JP3608756B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having improved luminance by using a hologram polarizing plate and a hologram color filter.
[0002]
[Prior art]
Conventionally, a backlight is indispensable for display in a color liquid crystal display device using an absorption color filter such as a pigment or a dye. However, just using white light as it is from behind the color liquid crystal display device, its utilization efficiency is very low. The main reasons are as follows.
[0003]
(1) The area occupied by the black matrix other than the cells of each color is large, and the light hitting it is wasted.
(2) Among white light incident on each pixel, the color components that pass through the color filters of R (red), G (green), and B (blue) are limited, so other complementary color components are wasted. End up.
(3) There is a loss due to absorption by the color filter.
[0004]
In order to solve such problems, for example, a microlens array is installed in front of the color filter, and the backlight of the white light is condensed on the color filter cells R, G, and B, respectively. Methods for increasing the utilization efficiency have been conventionally known.
[0005]
However, even with this method, since the white light 3 cannot be applied to each color filter cell R, G, B by being split, it is impossible to solve the problem (2).
[0006]
Furthermore, Japanese Patent Laid-Open No. 4-60538 proposes a liquid crystal projector that improves the light utilization efficiency by using three dichroic mirrors and a microlens array without using such a color filter. In this case, the absorption color filter using the above-mentioned pigments, dyes and the like is not necessary, and the above problems (1) to (3) are solved and the brightness of the color image is improved, but three dichroic mirrors are used. Since this is necessary, the optical system / device becomes large and bulky. In addition, there is a problem that the cost becomes high.
[0007]
In view of such circumstances, the present applicant used a color filter using a hologram and the same in Japanese Patent Application No. 5-12170 in order to greatly improve the utilization efficiency of a backlight for liquid crystal display and the like. A liquid crystal display device was proposed.
[0008]
Further, a liquid crystal projection display device that displays a bright color image on a screen by changing the liquid crystal display device using such a hologram color filter to a projection type has been proposed in Japanese Patent Application No. 5-242292.
[0009]
Hereinafter, a liquid crystal display device and a liquid crystal projection display device using such a hologram color filter will be briefly described.
First, a liquid crystal display device using a first type hologram color filter will be described with reference to a sectional view of FIG. In the figure, a hologram array 5 constituting a color filter is arranged on the backlight 3 incident side of a liquid crystal display element 6 regularly divided into liquid crystal cells 6 '(pixels). On the back surface of the liquid crystal display element 6, a black matrix 4 provided between the liquid crystal cells 6 'is disposed. In addition to the above, polarizing plates (not shown) are disposed on the incident side of the hologram array 5 and the emission side of the liquid crystal display element 6. In addition, an absorption color filter that passes light of colors corresponding to R, G, and B color separation pixels is additionally arranged between the black matrix 4 as in the conventional color liquid crystal display device. You may do it.
[0010]
The hologram array 5 corresponds to the repetition period of the color separation pixels of R, G, and B, that is, the repetition pitch corresponding to each set of three liquid crystal cells 6 'adjacent in the direction in the plane of the liquid crystal display element 6. The micro holograms 5 'are arranged in an array at the same pitch. The micro holograms 5' are arranged in groups of three liquid crystal cells 6 'adjacent to each other in the direction of the surface of the liquid crystal display element 6 and arranged one by one. Each of the micro-holograms 5 ′ has three components corresponding to the micro-hologram 5 ′ with the green component light in the backlight 3 incident at an angle θ with respect to the normal line of the hologram array 5. It is formed in a Fresnel zone plate shape so as to condense on the liquid crystal cell G at the center of the color separation pixels R, G, B. The micro-hologram 5 'is formed of a transmission type hologram such as a relief type, a phase type, and an amplitude type, which has little or no wavelength dependency of diffraction efficiency. Here, the fact that the diffraction efficiency has no or little wavelength dependency means that it is not a type that diffracts only a specific wavelength and hardly diffracts other wavelengths like a Lippmann hologram. The diffraction grating whose diffraction efficiency has little wavelength dependency diffracts at different diffraction angles depending on the wavelength.
