JPH09230125A - Hologram color filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to correct color balance of three colors R, G, B by lessening the dependence of diffraction efficiency on wavelengths. SOLUTION: This filter consists of an array of element condensable holograms 5'. The respective element condensable holograms 5' spectrally split the white light made incident at a prescribed angle θ with the normal of a hologram recording surface by wavelength dispersion in the direction approximately along the hologram recording surface. In such a case, the wavelength diffracted in the direction perpendicular to the hologram recording surface through the centers of the element condensable holograms 5' is set at the wavelength, etc., of the red region on the longer wavelength side than the green region, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram color filter, and more particularly to a hologram color for a liquid crystal display device in which the wavelength dependence of diffraction efficiency is further reduced to correct the color balance of R, G and B colors. It is about filters.

[0002]

2. Description of the Related Art As a color filter for a color liquid crystal display device, each wavelength component of a backlight can be incident on each liquid crystal cell without waste and absorption, as compared with a conventional wavelength absorption type filter. The present applicant has proposed a hologram color filter in Japanese Patent Application No. 5-12170 or the like to significantly improve the hologram color filter. There are two types of configurations, the first type is composed of an eccentric Fresnel zone plate-shaped micro-hologram array. The second type consists of a hologram or diffraction grating composed of parallel and uniform interference fringes and a microlens array superimposed thereon. Hereinafter, these hologram color filters will be briefly described.

A liquid crystal display device using a hologram color filter of the first type will be described with reference to a sectional view of FIG. In this figure, the liquid crystal cell 6 'is regularly arranged.
Backlight 3 of liquid crystal display element 6 divided into (pixels)
A hologram array 5 constituting the hologram color filter is arranged at a distance from the incident side. On the back surface of the liquid crystal display element 6, a black matrix 4 provided between the liquid crystal cells 6 'is arranged. In addition to the above, polarizing plates (not shown) are arranged on both sides 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 has a repetition period of R, G, and B color separation pixels, that is, a set of three liquid crystal cells 6 ′ adjacent to each other in the direction of the liquid crystal display element 6 in the plane of the paper. The micro holograms 5 'are arranged in an array at the same pitch as the repetition pitch. The micro holograms 5' are aligned with each set of three liquid crystal cells 6 'adjacent to each other in the direction of the plane of the liquid crystal display element 6, and each hologram 5' Each of the micro holograms 5 ′ corresponds to the light of the green component in the backlight 3 that enters at an angle θ with respect to the normal to the hologram array 5 and corresponds to the micro hologram 5 ′. It is formed in a Fresnel zone plate shape so that light is condensed on the liquid crystal cell G at the center of the three color separation pixels R, G, and B. The micro hologram 5 ′ has a relief type, which has no or little wavelength dependence of the diffraction efficiency.
It consists of transmission holograms such as phase type and amplitude type. Here, the term "diffraction efficiency has no or little wavelength dependency" does not mean that it is a type that diffracts only a specific wavelength and hardly diffracts other wavelengths like a Lippmann hologram. Is also diffracted, and the diffraction grating whose diffraction efficiency has little wavelength dependence diffracts at different diffraction angles depending on the wavelength.

With such a configuration, 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 to the wavelength. The diffraction angles of the minute holograms 5'are different depending on each other, and the focal positions for each wavelength are dispersed in a direction substantially 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.

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.

A liquid crystal display device using a second type hologram color filter will be described with reference to the sectional view of FIG. In the figure, a hologram color filter 10 of the second type comprises a hologram 7 and a condensing microlens array 8, and microlenses 8 'constituting the microlens array 8 are R, G, B color separation. The pixels are arranged in an array at the same pitch as the repetition cycle of the pixels, that is, each set of three liquid crystal cells 6 ′ adjacent to each other in the direction of the paper surface of the liquid crystal display element 6. The hologram 7 is composed of parallel and uniform interference fringes acting as a diffraction grating, and is formed of a transmission hologram such as a relief type, a phase type, and an amplitude type having little or no wavelength dependence 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 arranged. In addition to the above, polarizing plates (not shown) are arranged on both sides 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.

