JP3528992B2 - Liquid crystal display using hologram color filter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device using a holographic color filter, and in particular, it significantly improves the utilization efficiency of illumination light, prevents a reduction in display contrast, and enables easy-to-see image display. The present invention relates to a liquid crystal display device using a holographic color filter.

[0002]

2. Description of the Related Art Conventionally, in a color liquid crystal display device using an absorption color filter made of pigment, dye, etc.,
A backlight is essential for display.
However, if the white light is directly emitted from the back of the color liquid crystal display device, its utilization efficiency is very low. The main reasons are listed below.

The black matrix other than the cells of each color occupies a large area, and the light impinging on it is wasted. Of the white light incident on each pixel, R (red), G (green),
Since the color components that pass through the B (blue) color filter are limited, other complementary color components are wasted. There is a loss due to absorption in the color filter.

In order to solve such a problem, as shown in FIG. 6, for example, a microlens array 2 is installed in front of the color filter 1, and a white light backlight 3 is provided in each of the color filter cells R, G, B. Conventionally, a method of increasing the utilization efficiency of the backlight 3 by collecting the light is known. In FIG. 6, reference numeral 4 indicates a black matrix provided between the color filter cells R, G and B.

However, even with this method, the white light 3 cannot be spectrally applied to each of the color filter cells R, G, B, and therefore the above-mentioned problem cannot be solved.

Further, Japanese Patent Application Laid-Open No. 4-60538 proposes a liquid crystal projector which 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 due to the above-mentioned pigments, dyes, etc. is not necessary, the above-mentioned problems (1) to (3) are solved, and the brightness of the color image is improved, but since three dichroic mirrors are required, the optical The system / device becomes large and bulky. There is also a problem that the cost becomes high.

In view of such a situation, the present applicant has proposed in Japanese Patent Application No. 5-12170, etc. a color filter using a hologram and a color filter using the hologram in order to significantly improve the utilization efficiency of a liquid crystal display backlight or the like. We have proposed a liquid crystal display device using.

Further, a liquid crystal projection display device which changes the liquid crystal display device using such a hologram color filter to a projection type and displays a bright color image on a screen is proposed in Japanese Patent Application No. 5-242292. did.

[0009]

By the way, a linearly polarized backlight is made to enter the hologram color filter as described above at an incident angle of about 40 ° with respect to the normal line, but it is diffracted by the hologram color filter and wavelength-dispersed. It was found that a phase difference occurs in the light between the S-polarized component and the P-polarized component. Therefore, the light dispersed by the hologram color filter is not linearly polarized light, and when this hologram color filter is applied to the liquid crystal display device, due to this phase difference, when black display is performed by the polarizing plate on the exit side of the liquid crystal display device. However, the light was not completely blocked, which caused a reduction in display contrast, making it difficult to see the image.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to compensate a phase difference introduced by a hologram color filter to prevent a reduction in display contrast. Moreover, it is an object of the present invention to provide a liquid crystal display device using a hologram color filter which has a significantly improved utilization efficiency of illumination light.

[0011]

A liquid crystal display device using a hologram color filter of the present invention that achieves the above-mentioned object is provided with at least a liquid crystal display element and an illumination light incident side thereof, and is provided with an element condensing hologram. A hologram color filter consisting of an array, in which each element condensing hologram disperses white light incident at a predetermined angle with respect to the normal line of the hologram recording surface by wavelength dispersion in a direction substantially along the hologram recording surface. , Or a hologram or diffraction grating consisting of parallel and uniform interference fringes and an array of element condensing lenses arranged on the incident side or the exit side thereof,
The hologram or diffraction grating consisting of parallel and uniform interference fringes and the complex of the element condensing lens respectively emit white light incident at a predetermined angle with respect to the normal to the recording surface of the hologram or diffraction grating. A hologram color filter that disperses wavelengths in a direction substantially along a recording surface of a hologram or a diffraction grating to disperse light, a first polarization unit that converts white light incident on the hologram color filter into linearly polarized light, and exits from the liquid crystal display element. In a liquid crystal display device comprising a second polarizing means for extracting a linearly polarized light component of the polarized light in a predetermined direction, the hologram color is provided at any position between the first polarizing means and the second polarizing means. It is characterized in that a single or a plurality of phase plates are arranged for substantially compensating for the phase difference introduced by the filter.

In this case, the slow axis of the phase plate is in the P polarization direction,
It is desirable that the fast axis be arranged in the S polarization direction. Also,
The phase difference of the phase plate is in the range of 1 to 20 °, more preferably,
It is preferably in the range of 3 to 10 °.