[0011]
Because of such a configuration, when the white backlight 3 incident at an angle θ with respect to the normal line is incident from the surface of the hologram array 5 opposite to the liquid crystal display element 6, it depends on the wavelength. The diffraction angles by the micro-hologram 5 ′ are different, and the condensing position for each wavelength is dispersed in a direction parallel to the surface of the hologram array 5. Among them, the red wavelength component is at the position of the liquid crystal cell R that displays red, the green component is at the position of the liquid crystal cell G that displays green, and the blue component is at the position of the liquid crystal cell B that displays blue. By arranging the hologram array 5 so as to be diffracted and condensed, each color component passes through each liquid crystal cell 6 'with almost no attenuation in the black matrix 4, and the liquid crystal cell 6' at the corresponding position is passed through. Color display according to the state can be performed. The incident angle θ of the backlight 3 on the hologram array 5 is determined by various conditions such as the hologram recording conditions, the thickness of the hologram array 5, and the distance between the hologram array 5 and the liquid crystal display element 6.
[0012]
As described above, by using the hologram array 5 as a color filter, each wavelength component of the conventional color filter backlight can be incident on each liquid crystal cell 6 'without absorption without any waste. Can be improved.
[0013]
Next, a liquid crystal display device using a second type hologram color filter will be described with reference to a sectional view of FIG. In the figure, the second type hologram color filter 10 comprises a hologram 7 and a condensing microlens array 8, and the microlens 8 ′ constituting the microlens array 8 has R, G, and B color separations. Corresponding to each set of three liquid crystal cells 6 'adjacent in the direction of pixel repetition, that is, in the direction of the liquid crystal display element 6, the liquid crystal display element 6 is arranged in an array at the same pitch. The hologram 7 is composed of parallel and uniform interference fringes acting as a diffraction grating, and is composed of a transmission type hologram such as a relief type, a phase type, and an amplitude type, which has little or no wavelength dependency of diffraction efficiency. On the back surface of the liquid crystal display element 6, a black matrix 4 provided between the liquid crystal cells 6 'is disposed. In addition to the above, polarizing plates (not shown) are disposed on both sides of the liquid crystal display element 6. In addition, an absorption color filter that passes light of colors corresponding to R, G, and B color separation pixels is additionally arranged between the black matrix 4 as in the conventional color liquid crystal display device. You may do it.
[0014]
Due to such a configuration, when the backlight 3 is incident on the hologram 7 from the surface opposite to the liquid crystal display element 6 at an angle θ with respect to the normal line, it is diffracted at different angles depending on the wavelength. , Dispersed on the exit side of the hologram 7. The dispersed light is separated and condensed on the focal plane by the microlens 8 ′ disposed on the incident side or the exit side of the hologram 7. Among them, the red wavelength component is at the position of the liquid crystal cell R that displays red, the green component is at the position of the liquid crystal cell G that displays green, and the blue component is at the position of the liquid crystal cell B that displays blue. By arranging the color filter 10 so as to be diffracted and condensed, each color component passes through each liquid crystal cell 6 'with almost no attenuation in the black matrix 4, and the liquid crystal cell 6' at the corresponding position passes through. Color display according to the state can be performed.
[0015]
In such an arrangement, the hologram 7 can be a transmission hologram that is not condensing but has a uniform interference fringe and has little wavelength dependency of diffraction efficiency. It is not necessary to align with the lens 8 ', and the pitch of the microlens array 8 is three times that of the conventional case where one microlens is arranged corresponding to each liquid crystal cell 6', making it easy to make. And it is easy to align.
