JP2000132073A - Holographic display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a holographic display device where the blur of a display picture is restrained. SOLUTION: This display device is equipped with an information display source 1 emitting information to be displayed as a laser beam 3a, and a hologram optical device 10 diffracting the laser beam 3a so that an observer 11 may visually confirm the information. The display source 1 is provided with at least a laser beam source 2, a means 4 for deflecting the laser beam emitted from the laser beam source 2 and a diffusion type hologram 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a holographic display device, and more particularly to a holographic display device having improved chromatic aberration.

[0002]

2. Description of the Related Art With the recent development of hologram materials and laser technology, products using holograms are increasing. For example, a hologram is used as an optical element in a holographic display device that diffracts light containing information and displays the information to an observer, an optical scanner of a barcode reading device, and the like. As a display device for displaying information to a driver of a vehicle such as an automobile, there is a head-up display (hereinafter, referred to as a HUD).

The HUD displays optical information projected from an information display source such as a liquid crystal display device on a combiner including a hologram and a half mirror incorporated in a windshield of an automobile, etc. The information can be read without moving the viewpoint. In addition, forgery prevention marks on ID cards and credit cards, decorative holograms, hologram calendars, and the like use holograms on which images are recorded.

[0004] The hologram has advantages such as non-specular reflectivity in which the incident angle and the diffraction angle can be made different, a magnification effect in which distantly magnified display is possible, and wavelength selectivity in which high diffraction efficiency and high transmittance can be compatible. Therefore, it is used as an optical element for a display device such as a HUD.

[0005]

However, since the hologram is a kind of diffraction grating, it has a wavelength dependence such that the diffraction angle varies depending on the wavelength of light. For this reason, in a holographic display device using a light source having a wide half width of the emission wavelength, there is a problem that chromatic aberration occurs and a displayed image is blurred. In particular, in the case of a non-specular reflection type hologram or a hologram having a magnification, since a diffracted image is displaced in a direction perpendicular to the optical axis, a blur of a display image is increased.

FIG. 4 is a conceptual diagram showing an example of a conventional HUD. This is a small separate type HUD that is installed on the dashboard of a car or the like. Light 23 including information emitted from an information display source including a fluorescent display tube (VFD) 20 built in the HUD main body 13 is diffracted in the direction of the observer 11 by the hologram combiner 10 and visually recognized as a display image 12. You. The hologram combiner 10 is rotatably supported on the HUD body 13 by a support portion 14 in the vicinity of the lower side thereof. A leg 15 whose direction and inclination can be adjusted is arranged on the bottom surface of the HUD body 13 and is fixed on a dashboard or the like. The leg 15 is detachable and used as needed.

Here, light 23 containing information is transmitted to combiner 1
The incident angle with respect to the normal to 0 is θ ₁ , the diffracted angle is θ ₂ , the distance from the VFD 20 to the combiner 10 is r ₁ , and the distance from the combiner 10 to the display image 12 is r ₂ . As described above, in the case of non-specular reflection (θ ₁ ≠ θ
_{If 2)} or a hologram has a magnification _{(r 2 / r 1> 1} )
Chromatic aberration becomes remarkable. When the position of the observer 11 is on the optical axis, the chromatic aberration is relatively small. However, when the eyes move up, down, left, and right, and become distant from the optical axis, the chromatic aberration further increases, and the image blur becomes remarkable.

In order to improve chromatic aberration, a method using second and third holograms for correcting aberration is well known. However, the use of a plurality of holograms raises the cost and increases the size of the entire optical system.

In order to improve chromatic aberration, holograms having two different characteristics are subjected to multiple exposure, the half-width of the diffracted light wavelength at the periphery of the hologram is reduced, and the diffraction wavelength and efficiency are gradually changed. (JP-A-8-234022, JP-A-9-81020, and JP-A-10-78561). However, production of such a hologram is generally difficult, and there has been a problem that it is difficult to stably obtain complicated characteristics. Further, there is a problem that the manufacturing process becomes complicated and the cost increases.

[0010] Since the HUD observes the outside scene and the display image in a superimposed manner, a display device with high luminance and high contrast is required to obtain a display image with good visibility. Conventionally used displays are mainly a self-luminous type VFD and a light receiving type liquid crystal display device (LCD). VFDs include those in which phosphors are arranged in a segment shape and those in which phosphors are arranged in a dot matrix along with a drive circuit on a semiconductor substrate. Very high luminance is obtained for green. In addition, a high contrast can be obtained because of the self-luminous type.

