JP2000330459A - Production of hologram lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for the production of a hologram lens by which deformation or warpage of a glass substrate or a photopolymer applied thereon can be suppressed. SOLUTION: This method includes a process of applying a photopolymer 1 by coating or laminating on a glass substrate 2 as a supporting material, a process of exposing the photopolymer 1 by interference, and a process to develop by heating the photopolymer 1. In this method, before the heat developing process, another glass substrate is laminated on the photopolymer 1, and the polymer is subjected to heat development in this state or while applying load through a rigid plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hologram lens for diffracting and condensing incident light into a plurality of lights having different wavelength bands.

[0002]

2. Description of the Related Art Heretofore, the present applicants have developed a projection type color liquid crystal display device using a hologram lens array as a color filter. This color filter uses the hologram's diffraction spectral function to convert white light into R light.
Each color light of GB can be extracted in a predetermined direction. Unlike a normal color filter using a dye or a pigment, there is almost no loss of light due to absorption, so that high light use efficiency can be obtained in principle. Therefore, the present invention is effective in a projection type color liquid crystal display device in which improvement in brightness is particularly required.

FIG. 3 is a sectional view schematically showing a structure of a spatial light modulation element used in a projection type color liquid crystal display device disclosed in a prior application published by the present applicant (Japanese Patent Application Laid-Open No. 9-189809). FIG.

The liquid crystal panel 111 has a silicon substrate 121
And an active matrix drive circuit 122 formed on the silicon substrate 121, and a pixel electrode layer 123 in which pixel electrodes 123r, 123g, and 123b selectively controlled and driven by the active matrix drive circuit 122 are regularly arranged. , A dielectric mirror film 124, an alignment film 125, and a light modulation layer 12 in which liquid crystal is sealed with spacers.
6, an alignment film 127, and a transparent common electrode layer 128 are sequentially laminated.

The hologram color filter 113 is formed of a so-called hologram lens array in which unit hologram lenses are regularly arranged, and diffracts read light (white light) including three primary colors of R, G, and B for each color light. It has a function of splitting the light and condensing it at the positions of the pixel electrodes 123r, 123g, and 123b corresponding to R, G, and B in the liquid crystal panel 111. Therefore, it is possible to provide a projection type color liquid crystal display device using incident light without waste. Note that, as shown in FIG.
In the case of including 4, the light collecting destination is the dielectric mirror film 124.

A hologram filter used in the above-mentioned projection type liquid crystal display device is a hologram lens composed of a so-called "volume hologram" in which high refractive index layers and low refractive index layers are alternately arranged slightly obliquely to incident light. An array is used.

In manufacturing such a volume hologram, as shown in FIG. 4, an interference exposure method using a master hologram, which is a diffraction grating for hologram recording, has been conventionally used. The master hologram is a surface hologram in which a chromium thin film is coated on a glass substrate 240 and a diffraction grating is formed in a predetermined region on the substrate by, for example, a striped chrome thin film pattern.

In the interference exposure step, the glass substrate 22
A photopolymer (hologram photosensitive material) 210 serving as a hologram recording medium is coated or pasted on the hologram recording medium 0, and a chrome mask pattern 230 is formed so as to face the hologram recording medium.
Are placed in close proximity. The exposure recording light is a first-order diffracted light diffracted at a predetermined diffraction angle by the chrome mask pattern 230 and a zero-order diffracted light that passes straight through as it is.

Thereafter, when the photopolymer 210 is heat-treated, polymerization proceeds in the exposed and unexposed portions, respectively, and a volume hologram in which high-refractive-index layers and low-refractive-index layers are alternately formed is obtained.

[0010] This step is referred to herein as a heat development processing step.

[0011]

FIG. 5A to FIG. 5
(D) Glass substrate 2 after interference exposure and heat development
20 shows a cross-sectional shape of a photopolymer 210 (hologram lens). As shown in FIG. 5A, there is no noticeable deformation in the photopolymer 210 before development after the interference exposure step. However, the photopolymer 210 is then subjected to a heat development process performed at about 120 ° C for about 30 minutes to 2 hours.
The volume shrinks due to the effect of the progress of polymerization and the heat shrinkage of the polymer. However, the shrinkage of the photopolymer 210 on the lower layer side of the photopolymer 210 that is in close contact with the surface of the glass substrate 220 is limited by the adhesive force with the glass surface. For this reason, only the upper layer of the photopolymer 210 shrinks, and extremely, as shown in FIG.

