JPH09292527A - hologram - Google Patents

Abstract

(57) Abstract: To obtain a hologram in which even if the environmental temperature changes, the change in the fringe spacing is suppressed, and the change in the reproduction wavelength due to the temperature change is prevented. And a first fringe 1 and second fringe 7 forming an angle of the hologram surface and theta ₂ constituting the A hologram surface and theta ₁ angle, the first fringe 1 and second fringe 7
A hologram formed by a mesh structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram having excellent temperature characteristics which suppresses a change in reproduction wavelength due to a temperature change, and in particular, a vehicle mounted on a head-up display, a high mount stop lamp or the like in which an environmental temperature change is large. The present invention relates to a hologram suitable for use as a hologram optical element.

[0002]

2. Description of the Related Art Holograms are capable of reflecting or transmitting light incident at a predetermined angle at a desired angle, and thus have recently been used as an optical element used for a head-up display mounted on a vehicle or a high mount stop lamp. Proposed.

However, when the hologram is used in an environment where the temperature changes greatly such as in a vehicle, there are the following problems. That is, the thermal expansion or contraction of the material due to the temperature change changes the distance between the fringes formed on the material, so that the reproduction wavelength of the hologram changes. Therefore, for example, when the light emitted from the light source with a predetermined wavelength is diffracted toward the viewer through the hologram (reflection diffraction, transmission diffraction), the wavelength of the light visually recognized by the viewer deviates from the predetermined wavelength. Will end up. Further, in this case, not only the wavelength shift but also the display image distortion may occur.

As an example of the above problem, the case where a hologram is used as an optical element of a head-up display will be described. As the environmental temperature inside and outside the vehicle changes, the hologram material undergoes thermal expansion and contraction, the interval 2 between the fringes 11 of the hologram shown in FIG. 3 changes, and the reproduction wavelength changes.

The change in the reproduction wavelength is proportional to the change in the fringe distance 2, as shown in the following Bragg equation.

[0006]

[Equation 1]

Where n is the average refractive index of the hologram, θ
Is the incident angle, d is the fringe distance, Δd is the change in fringe distance, and Δλ is the change in reproduction wavelength. As a result, in a vehicle holographic head-up display, due to a change in ambient temperature, the matching of the wavelength with the display light source is deviated, and a desired display color cannot be obtained or the display image becomes dark. It was

[0008]

In order to reduce the wavelength change due to such temperature change, it has been proposed to use a material having a low coefficient of thermal expansion, such as a carbazole-based photopolymer, as the hologram material. .

In general, when selecting the hologram material, it is necessary to consider not only the temperature characteristics but also the exposure characteristics, the appearance characteristics, etc. depending on the application. Therefore, it is not always necessary to use the above-mentioned carbazole-based material considering only the temperature characteristic, and it is not sufficient to rely on the material for the conventional means for improving the temperature characteristic.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a hologram photosensitive material is irradiated with an object beam and a reference beam having a first wavelength and recorded. A hologram having a fringe and a second fringe recorded by irradiating a hologram photosensitive material with object light and reference light of a second wavelength, wherein the first fringe and the second fringe are not parallel to each other. , A first fringe and a second fringe form a mesh structure to provide a hologram.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a conceptual sectional view showing an example of the hologram of the present invention. The hologram 10 has a first fringe 1 and a second fringe 7. The two are not parallel to each other, the first fringe makes an angle of θ _{1 with} the hologram surface, and the second fringe makes an angle of θ _{2 with} the hologram surface. Therefore, the first hologram and the second hologram are different from each other. The angle is (θ ₁ −θ ₂ ). Thus, the hologram 10 has a mesh structure formed of the first fringe 1 and the second fringe 7.

Such a hologram is produced, for example, by the method shown in FIG. The reference light 5 and the object light 6 having the first wavelength are applied to the hologram photosensitive material 3 held on the transparent substrate 4 such as a glass plate at angles of θ ₁₁ and θ ₁₂ , respectively. On the other hand, the reference light 8 and the object light 9 having the second wavelength are applied to the hologram photosensitive material 3 held on the transparent substrate 4 such as the glass plate described above at angles of θ ₂₁ and θ ₂₂ , respectively.

At this time, the object light of the first wavelength and the reference light are irradiated from both sides of the hologram photosensitive material,
The object light of the second wavelength and the reference light are emitted from one surface side of the hologram photosensitive material. In this way, the hologram photosensitive material is subjected to multiple exposure by the light of the first and second wavelengths,
A hologram is created that has fringes that form a mesh structure inside.

The holographic light-sensitive material used in the present invention for improving the temperature characteristics is not limited to the carbazole-based material as in the conventional case, and for example, an acrylic-based photopolymer, a silver salt, a dichromated gelatin, an optical material. Various resists and the like can be used depending on the application.

Further, in the present invention, various kinds of object light can be used depending on the image displayed using the hologram. For example, when a flat or curved fringe is simply formed to record a specific shape image of an object (the hologram light-sensitive material is irradiated with the reflected light of the light irradiated to the object having a specific shape image as the object light). In addition to the reference light, the light illuminating the hologram photosensitive material without passing through an object (excluding optical elements such as mirrors and lenses) like the reference light is also included in the object light for convenience.