However, the half width of the emission wavelength of the phosphor is 1
Since it is very wide at about 00 nm, there is a problem of the chromatic aberration as described above, and there has been a problem that the angle difference and the magnification between the incidence and the diffraction in the non-specular reflection cannot be increased. Further, since the hologram has a half-width of the diffracted light wavelength of about 20 nm, there is a problem that light having a wavelength other than the half-width is not used.

On the other hand, an LCD is used in combination with a backlight. The segment type LCD has a relatively high transmittance and contrast and is easy to obtain a bright and highly visible display image, but has a limited application because it can only display a fixed pattern. The dot matrix type allows the display content to be changed freely, but the transmittance and contrast are low, so the HU
When used as an information display source for D, there is a problem that the quality of a displayed image is not sufficient.

The backlight includes a broadband type such as a halogen lamp and a bright line type such as a cathode ray tube. Since the emission wavelength of the broadband type is a continuous spectrum, in order to use it in combination with a hologram, a narrow-band interference filter is required, which increases the cost and reduces the light utilization rate. In the case of the bright line type, since the half width of the emission wavelength is as narrow as several nm, the compatibility with the hologram is good, but the luminance cannot be sufficiently modulated. Further, even when the hologram has a half-value width of several nm, if the magnification of the hologram or the angle difference between the incidence of non-specular reflection and the diffraction increases, the displayed image is blurred. As described above, each of the light emission characteristics of the conventional display and light source has advantages and disadvantages, and is not optimal as an information display source of a holographic display device.

Further, it has been proposed to display information by sweeping a laser beam onto a combiner of a hologram recording an image of a plane board (Japanese Patent Application Laid-Open Nos. 62-5288 and 63-227823). However, since the hologram combiner itself has a diffusive property, there is a problem in that a display image is blurred when a laser beam is directly projected onto the combiner.
An object of the present invention is to provide a holographic display device that solves the problems of the prior art.

[0015]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has an information display source having a laser light source for emitting information to be displayed as light, and an observer which diffracts the light to obtain an information. A holographic display device provided with a holographic optical element for visually recognizing information, wherein the information display source has at least a laser light source, a laser beam deflecting unit, and a diffusion hologram. I do.

Further, the present invention provides the holographic display device, wherein a volume phase hologram is used as the diffusion hologram. Further, the present invention provides the holographic display device, wherein a semiconductor laser is used as the laser light source and a photopolymer is used as the volume phase hologram.

The present invention improves the chromatic aberration in the holographic display device described above, realizes an information display source optimal for the holographic display device, and reduces the visibility of an image displayed on the hologram combiner due to blur. Can be suppressed.

[0018]

Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a schematic diagram of an information display source in the holographic display device of the present invention. The information display source 1 has a laser light source 2, a laser beam deflecting means 4 and a diffusion hologram 5 as main components. The laser light 3 emitted from the laser light source 2 is scanned in the horizontal (x) and vertical (y) directions by the laser light deflecting means 4 based on a control signal from the control device 6. Further, it is very preferable to provide at least one means for modulating the laser light from the laser light source in the information display source.

The laser light modulation means controls on / off of the laser light or gradation control of the intensity of the laser light so that information to be displayed can be drawn on the diffusion hologram 5, and color display is performed as described later. In some cases, RGB colors can be modulated and combined to display various colors. Although not shown, an optical system for condensing the laser beam 3 on the diffusion hologram 5 may be used as necessary.

Since the diffusion hologram 5 diffracts the irradiated laser beam 3 diffusively, the surface of the diffusion hologram 5 functions as a light emitting surface of a display, and is regarded as one display device or information display source as a whole. be able to. By irradiating this diffused light to a hologram combiner or the like, H
A holographic display device such as a UD can be configured. Since the laser light has high monochromaticity and an extremely narrow half-width of the oscillation wavelength, a holographic display device using the information display source of the present invention can obtain a display image without blur due to chromatic aberration.

Further, since the drawing by the laser beam on the diffusion type hologram is projected onto a normal hologram combiner having no diffusivity, a display image with good visibility without image blur can be obtained. Further, if the diffraction wavelength of the hologram is made to coincide with the oscillation wavelength of the semiconductor laser (LD), the light utilization factor becomes extremely high. The holographic display device of the present invention can exhibit its features more particularly when the display magnification is large or when the angle difference between the incidence of non-specular reflection and the diffraction is large. Further, if the half width of the diffraction wavelength of the hologram combiner is widened, a holographic display device in which the observation position of the display image of the combiner is widened can be obtained.

