JPH095526A - Superimposed hologram - Google Patents

Abstract

PURPOSE: To prevent the swelling of diffraction grating formed on a hologram by constituting so as to superimpose a plurality of the hologram through a protective film for preventing the diffusion of component materials of the hologram in each of the holograms. CONSTITUTION: This superimposed hologram is constituted so as to superimpose the hologram 1/the protective film 11/the hologram 2/the protective film 12/the hologram 3 in this order. The surface of the opposite side to the protective layer 11 of the hologram 1 can be supported by a transparent substrate, the surface of the opposite side to the protective layer 12 of the hologram 3 can be also supported by the transparent substrate and further one side face of the hologram 2 can be also supported by the transparent substrate. The protective layer 11 prevents the diffusion of the component materials of the hologram 1 or the hologram 2 to each other. And the protective layer 12 prevents the diffusion of the component materials of the hologram 2 or the hologram 3 to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superposition hologram in which a plurality of holograms are superposed.

[0002]

2. Description of the Related Art With the recent progress in hologram materials and laser technology, many products using holograms have been proposed. For example, a laser scanner for a bar code reader, a diffraction grating for a pickup used for recording or reading of an information recording medium using a laser beam such as a compact disc or a magneto-optical disc, or a light including information is diffracted to an observer. It has been proposed to use a hologram as an optical element in a holographic display device or the like for displaying. In addition, forgery prevention marks for ID cards and credit cards, decoration holograms, hologram calendars, and the like use holograms on which images are recorded.

However, although the hologram material has improved, it cannot be said that it has sufficient characteristics. Considering the diffraction efficiency, for example, there are problems that the S / N ratio for reading information is insufficient and the display image is dark and difficult to see because sufficient diffraction efficiency cannot be obtained. Further, for example, even when recording a full-color image of an object or obtaining a multicolor holographic display image, a single hologram material could not be exposed or could not be exposed in a wide wavelength range. However, sufficient diffraction efficiency was not obtained for each color.

The diffraction efficiency of the volume phase hologram is determined by the refractive index modulation value Δn of the hologram material and the thickness t of the hologram layer.
It is determined by the product Δn · t of Therefore, conventionally, in order to obtain high diffraction efficiency, Δn of the material has been increased or the thickness has been increased. However, the increase of Δn requires development of a basic hologram material, which is not easy. Further, increasing the thickness also decreases the transmittance, so that the laser light used for exposure is attenuated and the exposure cannot be performed sufficiently, so that the diffraction efficiency is not improved as expected.

[0005]

Therefore, in order to improve various characteristics of the hologram, it is conceivable to stack a plurality of holograms instead of a single hologram. But,
If the holograms are simply overlapped by the conventional method shown in FIG. 6, there is a problem that the hologram characteristics change.

For example, in the case of a photopolymer material which has recently been improved in performance and is about to be put into practical use, the material contains a component substance such as a photopolymerizable monomer which easily diffuses. Therefore, when the holograms are simply superposed, there is a problem that the component materials mutually diffuse, the diffraction grating of the hologram swells, and the diffraction wavelength and the diffraction angle deviate from the set values.

In addition, for example, when a plurality of holograms are superposed, if the coefficients of thermal expansion of the holograms are different, stress is generated at the interface between adjacent holograms in the process of heat treatment associated with hologram production, and the diffraction grating inside the hologram is formed. There was a problem that it was deformed and the diffraction angle and the diffraction wavelength were changed.

[0008]

The present invention has been made to solve the above-mentioned problems, and a plurality of holograms are
Provided is a superposition hologram in which each hologram is superposed with a protective layer for preventing diffusion of a component material of the hologram interposed therebetween.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of the superposition hologram of the present invention. 1 to 3 are holograms to be superimposed, and 11 and 12 are protective layers. That is,
This superposition hologram is a hologram 1 / protective layer 11 /
The hologram 2 / the protective layer 12 / the hologram 3 are superposed in this order.

Although not shown, the surface of the hologram 1 opposite to the protective layer 11 may be held by a transparent substrate,
The surface of the hologram 3 opposite to the protective layer 12 may also be held by the transparent substrate, and at least one side surface of the hologram 2 may also be held by the transparent substrate. In this case, the work for superposing the holograms via the protective layer becomes easy.

The protective layer 11 prevents the constituent material of the hologram 1 and the constituent material of the hologram 2 from diffusing to the other party. Further, the protective layer 12 prevents the constituent substance of the hologram 2 and the constituent substance of the hologram 3 from diffusing to the other party.

Each of the holograms used in this embodiment was exposed by a dye laser. The laser light is split into two by a beam splitter, and then collimated into parallel light, and the two lights are incident on the hologram photosensitive material at incident angles of 40 ° and 60 ° with respect to the hologram photosensitive material. Then, the wavelength of the laser light incident on each of the hologram photosensitive materials is changed, and the hologram 1 is 535 nm, the hologram 2 is 550 nm, and the hologram 3 is
Were separately exposed to diffract light at 565 nm. The diffraction efficiency of each is about 60%.