In the present invention, a single sheet or a plurality of sheets for substantially compensating for the phase difference introduced by the hologram color filter at any position between the first polarizing plate and the second polarizing plate of the liquid crystal display device. Since the phase plate of 1 is arranged, it is possible to prevent the display contrast from being lowered and to significantly improve the utilization efficiency of the illumination light.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A liquid crystal display device using the hologram color filter of the present invention will be described below based on embodiments. First, a liquid crystal display device using a hologram color filter of the first type, which is the object of the present invention, will be described with reference to the sectional view of FIG. In the figure, a hologram array 5 constituting a color filter is arranged at a distance from the backlight 3 incident side of a liquid crystal display element 6 which is regularly divided into liquid crystal cells 6 '(pixels). On the rear surface of the liquid crystal display element 6, the black matrix 4 provided between the liquid crystal cells 6'is arranged. Other than the above,
Polarizing plates (not shown) are arranged on the entrance side of the hologram array 5 and the exit side of the liquid crystal display element 6. An absorption type color filter that transmits light of colors corresponding to the R, G and B color separation pixels is additionally arranged between the black matrixes 4 as in the conventional color liquid crystal display device. You may do it.

The hologram array 5 corresponds to a repeating period of R, G, and B color-separating pixels, that is, a set of three liquid crystal cells 6'adjacent to each other in the in-plane direction of the liquid crystal display element 6. It is composed of minute holograms 5'arranged in an array at the same pitch as the repeating pitch, and the minute holograms 5'are aligned in groups of three liquid crystal cells 6'adjacent to each other in the direction of the paper surface of the liquid crystal display element 6 to form one group. The micro holograms 5'are arranged one by one, and each micro hologram 5'corresponds to the micro hologram 5'the light of the green component in the backlight 3 which is 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 collect light on the liquid crystal cell G at the center of the three color-dividing pixels R, G, and B. The minute hologram 5'is a relief type which has little or no wavelength dependence of diffraction efficiency,
It consists of transmission holograms such as phase type and amplitude type. Here, the fact that the diffraction efficiency has no or little wavelength dependence does not mean that it does not diffract only a specific wavelength and does not diffract other wavelengths like a Lippmann hologram.
It means a single diffraction grating that diffracts any wavelength,
The diffraction grating whose diffraction efficiency has little wavelength dependence diffracts at different diffraction angles depending on the wavelength.

With such a structure, when the white backlight 3 which is incident at an angle θ with respect to the normal line from the surface of the hologram array 5 on the side opposite to the liquid crystal display element 6, is incident, the wavelength is changed. The diffraction angles of the minute holograms 5'are different depending on the wavelengths, and the focusing positions for each wavelength are dispersed in the direction parallel to the surface of the hologram array 5. Among them, the red wavelength component is located at the position of the liquid crystal cell R displaying red, the green component is located at the position of the liquid crystal cell G displaying green, and the blue component is located at the position of the liquid crystal cell B displaying blue. By arranging the hologram array 5 so as to diffract and collect light, 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. Color display can be performed according to the state. The angle of incidence θ of the backlight 3 on the hologram array 5 depends on the hologram recording conditions, the hologram array 5
And the distance between the hologram array 5 and the liquid crystal display element 6 and the like.

As described above, by using the hologram array 5 as a color filter, each wavelength component of the conventional color filter backlight can be made incident to each liquid crystal cell 6'without being absorbed, and its utilization efficiency is improved. Can be significantly improved.

Next, a liquid crystal display device using a second type hologram color filter, which is the object of the present invention, will be described with reference to the sectional view of FIG. In the figure, the second type hologram color filter 1
0 is composed of a hologram 7 and a condensing microlens array 8, and a microlens 8 ′ forming the microlens array 8 has a repeating period of R, G, and B color separation pixels,
That is, the three adjacent liquid crystal display elements 6 in the direction of the paper surface
Corresponding to each set of two liquid crystal cells 6 ', they are arranged in an array at the same pitch as the repeating pitch. Also,
The hologram 7 is formed of parallel and uniform interference fringes acting as a diffraction grating, and is a relief type, phase type, amplitude type, or other transmission type hologram having no or little wavelength dependence of diffraction efficiency. On the rear surface of the liquid crystal display element 6, the black matrix 4 provided between the liquid crystal cells 6'is arranged. In addition to the above, the polarizing plate not shown is the liquid crystal display element 6.
Placed on both sides of. Black Matrix 4
In between, as in the conventional color liquid crystal display device, R,
An absorptive color filter that transmits light of colors corresponding to the G and B color separation pixels may be additionally arranged.