[0016]
Further, the liquid crystal display device using the hologram color filter having the configuration shown in FIGS. 3 and 4 is used as it is as a direct-view type liquid crystal display device or as a spatial light modulation element for projection display. It can be used as a projection display device. FIG. 5 is a cross-sectional view when the liquid crystal display device of FIG. 3 is configured as a liquid crystal projection display device (the same applies to FIG. 4), and the first polarizing plate 12 is close to or integrally with the incident side of the hologram array 5. The second polarizing plate 13 is disposed close to or integrally with the emission side of the liquid crystal display element 6. The color liquid crystal display device 11 is illuminated by the white parallel backlight 3 from the illumination device 14 composed of a combination of, for example, a metal halide lamp 15 and a parabolic mirror 16, and is modulated by the color liquid crystal display device 11. The image passes through a field lens 17 disposed in the vicinity of the liquid crystal display device 11 and is magnified by the projection lens 18 and magnified on the screen 19 to obtain a bright projected image.
[0017]
In the liquid crystal display device using the hologram color filter as described above, the liquid crystal display element 6 including the black matrix 4 is actually, for example, as shown in a cross section in FIG. It consists of a liquid crystal layer 25 such as twisted nematic sandwiched between two glass substrates 21, 22, and a black matrix 4 and a uniform transparent counter electrode 23 are formed on the inner surface of the glass substrate 21 on the backlight side. A transparent pixel electrode 24 and a TFT (not shown) are provided independently for each of the liquid crystal cells R, G, and B on the inner surface of the glass substrate 22 on the display surface side. Further, an alignment layer (not shown) is also provided on the liquid crystal layer 25 side of the electrodes 23 and 24. Then, the hologram color filter 5 or 10 provided on the liquid crystal display element 6 side surface of the substrate 26 is disposed close to or bonded to the glass substrate 21 on the backlight side, and the polarizing plate 12 is disposed on the backlight side of the substrate 26. Polarizing plates 13 are attached to the outer surface of the observation-side glass substrate 22 of the liquid crystal display element 6, respectively. For example, their transmission axes are arranged to be orthogonal to each other. Note that the polarizing plate 12 on the backlight side is disposed in the optical path of the backlight 3 apart from the hologram color filter 5 as shown by a dotted line in FIG. 6 instead of being attached to the backlight side of the substrate 26. There is also.
[0018]
By controlling the voltage applied between the transparent pixel electrode 24 and the transparent counter electrode 23 for each pixel of the liquid crystal display element 6 as described above to change its transmission state, color display is possible.
[0019]
[Problems to be solved by the invention]
In the liquid crystal display device having the configuration as shown in FIG. 6, the backlight 3 passes through the polarizing plate 12, the hologram color filter 5 (10), the black matrix 4, the liquid crystal layer 25, and the polarizing plate 13 in this order and finally observed. Although these are emitted to the projection side or the projection side, light loss (loss) occurs due to these elements. By using the hologram color filter 5 or 10 as described above, the loss in the hologram color filter 5 or 10 and the loss due to the opening of the black matrix 4 can be improved.
[0020]
However, in such a liquid crystal display device, the polarizing plates 12 and 13 must be used. Usually, as a polarizing plate, since what extended | stretched the PVA (polyvinyl alcohol) film which added the iodine or the pigment | dye is used, the absorption by an iodine or a pigment | dye inherently exists, and the transmittance | permeability will fall ( At present, the portion of the two polarizing plates that transmits the incident light 100 is about 35). That is, even in the method using the hologram color filter proposed by the applicant, the use efficiency of light is reduced by using such a polarizing plate.
[0021]
Further, as shown by the solid line in FIG. 6, the backlight side polarizing plate 12 has a problem that the contrast is lowered due to the deterioration of the polarization characteristics when the backlight 3 is arranged not vertically but obliquely.
[0022]
The present invention has been made in view of such problems of the prior art, and its purpose is to eliminate the loss of light amount due to absorption by using a hologram polarizing plate having no absorption and high diffraction efficiency as a polarizing plate, making it brighter. An object of the present invention is to provide a liquid crystal display device using a hologram color filter having high brightness and good contrast, in particular.
