° and d = 691 nm. It is a figure which shows the transmittance | permeability when ((theta) _i ) is enlarged. FIG. 12 is a figure which shows the relative intensity when the incident angle (theta) _i is enlarged.

According to the present invention, a plurality of wavelength regions include a linear or planar light source, a wedge-shape light guide to which light irradiated from the illumination light source is incident, and light emitted obliquely and approximately parallel from the wedge-shaped light guide. A transmission type consisting of a wavelength separation means for separating light into a light, a light converging means for receiving light separated by the wavelength separation means and condensing light of a predetermined wavelength region to a predetermined sub pixel, and a liquid crystal layer controllable for each sub pixel. It relates to a liquid crystal display device.

The light source of the present invention is preferably a fluorescent lamp. The light collecting means of the present invention is preferably a microlens array, such as a cylindrical lens array. The wedge-shaped light guide of the present invention reflects light on the opposite side of the light exit surface of the light guide, and may have a metal reflector, and may be 0.1 ° to 3 °, more preferably 0.3 ° to It has a vertical angle of 1 °. The wavelength separation means of the present invention is a diffraction grating. In the diffraction grating, a part of incident light is specularly reflected from the incident surface, and the exit surface has a sawtooth shape, and in the saw shape, the side far from the illumination light source is 5 ° to 20 ° with respect to the vertical direction of the exit surface. More preferably, an angle of 10 ° to 15 ° is achieved. In the transmissive liquid crystal display of the present invention, a diffusion plate may be disposed.

1 is a cross-sectional view of a transmissive liquid crystal display device according to an exemplary embodiment of the present invention. The liquid crystal display device according to the present invention is composed of 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 therebetween. The cylindrical lens array 20 is provided in the outer side of the lower glass substrate 26, and the polarizing plate 18 may be provided. The polarizing plate 18 and the diffuser plate 28 may be provided in the outer side of the upper glass substrate 26. The backlight unit 2 consists of a fluorescent lamp 3, a light guide 4, and a diffraction grating 16. The light guide 4 may have the metal reflecting plate 6.

The light irradiated from the linear fluorescent lamp 3 is incident on the light guide 4, and the light 12 is gradually inclined at an angle while repeating the reflection on the lower surface 8 and the upper surface 10 of the light guide. When the direction of the light 12 on the upper surface 10 exceeds the critical angle, light 14 is emitted from the upper surface of the light guide. Since the light is emitted for the first time beyond the critical angle, the light 14 is substantially parallel light. Light 14 is separated into light of RGB in diffraction grating 16. The separated RGB light is incident on the cylindrical lens array 20. The cylindrical lens array 20 is composed of 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 32R, 32G, and 32B. The light incident on the cylindrical lens 22 has R light incident on the subpixel 32R, G light incident on the subpixel 32G, B light incident on the subpixel 32B, and light for each subpixel. The transmission or blocking of is controlled. As the liquid crystal, any system may be used as long as it can control the transmittance. In the case of the method of controlling the transmittance by changing the polarization state, it is necessary to arrange the polarizing plate as shown in Fig. 1, but the polarizing plate is not necessary when using other methods.

2 shows the spectral characteristics of the irradiation light of the fluorescent lamp 2 used in the present invention. In the present invention, it is necessary to separate the light by a diffraction grating or the like. However, since the emission angle of the diffracted light is affected by the incident light wavelength, it is possible to use discontinuous light having several stronger peaks than light having the same continuous spectral characteristics. It is easy to separate the light. For example, typical blue, green, and red wavelengths are 445 nm, 530 nm, and 615 nm, and the blue, green, and red light are separated by separating the light in the wavelength region corresponding to the peak of the fluorescent lamp shown in FIG. It becomes possible.

In the present invention, it is necessary to pass a predetermined light among RGB separated in a predetermined sub pixel of the liquid crystal layer. For example, in FIG. 1, the light of the red light 16R, the green light 16G, and the blue light 16B needs to pass through the sub-pixels 32R, 32G, and 32B, respectively. 3 schematically shows an enlarged area of the pixel 32. The red light 16R is incident on the sub pixel 32R, and the green light 16G is incident on the sub pixel 32G. a represents the distance from the point where light enters the cylindrical lens 22 to the liquid crystal layer, and b represents the pitch of the sub-pixels. The angle formed by the red light 16R and the green light 16G can be obtained by the following equation. For example, since a has a thickness of 0.5 to 0.7 mm, the widely used glass has a slightly larger value than this. b is 0.04 to 0.1 mm in the direct view type, for example, 0.088 mm in the case of a diagonal 13.3 inch XGA liquid crystal panel (resolution 1024x768). As a result, tan θ = b / a is a 13.3 inch XGA liquid crystal panel, which is around 0.088 / 0.9, and θ is only about 5.5 °. Even if it was a very rough old-fashioned liquid crystal panel, (theta) is only about 8 degrees. In order to achieve this, it is understood that the light directivity of RGB must be very high. For that purpose, the directivity of the light from the light source must also be very high.

4 shows a diffraction phenomenon of light by a diffraction grating. Light of wavelength λ is incident light θ _i into a transmissive diffraction grating made of a medium of refractive index n and having a lattice spacing of pitch d, and emitted at an exit angle θ _o . When the diffraction grating is present in air, there is a relation of Equation 1.

It can be seen from Equation 1 that when θ _i is sufficiently large (close to 90 °), even though there is a slight variation in the θ _i value, there is little change in the sin θ _i value, so that the change in θ _o is not so large. That is, as light incident on the diffraction grating enters at an angle close to parallel with respect to the diffraction grating, even though the incident light is somewhat low in directivity, the light emitted from the diffraction grating increases in directivity. Further, when the value of d is determined so that the wavelength component of the green light (530 nm) is directly emitted as incident light having θ _i of 80 °, d = 530 / sin 80 ° = 538 nm.

8 shows the exit angle θ _o when the incident angle θ _i is 70 °, 80 °, and 90 °. From this figure, it can be seen that the output light having directivity of less than 4 ° can be obtained by allowing the green light to be emitted directly above by using the incident light having a center incident angle of 80 ° and a range of ± 10 °. In FIG. 8, it calculates using the value of d = 548.5 nm. 9 similarly shows a calculation result at a center incident angle of 60 °, d = 612 nm, a center incident angle of 50 °, and d = 691 nm. It is understood that the directivity of the emitted light is lowered as the center incident angle is smaller.

On the other hand, when the angle of incidence is made larger and closer to 90 °, the reflectance of incident light on the surface of the diffraction grating becomes too high, which causes a problem that the optical power of the incident light is not introduced into the diffraction grating. Fig. 11 shows the transmittance when the incident angle θ _i is increased. The refractive index of the diffraction grating is 1.5. It can be seen that even the polarized light having the higher transmittance is 76% at 80 ° incidence and only 50% at 85 ° incidence. Light that does not transmit reaches various components and is diffusely reflected, resulting in stray light, which degrades color separation characteristics.

From the above, it can be seen that the transmission liquid crystal display device of the present invention can be obtained by reaching the diffraction grating with light having a range of about ± 10 ° at an incident angle of about 80 °. 5 is an example of a light guide useful in the present invention. This total reflection type light guide is a wedge-shaped transparent light guide having a very small vertex angle of 0.1 ° to 3 °, more preferably 0.3 ° to 1 °. It is preferable that the light guide has the metal reflecting plate 6 on the back surface. It is sufficient that the angle formed between the upper and lower surfaces of the light guide is such an angle, and may have a triangular cross section as shown in FIG. 5, or a quadrangular cross section as shown in FIG. 1. When light from a fluorescent lamp is induced to such a light guide, the light is first totally reflected at the surface and returned to the inside of the light guide. In each total reflection, the incident light becomes smaller by the size of the vertex angle, and eventually, the incident light does not satisfy the total reflection condition, so that some light is emitted to the outside. At the lower surface, light is totally reflected by the metal reflector 6. The components not emitted from the upper surface are returned to the inside of the light guide body and totally reflected at the lower surface, and the incident angle decreases by twice the vertex angle and is incident again on the boundary surface of the upper surface. Since the transmittance increases as the angle of incidence decreases, part of the light exits and the rest returns to the inside of the light guide. The same is repeated after that. Since the intensity of the remaining light decreases each time it exits, the optical power is substantially emitted by repeating 4 to 5 times in reality.

Fig. 10 shows the intensity distribution with respect to the exit angle when a wedge-shaped light guide having a vertex angle of 0.5 ° and a refractive index of 1.5 is used by simulation. It can be seen that the emitted light having a high directivity and sufficient intensity can be obtained with a central exit angle of about 80 °. The incident light having a high directivity can be obtained by injecting the highly directional light into the diffraction grating at a large angle of 80 degrees.

Only in order to increase the angle of incidence to the diffraction grating, by using a light guide whose emission angle from the light guide is smaller than that of the present invention, the upper surface of the light guide and the lower surface of the diffraction grating are disposed obliquely and relatively incident to the diffraction grating. It is not impossible to set the angle to, for example, about 80 °. However, when the light guide and the diffraction grating are disposed in parallel, the light reflected from the bottom surface of the diffraction grating and returned to the top surface of the light guide can be used again. FIG. 6 shows a state in which the reflected light 42 reflected from the lower surface of the diffraction grating 16 and returned to the upper surface of the light guide 4 is used again. In the present invention, since the incident light 40 to the diffraction grating 16 has a large incidence angle θ, the reflected light 42 that is reflected on the lower surface of the diffraction grating 16 and is not separated by the diffraction grating also occurs. many. When the upper surface of the light guide and the diffraction grating sheet are parallel, the reflected light 42 totally reflects on the surface of the light guide 4 to be reincident light 44. The reincident light 44 enters the diffraction grating 16 at the same incident angle θ, and is used again. The light guide 4 and the diffraction grating 16 are arranged at appropriate intervals, for example at intervals of 1 μm to 2 mm. In order to effectively use the reflected light of the diffraction grating surface again, it is preferable that the upper surface of the light guide 4 and the lower surface of the diffraction grating 16 are smooth surfaces.