Due to such a structure, the hologram 7
When the backlight 3 is incident on the surface of the liquid crystal display element 6 opposite to the normal to the liquid crystal display element 6, the light is diffracted at different angles depending on the wavelength and is dispersed on the exit side of the hologram 7. . Due to the microlens 8 ′ arranged on the entrance side or the exit side of the hologram 7, this dispersed light is
The light is separated and condensed for each wavelength on the focal plane. Among them,
The red wavelength component is diffracted and focused on the position of the liquid crystal cell R displaying red, the green component is focused on the position of the liquid crystal cell G displaying green, and the blue component is focused on the position of the liquid crystal cell B displaying blue. By arranging the color filters 10 as described above, the respective color components pass through the respective liquid crystal cells 6 ′ with little attenuation in the black matrix 4 and correspond to the state of the liquid crystal cells 6 ′ at the corresponding positions. Color display can be performed.

In such an arrangement, as the hologram 7, it is possible to use a transmissive hologram having uniform diffraction fringes having a small wavelength dependence of diffraction efficiency instead of a condensing property. No need to be aligned with each microlens 8 ', and the pitch of the microlens array 8 depends on each liquid crystal cell 6'.
This is three times as large as that in the conventional case of FIG. 6 in which one microlens is arranged corresponding to each, and is characterized in that it is easy to make and aligns easily.

Further, the liquid crystal display device using the hologram color filter having the structure shown in FIGS. 3 and 4 is used as it is as a direct-view type liquid crystal display device, or
It can be used as a liquid crystal projection display device by utilizing it as a spatial light modulator for projection display. FIG. 5 is a sectional view when the liquid crystal display device of FIG. 3 is configured as a liquid crystal projection display device (similarly in the case of FIG. 4), in which the first polarizing plate 12 is provided close to or integrally with the incident side of the hologram array 5. , The second polarizing plate 1 close to or integrally with the exit side of the liquid crystal display element 6.
3 are arranged. The color liquid crystal display device 11 includes, for example, a metal halide lamp 15 and a parabolic mirror 1.
The display image illuminated by the white parallel backlight 3 from the illumination device 14 including the combination of 6 and modulated by the color liquid crystal display device 11 passes through the field lens 17 disposed near the liquid crystal display device 11, It is enlarged by the projection lens 18 and is enlarged and imaged on the screen 19, so that a bright projected image can be obtained.

The polarization anisotropy of the hologram color filter 5 as shown in FIG. 3 with respect to the backlight 3 was measured. That is, the glass substrate 9 supporting the hologram array 5 in the arrangement as shown in FIG. 2 (FIG. (A)).
And a linearly polarized light having a wavelength of 633 nm and a polarization plane of 45 ° with respect to the incident surface within the paper (S-polarized light:
The incident light 21 composed of P-polarized light = 1: 1) is reflected by the glass substrate 9
In the case of Figure (a) consisting of only the incident angles 0 ° and 40 °
Further, in the case of the diagram (b) in which the hologram array 5 is laminated on the glass substrate 9, the light is incident at an incident angle of 40 ° corresponding to the incident angle of the backlight 3 of the hologram array 5,
Using an automatic ellipsometer (manufactured by Mizojiri Optical Industry Co., Ltd.), the phase difference between the S-polarized light and the P-polarized light of the transmitted light in the case of FIG. The phase difference between the S-polarized light and the P-polarized light was measured respectively. The measurement is performed at 5 points, and the average value is shown. The glass substrate 9 is OA-2 manufactured by Nippon Electric Glass Co., Ltd., the thickness is 1.1 mm, the refractive index is 1.54, and the hologram array 5 is 6.0 μm.
Of a photopolymer having an average refractive index of 1.52, a refractive index modulation of 0.035, and a minute hologram 5'having a focal length of infinity. The measurement results are as follows.

[0023] (Note) Retardation is defined as + when P-polarized light is ahead of S-polarized light. The contrast was measured by the ratio of the light amount when the parallel Nicols were used (light amount of light) to the light amount when the orthogonal Nicols were used (dark light amount). (Note 2) The contrast decreased from 2000 to 500.

From the above measurement results, the hologram color filters 5 and 10 for diffracting the obliquely incident backlight 3 by diffracting at different angles depending on the wavelength and wavelength-dispersing the light are used as the S-polarized component of the diffracted light and P. It can be seen that a phase difference occurs between the polarized components. Therefore, when the hologram color filters 5 and 10 are used in the liquid crystal display device as shown in FIGS. 3 to 5, the display contrast is lowered.