Since the laser light source is desired to be small in size for the light source of the HUD, an LD can be preferably used. A red LD having an oscillation wavelength of 630 nm or 670 nm can be exemplified. GaN-based or ZnSe-based blue or green LD
Is expected to be put to practical use in the near future, and is considered to be preferable as a laser light source used in the present invention. Also, LD
The second harmonic laser light (for example, blue laser light having an oscillation wavelength of 430 nm) and the second harmonic of an LD-excited solid-state laser device (green laser light having an oscillation wavelength of 532 nm) are also relatively small and can be used. In applications where a large light source can be used in a holographic display device other than the HUD,
Various gas laser devices, solid-state laser devices, and dye laser devices can be used.

FIG. 2 shows an example of a single color display, but a color display can also be performed by combining laser beams of the above-described wavelengths.
For example, after the RGB laser light is converted into a coaxial beam light by a dichroic mirror or the like, information to be displayed may be drawn on a diffusion hologram (a color diffusion hologram corresponding to RGB) as in FIG. In order to control the RGB laser light intensity independently, it is preferable that the laser light modulating means is installed at a position before the three light beams are made coaxial.

Incidentally, the LD has a characteristic that the oscillation wavelength changes depending on the environmental temperature. When the device is used in an environment where the temperature changes drastically, temperature control may be performed. The laser light modulating means may be of an internal modulation type in which current control is performed based on a control signal from the control device 6 to modulate the light output of the LD, or an acousto-optic element provided separately with laser light emitted from a laser light source. For example, an external modulation method that modulates with an external device may be used. Any system can be used as long as it can be modulated at a required response speed.

The laser beam deflecting means scans the laser beam in the x and y directions based on a control signal from the control device 6. Examples of the method include a galvano mirror, a polygon mirror, and a combination thereof. Further, by moving the imaging lens by an actuator, the laser light is converted into x,
There is also a method of scanning in the y direction. If one screen is scanned at a speed of 20 to 30 images per second, that is, if one image is scanned at 1/30 to 1/20 second, the scanned image becomes 1 due to the afterimage characteristics of human vision. This is visually recognized as a single image. When it is possible to understand how the laser light is sequentially scanned, the scanning speed may be reduced.

As a new device, there is a device in which an actuator and a micro mirror are integrated on a semiconductor substrate by utilizing a micromachine technology. Such a device can also be used as a means for deflecting laser light. As a means for deflecting the laser light, a means in which a galvanometer mirror and a polygon mirror are operated by a control signal from a combination control device is preferable from the viewpoint of quickness and stability of scanning.

The scanning method of the laser beam may be appropriately selected from methods such as interlaced scanning (interlaced scanning) and progressive scanning (progressive scanning) used in television scanning and the like. These methods are suitable for performing dot matrix type display. In the case of displaying only alphanumeric characters and simple line drawings, laser light may be scanned by a method such as an xy plotter.

There are a reflection type and a transmission type as the type of the diffusion type hologram, which can be appropriately selected depending on the layout of the optical system. When the diffusion hologram is provided with directivity, the direction of diffusion can be controlled and guided only in the direction of the hologram combiner, and light can be effectively used, which is preferable.

FIG. 3 is a schematic view showing an example of a method for manufacturing a diffusion hologram. The laser light beam from the laser device is split into two by a half mirror (not shown) or the like, and then diffused by an objective lens or the like like laser light 33 and laser light 34 and used for exposure. If the diffused light transmitted by irradiating the diffuser plate 32 with one laser beam 34 and the other laser beam 33 interfere with each other and are recorded on the hologram material 31, a light diffusion hologram can be obtained. Directivity can be controlled by the position and size of the diffusion plate 32 with respect to the hologram material 31.

Although not shown, as another method, there is a method in which a hologram material and a diffuse reflector are juxtaposed and light is irradiated from the hologram material side. The recording is performed by causing the irradiated light to interfere with the diffused light that has once passed through the hologram material and has been reflected back by the diffuse reflector. When a retroreflective film is used as a diffuse reflector, a hologram with higher directivity can be produced.