[0023]
[Means for Solving the Problems]
The liquid crystal display device of the present invention that achieves the above object includes a backlight light source, a liquid crystal display element having a color filter and a black matrix, and two sheets provided on the incident side and the emission side of the liquid crystal display element. In the liquid crystal display device comprising a polarizing plate, at least one polarizing plate is composed of a volume phase type hologram polarizing plate in which an angle formed between incident light and diffracted light is set to 90 ° in the hologram medium. Is.
[0024]
In this case, the color filter is composed of an array of element condensing holograms, and each element condensing hologram transmits illumination light incident at a predetermined angle with respect to the normal line of the hologram recording surface. From a hologram color filter that disperses light in the direction substantially along the direction of the spectrum, or a hologram or diffraction grating that consists of parallel and uniform interference fringes and an array of element condensing lenses arranged on the incident side or the exit side thereof Illumination in which a hologram or diffraction grating composed of parallel and uniform interference fringes and an element condensing lens complex are incident at a predetermined angle with respect to the normal of the recording surface of the hologram or diffraction grating. It is desirable to comprise a hologram color filter that spectrally disperses light in the direction substantially along the recording surface of the hologram or diffraction grating.
[0026]
In addition, when the incident side polarizing plate of a liquid crystal display element is comprised with a hologram polarizing plate, it is desirable to arrange | position a transparent prism body in the backlight light source side.
[0027]
In the present invention, a backlight source, a backlight source, a liquid crystal display element including a color filter and a black matrix, and two polarizing plates provided on the incident side and the emission side of the liquid crystal display element In this liquid crystal display device, at least one polarizing plate is composed of a volume phase type holographic polarizing plate in which the angle between incident light and diffracted light is set to 90 ° in the holographic medium. Therefore, it is possible to realize a liquid crystal display device that has very little light loss due to diffraction, is brighter, has higher brightness, and good contrast. The present invention is particularly suitable for a liquid crystal display device using a hologram color filter.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
First, the basic principle of the present invention will be described. In a volume phase hologram in which the angle between incident light and diffracted light is set to 90 °, the incident light is randomly polarized (polarized light in which S-polarized light and P-polarized light are mixed). Even in this case, the diffracted light is only the S-polarized component. This is described in "The Bell System Technical Journal" 48 (9) 1969, pp. 2909-2947, especially p. 2943-2945, APPENDIX. Therefore, the volume phase hologram having interference fringes set in such an angular relationship with respect to the backlight 3 of FIGS. 3 to 6 is used as a polarizing plate on the incident side of a liquid crystal display device using a hologram color filter. Is possible. Hereinafter, a polarizing plate using such a volume phase hologram is referred to as a hologram polarizing plate.
[0029]
The transmission efficiency of such a hologram polarizing plate is
(Transmission intensity) = (Diffraction efficiency of S-polarized light) × (incident light intensity) × 0.5
It becomes. Since a volume phase hologram having a diffraction efficiency of S-polarized light of about 1 can be produced, a polarizing plate having no loss in principle can be produced.
[0030]
The polarizing plate on the emission side of the liquid crystal display element can be a hologram polarizing plate based on the same concept.
[0031]
FIG. 1 is a cross-sectional view of a liquid crystal display device using the above-described hologram polarizing plate as an incident side polarizing plate constituting the liquid crystal display device, and is provided on the incident side hologram polarizing plate 12 ′ and its incident side. Other than the prism body 31 is the same as the conventional example of FIG. The prism body 31 is a transparent block having substantially the same refractive index as that of the medium of the incident side hologram polarizing plate 12 ′, and is used to allow the backlight 3 to enter the incident side hologram polarizing plate 12 ′ at a predetermined angle. If the predetermined angle is smaller than the critical angle, the prism body 31 is not necessarily required.