As shown in FIG. 5C, the developed photopolymer 210 becomes a volume hologram in which layers of a high refractive index material and layers of a low refractive index material are alternately arranged. Difference between the refractive index material and the low refractive index material Δn, the width of each layer,
The recording angle θ which is the inclination angle of each layer together with the film thickness of each layer, etc.
₀ is an important factor that determines the diffraction characteristics of the hologram lens.

However, when only the upper layer of the photopolymer 210 shrinks as shown in FIG.
The volume hologram designed to have the recording angle θ ₀ as shown in FIG.
As shown in (d), the inclination of each layer rises, and the recording angle spreads to (θ ₀ + α) degrees. For example, at present, in a volume hologram having a design recording angle θ ₀ of 60 degrees, the spread angle α of the recording angle after thermal development processing may be 7 degrees or more.

[0014] The above-mentioned problem is caused particularly by the shrinkage of the photopolymer itself during the heat treatment in the development step, but another problem is pointed out with the heat treatment in the development step. This is the occurrence of warpage of the glass substrate 220 due to thermal stress or the like generated between the front surface and the back surface of the photopolymer and the substrate or the glass serving as the substrate.

FIGS. 6A and 6B are somewhat exaggerated, but the glass substrate 220 after the heat development processing is shown.
Causes a warp as shown in FIG. It should be noted that, depending on the conditions, there may be a case where the photopolymer forming surface is inwardly curved, contrary to the case shown in the figure. In any case, the recording angle θ of the hologram lens changes due to the warpage. In particular, these warpages tend to cause a recording angle difference between the central portion and the peripheral portion in the plane of the hologram lens.
If the hologram lens support substrate is warped, it causes color unevenness between the center and the periphery of the screen when incorporated in a liquid crystal display device as a filter.

The present invention has been made in view of the above problems, and has as its object to provide a method of manufacturing a hologram lens capable of suppressing the occurrence of deformation and warpage of a glass substrate and a photopolymer formed thereon.

[0017]

A first feature of the method of manufacturing a hologram lens according to the present invention is that a hologram photosensitive material is coated or adhered on a first glass substrate serving as a support, In the method for manufacturing a hologram lens having a step of subjecting the hologram photosensitive material to interference exposure and a step of thermally developing the hologram photosensitive material, before the thermal development processing step, a second glass substrate is attached to the surface of the hologram photosensitive material, The heat development process is performed in this state.

According to the first feature, since the upper surface of the lower surface of the hologram photosensitive material is in close contact with the glass substrate, thermal contraction of the hologram photosensitive material is suppressed by the adhesive force. When the first glass substrate and the second glass substrate are made of the same material and have substantially the same thickness, the thermal stress generated between the upper and lower glass substrates and the hologram photosensitive material is offset to generate warpage of the substrate. Can also be suppressed.

According to a second feature of the hologram lens of the present invention, in the method of manufacturing a hologram lens having the above-mentioned first feature, the thickness of the second glass substrate is set equal to the first glass substrate.
Performing the thermal development while applying a load on the second glass substrate via a rigid flat substrate.

As the rigid flat base material, a glass material,
Any material that hardly causes thermal deformation in the heat development process, such as a metal material or a ceramic material, may be used.

According to the second feature, the thermal development is performed in a state in which a load is applied to the second glass substrate via the rigid flat substrate, so that the second glass substrate faces the second glass substrate. Even if it is thinner than one glass substrate, the occurrence of warpage can be forcibly suppressed. Therefore, the thickness of the second glass substrate can be made sufficiently thinner than the current focal length of the hologram lens.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, a method for manufacturing a hologram lens having a single-layer structure will be described.

(First Embodiment) The main feature of the method for manufacturing a hologram lens according to the first embodiment is that the same material as that of the glass support substrate is formed on the upper surface of the photopolymer in the heat development process of the photopolymer. And a glass substrate having a thickness. Thermal shrinkage of the photopolymer and occurrence of warpage of the glass support substrate can be suppressed. Less than,
The contents will be specifically described with reference to the drawings.