After exposure, each hologram has a film-like polyvinyl alcohol (PVA) coated with an adhesive on both sides.
The protective layers 11 and 12 are made to overlap each other. In the present embodiment, the superimposing hologram is superposed after each hologram is exposed, but it is also possible to expose the hologram photosensitive material which has been superposed in advance before the exposure. In that case, it is desirable to shift the wavelength sensitivity of each photosensitive material so that mainly one hologram photosensitive material is selectively exposed to one laser wavelength.

The diffraction spectrum of the superposition hologram of this embodiment is shown at 20 in FIG. On the other hand, what is indicated by a dotted line in FIG. 2 is a diffraction spectrum in the case where each of the superimposed holograms is alone, 21 is a hologram 1, 22 is a hologram 2 and 23.
Is the diffraction spectrum of hologram 3.

Diffraction spectrum of superposition hologram 20
Is almost the same as that obtained by superimposing the diffraction spectra 21 to 23 of each hologram, and the characteristics of each hologram may not be changed by interposing the protective layers 11 and 12 between the holograms. Recognize. In addition, the full width at half maximum of the diffraction spectrum of a single hologram is approximately 15 n each.
Although it was m, it is about 50n as a whole by overlapping.
A superposition hologram having a half-width of m was obtained.

In this embodiment, the hologram material is 10 in width.
A volume phase reflection hologram was prepared using a photosensitive material made of an acrylic photopolymer having a size of 0 mm × 100 mm in length and a thickness of 20 μm. However, the present invention is not limited to the above size and material.

In this embodiment, the above-mentioned diffraction angle, diffraction wavelength,
Although an example in which three holograms having a diffraction efficiency and a full width at half maximum are superimposed is shown, the present invention is not limited to the above diffraction angle, diffraction wavelength, diffraction efficiency, and full width at half maximum, and the number thereof is not limited to three.

FIG. 3 shows a second embodiment. The structure of the superposition hologram is the same as that described in the first embodiment. However, the characteristics of each hologram are different. The hologram 1 diffracts the incident light 35 having an incident angle of 45 ° at a diffraction angle of 55 ° ± 5 ° as 31. Hologram 2 has a diffraction angle of 45 ° ±
Like 32 at 5 °, hologram 3 has a diffraction angle of 35 ° ± 5
Diffracts like 33 at °. All diffraction wavelengths are 545n
m.

Diffracted light, which was spread by about 10 ° in a single hologram, can be spread by 30 ° or more by using the superposition hologram of the present invention.
Even if it is a single hologram, if the decrease in diffraction efficiency is tolerated, 3
A spread of 0 ° or more can be obtained. However, according to the present invention, both high diffraction efficiency and wide spread angle are compatible.

In this embodiment, the diffraction wavelengths of the holograms are the same, but if the wavelengths corresponding to the respective colors of RGB are diffracted, the incident white light 35 will be R.
It can be separated into three colors of GB, and on the other side (31, 32 in the figure,
It is also possible to make separate lights of three colors enter from 33 side) and combine them into one light 35.

When the superimposing hologram according to the present invention is used, even when a plurality of holograms are superposed, a protective layer is provided between the holograms, so that the holograms are deformed due to mutual diffusion of hologram component materials and differences in thermal expansion coefficient. Can be effectively prevented. Further, by using as the protective layer of the present invention, a material that does not diffuse and move to adjacent holograms, for example, a material that does not contain a material such as a plasticizer, it is possible to prevent changes in hologram characteristics.

Various functions such as predetermined optical characteristics, physical characteristics and chemical characteristics can be imparted to the protective layer in the present invention.
The function is exemplified as follows.

A value between the refractive indices of adjacent holograms,
In particular, when a protective layer having an average refractive index of both is used, reflection of light incident on the hologram at the hologram / protective layer interface can be minimized. Therefore, even when the superimposing hologram is used as an optical element, there is almost no concern that incident light is reflected at the hologram / protective layer interface to generate unnecessary reflected light such as halation. In addition, even when multiple exposure is performed after laminating hologram photosensitive materials, it is possible to prevent unnecessary noise holograms from being exposed due to the laser light for exposure being reflected at the interface.

When the protective layer has no birefringence, the polarization state of incident light is not affected by the protective layer and can be diffracted by the hologram under desired conditions.

On the contrary, the protective layer may have birefringence. By thus providing the protective layer with birefringence, it becomes possible to control the change in the polarization state of the light passing through the protective layer. For example, if the degree of birefringence is such that a phase difference corresponding to about a quarter of the diffraction wavelength is generated at the diffraction wavelength of the hologram, and if the incident light is linearly polarized light, circularly polarized light after passing through the protective layer. Changes to. If the incident light is circularly polarized light, it changes to linearly polarized light after passing through the protective layer.

Further, for example, when the degree of birefringence is such that a phase difference corresponding to about one half of the diffraction wavelength is generated at the diffraction wavelength of the hologram, if the incident light is linearly polarized light, the protective layer After passing, it changes to linearly polarized light which is orthogonal to the polarization direction of the incident light. For example, s-polarized light changes to p-polarized light. If the incident light is circularly polarized light, it also changes to circularly polarized light after passing through the protective layer.

In addition, when the degree of birefringence is such that the hologram has a phase difference corresponding to the diffraction wavelength at the diffraction wavelength, the polarization state of the incident light remains the same even after passing through the protective layer. . In this way, the superposition hologram according to the present invention can be used to control the polarization state of incident light.