With such a configuration, the hologram 7
When the backlight 3 is incident on the surface opposite to the liquid crystal display element 6 at an angle θ with respect to the normal line, the light is diffracted at different angles depending on the wavelength and dispersed on the exit side of the hologram 7. . Due to the microlenses 8 ′ arranged on the entrance side or the exit side of the hologram 7, this dispersed light
The light is separated and focused on the focal plane for each wavelength. Among them,
The red wavelength component is diffracted and condensed at the position of the liquid crystal cell R for displaying red, the green component is diffracted and condensed at the position of the liquid crystal cell G for displaying green, and the blue component is condensed at the position of the liquid crystal cell B for displaying blue. As described above, by arranging the color filter 10, each color component passes through each liquid crystal cell 6 'with little attenuation by the black matrix 4, and corresponds to the state of the liquid crystal cell 6' at the corresponding position. Color display can be performed.

In such an arrangement, as the hologram 7, a transmission hologram having uniform interference fringes and having a small wavelength dependency of diffraction efficiency, which is not a light-collecting property, can be used. And the pitch of the microlens array 8 is different from that of each liquid crystal cell 6 '.
It is three times as large as the conventional case where one microlens is arranged corresponding to each, and is characterized in that it is easy to manufacture and easy to align.

[0010]

By the way, in the hologram color filter proposed by the present applicant, a hologram having no or little wavelength dependence of diffraction efficiency is used for wavelength dispersion, but in reality, However, due to the diffraction theory itself, the hologram has a thickness, so that the diffraction efficiency varies depending on the wavelength. Especially R, G, B
In the hologram color filter for the color liquid crystal display with the three colors, it is desirable that the peak of the diffraction efficiency in the shape of a mountain is located in the central wavelength region G to achieve the balance. The diffraction efficiency in the wavelength regions of B and B is lower than that in the wavelength region of G. As a result, the three colors R, G, and B are not uniform in intensity, and appear as poor color balance during color display.

The present invention has been made in view of the problems of the conventional hologram color filter, and an object thereof is to reduce the wavelength dependence of the diffraction efficiency,
It is to provide a hologram color filter in which the color balance of R, G, and B colors is corrected.

[0012]

The hologram color filter of the present invention which achieves the above object comprises an array of element condensing holograms, each element condensing hologram with respect to the normal to the hologram recording surface. In a hologram color filter that disperses wavelengths of white light incident at a predetermined angle in a direction substantially along a hologram recording surface, and is dispersed in a direction perpendicular to the hologram recording surface through the center of the element condensing hologram. The wavelength is set to a longer wavelength side than the green region.

In this case, the wavelength diffracted through the center of the element condensing hologram in the direction perpendicular to the hologram recording surface may be any wavelength within 590 to 700 nm.
It is realistic.

Another hologram color filter of the present invention comprises a hologram having parallel and uniform interference fringes and an array of element condensing lenses arranged on the incident side or the exit side of the hologram, and the holograms are arranged in parallel with each other. Each of the composite of the hologram and the element condensing lens composed of such interference fringes wavelength-disperses white light incident at a predetermined angle with respect to the normal line of the hologram recording surface in a direction substantially along the hologram recording surface. In the hologram color filter for spectrally splitting, the wavelength diffracted through the center of the element condensing lens in the direction perpendicular to the hologram recording surface is set to a longer wavelength side than the green region.

Also in this case, the wavelength diffracted through the center of the element condensing lens in the direction perpendicular to the hologram recording surface is 5
It is realistic that the wavelength is any one of 90 to 700 nm.

In the present invention, the wavelength diffracted in the direction perpendicular to the hologram recording surface through the center of the element condensing hologram or the center of the element condensing lens is set to a longer wavelength side than the green region. The arrangement is such that the pitch of the interference fringes of the hologram is larger, the diffraction efficiency and the wavelength dependence can be further reduced, and the R, G, and B three colors can be well balanced.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The principle of the hologram color filter of the present invention and an example of its manufacturing method will be described below. The diffraction efficiency characteristic of a transmission hologram is related to the pitch of its interference fringes. That is, the diffraction efficiency η of a transmissive hologram can be written as follows (for example, Nishihara et al., "Optical Integrated Circuits", pp. 86-90, "The Bell System T").
echnical Journal ”48 (9) 1969, pp.2909-2947).