Most preferably, the angle formed by the first fringe and the second fringe is 90 °. This is because the two are orthogonal to each other, so that the change in the fringe spacing due to the thermal expansion or thermal contraction of the material can be preferably prevented.

On the other hand, depending on the application of the hologram, the presence of the second fringe orthogonal to the first fringe may hinder its use. In that case, the angle between the two should be changed from 90 ° as much as possible while keeping a balance with the degree of change in the fringe distance.

The case where the hologram of the present invention is used as a combiner for a head-up display will be described. The first flange for diffracting the light from the light source toward the observer such as the driver corresponds to the wavelength of the light emitted from the light source. On the other hand, since the hologram has a second fringe that forms a mesh structure with the first flange, the light emitted from the light source is transmitted and diffracted by this second flange, which causes a problem in appearance. May occur. On the contrary, the light incident from the outside of the vehicle toward the inside of the vehicle may become unnecessary transmitted diffracted light due to the second flange.

Therefore, when the hologram of the present invention is used as such a combiner, it is preferable that the wavelength of the light diffracted by the second fringe is outside the visible light range. That is, even if the light from the outside of the vehicle is transmitted and diffracted by the second fringe and enters the inside of the vehicle, if the light has a wavelength outside the visible light region, the light is visually recognized by the observer. Because there is nothing. The same applies to the diffracted light transmitted from the inside of the vehicle to the outside of the vehicle.

Further, as one of the specifications of the head-up display, there is one that hides a portion provided with a hologram from the outside of the vehicle. As described above, when the concealing means for the hologram is provided and the light corresponding to the second flange for preventing the change in the flange interval is configured not to be unnecessary diffracted light, the second flange The corresponding wavelength may be the same as or different from the wavelength corresponding to the first flange, or may be a wavelength in the visible light region, and there is no particular limitation.

In the above example, for convenience, the first flange is used as a flange and the second flange is used as a flange for preventing a change in flange spacing. That is, as shown in the figure, the first flange having the characteristic of the reflection hologram is used for display, and the second flange having the characteristic of the transmission hologram is consequently used as the flange for preventing the change of the flange spacing. I am trying. On the contrary, the second flange having the characteristics of the transmission hologram is used as a flange for displaying, and the second flange having the characteristics of the reflection hologram is used as a flange for preventing a change in flange spacing. Of course it is possible.

[0023]

Embodiments of the present invention will be described below.

A hologram was prepared by using the method shown in FIG. At this time, a dye laser having a wavelength of 555 nm with θ ₁₁ = 40 ° and θ ₁₂ = 60 ° was used, and θ ₂₁ = 0 ° and θ ₂₂ = 1.
A Kr laser having a wavelength of 647 nm at 4.8 ° was made incident on each photosensitive material made of an acrylic photopolymer for multiple exposure. The hologram thus created is
As shown in FIG. 1, the first fringe 1 and the second fringe 7 are orthogonal holograms in which θ ₁ = 4.9 ° and θ ₂ = 85.1 °.

The temperature characteristic of this hologram was compared with that of a conventional hologram. 10 conventional holograms
While the reproduction wavelength changes by about 20 nm with respect to the temperature change of 0 ° C., the hologram according to the present invention can suppress the change of the reproduction wavelength by about several nm with respect to the temperature change of 100 ° C.

The hologram thus obtained was mounted on a vehicle-mounted holographic head-up display, and as a result, the brightness change of the display image was small and the effectiveness of the present invention was shown.

[0027]

According to the present invention, since the fringes recorded inside form a lattice-like or mesh-like structure, the fringe spacing is less susceptible to thermal changes, and the wavelength of the light to be reproduced is reduced. A hologram with reduced variation can be obtained.

In particular, when the hologram is used in an environment in which the temperature of a vehicle changes with temperature, such as when a hologram is used in a vehicle head-up display, etc., the hologram of the present invention can be used to display a display image due to the temperature change of the environment. It is possible to reduce changes in brightness and the like.

[Brief description of drawings]

FIG. 1 is a conceptual sectional view showing an example of a hologram of the present invention.

FIG. 2 is a schematic sectional view showing an example of a method for producing a hologram of the present invention.

FIG. 3 is a conceptual sectional view showing an example of a conventional hologram.

[Explanation of symbols]

 1: first fringe 2: fringe spacing 3: hologram photosensitive material 4: transparent substrate 5: reference light for recording first fringe 6: object light for recording first fringe 7: second Fringe 8: Reference light for recording second fringe 9: Object light for recording second fringe 10: Hologram

Claims (5)

[Claims] 1. A first fringe recorded by irradiating a hologram photosensitive material with object light and reference light of a first wavelength, and irradiating a hologram photosensitive material with object light and reference light of a second wavelength. A hologram having a recorded second fringe, wherein the first fringe and the second fringe are not parallel to each other, and the first fringe and the second fringe form a mesh structure. Characteristic hologram. 2. The hologram according to claim 1, wherein the first fringe and the second fringe are substantially orthogonal to each other, and the first fringe and the second fringe form a lattice structure. . 3. The hologram according to claim 1 or 2, wherein the first wavelength and the second wavelength are different. 4. The hologram according to claim 3, wherein the second wavelength is a wavelength outside the visible light region. 5. The hologram according to claim 1, wherein the first wavelength and the second wavelength are the same.