Utilizing this phenomenon has the following advantages. A hologram may have different diffraction efficiency depending on the polarization of incident light. For example, a high diffraction efficiency of 90% or more for s-polarized light may be less than several percent for p-polarized light. When random-polarized light is incident on such a hologram, the s-polarized light component may be mostly diffracted, but the p-polarized light component occupying the other half may be hardly diffracted.

However, by providing the protective layer with birefringence, the p-polarized component not diffracted by the first hologram can be changed to the s-polarized component, and the diffracted light can be efficiently diffracted by the second hologram. , The total diffraction efficiency can be significantly improved. It is also possible to apply this in the opposite way so that it is not diffracted by a specific hologram among the superposition holograms.

Polarizing characteristics can be imparted to the protective layer. Therefore, even when random light enters the superposition hologram, the polarized light of the diffracted light can be a specific polarized light. Therefore, when the superposition hologram according to the present invention is used together with an optical device (such as a liquid crystal display) that utilizes a specific polarized light, the polarizing plate that has been conventionally used becomes unnecessary.

By making the protective layer heat-resistant, it can be carried out without problems even when the superposition hologram needs to be heat-treated. For example, some photopolymer hologram materials can be subjected to heat treatment after laser exposure to increase the refractive index modulation Δn and improve the diffraction efficiency. In such a case, it is preferable that the protective layer is heat resistant.

When the superposition hologram is to be enclosed in laminated glass, it can be removed by an autoclave.
It is subjected to heat treatment at 140 ° C. Also in this case, it is preferable that it is heat resistant. Further, depending on the usage conditions of the superposition hologram, it may be used near a light source that generates heat or used in a closed environment in which heat is accumulated. Even in such a case, the heat-resistant protective layer of the present invention may be used.

By using a flat protective layer having no irregularities or pinholes, it is possible to prevent the irregularities of the protective layer from being transferred to the adjacent hologram or changing the characteristics of the hologram by deforming the hologram diffraction grating. . It is also possible to prevent the component material from diffusing and moving from adjacent holograms through the pinhole and partially changing the characteristics of the hologram.

As the protective layer, it is preferable to use a transparent layer having a haze (haze value) of 1.0% or less. This is because the incident light is attenuated to reduce the light utilization rate of the entire superposition hologram, and the haze is small, so that the incident light is scattered and the occurrence of halation, halo, image blurring, and the like can be effectively suppressed.

As the protective layer, a layer that selectively transmits, absorbs, or reflects light in a specific wavelength range can be adopted. A hologram has the property of diffracting only light in a specific wavelength range. Therefore, light in other wavelength regions is transmitted without being diffracted. Since this transmitted light may become unnecessary scattered light or noise light, it is effective to previously absorb or reflect light other than the wavelength range diffracted by the hologram using the protective layer.

Further, in the case of a hologram material made of an organic substance, there is a possibility that it will be yellowed or decomposed by irradiation of ultraviolet rays. Further, there is a possibility that the temperature rises due to the irradiation of infrared rays, the hologram expands, and its characteristics change. Therefore, by using, for example, a protective layer having a function of absorbing or reflecting ultraviolet rays or infrared rays as the protective layer in the present invention, the characteristic change of the hologram can be prevented.

The hologram and the protective layer are, for example, adhesive or sticky (hereinafter simply referred to as "adhesive") to the adjacent hologram, or adhesive for imparting adhesiveness to the protective layer. Adhesion with sufficient strength can be achieved by using the agent.

There are various means for interposing the protective layer between the holograms. For example, a film-shaped protective layer may be used. In this case, the film-shaped protective layer is laminated on one surface of the hologram, and then the next hologram is laminated thereon,
A superposition type hologram is obtained. Alternatively, a hologram having a film-like protective layer on one surface is joined to the surface having the protective layer and the surface not having the protective layer to obtain a superposition hologram. It is also possible to previously provide film-like protective layers on both sides of the hologram, and in this case, the protective layers are joined together.

In these cases, as will be described later, the hologram also includes a photosensitive material having a protective layer as a photosensitive material before exposure.

A protective layer may be coated on one surface of the hologram. In this case, a superposition hologram can be obtained by joining the surface having the coated protective layer and the surface having no protective layer in the hologram. Alternatively, a hologram having a protective layer coated on both sides can be used, and in this case, the protective layers are joined together. In these cases, as will be described later, the hologram also includes a hologram having a protective layer as a photosensitive material before exposure.

The hologram and the protective layer are superposed by various means such as being bonded to each other via an adhesive or the hologram itself and the protective layer having adhesiveness. That is, when a film-like protective layer is used and the film-like protective layer itself and the hologram itself have adhesiveness, they can be laminated by directly joining them. In addition, even if there is no or poor adhesiveness, or even if there is adhesiveness,
It is also possible to bond both via an adhesive and stack them.

On the other hand, when the surface of the hologram is coated with the protective layer, the same applies to the case where the surface of the hologram coated with the protective layer and the surface of the hologram which is not coated are bonded to each other. If it has, it may be joined as it is. Further, even if the above-mentioned adhesiveness is not present or is poor, or even if the above-mentioned adhesiveness is present, it is possible to bond both via an adhesive and laminate them. This is also the case when the protective layers are coated on both sides of the hologram.