Η = sin ² (ν ² + ξ ² ) ^1/2 / (1 + ξ ² / ν ² ) where ν = πΔn / λ × T / (cos θ _i cos
θ _d ) ^1/2 ξ = (β _d cos θ _d −β _i cos θ _i −2 π cos φ
/ Λ) × T / 2 where λ is the wavelength, Δn is the refractive index modulation of the medium of the hologram recording film, T is the thickness of the film, θ _i is the incident angle in the medium with respect to the normal line of the film, and θ _{i d} is the diffraction angle in the medium with respect to the normal line of the film, β _i = β _d = 2πn / λ, n is the refractive index of the medium, φ is the angle of the normal line of the interference fringes to the normal line of the film, Λ
Is the pitch of the interference fringes.

FIG. 4 is a graph showing, as an example, the wavelength dependence of the diffraction efficiency of a hologram having uniform interference fringes using the pitch (800 nm, 1000 nm, 1500 nm) of the interference fringes as a parameter. It can be seen that the larger the pitch, the smaller the wavelength dependence of the diffraction efficiency.

From the above, in the hologram color filters 5 and 10 as shown in FIGS. 5 and 6, if the pitch of the interference fringes of the holograms 5'and 7 is made larger, the diffraction efficiency curve becomes more excellent. It becomes flat and the intensity of R and B colors increases compared to the intensity of G color that is diffracted,
It can be seen that the color balance of R, G, and B colors is improved.

In order to increase the pitch of the interference fringes of the holograms 5'and 7 without changing the incident angle θ of the backlight 3, the hologram 5'is passed through the center of the hologram 5'or the center of the microlens 8 '. , 7, the wavelength diffracted in the direction perpendicular to the direction may be shifted to the longer wavelength side than in the case of FIGS.

That is, in the case of FIGS. 5 and 6, the wavelength diffracted in the direction perpendicular to the holograms 5'and 7 through the center of the hologram 5'or the microlens 8'is within the wavelength range of G. Was 545 nm (pitch of interference fringes with respect to the principal ray: 828 nm), but this wavelength is a wavelength in the wavelength region 590 to 700 nm of R, for example, 630 nm (pitch of interference fringes with respect to the principal ray: 95
6 nm), the same incident angle θ (40
For the white backlight 3 of (°), as illustrated in FIG. 3, the diffraction efficiency curve changes from the solid line to the broken line and becomes flatter. Therefore, the diffraction efficiencies of the R color region and the B color region are not much lower than those of the G color region, and R,
The intensities of the three colors G and B become substantially the same, and the color balance is corrected when performing color display.

FIG. 1 shows a hologram of the first type when the wavelength diffracted in the direction perpendicular to the hologram 5'through the center of the hologram 5'is set to 630 nm in the R wavelength region 590 to 700 nm. A sectional view similar to FIG. 5 of the liquid crystal display device using the color filter 5 is shown. The difference from the configuration of FIG. 5 is that each of the minute holograms 5 ′ has three liquid crystal cells R adjacent to each other in the direction of the paper surface of the liquid crystal display element 6.
It is not aligned with each group of G and B, and the center of each minute hologram 5'and the liquid crystal cell R in each group of liquid crystal cells R, G and B
5 is the same as that of FIG. 5.

Therefore, when the white backlight 3 is incident from the surface of the hologram array 5 opposite to the liquid crystal display element 6 at an angle θ with respect to the normal line, the minute hologram 5 depends on the wavelength. The diffraction angles due to ‘′ are different, and the focal positions for each wavelength are dispersed in a direction substantially 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. Diffracted and condensed, the respective color components pass through each liquid crystal cell 6 ′ with almost no attenuation by the black matrix 4, and the liquid crystal cell 6 ′ at the corresponding position.
It is possible to perform color display according to the state of.

Further, in FIG. 2, the wavelength diffracted in the direction perpendicular to the hologram 7 through the center of the microlens 8'is represented by R
7 is a sectional view similar to FIG. 6 of a liquid crystal display device using the second type hologram color filter 10 when it is set to 630 nm in the wavelength region 590 to 700 nm. The difference from the configuration of FIG. 6 is that each microlens 8 '
Is not aligned with each set of three liquid crystal cells R, G, B which are adjacent to each other in the direction of the plane of the liquid crystal display element 6, and the center of each microlens 8 ′ and the liquid crystal cells R, G, B are not aligned. The point is that the centers of the liquid crystal cells R in each set are aligned, and the other points are the same as in FIG.

Therefore, when the backlight 3 is made incident from the surface of the hologram 7 on the side opposite to the liquid crystal display element 6 with respect to its normal, the backlight 3 is diffracted at different angles depending on the wavelength, and the hologram 7 Are dispersed on the exit side of. By the microlens 8'disposed on the incident side or the emitting side of the hologram 7, the dispersed light is separated into wavelengths and condensed on the focal plane thereof. 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. Diffracted and condensed, the respective color components pass through each liquid crystal cell 6 ′ with almost no attenuation by the black matrix 4, and the liquid crystal cell 6 ′ at the corresponding position.
It is possible to perform color display according to the state of.

In the above example, the wavelength diffracted in the direction perpendicular to the holograms 5'and 7 passing through the center of the hologram 5'or the microlens 8'is the R wavelength region 590 to 70.
Although the positional relationship between the hologram filters 5 and 10 and the liquid crystal display element 6 is illustrated when the wavelength is set to 0 nm, the above wavelength may be set to a longer infrared wavelength. In that case, the color separation pixels aligned with the center of the hologram 5 ′ or the microlens 8 ′ are the liquid crystal cells B, G, or R of the adjacent color separation pixel group of R, G, B, or one. Liquid crystal cells B, G of a set of R, G, B color separation pixels next to the
Alternatively, it becomes R.

Although the principle and embodiments of the hologram color filter of the present invention have been described above, the present invention is not limited to these and various modifications are possible. Further, the liquid crystal display device using the hologram color filter of the present invention can be used as it is as a direct-viewing type liquid crystal display device or as a liquid crystal projection display device by using it as a spatial modulation element for a projection display device.

[0029]

As is apparent from the above description, according to the hologram color filter of the present invention, it is possible to pass through the center of the element condensing hologram or the center of the element condensing lens in the direction perpendicular to the hologram recording surface. Since the diffracted wavelength is set to the longer wavelength side than the green region, the pitch of the interference fringes of the hologram becomes larger, the diffraction efficiency and the wavelength dependence can be further reduced, and the color balance of R, G, and B colors can be reduced. Can be satisfactorily taken.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of a liquid crystal display device using a second type hologram color filter according to the present invention.

FIG. 3 is a diagram showing a change in wavelength dependence of diffraction efficiency when a hologram interference fringe is set according to the present invention.

FIG. 4 is a graph showing the wavelength dependence of the diffraction efficiency of a hologram with the pitch of interference fringes as a parameter.

FIG. 5 is a cross-sectional view of a conventional liquid crystal display device using a first type of hologram color filter.

FIG. 6 is a cross-sectional view of a conventional liquid crystal display device using a second type of hologram color filter.

[Explanation of symbols]

 3 ... Backlight 4 ... Black matrix 5 ... Hologram array (hologram color filter) 5 '... Micro hologram 7 ... Hologram 8 ... Micro lens array 8' ... Micro lens 10 ... Hologram color filter

Claims (4)

[Claims] 1. An array of element-concentrating holograms, each element-converging hologram injecting white light incident at a predetermined angle with respect to a normal line of the hologram recording surface substantially along the hologram recording surface. In a holographic color filter that disperses wavelengths in a direction and disperses the light into a spectrum, the wavelength diffracted in the direction perpendicular to the hologram recording surface through the center of the element converging hologram is set to a longer wavelength side than the green region. Hologram color filter. 2. The wavelength diffracted in the direction perpendicular to the hologram recording surface through the center of the element condensing hologram is 5
The hologram color filter according to claim 1, wherein the hologram color filter has any wavelength in the range of 90 to 700 nm. 3. A hologram and an element which are composed of parallel and uniform interference fringes and an array of element condensing lenses arranged on the incident side or the exit side of the hologram, and which are parallel and uniform interference fringes. In each of the hologram color filters, each of the composites of the condensing lenses 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, A hologram color filter characterized in that the wavelength diffracted in the direction perpendicular to the hologram recording surface through the center of the element condensing lens is set to a longer wavelength side than the green region. 4. A wavelength of 590 which is diffracted in a direction perpendicular to a hologram recording surface through the center of the element condensing lens.
The hologram color filter according to claim 1, wherein the hologram color filter has any wavelength in the range of to 700 nm.