Therefore, it is preferable to use a reflection type hologram produced by using a retroreflective film as the diffusive hologram because it has strong light directivity and high light use efficiency. A bright display image can be obtained by using this hologram.

The type of the hologram used in the present invention is preferably a volume phase hologram. Since the volume phase hologram has good wavelength selectivity for a specific wavelength and high diffraction efficiency, when the volume phase hologram is used as a diffusion hologram of an information display source, a display image has high brightness and is sharp. In the case of a transmission type, a hologram having good transparency is preferable. In the reflection type, an emboss type hologram can be used. As a hologram material, a photopolymer, gelatin dichromate, a silver salt-based material, a photoresist, or the like can be used. From the viewpoints of durability and transparency, a volume phase hologram using a photopolymer is more preferable.

In the case of a hologram using a photopolymer, the diffraction wavelength changes to the longer wavelength side due to thermal expansion.
The effects of these temperature changes can be compensated for by making the oscillation wavelength longer based on the temperature characteristics of the LD described above. Therefore, it is preferable to use an LD as a laser light source and use a photopolymer as a hologram material.
Examples of the material of the photopolymer used here include acrylic ones and polyvinyl carbazole.

Examples of the form of the diffusion hologram include a form in which the hologram produced as described above is attached to a transparent substrate made of resin, glass, or the like. Further, in consideration of protection of the hologram, a transparent protective cover may be provided. In particular, for a material that is sensitive to humidity such as gelatin dichromate, it is preferable to seal the hologram between the transparent cover and the transparent substrate.

When the chromatic aberration of the holographic display device is improved by the present invention, the remaining display image is deteriorated by blurring (monochromatic blurring) due to the lens aberration of the hologram combiner.
And image distortion. The lens aberration can be improved by the exposure condition of the hologram combiner, but may have a trade-off relationship with the image distortion. In this case, the pattern to be drawn on the diffusion hologram by the information display source may be modified in advance so that the lens aberration is optimized first and the image distortion is corrected. For example, when the display image is distorted in an upwardly convex shape, it may be drawn in advance in a downwardly convex shape.

[0036]

FIG. 1 is a schematic diagram showing a holographic display device according to the present embodiment. The laser light 3a emitted from the information display source 1 is diffracted by the hologram combiner 10 and guided to the observer 11. A display image 12 free from blur due to chromatic aberration was obtained as this image.

The information display source 1 is an LD as the laser light source 2
And a deflecting means 4 for laser light and a diffusion hologram 5. LD is red L of oscillation wavelength 630nm band
D was used, and light modulation was performed by controlling the current of the LD. As the laser beam deflecting means 4, a combination of a polygon mirror (scanning in the x direction) and a galvano mirror (scanning in the y direction) was used. The diffusion hologram 5 was exposed and manufactured using an optical system as shown in FIG. 3 using light having a wavelength of 647 nm of a Kr laser device. An acrylic photopolymer was used as the material of the hologram. In addition, the code | symbol 1 without description
3, 14 and the like mean the same as those in FIG.

[0038]

According to the present invention, a holographic display device in which chromatic aberration is improved and display image blur is small can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a holographic display device of an embodiment.

FIG. 2 is a schematic diagram of an information display source in the holographic display device of the present invention.

FIG. 3 is a schematic view illustrating an example of a method for manufacturing a diffusion hologram.

FIG. 4 is a conceptual diagram showing an example of a conventional HUD.

[Explanation of symbols]

 1: information display source 2: laser light source 3, 3a: laser beam 4: laser beam deflecting means 5: diffusion hologram 6, 6a: control device 10: combiner 11: observer 12: display image 13: HUD main unit 14 : Supporting part 15: Leg part 20: Fluorescent display tube (VFD) 23: Light containing information 31: Hologram material 32: Diffusion plate 33, 34: Laser light

Claims (3)

[Claims] 1. A holographic display device comprising: an information display source having a laser light source that emits information to be displayed as light; and a hologram optical element that diffracts the light to allow an observer to visually recognize the information. A holographic display device comprising: a display source having at least a laser light source, a laser beam deflecting unit, and a diffusion hologram. 2. The holographic display device according to claim 1, wherein a volume phase hologram is used as the diffusion hologram. 3. The holographic display device according to claim 2, wherein a semiconductor laser is used as the laser light source, and a photopolymer is used as the volume phase hologram.