[0032]
In this embodiment, the white backlight 3 incident perpendicularly to the inclined surface of the prism body 31 reaches the incident-side hologram polarizing plate 12 ′, and only the S-polarized light component therein forms 90 ° with respect to the incident direction. The light diffracted in the direction and selected, and the light having the S-polarized component becomes the backlight 3 ′ that enters the hologram color filter 5. The S-polarized white backlight 3 ′ is spectrally separated by the hologram color filter 5, and the color components of R, G, and B that are spectrally separated are the apertures of the black matrix 4 of the corresponding R, G, and B pixels. The light is condensed inside, passes through the liquid crystal layer 25 without being attenuated by the black matrix 4, the polarization plane is rotated according to the pixel state at the corresponding position, and according to the transmission axis direction of the polarizing plate 13 on the exit side. Therefore, normally black (when the transmission axis of the polarizing plate 13 is in the S-polarization direction) or normally white (when the transmission axis of the polarizing plate 13 is in the P-polarization direction) is displayed with good color reproducibility and bright color display.
[0033]
In this embodiment, when the backlight incident angle θ (FIG. 3) from the air of the hologram color filter 5 is 40 ° and the average refractive index of the hologram color filter 5 is 1.5, the hologram color filter 5 Inside, the incident angle of the backlight 3 ′ must be 25.4 °. Therefore, the angle inside the backlight 3 incident on the incident-side hologram polarizing plate 12 ′ is 64.6 °. Since this angle is equal to or larger than the critical angle of the medium of the incident side hologram polarizing plate 12 ′, the prism body 31 is necessary. The shape of the prism body 31 is set so that the backlight 3 is incident on the incident side hologram polarizing plate 12 ′ at such an angle (64.6 °).
[0034]
FIG. 2 is a cross-sectional view of the liquid crystal display device in which the polarizing plate 13 on the exit side of the liquid crystal display element 6 in the liquid crystal display device of FIG. The structure up to the glass substrate 22 of the element 6 is the same as that shown in FIG. In this embodiment, the same hologram as the hologram polarizing plate 12 ′ is used as the hologram polarizing plate 13 ′, and the exit side hologram polarizing plate 13 ′ is inclined with respect to the surface of the liquid crystal display element 6. This tilt angle is an angle at which the interference fringes in the exit side hologram polarizing plate 13 ′ are 45 ° with respect to the normal line of the surface of the liquid crystal display element 6. In the numerical example of FIG. The inclination angle of the plate 13 'is 25.4 °. Then, a prism body 32 having substantially the same refractive index as that of the medium of the exit side hologram polarizer 13 ′ is disposed between the glass substrate 22 of the liquid crystal display element 6 and the hologram polarizer 13 ′, and the exit side hologram polarizer 13 ′. A prism body 33 having substantially the same refractive index as that of the medium of the exit-side hologram polarizing plate 13 'is disposed on the exit side in order to output the S-polarized component 34 diffracted in step S3 to the outside and simultaneously correct the bending in the display direction. . However, these prism bodies 32 and 33 are not necessarily required. 2 is a normally white state in which the transmission axes of the incident-side hologram polarizing plate 12 ′ and the exit-side hologram polarizing plate 13 ′ are orthogonal to each other. It can be changed to a normally black arrangement by rotating 90 ° around the surface normal. Further, an absorption layer may be provided on the side surface of the prism body 33 in order to absorb the unnecessary component 34 diffracted by the exit side hologram polarizing plate 13 ′.
[0035]
As described above, the liquid crystal display device of the present invention has been described taking the liquid crystal display device using the hologram color filter as an example. However, the present invention is a liquid crystal display device using a normal absorption type color filter instead of the hologram color filter. Alternatively, it can be applied to a liquid crystal display device that does not use any color filter. The liquid crystal is not limited to a twisted nematic liquid crystal and can be applied to a liquid crystal display device using another liquid crystal. As a polarizing plate using a hologram polarizing plate, only the exit side can be used. In the case of a liquid crystal display device using a hologram color filter, the hologram of the hologram color filter 5 is not limited to a single layer or a single hologram, but Japanese Patent Application Nos. 7-290820 and 7-290820. As described, the spatial wavelength distribution of chromatic dispersion is substantially the same, and two or more layers or two or more layers having different peak wavelengths of diffraction efficiency are superimposed or multiplexed. It may consist of a hologram.
[0036]
【The invention's effect】
As is apparent from the above description, according to the liquid crystal display device of the present invention, a backlight light source, a backlight light source, a liquid crystal display element including a color filter and a black matrix, and an incident side of the liquid crystal display element In the liquid crystal display device comprising two polarizing plates provided on the exit side, at least one polarizing plate is a volume phase type in which the angle formed by incident light and diffracted light is set to 90 ° in the hologram medium Since it is composed of a hologram polarizing plate, it is possible to realize a liquid crystal display device that is extremely bright and has high brightness and good contrast with little loss of light quantity due to absorption and diffraction by the polarizing plate. The present invention is particularly suitable for a liquid crystal display device using a hologram color filter.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an embodiment of a liquid crystal display device according to the present invention.
FIG. 2 is a cross-sectional view of another embodiment.
FIG. 3 is a schematic cross-sectional view of a liquid crystal display device using a first type hologram color filter.
FIG. 4 is a schematic cross-sectional view of a liquid crystal display device using a second type hologram color filter.
5 is a cross-sectional view of a liquid crystal projection display device using the liquid crystal display device of FIG.
FIG. 6 is a cross-sectional view of a conventional liquid crystal display element.
[Explanation of symbols]
3 ... Backlight 3 '... Backlight incident on hologram color filter 4 ... Black matrix 5 ... Hologram array (hologram color filter)
6 ... Liquid crystal display element 5 '... Micro hologram 6' ... Liquid crystal cell 7 ... Hologram 8 ... Condensing microlens array 8 '... Micro lens 10 ... Hologram color filter 11 ... Color liquid crystal display device 12, 13 ... Polarizing plate 12' , 13 '... Hologram polarizing plate 14 ... Illumination device 15 ... Metal halide lamp (line light source)
16 ... Parabolic mirror 17 ... Field lens 18 ... Projection lens 19 ... Screen 21 ... Backlight side glass substrate 22 ... Display side glass substrate 23 ... Transparent counter electrode 24 ... Transparent pixel electrode 25 ... Liquid crystal layers 31, 32, 33 ... Prism body 34 ... Diffraction light (unnecessary component)

Claims (3)

In a liquid crystal display device comprising a backlight light source, a liquid crystal display element having a color filter and a black matrix , and two polarizing plates provided on the incident side and the emission side of the liquid crystal display element, at least one sheet A liquid crystal display device, wherein the polarizing plate is a volume phase hologram polarizing plate in which an angle formed by incident light and diffracted light is set to 90 ° in the hologram medium . The color filter is composed of an array of element condensing holograms, and each element condensing hologram substantially follows illumination light incident on the hologram recording surface at a predetermined angle with respect to the normal line of the hologram recording surface. It consists of a hologram color filter that disperses the wavelength in the direction of the spectrum, or a hologram or diffraction grating composed of parallel and uniform interference fringes and an array of element condensing lenses arranged on the incident side or the emission side thereof. A hologram or diffraction grating composed of parallel and uniform interference fringes and an element converging lens complex each emits illumination light incident at a predetermined angle with respect to the normal of the recording surface of the hologram or diffraction grating. or liquid crystal of claim 1 is chromatic dispersion in the direction substantially along the recording surface of the diffraction grating, characterized in that it consists of a hologram color filter spectrally by Display devices. The liquid crystal light-incident side polarizing plate of the display device is composed of the hologram polarizing plate, a liquid crystal display device according to claim 1 or 2, characterized in that a transparent prism body on the backlight light source.

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