The protective layer in the present invention preferably has a water content of 1% or less. Thus, by making the water content of the protective layer small, it is also effective for hologram materials such as dichromated gelatin, which are weak against water. In addition, polyvinyl butyral (PVB) film is used as an intermediate film in vehicle safety glass.
Since the adhesive strength of glass changes depending on the amount of water contained in, it is necessary to control the amount of water to be appropriate. Therefore, if the protective layer having the above water content is used, the influence on the water content of PVB can be reduced even if it is used by being enclosed in the vehicle safety glass.

In exposing the hologram, the photosensitive material is superposed through the protective layer before the exposure, and then the exposure is performed, so that the characteristic change due to the interaction between the holograms during the exposure or the post-treatment can be prevented. Further, by superposing the exposed holograms via the protective layer, it is possible to prevent changes in characteristics not only during post-processing but also over a long period of time.

The reproduction wavelengths and diffraction angles of a plurality of holograms are
By making the reproduction wavelengths and diffraction angles substantially the same, it is possible to improve the diffraction efficiency by superimposing them.

By superimposing a plurality of holograms as holograms having substantially the same diffraction angle and different reproduction wavelengths, the reproduction wavelength band can be improved as in the first embodiment.

For example, in a single hologram, the standard half-width of the diffraction spectrum is 10 to 20 nm.
If a plurality of holograms are superposed to form the superposition hologram of the present invention, the half width can be expanded to 100 nm or more, and in some cases, light in the entire visible light region can be diffracted. Further, it is also possible to diffract light in the infrared region to form a superposition type hologram having a heat ray reflecting performance, and diffract light in the ultraviolet region to impart ultraviolet ray cutting performance.

On the contrary, by superimposing a plurality of holograms as holograms having substantially the same reproduction wavelength and different diffraction angles, the diffraction angle band can be improved as in the second embodiment.

For example, in the case of a hologram in which an image of an object is recorded, the visible range of the image is narrow with a single hologram, but by adding the diffraction angle of each hologram, a superimposing hologram that can be observed from a wide range can be obtained. . Further, in a holographic display device that diffracts light containing information toward an observer, light is normally diffracted only in a specific direction, so that only one observer can observe the display. However, by using the superposition hologram of the present invention in which holograms having different diffraction angles are superposed, a holographic display device can be obtained in which a plurality of observers can observe at the same time.

Further, a plurality of holograms may be holograms having different reproduction wavelengths and different diffraction angles. When such superposed hologram is irradiated with white light, light of various colors (wavelengths) is diffracted in various directions, and a very beautiful decorative hologram shining in a rainbow color can be obtained. When such a superposition hologram is used in a holographic display device that diffracts light containing information toward an observer, it is possible to change the display color and the display direction depending on the type of information. . For example, if the normal information is displayed in green and the caution / warning display is displayed in red, the information can be more accurately transmitted to the observer.

Further, the plurality of holograms may be holograms having different magnifications. For example, if an image of an object is recorded by using such a superposition hologram, it is possible to superimpose images having different distances and different sizes, such as a laminated mirror, and it is possible to produce an interesting decorative hologram. In addition, when such a superposition type hologram is used in a holographic display device that diffracts light containing information toward an observer,
Since the distance of the display virtual image formed at a distance changes depending on the magnification, for example, when applied to a vehicle, a distance marker that displays an image at a constant distance can be easily manufactured with only a single light source.

Each of the plurality of holograms may have a light diffusing function. If such a superposition hologram is used, it can be used as a light guide plate of a backlight of a liquid crystal display device or a screen of a projection display.

Further, by optimizing the combination of the diffraction efficiency, the reproduction wavelength, and the half-value width of wavelength of each of the plurality of holograms, the color tone of the diffracted light of the entire superposition hologram can be set to a desired color tone.

For example, in the case of recording a full-color image of an object on a hologram, if the combination of the diffraction efficiency, reproduction wavelength, and half-value width of wavelength is inappropriate, the color tone of the actual object and the color tone of the hologram are different. Will end up.
Further, when the superimposing hologram is used in a holographic display device, the color tone of the superimposing hologram itself may be a problem. In particular, when it is used as a head-up display for vehicles or as a partition between buildings for advertising and decoration in stores, etc., the superposition hologram itself touches the human eye, so its appearance should be as inconspicuous white or a color tone with less irritation. It is important to.

Therefore, by optimizing the combination of the diffraction efficiency, the reproduction wavelength, and the half-value width of the wavelength using the above-mentioned superimposing hologram, the appearance of the hologram can be made inconspicuous white or a color tone with less irritation.

The transparent substrate that holds the hologram may be one that holds at least one surface of each hologram, or one that holds only the outer surface of the outermost layer of the superimposed holograms. For example, when the holograms themselves are poor in handling during superimposing work, it is preferable that each hologram be held by a transparent substrate. The substrate that holds the photosensitive material during exposure of the hologram may be this transparent substrate. Further, when a hologram described later is enclosed in laminated glass or laminated on a glass plate, this glass plate can hold the hologram as a transparent substrate.