Therefore, in the present invention, the hologram color filter is provided at any position between the first polarizing plate that makes the backlight 3 linearly polarized and the second polarizing plate arranged on the emission side of the liquid crystal display element 6. A phase plate (wave plate) for canceling the phase difference introduced by 5 and 10 is arranged, and the phase difference is compensated to prevent a reduction in display contrast. One embodiment for that purpose is shown in FIG. 1 is a liquid crystal projection display device corresponding to FIG. 5, and is a cross-sectional view in the case where the liquid crystal display device of FIG. 3 is configured as a liquid crystal projection display device. Of course, the same applies when the liquid crystal display device of FIG. 4 is used as a liquid crystal projection display device. The color liquid crystal display device 11 is
A glass substrate 9, a hologram array 5 supported on the back surface of the glass substrate 9, a liquid crystal display element 6 in which a black matrix 4 is arranged on the incident side, a phase plate 20 according to the present invention,
Second polarizing plate 13 on the emission side that constitutes the liquid crystal display device 11
Are arranged in this order. Further, the white parallel backlight 3 for illuminating the liquid crystal display device 11 is adapted to be illuminated at a predetermined incident angle from an illumination device 14 including a combination of a metal halide lamp 15 and a parabolic mirror 16. A first polarizing plate 12 on the incident side that constitutes the liquid crystal display device 11 is disposed in the optical path.

Here, as the liquid crystal display element 6, for example, a TFT type in a twisted nematic mode is used, and the first polarizing plate 12 and the second polarizing plate 13 are orthogonal Nicols in the case of normally white. In the case of normally black, it is arranged in the state of parallel nicols. Further, as the phase plate 20, the hologram color filter 5 normally causes a phase difference in which the P-polarized light advances with respect to the S-polarized light, so that the P-polarized light, that is, the slow axis in the vertical direction on the paper surface of FIG. Are arranged so that the fast axis is arranged at right angles to the paper surface, and the phase difference is the hologram color filter 5
A value that is approximately equal to the phase difference introduced in step 1 is selected.

With this arrangement, the lighting device 14
When the color liquid crystal display device 11 is illuminated by the white parallel backlight 3 from, the backlight 3 which has become a predetermined linear polarization by the first polarizing plate 12 is dispersed by the hologram color filter 5, and the color liquid crystal display device is displayed. The display image modulated by 11 passes through a field lens 17 arranged in the vicinity of the liquid crystal display device 11 and is enlarged by a projection lens 18 to be enlarged and focused on a screen 19 to obtain a bright projected image. At that time, a phase difference in which the P-polarized light advances with respect to the S-polarized light is generated in the hologram color filter 5, but the phase difference is compensated by the phase plate 20, and by the action of the polarizing plates 12 and 13 sandwiching the liquid crystal display device 11, In black display, light is almost completely blocked, and in white display, light is scarcely blocked and high-contrast display is performed.

Here, the hologram array 5 and the glass substrate 9 shown in FIG. 1 are as shown in FIG. 2B, and the incident angle is 40.
When the backlight is incident at a temperature of 5 °, the retardation introduced in the hologram array 5 is about 4 °,
Phase plate 20 with retardation of 5.69 ° (10 nm)
When the contrast is measured with the above arrangement by using, the contrast 500 before the arrangement of the phase plate 20 becomes 1 after the arrangement.
It was 400, which clearly prevented the reduction in display contrast.

The same effect can be obtained by arranging the phase plate 20 not only between the liquid crystal display element 6 and the second polarizing plate 13 but also between the hologram array 5 and the liquid crystal display element 6. can get. Further, it may be arranged at a position between the first polarizing plate 12 and the hologram array 5. Further, the number of sheets is not limited to one, and a relatively small retardation may be obtained by using two or more sheets (by disposing two phase plates having a small difference in retardation so that the slow axis and the fast axis are aligned with each other). , It is possible to obtain a phase plate with a small retardation. Not only in the liquid crystal projection display device of FIG. 5, but also in the case of the direct-view type liquid crystal display device of FIGS. 3 and 4, a similar position is provided at any position between the first polarizing plate and the second polarizing plate. By arranging the phase plate 20 for compensating for the phase difference, similarly, the effect of preventing the deterioration of the display contrast can be obtained.

The hologram color filters 5, 1
The incident angle to 0 is practically in the range of 35 to 45 °, and in that case, the phase difference between the S-polarized light and the P-polarized light introduced by the hologram color filters 5 and 10 made of photopolymer is in the middle of the visible range. Since the reference wavelength is about 1 to 20 °, the phase difference of the phase plate 20 is also about 1 to 20 °,
It is more desirable that the angle is about 3 to 10 °.

The liquid crystal display device using the hologram color filter of the present invention has been described above based on the embodiments, but the present invention is not limited to these embodiments and various modifications can be made.

[0032]

As is apparent from the above description, according to the liquid crystal display device using the hologram color filter of the present invention, the liquid crystal display device is provided at any position between the first polarizing plate and the second polarizing plate of the liquid crystal display device. , A single or multiple phase plates are arranged for substantially compensating for the phase difference introduced by the hologram color filter, so that the contrast of the display is prevented from being lowered and the utilization efficiency of the illumination light is significantly improved. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a liquid crystal projection display device using a hologram color filter of a first type according to the present invention.

FIG. 2 is a diagram showing an arrangement for measuring polarization anisotropy of a hologram color filter with respect to a backlight.

FIG. 3 is a cross-sectional view of a liquid crystal display device using a hologram color filter of a first type, which is a target of the present invention.

FIG. 4 is a cross-sectional view of a liquid crystal display device using a second type hologram color filter which is an object of the present invention.

5 is a sectional view of a liquid crystal projection display device using the liquid crystal display device of FIG.

FIG. 6 is a diagram for explaining a conventional illumination method for a liquid crystal display device.

[Explanation of symbols]

3 ... Backlight 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 9 ... Glass substrate 10 ... Hologram color filter 11 ... Color liquid crystal display device 12 ... First polarizing plate 13 ... Second polarizing plate 14 ... Lighting device 15 ... Metal halide lamp (line light source) 16 ... Parabolic mirror 17 ... Field lens 18 ... Projection lens 19 ... Screen 20 ... Phase plate 21 ... Incident light

Continuation of the front page (56) Reference JP-A-8-334624 (JP, A) JP-A-9-5525 (JP, A) JP-A-9-73014 (JP, A) JP-A-9-171110 (JP , A) JP 9-33913 (JP, A) JP 6-258632 (JP, A) JP 8-220534 (JP, A) JP 4-60538 (JP, A) JP 5-158016 (JP, A) JP 5-264957 (JP, A) JP 5-323237 (JP, A) JP 6-3661 (JP, A) JP 6-222361 (JP, A) JP 6-222362 (JP, A) JP 6-230377 (JP, A) JP 6-230384 (JP, A) JP 6-258630 (JP, A) JP 6 -308332 (JP, A) JP 7-5457 (JP, A) JP 7-92328 (JP, A) JP 7-98454 (JP, A) JP 8-29769 (JP, A) ) JP-A-8-179303 (JP, A) JP-A-8-234143 (JP, A) JP-A-8-240801 (J P, A) JP 9-44103 (JP, A) JP 9-5743 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/13-1/141

Claims (4)

(57) [Claims] 1. A liquid crystal display element, and an array of element light converging holograms provided on the illumination light incident side thereof, each element light converging hologram having a predetermined distance from a normal line of a hologram recording surface. , A hologram color filter that disperses wavelengths of white light incident at an angle of approximately in the direction along the hologram recording surface, or a hologram or diffraction grating consisting of parallel and uniform interference fringes and its entrance side or exit side. And a composite of a hologram or diffraction grating and an element condensing lens, each of which is composed of an array of element condensing lenses arranged in parallel with each other, and is composed of parallel and uniform interference fringes, and A hologram color filter for wavelength-dispersing white light incident at a predetermined angle with respect to a line in a direction substantially along a recording surface of a hologram or a diffraction grating, and First polarizing means for converting the white light incident on the hologram color filter into linearly polarized light,
A liquid crystal display device comprising a second polarization means for extracting a linearly polarized light component of a light emitted from the liquid crystal display element in a predetermined direction, wherein any one of the first polarization means and the second polarization means is provided. A liquid crystal display device using a hologram color filter, wherein a single or a plurality of phase plates for substantially compensating for the phase difference introduced by the hologram color filter is arranged at a position. 2. A liquid crystal display device using a hologram color filter according to claim 1, wherein the slow axis of the phase plate is arranged in the P polarization direction and the fast axis is arranged in the S polarization direction. 3. The liquid crystal display device using the hologram color filter according to claim 1, wherein the phase difference of the phase plate is in the range of 1 to 20 °. 4. A liquid crystal display device using a hologram color filter according to claim 3, wherein the phase difference of the phase plate is in the range of 3 to 10 °.