First, as shown in FIG. 1A, a photopolymer 1 as a film-shaped hologram photosensitive material having a thickness of about 3 μm to 5 μm is placed on a glass substrate 2 having a thickness of about 1 mm serving as a support for the hologram lens. paste. As the photopolymer 1, for example, a commercially available material such as Omnidex (trade name) manufactured by DuPont can be used. In addition, a hologram photosensitive material made of silver salt sensitive material, photoresist, dichromated gelatin or the like may be used. Note that the glass substrate 2 may be coated using a liquid photosensitive material instead of a film-shaped photosensitive material.
As the glass substrate, for example, it is preferable to use barium borosilicate glass having a relatively small coefficient of thermal expansion and a high transmittance.

Next, interference exposure is performed using the conventional method shown in FIG. That is, the photopolymer 1 and the chrome mask of the master hologram are arranged so as to be closely opposed to each other via the oil for contact, and the exposure recording light is irradiated obliquely. By arranging the prism on the master hologram, it is possible to suppress the loss due to reflection when the exposure recording light enters.

After exposure, photopolymer 1 and glass substrate 2
Then, as shown in FIG. 1B, another glass substrate 3 having the same expansion coefficient and the same thickness as the glass substrate 2 used as the support of the hologram lens is prepared.
For example, each glass substrate uses barium borosilicate glass and has a thickness of about 1 mm. The glass substrate 3 is stuck on the exposed photopolymer 1 using a commercially available ultraviolet curable resin.

With the glass substrate 3 adhered to the upper surface of the photopolymer 1, a heat development process is performed at 120 degrees for about 2 hours. Since the upper surface of the photopolymer 1 is also attached to the glass substrate 3 having a sufficiently smaller thermal expansion coefficient than the photopolymer 1 like the lower surface, the contraction of the polymer due to the heat development is suppressed by this adhesive force. . As a result, FIG.
Trapezoidal deformation due to shrinkage of the upper photopolymer 1 as shown in FIG.

In addition, since substrates of the same thickness having the same expansion coefficient face each other up and down with the photopolymer 1 interposed therebetween,
The thermal stress generated between each of the glass substrates 2 and 3 and the photopolymer 1 is balanced and canceled up and down, so that warpage of the substrate can be prevented. As a result, the in-plane recording angle difference of the hologram lens layer manufactured according to the present embodiment can be made within 0.5 degrees. In a liquid crystal display device using a hologram lens having such a difference in recording angle, color unevenness on a screen hardly causes a problem.

(Second Embodiment) The main feature of the method for manufacturing a hologram filter according to the second embodiment is that, in the heat development process of a photopolymer, a glass substrate is attached to the upper surface of the photopolymer, Applying a load from above through a rigid substrate. According to this method,
The heat shrinkage of the photopolymer and the occurrence of warpage of the glass support can be suppressed while the glass substrate attached to the upper surface of the photopolymer is sufficiently thin. Hereinafter, a method for manufacturing the hologram lens according to the second embodiment will be specifically described.

In the second embodiment, as in the first embodiment, as shown in FIG. 1A, first, a glass substrate 2 having a thickness of about 1 mm serving as a support for a hologram lens is formed.
A film-shaped photopolymer 1 having a thickness of about 3 μm to 5 μm such as Omnidex (trade name) manufactured by DuPont is adhered on the top. A liquid hologram photosensitive material may be used in place of the film-shaped photosensitive material to coat the glass substrate. As the glass substrate 2, as in the first embodiment,
Barium borosilicate glass can be used.

Thereafter, in the same manner as in the first embodiment, the photopolymer 1 is subjected to interference exposure using a master hologram.

After the exposure, as shown in FIG. 1C, another thin glass 4 having the same expansion coefficient as the glass substrate 2 used as the support of the hologram lens is prepared. The thickness of the thin glass 4 is set so that the focal length of the hologram lens used in the current liquid crystal display device is 70 μm to 100 μm.
m, etc., so that it is thinner. For example, a commercially available barium borosilicate glass having a thickness of 50 μm is used. This is stuck on the exposed photopolymer 1 using a commercially available ultraviolet curable resin.

Further, a rigid plate-like body 5, for example, a barium borosilicate glass having a thickness of about 1 mm is placed on the thin glass 4, and a load G of 1 kg is applied thereon to hold the thin glass 4. In this state, the photopolymer 1 is subjected to a heat development treatment at 120 ° C. for 2 hours.