Next, a third embodiment in which the superposition hologram of the present invention is applied to a holographic display device using as a hologram combiner will be described. FIG. 5 shows a conceptual diagram of a vehicle head-up display (hereinafter referred to as HUD) as an example of a holographic display device.

HUD has been recently used as a method of displaying information to a driver in an automobile or the like. This is because the optical information projected from the information projection means such as a liquid crystal display device is projected on a combiner composed of a hologram or a half mirror incorporated in the windshield of an automobile, etc., and the driver almost moves the viewpoint from the driving state. The information can be read without any need.

In this HUD, the light 43 containing the information to be displayed, which has passed through the transmissive liquid crystal display element 45 through the lens system 44, is applied to the hologram combiner 42 provided on the windshield 47 of the vehicle body and diffracted. It is visually recognized by the driver at the observation position 41. The hologram 42 can be made to have a magnification, and the display images of the speed display 48 and the warning display 49 can be formed at a distance. If necessary, another hologram or lens for aberration correction may be arranged between the transmissive liquid crystal display element 45 and the combiner 42.

Since the hologram 42 has a wavelength selecting function, an image of a desired color can be displayed. Although the color is often single, the present invention enables multicolor display by superimposing a plurality of holograms, thereby improving the amount and quality of display information. In this embodiment, 545n corresponding to green
A hologram for diffracting 640 nm light corresponding to m and red toward an observer is superimposed and used, the speed display 8 is green,
The warning display 9 is displayed in red. As a result, more accurate information can be transmitted to the driver.

Since the hologram diffracts only the light of a specific wavelength, when the outside world is viewed through the hologram, the light of the diffraction wavelength of the hologram is diffracted, and the color tone of the transmitted color becomes a complementary color of the diffraction wavelength. Also, when the hologram combiner is viewed from the outside, the diffracted color is a highly pure color and thus has a glaring color tone, and the color changes depending on the viewing direction. To improve these problems, at least RGB
Holograms corresponding to the three primary colors may be used. In the above case, another hologram for diffracting the light of the wavelength of 470 nm corresponding to blue may be superposed with the configuration of the present invention. These wavelengths may be optimized as appropriate and are not limited to the wavelengths in this embodiment.

Light containing information to be displayed from the light emitting display light source enters a combiner composed of a superposition hologram at an incident angle θ ₁ , is diffracted by the superposition hologram and exits at an exit angle θ ₂ , and is displayed to an observer. Consider a holographic display device that is perceived as an image.

When external unnecessary light enters such a superimposing hologram from the side opposite to the light emitting display light source at an angle of θ ₁ , the external unnecessary light passes through the superimposing hologram and the superimposing hologram or the substrate holding the superimposing hologram. It is reflected at the interface and again enters the superposition hologram. Since the incident angle at this time corresponds to the incident angle of light when the light is emitted from the light emitting display light source at θ ₁ , the external unnecessary light is diffracted by the superposition hologram and is observed by the observer as an unnecessary diffraction image. When such a holographic display device is used in a vehicle head-up display or the like, external light 51 such as street lights or sunlight (50 in FIG. 5) is an unnecessary diffraction image such as a driver 52. It was annoying to be observed by the observer.

Therefore, the second hologram set is superimposed on the first hologram set on the opposite side of the light emitting display light source, and the second hologram set is incident from the opposite side of the light emitting display light source. By diffusing the external unnecessary light so as to prevent the unnecessary light from being diffracted by the first hologram set and being observed by the observer as an unnecessary diffraction image, the annoyance of the observer can be reduced.

Specifically, as shown in FIG. 4, the hologram combiner has a safety alignment in which two glass plates (a car-side glass 61 and a car-side glass 60) are stacked via an intermediate film 62 made of PVB. It is enclosed in glass and is arranged between the vehicle interior glass 60 and the intermediate film 62. The hologram combiner consists of a first set 71 of superposed holograms.

The first set 71 is formed by laminating three holograms corresponding to the above-mentioned RGB through a protective layer, and is used for diffracting the light 43 containing information toward the observer. . The protective layer is PVA with an adhesive as in the first embodiment. The second hologram set 72 diffracts the external unwanted light 51 so that the observer cannot see the unwanted diffracted image, and diffracts unwanted light having a wavelength corresponding to the diffraction wavelength of the first set 71. It is also a superposition of three holograms.

Thus, the angle (θ) at which the second hologram group of the superposition holograms is approximately equal to the angle (θ _{1 in the} above example) at which the light containing information is incident on the first hologram group used as the combiner. By diffracting the unwanted light incident in ₁ ), it is possible to effectively suppress the generation of the unwanted diffraction image.

Also, the second set of holograms has a wavelength of light containing information diffracted by the first set of holograms,
By diffracting unnecessary light having substantially the same wavelength, it is possible to more effectively suppress the occurrence of the above-mentioned unnecessary diffraction image.

When the second set of holograms diffracts the incident unnecessary light at a certain diffraction angle θ ₃ , this angle θ
_{If the value of 3} is inappropriate, it may be reflected again by an interface on the incident side of unnecessary light and may be observed by an observer as an unnecessary diffraction image. In order to prevent this, the diffraction angle θ ₃ may be set to an angle such that total reflection occurs in the superposition hologram or the substrate holding the superposition hologram, that is, in the laminated glass in this embodiment. Then, the diffracted light can be confined in the superposition hologram or its substrate, and unnecessary light can be prevented from being observed by an observer.

When the first hologram set used for the combiner has a magnification, the diffraction grating inside the hologram has a complicated three-dimensional curved surface shape, and the diffraction wavelength and the diffraction angle are in the plane of the hologram. Is not uniform. To prevent the generation of unnecessary diffraction images in the entire plane of the hologram,
Optimization of the diffraction grating shape of the hologram set of is required. As an effective means for that purpose, the f value of the second hologram set may be made substantially equal to the f value of the first hologram set. Since the diffraction grating shapes inside the hologram having substantially the same f values are similar, it is possible to prevent the generation of unnecessary diffraction images over the entire hologram surface.

Another effective means for preventing unnecessary light diffracted by the second hologram set from being reflected again or diffracted and observed by an observer as an unnecessary diffraction image will be exemplified.
That is, the second set of holograms diffracts the incident unwanted light to diffuse it. By doing so, even if the unnecessary light is diffused and reaches the eyes of the observer, it is only a faint weak light, and it can no longer be recognized as an unnecessary diffraction image.

By appropriately combining the incident angle, the diffraction wavelength, the outgoing diffraction angle, the magnification, and the diffusing function of the second hologram set as described above, it is possible to more effectively prevent the generation of the unnecessary diffraction image.

In the superimposing hologram of the present invention, if a protective layer is provided between the substrate holding one or both of the superimposing holograms, if necessary, a change in the characteristics of the hologram due to the influence from the substrate side. Can be prevented. For example, some plastic substrates release volatile components by heat treatment. When the superposition hologram is held on such a substrate, the characteristics of the hologram may change due to the influence of the volatile component. In such a case, if the protective layer is also provided between the hologram holding substrate as in the superposition hologram of the present invention, it is possible to effectively prevent the characteristic change of the hologram.

Further, since the protective layer in the superposition hologram according to the present invention has an area larger than that of the hologram to be superposed and can cover and protect the hologram over the entire area, not only from the adjoining hologram but also from the end face in the lateral direction. It can also protect against diffused substances. Therefore, the hologram can be effectively protected even when the entire superposition hologram is enclosed in some medium (laminated glass in this embodiment).

The superimposing hologram of the present invention can employ various variations as described above depending on the application and the like. In the present embodiment using the superimposing hologram for the HUD,
A protective layer was also superposed between the first hologram set and the second hologram set to form a superposition hologram as a whole. Further, a protective layer 63 made of PVA for protecting the hologram from the influence of the plasticizer contained in the intermediate film 62 is provided between the superposition hologram (71 + 72) and the intermediate film.
Is provided.

The protective layer used in the superposition hologram (71 + 72) had the same area and shape as the hologram, but the protection layer 63 had an area larger than that of the superposition hologram (71 + 72) and covered the hologram over the entire area to protect it. It is possible, and it can also protect against the plasticizer that diffuses laterally from the side.

In the present embodiment, the second set of holograms is superimposed on the opposite side of the light emitting display light source to the first set of holograms. The external light 51 that is incident at an angle θ ₁ that is substantially the same as the incident angle θ ₁ is diffracted, and the diffraction wavelength at that angle is approximately the same as the diffraction wavelength of the first hologram set.

The unnecessary light 53 diffracted by the second set of holograms is diffracted at an angle such that it is totally reflected so as to be confined inside the safety glass. In this embodiment, the internal angle of the glass is 50 °.

A diffusion type hologram was used as the second hologram so that the unnecessary light is not only diffracted diffractively but also diffused and reflected. Therefore, the unnecessary light 53 confined in the safety glass is again diffracted by the hologram 72 or 71 and diffuses even if it is emitted toward the observer, and it can no longer be recognized as an unnecessary diffraction image.

The first set of holograms has a magnification of about 3.5 times, and its exposure is such that the incident light source side diverges from a pinhole placed at a distance of 350 mm at θ ₁ = 40 °, the display image side. As a result, a hologram was recorded by causing two parallel rays of θ ₂ = 60 ° to interfere with each other. The f value is 1 / f = 1/350
Since −1 / ∞ = 1/350, f = 350 mm. The laser used as the exposure light source is a Kr laser having a wavelength of 647 nm for red, a dye laser having a wavelength of 555 nm for green, and an Ar laser having a wavelength of 476 nm for blue.

As the second hologram set, divergent light from a pinhole placed at a distance of 350 mm at θ ₁ = 40 ° was used on the outside light incident side, and parallel light was passed through the diffuser plate on the diffracted light 53 side. The light thus obtained was used so as to have an average internal angle of 50 ° by using a prism, and two lights were caused to interfere with each other to record a hologram. Therefore, the second set of holograms has an f-value that is approximately equal to the first set of holograms. In this way, since the f values of the first and second hologram sets are made substantially equal, the diffraction grating shapes inside the hologram are similar, and it is possible to prevent the generation of unnecessary diffraction images within the entire area of the hologram combiner. The prevention effect was also obtained when the observer's viewpoint was moved.

In this embodiment, three holograms are superposed as a set of the first and second holograms, but the present invention is not limited to this, and four or more holograms are superposed. Alternatively, two holograms obtained by multiple-exposure one hologram with three-color holograms may be superimposed via a protective layer.

Further, in the present embodiment, the second hologram set is superimposed on the opposite side of the light emitting display light source to the first hologram set, but the second hologram set is the first hologram set. It may be superposed on the same side as the light emitting display light source with respect to the hologram set. In this case, unnecessary light other than the light including the information that is incident from the light emitting display light source side is diffracted by the first hologram set, and the unnecessary light that is incident so as to prevent the observer from observing it as an unnecessary diffraction image. If it is diffracted,
It is possible to prevent generation of unnecessary diffraction images from the light emitting display light source side.

A transparent resin film or resin coating is desirable for the protective layer in the present invention. For example, acrylic resin such as polymethylmethacrylate (PMMA) or polyisobutyl methacrylate, polyester resin such as diethylene glycol bisallyl carbonate (CR-39), polycarbonate (PC), polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), Polyvinyl alcohol (PV
A), ethylene-vinyl alcohol copolymer (EVO
H), polyethylene (PE), polyvinyl acetate (PVA)
c), polyvinyl butyral (PVB), polyarylate (PAR), polyether sulfone (PES), polyvinyl chloride (PVC), triacetyl cellulose (TA)
C), amorphous polyolefin, amorphous fluororesin, polyurethane, norbornene-based resin and the like are conceivable, but not limited thereto.

Further, not only resin materials but also inorganic materials such as thin glass plates, vapor-deposited films or sputtered films of dielectrics and metals, CV
The D film itself may be a film formed on the resin film.

In actual use, a material suitable for the purpose may be selected from these materials. For example, when the refractive index of the hologram is close to 1.5, PMMA, PVA, EVOH, TAC and the like are preferably used as the protective layer.

Further, for example, when a protective layer having a birefringence is required, a film obtained by appropriately stretching the above PC or PVA can be preferably used. Further, for example, when it is desired to impart polarization characteristics to the protective layer, a polarizing film obtained by containing iodine in PVA and stretching it can be used. When it is desired to obtain a protective layer that absorbs light in a specific wavelength range, the resin film may contain an appropriate dye or dye. To obtain a protective layer that transmits or reflects light in a specific wavelength range, a selective transmission or reflection film may be deposited on a suitable resin film or glass thin plate.

The preferred thickness of these protective layers is from 1 to 20.
It is about 0 μm, more preferably about the same as the thickness of the hologram and 100 μm or less.

It should be noted that holograms are usually several 10 mm to several 1
The area is about 00 mm square and the thickness is about several μm to several tens of μm. Such a hologram is desirable because a volume / phase type hologram such as a Lippmann type hologram can obtain high diffraction efficiency, but a hologram called an emboss type hologram or a rainbow type hologram can also be widely adopted. As the hologram material, various photosensitive materials such as photopolymers such as polyvinyl carbazole and acrylic, gelatin dichromate, photo resist, and silver salt can be used.

The light emitting display light source in the present invention has a function of emitting light to display, and a hot cathode tube (HC) is attached to a display body composed of a so-called light receiving type display element such as a liquid crystal display element.
T), a cold cathode tube, a fluorescent display tube (VF), a halogen lamp, an LED, or the like which emits light emitted from a light source, or may have these functions together.

When the superimposing hologram combiner of the present invention is used for color display, the liquid crystal display element includes a color filter and a transmission type twisted nematic type liquid crystal element, a super twisted nematic type liquid crystal display element, or the like. Elements can be used preferably,
The light emitted from one light source can be emitted as light of a desired color.

In this way, the lights of a plurality of colors can be emitted from the same information display source, and when the lights of a plurality of colors are simultaneously displayed, the display images are displayed in an overlapping manner.
On the contrary, in order to prevent the overlapping of the displayed images, it is possible to prevent light of a plurality of colors from being simultaneously irradiated by a combination of a color filter and a light source or by controlling a color liquid crystal display element, if necessary.

Alternatively, instead of using the light receiving display element, the light source itself may be patterned and arranged to generate specific information as light. In the case where the light source is used together with the light receiving display element, an appropriate light collimating means such as a lens system or a curved reflecting mirror, and a suitable light guiding means such as a light guide plate are provided between the light receiving display element and the light source. You may arrange. Further, if necessary, an optical polarization means or KNO ₃ is provided in the optical path until the light is projected on the hologram.
Non-linear optical elements such as may be arranged.

Here, the information to be displayed in the present invention is appropriately selected according to its display application. In the case of a vehicle display device, a vehicle speedometer, a tachometer, a shift lever display, various warning lamps, navigation information, information on auxiliary equipment such as an air conditioner, audio equipment, and the like can be given as examples. It is also possible to display information from outside the vehicle, such as road information and parking lot availability information. For aircraft, ships, trains, etc., various information related to vehicle operation and business such as position and direction information such as latitude, longitude, altitude, traveling direction, weather information, radar obstacle information, fish finder information, etc. Conceivable. Further, the observer is mainly a driver of a vehicle such as a vehicle, but may include a passenger seat, other passengers, and all of them.

Further, for example, by arranging a hologram on the rear glass and diffracting the braking information toward the observer such as the driver of the vehicle behind by the hologram, the light from the light emitting display means that emits light in synchronization with the braking operation of the driver is hologramed. The present invention can be applied to a high mount stop lamp that operates. Further, the present invention can be applied to a partition of a building or the like, or a holographic display device that adds a decorative effect to a window glass of a store, and can be widely applied to other display devices using holograms.

[0096]

According to the present invention, when holograms are appropriately overlapped for various purposes, a protective layer for preventing the diffusion of the component material of the holograms is interposed between the holograms. Swelling of the formed diffraction grating can be prevented. Therefore, it is possible to prevent the diffraction wavelength and the diffraction angle of the hologram from deviating from a predetermined value.

In this way, various functions obtained by superimposing a plurality of holograms can be exerted without degrading the holograms, and the characteristics of the holograms can be obtained as set.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a superposition hologram of the present invention.

FIG. 2 is a diffraction spectrum diagram showing an example of a superposition hologram of the present invention.

FIG. 3 is a conceptual diagram showing a second embodiment of the superposition hologram of the present invention.

FIG. 4 is a sectional view of an essential part showing an example in which the superimposing hologram of the present invention is enclosed in laminated glass.

FIG. 5 is a conceptual diagram of an automobile HUD using the superimposing hologram of the present invention as a combiner.

FIG. 6 is a conceptual diagram showing a conventional superposition hologram.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1: Hologram 2: Hologram 3: Hologram 11: Protective layer 12: Protective layer 20: Diffraction spectrum of the entire superposition hologram 21: Diffraction spectrum of the superposed hologram 1 alone 22: Single superposed hologram 2 Diffraction spectrum of case 23: Diffraction spectrum of hologram 3 to be superimposed alone: 31: Light diffracted by hologram 1 to be superposed 32: Light diffracted by hologram 2 to be superposed 33: By hologram 3 to be superposed Diffracted light 35: Incident light 41: Observer 42: Holographic combiner 43: Light beam containing information 44: Lens system 45: Transmission type liquid crystal display element 46: Light source 47: Windshield 48: Speed display 49: Warning display 50: External light source (sun) 51: External unnecessary incident light 52: External unnecessary diffracted light 53: External unwanted light diffracted by the second hologram set 72 of the superimposing hologram 60: Car interior glass 61: Car exterior glass 62: Intermediate film 63: Protective layer 71: First superimposing hologram used as a combiner
Set 72 of holograms: second set of superimposing holograms for diffracting external unwanted light

Claims (12)

[Claims] 1. A superposition hologram in which a plurality of holograms are superposed on each other via a protective layer for preventing diffusion of a component material of the hologram. 2. The superposition hologram according to claim 1, wherein at least the outermost hologram of the plurality of holograms has an outer surface held by a transparent substrate. 3. The superposition hologram according to claim 1, wherein the coefficient of thermal expansion of the protective layer is a value between the values of the coefficients of thermal expansion of the holograms on both sides of the protective layer. 4. The protective layer is in the form of a film, and the film-shaped protective layer itself and the hologram itself have adhesiveness or adhesiveness, or an adhesive is interposed between the film-shaped protective layer and the hologram. The superimposing hologram according to any one of claims 1 to 3, wherein 5. A hologram, wherein the protective layer is coated on at least one surface, and the opposing hologram and the protective layer or the opposing protective layers have adhesiveness or adhesiveness or are protected from the opposing hologram. The superposition hologram according to any one of claims 1 to 3, wherein an adhesive agent is interposed between the layers or between protective layers facing each other. 6. A set of a plurality of holograms has a function as a combiner of a holographic display device that diffracts light containing information to be displayed from a light emitting display light source toward an observer. The superimposing hologram according to claim 1 or 2. 7. A first set of a plurality of holograms has a function as a combiner of a holographic display device that diffracts light containing information to be displayed from a light emitting display light source toward an observer, The second set is superposed on the opposite side of the light emitting display light source with respect to the first hologram set, and external unnecessary light incident from the opposite side of the light emitting display light source is diffracted by the first hologram set, 7. The superposition hologram according to claim 6, wherein external unnecessary light is diffracted so as to prevent it from being observed by an observer as an unnecessary diffraction image. 8. A first set of a plurality of holograms has a function as a combiner of a holographic display device that diffracts light containing information to be displayed from a light emitting display light source toward an observer, The second set is superposed on the same side as the light emitting display light source with respect to the first hologram set, and unnecessary light other than light including information incident from the light emitting display light source side is included in the first hologram set. 7. The superposition hologram according to claim 6, wherein unnecessary light incident from the light emitting display light source side is diffracted so as to prevent it from being diffracted and observed by an observer as an unnecessary diffraction image. 9. The method according to claim 7, wherein the second hologram set diffracts unnecessary light incident on the first hologram set at an angle substantially equal to the incident angle of the information-containing light. 8 superposition holograms. 10. The second hologram set diffracts unnecessary light having a wavelength substantially equal to the wavelength of light containing information diffracted by the first hologram set. One of the superposition holograms. 11. The second hologram set is diffracted at an angle such that incident unwanted light is totally reflected in the superposition hologram or the substrate holding the superposition hologram. One of the superposition holograms. 12. The superposition hologram according to claim 6, wherein the second set of holograms has an f-value approximately equal to that of the first set of holograms.