JPH05241492A - Hologram and method for exposing photosensitive material for hologram - Google Patents

Abstract

PURPOSE:To obtain the hologram which effectively decreases flares at the time of image reconstruction and the process for production thereof by having a layer having the intermediate refractive index between the refractive index of a high-refractive index part and the refractive index of a low-refractive index part on at least one surface. CONSTITUTION:The refractive index of a surface layer 3 is the intermediate value of the respective refractive indices of the high-refractive index part 4 and the low-refractive index part 5 if monochromatic light is made incident from the surface 1 side and, therefore, the refractive index differences between the surface layer 3 and the high-refractive index part 4 and between the surface layer 3 and the low-refractive index part 5 decrease. The change in the incident angle and refractive angle at the boundaries thereof and the reflectivity decrease. The above-mentioned change in the incident angle and refraction angle and the reflectivity are smaller than the change in the incident angle and refraction angle and the reflectivity at the boundaries of the surface 2 and the low-refractive index part 5 as well as the surface 2 and the high-refractive index part 4 at the incidence on the surface 2 side and, therefore, the cause of scattering, i.e., the cause for the flares, is eventually decreased. Such decreases signifies that the dispersion of the light decreases when white light is made incident.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram in which flare light during reproduction is reduced and an exposure method for producing the hologram.

[0002]

2. Description of the Related Art A head-up display has recently been used as a method of displaying information to a driver or the like in an automobile. This is because the optical information projected from the information projecting means such as a liquid crystal display device is projected on a half mirror which is a combiner incorporated in the windshield of an automobile, etc. Is designed to be read.

Recently, as the above combiner, due to its simplicity as an optical element and the abundance of added functions,
Holograms are gaining attention. Since this holographic combiner can have not only a reflection function but also a lens function and the like, it is possible to diffract optical information in the driver's visual field direction or form an image at any position. Become.

FIG. 4 is a conceptual diagram showing the structure of such a vehicle-mounted HUD. Here, 31 is a driver's observation position, 32 is a holographic combiner, 33 is a light beam containing information, 34 is a lens system that is a collimator, 35 is a transmissive liquid crystal display element that is a display, and 36 is a halogen lamp or the like. Is a light source, 37 is a windshield, and 38 is a vehicle body.

The light emitted from the light source 36 passes through the transmissive liquid crystal display element 35 through the lens system 34, and the holographic combiner 32 provided on the windshield 37 of the vehicle.
It is irradiated on the vehicle and reflected (diffracted) to the driver at the observation position 31.
Is visible in.

In FIG. 5, if the holographic combiner 32 is provided with a lens function, it is possible to form a distant image on the display. In addition, the function of the lens system 4 which is the above collimator is changed to the holographic combiner 32.
You can also have it.

Such a holographic combiner is usually a reflection type hologram, and irradiates reference light from one surface of the photosensitive material surface of the hologram and object light from the other surface to form a diffraction grating. Particularly in the case of a phase hologram, these two laser beams interfere with each other to generate light and dark interference fringes in the hologram material, and the monomer is polymerized in the bright portion to become a polymer, and in the dark portion, the monomer is polymerized. Since polymerization does not occur, it becomes a portion having a low refractive index, and a diffraction grating is formed due to the difference in refractive index. A hologram of this type usually has its diffraction grating surface inclined with respect to the hologram material surface and is not parallel to the photosensitive material surface. For this reason,
Although it is a reflective type, it also has a transmissive property of transmitting the light outside the vehicle.

[0008]

Since the hologram as described above also has a transmission type property, white light or the like is incident on the inside of the vehicle from the outside of the vehicle. At this time, since the diffraction grating fringe is in contact with the surface of the photosensitive material, incident light is diffracted on the surface and causes so-called flare that appears as bright unevenness. With this, there will be multiple outside lights,
It seems to disperse, which is not desirable in appearance.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a diffraction grating having a layered structure consisting of a surface, an inclined high refractive index portion and a low refractive index portion inside. In the hologram formed with, a hologram having at least one surface thereof a layer having an intermediate refractive index between the refractive index of the high refractive index portion and the refractive index of the low refractive index portion, and the production thereof. It provides a method.

FIG. 1 shows a structural diagram of a diffraction grating fringe in a hologram produced by the exposure method according to the present invention. 1 and 2 are the surface of the hologram material, 4 and 5 are the high refractive index part and the low refractive index part of the hologram, respectively, and 3 is the surface layer on the 1 side. On the other hand, the surface portions 6 and 7 on the surface 2 side show that the low refractive index portion and the high refractive index portion are in contact with the hologram material surface. The refractive index of the surface layer 3 has an intermediate value between the refractive indexes of the high refractive index portion 4 and the low refractive index portion 5.

The difference in refractive index between the high refractive index portion and the low refractive index portion is usually about 0.02 to 0.10. However, the refractive index of the surface layer may be in the middle value.

[0012]

When the monochromatic light is incident from the surface 1 side, the surface layer 3
Has an intermediate value between the refractive index of the high refractive index portion and the refractive index of the low refractive index portion, the refractive index of the surface layer 3 and the high refractive index portion 4, and the refractive index of the surface layer 3 and the low refractive index portion 5. The difference becomes smaller, and the change in the incident angle and the refraction angle at the boundary and the reflectance become smaller. This is smaller than the change in the incident angle and the refraction angle at the boundary between the surface 2 and the low refractive index portion 5 and the boundary between the surface 2 and the high refractive index portion 4 and the reflectance at the incidence on the surface 2 side. That is, the cause of flare is reduced. This means that when white light is incident,
It also means that the dispersion of light is small.

[0013]

【Example】

Example 1 An optical system for producing the hologram of the present invention is shown in FIG. The hologram photosensitive material 18 here is a material that absorbs green light and thereby photopolymerizes. 8 has a wavelength of 514.5 nm
Is a laser device that oscillates the green laser beam 9 of, and is reflected by a mirror 10, divided by a beam splitter 11, and objective lenses 14, 1 by mirrors 12, 13.
Incident on 5. The shutters 16 and 17 control the timing of irradiating and non-irradiating the hologram photosensitive material 18 with the diffused laser beams 9a and 9b. The irradiation light from the objective lens 14 is object light, and in the case of producing a hologram for a combiner, the position of the objective lens 14 becomes the position of the display image. The irradiation light from the objective lens 15 is reference light, and the position of the objective lens 15 is the reproduction light source position.
When the shutters 16 and 17 are opened at the same time, the normal reflection hologram production method is performed, and the interference fringes of the diffused laser beams 9a and 9b are recorded on the hologram photosensitive material 18.

Here, first, only the shutter 16 is opened, and the shutter 17 is closed to obtain 1/100 of the total exposure time.
Then, the hologram photosensitive material 18 was previously irradiated with the laser light for about 1/10 of a time, and the entire surface layer of the hologram photosensitive material 18 on the object light side of the shutter 17 was polymerized. Then, the shutter 17 is immediately opened to form a normal reflection type diffraction grating. The exposure time for forming the diffraction grating is 9/10 to 99/100 of the total exposure time.
It becomes a degree.

In this way, a hologram having a cross sectional structure substantially as shown in FIG. 1 was obtained. When this hologram was used as a combiner for a head-up display for automobiles, a head-up display with less flare even when external light was incident was obtained.

The hologram material used here is a photopolymer material, and acrylic materials, polyvinylcarbazole and the like can be used. Further, dichromated gelatin is also possible.

Example 2 In Example 1, only the object light side of the hologram photosensitive material 18 was surface-polymerized, but in this Example, the hologram photosensitive material 1 was used.
The surface layers on both sides of No. 8 were polymerized. That is, first, the shutter 17 is closed and the shutter 16 is opened to set the total exposure time to 1
Exposure was performed for about / 100, then the shutter 17 was opened, the shutter 16 was closed, and exposure was performed for about 1/100 of the total exposure time. After alternately exposing three times in this way, the shutters 17 and 16 are both opened to perform normal exposure. Other conditions such as the material for exposure were the same as those in the above-mentioned embodiment. Alternate exposure is performed because the diffraction grating is not formed in the hologram photosensitive material, and the number of alternate exposures is not limited to three and can be appropriately adjusted.

Thus, a hologram having a cross-sectional structure substantially as shown in FIG. 1 and having surface layers 3 on both surfaces was obtained.

Example 3 A hologram photosensitive material having a photosensitive region in the wavelengths of green and blue was used, a diffraction grating was exposed and formed in green, and a surface layer was exposed in blue. In this case, it is necessary to add a blue optical component to the green optical component arrangement shown in FIG. That is, as shown in FIG. 3, the blue laser light 19 is made incident on the objective lens 20 and diffused, and the shutter 21 is installed behind it.

The exposure method was as follows. The shutters 16 and 17 are opened to start recording a normal diffraction grating, and at the same time, the blue shutter 22 is opened to irradiate the surface layer with blue light for 1/100 to 1/10 of the total exposure time with green. To polymerize. After a lapse of a predetermined time, 22 is closed. The shutters 16 and 17 are
Open as it is to continue the diffraction grating formation.

Before the exposure for forming the diffracted light with the green light, the blue light may be previously irradiated for 1/100 to 1/10 of the exposure time, or the blue irradiation may be started before the green dew. Alternatively, the green exposure time may be partially overlapped, and the front-back relation of the exposure is arbitrary.

As a result, a hologram almost similar to that of Example 1 was obtained.

Example 4 Another set of the blue irradiation objective lens and shutter shown in FIG. 3 was installed on the opposite side of the hologram 18, and the surface layers on both sides of the hologram photosensitive material were exposed in blue. The irradiation method and irradiation time were the same as in Example 2. The relationship between the exposure for forming the diffraction grating in green and the exposure for the surface layer in blue was the same as in Example 3.

As a result, a hologram almost similar to that of Example 2 was obtained.

[0025]

According to the present invention, a hologram in which flare during image reproduction is effectively reduced and a method for manufacturing the hologram can be obtained.

The present invention also has an effect on a transmission hologram. Also in this case, the surface layer on the external light side of the hologram may be polymerized. Further, in this case, it also has an effect of reducing dispersion for incident light.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a hologram of the present invention.

FIG. 2 is a conceptual diagram showing an optical arrangement when producing a hologram of the present invention.

FIG. 3 is a conceptual diagram showing another optical arrangement for producing the hologram of the present invention.

FIG. 4 is a conceptual diagram showing a vehicle head-up display.

[Explanation of symbols]

 1, 2 hologram surface 3 surface layer 4 high refractive index part 5 low refractive index part 6 boundary between low refractive index part and surface 7 boundary between high refractive index part and surface 8 laser device 9 green laser light 11, 12, 13 Mirror 11 Beam splitter 14,15 Objective lens 16,17 Shutter 9a Object light 9b Reference light 18 Hologram 19 Blue laser light 20 Objective lens 21 Shutter

Claims (3)

[Claims] 1. A hologram in which a diffraction grating is formed by a layer structure consisting of a high refractive index portion and a low refractive index portion which are inclined with respect to the surface, and at least one surface of which has a high refractive index portion and a low refractive index portion. A hologram having a layer having an intermediate refractive index between those of the refractive index portion. 2. The exposure method for producing a hologram according to claim 1, wherein at least one surface layer of the hologram photosensitive material surface is exposed when performing the exposure for forming a predetermined diffraction grating. Method of exposing photosensitive material for hologram. 3. A light ray having a wavelength substantially the same as that of an exposure light ray used for forming a diffraction grating is used as an exposure light ray for exposing the surface layer of the hologram photosensitive material surface. Item 2. A method for exposing a hologram photosensitive material according to item 2.