Since the upper surface of the photopolymer 1 is also attached to the thin glass plate 4 having a sufficiently smaller coefficient of thermal expansion than the photopolymer similarly to the lower surface, shrinkage of the polymer due to the heat development is suppressed. As a result, trapezoidal deformation due to shrinkage of the upper layer photopolymer 1 as shown in FIG. 5B can be prevented.

In the present embodiment, when the thin glass 4 is subjected to thermal development without applying a load, the thin glass 4 and the glass substrate 2 are warped as shown in FIG. 6B. I do. For example, as described above, the thin glass 4
When barium borosilicate glass of 50 μm is used, the in-plane recording angle difference of the hologram lens caused by the warpage is as large as 4 degrees. The warpage of the substrate is eliminated when the glass substrate 4 is made of glass of the same material and has substantially the same thickness as in the first embodiment described above, but the warpage increases as the thickness becomes thinner.

In the manufacturing method according to the second embodiment,
The occurrence of substrate warpage that cannot be sufficiently suppressed by the thin glass 4 is forcibly prevented by performing a thermal development process while applying a load in the direction perpendicular to the substrate surface from above the thin glass 4.

Meanwhile, the glass substrate 4 placed on the photopolymer 1 during the thermal development processing is
(Hologram lens) and is integrated into each device or the like. When a hologram lens is used as a hologram filter of the liquid crystal display device, as shown in FIG. 3, the hologram lens has a focusing lens function and is designed to focus on the pixel electrode surface of each color light. Therefore, if the thickness of the thin glass 4 placed on the photopolymer 1 is thicker than the focal length of the hologram lens, it becomes impossible to focus on the pixel electrode surface, and a design change is required. In this method, the thickness of the thin glass is set to 60 μm, which is the focal length of the current hologram lens.
Since it can be thinner than m to 100 μm, there is no need to change the design of the hologram lens.

In general, increasing the focal length is
It is not preferable because the optical path length becomes longer and light loss due to absorption increases. From this point as well, it is preferable to reduce the thickness of the thin glass 4 by the method according to the above-described second embodiment.

In the second embodiment, a change in the recording angle due to the thermal shrinkage of the photopolymer itself is suppressed by attaching the thin glass 4 to the photopolymer 1 in the thermal development process, By applying a load perpendicular to the substrate surface from above the thin glass 4,
Forcibly prevent warpage. As a result, similarly to the first embodiment, the difference in the recording angle in the plane of the hologram lens layer manufactured according to the present embodiment can be kept within 0.5 degrees.

As described above, according to the method of manufacturing the hologram lens according to the second embodiment, the change in the recording angle due to the developing step is small, and the support substrate is hardly warped. The liquid crystal display device used as a filter can provide good image characteristics without color unevenness.

There are various methods for applying a load. By applying a load via the rigid plate-like body 5,
A load can be applied almost uniformly to the entire thin glass 4. Further, if a weight or the like is directly placed on the thin glass 4, there may be a problem in the uniformity of the processing temperature such that only the surrounding area has a locally low temperature. There is also an effect that the temperature of the photopolymer 1 during the development processing can be prevented from becoming non-uniform.

The rigid flat plate to be superimposed on the thin glass plate during the heat development process may be a glass substrate as described above, but it does not need to be transparent and has a rigid ceramic substrate or brick plate,
It may be a metal plate. The load applied on the top is 1kg
The load is not limited to this, but may be any load that can suppress the occurrence of warpage in the heat development processing step. If the rigid flat plate itself is sufficiently heavy, there is no need to apply a separate load.

(Application to Liquid Crystal Display Device) The present applicant has recently proposed a liquid crystal display device using a hologram color filter having a single-layer structure. FIG. 2 is a configuration diagram showing a structure of a liquid crystal display device using the hologram lens according to the above embodiment as a hologram color filter. Hereinafter, the structure of the liquid crystal display device will be briefly described.

For example, the reflection type spatial light modulator 30 is composed of a hologram color filter and a liquid crystal panel. The hologram color filter is the first or second hologram described above.
The hologram lens manufactured by the method according to the embodiment can be used. That is, it is composed of a glass substrate 23 as a support, a single hologram lens layer 24 formed on this surface, and a thin glass plate 25 adhered to the surface thereof.