7 is a cross-sectional view showing an example of the diffraction grating 16 in the present invention. The lower surface 52 of the diffraction grating 16 is a smooth surface, and the upper surface has the sawtooth shape. The sawtooth shape of the upper surface is an optical refractive index modulation structure, and is composed of a triangular protrusion [50] formed of a streaky triangle having a cross section in the shape of a triangle ABC at a constant pitch. The period of the refractive index modulation structure is preferably 0.2 to 2 m, more preferably 0.4 to 0.71 m or 0.9 to 1.3 m. Adjacent triangular protrusions may be formed continuously, and the surface parallel to the lower surface 52 may exist between adjacent triangular protrusions, as shown in FIG. What is important in the structure of the diffraction grating 16 is the angle (alpha) which AB makes in the triangular protrusion which is far away from an illumination light source, ie, in FIG. However, it is assumed here that the illumination light source is located on the right side of the drawing as shown in FIG. 1. Most of the light incident on the diffraction grating is emitted as an spectral of RGB from the AB plane. In the design of the liquid crystal display device, it is preferable to design the green light to be almost immediately above, and in consideration of the wavelength characteristics of the fluorescent lamp, the green light may be inclined by about 1 ° to 4 ° on the red side. In order to make the emission angle of green light into this range, preferable angle (alpha) is 5 degrees-20 degrees, More preferably, it is 10 degrees-15 degrees. Since the BC surface does not contribute much to light separation, various structures other than the structure shown in FIG. 7 can be used.

In the present invention, since the directivity of light is very high for each RGB, there are cases where the disadvantages peculiar to the direct-view liquid crystal device are that color changes depending on the viewing direction. Therefore, in the present invention, as shown in Fig. 1, a diffusion plate 28 may be provided. As long as the diffusion plate 28 changes polarization characteristics, it is preferable to place it on the outer side of a polarizing plate like FIG. However, when placed outside, the path of the RGB light becomes long, so the precision is inferior. As long as it is a diffuser plate which does not change the polarization characteristic, it may be placed inside the polarizer.

As mentioned above, although the content of this invention was demonstrated based on the specific example, the content of this invention is not limited to these examples, You may change or modify what kind of thing within the scope of the summary of this invention.

In the present invention, since RGB light having extremely high directivity can be incident on the liquid crystal layer, it becomes possible to provide a direct-view transmissive liquid crystal display device that does not use a color filter.

Claims (12)

A light source; A wedge-shape light guide member through which light irradiated from the light source is incident; Wavelength separation means including one diffraction grating, which partially obliquely emits light from the wedge-shaped light guide and which is substantially parallel to each other, into light of a plurality of wavelength regions, wherein a part of incident light is specularly reflected at the incident surface; Light concentrating means for receiving light separated by the wavelength separating means and condensing light of a predetermined wavelength region to a predetermined sub-pixel; A transmissive liquid crystal display device comprising a liquid crystal layer that can be controlled for each sub pixel. The transmissive liquid crystal display of claim 1, wherein the light source is a fluorescent lamp. The transmissive liquid crystal display device according to claim 1, wherein the light collecting means is a cylindrical lens array. 4. The transmissive liquid crystal display device according to claim 3, wherein the wedge-shaped light guide is specularly reflected from the opposite side of the emission surface. The transmissive liquid crystal display of claim 4, wherein the wedge-shaped light guide has a vertical angle of 0.1 ° to 3 °. The transmissive liquid crystal display of claim 4, wherein the wedge-shaped light guide has a vertex angle of 0.3 ° to 1 °. The transmissive liquid crystal display of claim 4, wherein the wedge-shaped light guide member includes a metal reflector on an opposite surface of the exit surface. delete delete The transmissive liquid blue according to claim 3, wherein the diffraction grating has a sawtooth shape in which the exit face has a sawtooth shape, and a side far from the illumination light source forms an angle of 5 ° to 20 ° with respect to the vertical direction of the exit face. Display device. 4. The transmissive liquid crystal of claim 3, wherein the diffraction grating has a sawtooth shape in which the exit face has a sawtooth shape, and a side of the sawtooth shape far away from the illumination light source forms an angle of 10 degrees to 15 degrees with respect to the vertical direction of the exit face. Display device. The transmissive liquid crystal display of claim 3, wherein the transmissive liquid crystal display further comprises a diffusion plate.