The liquid crystal panel includes a transparent electrode 26, a liquid crystal layer 27 which is a light modulation layer, and a pixel electrode 28 which is also a light reflection surface.
An active matrix drive circuit 29 for selectively controlling and driving the pixel electrode 28 is provided. The pixel electrode 28 and the active matrix drive circuit 29 are formed on a silicon substrate (not shown).

As shown here, in the first and second embodiments, a glass substrate (thin glass) 25 attached to the photopolymer surface is used as a support substrate for a transparent electrode 26 constituting a liquid crystal panel. You may. Further, when the thickness of the thin glass plate 25 is 50 μm as in the second embodiment, the focal length of the hologram lens can be set to about 60 μm to 100 μm, so that there is no need to change the design of the current hologram lens. .

As shown in FIG. 2, white light emitted from the light source 1 is converted into B light and R light by using a dichroic mirror 22.
The light is separated into light and G light, and is incident on the reflective spatial light modulator 30 at a specific incident angle so that the diffraction efficiency is highest for each of the B light, the R light, and the G light.

The incident light is diffracted and emitted in a specific direction for each color light by the hologram lens, undergoes necessary modulation in the liquid crystal layer on the way, and is condensed on a predetermined pixel electrode. In the case of the reflective spatial light modulator 30, the light is reflected on the electrode surface and is projected on a screen (not shown) via the projection lens system 31.
Note that the hologram lens according to the present embodiment can be similarly used in the case of a transmission type spatial light modulation element.

When a single-layer hologram lens is used, the number of hologram lenses to be manufactured is one more than when a conventional hologram lens having a three-layer structure as shown in FIG. 3 is used, and alignment between hologram lens layers is unnecessary. The fabrication process can be greatly simplified. When the hologram lens according to the present embodiment is used, a change in the recording angle of the hologram during the manufacturing process is small, so that a hologram filter having diffraction characteristics almost as designed can be obtained, and the hologram lens can be warped or shrunk. Occurrence of color unevenness on the screen due to this is also suppressed, and good image quality can be obtained.

As described above, the contents of the present invention have been described in accordance with the embodiments, but the present invention is not limited to the above-described embodiments. It will be apparent to those skilled in the art that various modifications and improvements other than the above are possible.

[0051]

As described above, the step of coating or attaching the hologram photosensitive material on the first glass substrate serving as the support material, the step of subjecting the hologram photosensitive material to interference exposure, and the step of thermally developing the hologram photosensitive material. The thermal development process in a state where the second glass substrate is attached to the surface of the hologram photosensitive material, thereby suppressing the thermal shrinkage of the photopolymer, and causing the hologram lens Of the recording angle can be prevented.

Further, by performing the thermal development while applying a load on the second glass substrate via the rigid flat base material, the occurrence of the warpage of the support substrate can be suppressed regardless of the thickness of the second glass substrate. In addition, in-plane variation of the recording angle of the hologram lens can be suppressed.

Therefore, the liquid crystal display device using the hologram lens obtained by the manufacturing method of the present invention as a color filter can obtain good image characteristics without color unevenness.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration in a manufacturing process of a hologram lens according to first and second embodiments of the present invention.

FIG. 2 is a diagram showing a configuration of a liquid crystal display device using a single-layer hologram lens according to an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a conventional projection type liquid crystal display device using a hologram lens.

FIG. 4 is a diagram illustrating a configuration of an interference exposure step in the method of manufacturing a hologram lens.

FIG. 5 is a cross-sectional view of a photopolymer for explaining a problem in a heat development processing step in a conventional method of manufacturing a hologram lens.

FIG. 6 is a cross-sectional view of a photopolymer for explaining another problem in a heat development processing step in a conventional method for manufacturing a hologram lens.

[Explanation of symbols]

 Reference Signs List 1 photopolymer 2 glass substrate 3 glass substrate 4 thin glass 5 plate

Claims (2)

[Claims] 1. A step of coating or attaching a hologram photosensitive material on a first glass substrate serving as a support material, a step of subjecting the hologram photosensitive material to interference exposure, and a step of thermally developing the hologram photosensitive material. A method for manufacturing a hologram lens, comprising: attaching a second glass substrate to the surface of the hologram photosensitive material before the heat development process, and performing the heat development process in this state. . 2. The second glass substrate has a thickness smaller than that of the first glass substrate, and performs the heat development process while applying a load to the second glass substrate via a rigid flat substrate. The method for manufacturing a hologram lens according to claim 1, wherein: