JPS63246781A - Method and device for reproduction hologram - Google Patents

Abstract

PURPOSE:To permit obtaining of a sharp reproduced image by using a white light source by projecting white light on a Lippmann hologram and projecting the diffracted light from the Lippmann hologram as illumination light for reproduction to a hologram for reproduction. CONSTITUTION:The reconstructed image is obtd. by projecting the diffracted light from the Lippmann hologram 1 on the hologram 2 for reconstruction. More specifically, the white light from a white light source 3 is condensed by an optical system 4 to form the illumination light L1 which is projected on the Lippmann hologram 1. The diffracted light thereof is utilized as the illumination light L2 for reconstruction. The stereoscopic hologram image is obtd. when the hologram 2 for reconstruction is observed for a visual point 5a if said hologram is of a transmission type and when the hologram is observed from a visual point 5b if said hologram is of a reflection type. The sharp reconstructed image is thus obtd. in spite of illuminating the hologram with the white light when the reconstruction of the stereoscopic hologram image is executed by utilizing the Lippmann hologram 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for reproducing a hologram, and particularly to a method and apparatus for reproducing a hologram for obtaining a clear reproduced image using a white light source.

[Prior Art] Holography is an extremely effective technology for recording and reproducing three-dimensional images, and holograms made using this technology are widely used as three-dimensional displays. Conventionally, laser light was used to record and reproduce such holograms, but in recent years, laser light has been used only for recording.
A white light reproduction type hologram, in which reproduction is performed using white light, has been developed.

Since such white light reproduction type holograms do not require a laser during reproduction, they are beginning to be used in a wide range of fields as three-dimensional displays.

[Problem that the invention seeks to solve]

As mentioned above, white light reproduction type holograms have the advantage of not requiring laser light for reproduction and can be used for a wide variety of purposes, but compared to laser beam reproduction type holograms, they cannot be reproduced clearly. There is a problem that an image cannot be obtained. In other words, normal white light contains light of various wavelengths, especially in the part far from the hologram recording surface.
The chromatic dispersion of the diffracted light that reproduces the image increases, resulting in blur. Therefore, when an object with depth is recorded, only an overall unclear reproduced image is obtained.

In order to solve this problem of white light reproduction type holograms, attempts have been made to observe the diffracted light from the hologram through a transmission type diffraction grating and compensate for the wavelength dispersion of the diffracted light. However, it is difficult to perform sufficient compensation, and a sufficiently clear reconstructed image cannot be obtained. Also,
When observing through a transmission type diffraction grating in this way, the diffraction efficiency of the aperture grating has a limit, so the reproduced image becomes dark.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a hologram reproducing method and a reproducing apparatus that can obtain a clear reproduced image even when illuminated with white light.

[Means for solving problems]

The first feature of the present invention is a hologram reproduction method that uses white light to reproduce a reproduction hologram in which a three-dimensional image is recorded. The hologram for reproduction is irradiated with the illumination light to obtain a reproduced image,
The key point is that a clear reproduced image can be obtained even when illuminated with white light.

A second feature of the present invention is that a hologram reproduction device includes a reproduction hologram on which a three-dimensional image is recorded, a white light source for illuminating the reproduction hologram, and a limited light source that receives light from the white light source. A Lippmann hologram that emits only light in the wavelength range as diffracted light and irradiates it to the reproduction hologram is installed, and the reproduction image is formed by the diffracted light from the reproduction hologram, so that it is clear even when illuminated with white light. The main point is that it is possible to obtain a reproduced image.

[Function] Fig. 1 shows the basic configuration of the present invention. The characteristic component of the present invention is the Lippmann hologram 1. The diffracted light from this Lippmann hologram 1 is converted into a reproduction hologram 2.
A reconstructed image is obtained by irradiating the That is, the white light from the white light source 3 is collected by the optical system 4 as illumination light L1,
The Lippmann hologram 1 is irradiated with this light, and the diffracted light is used as the reproduction illumination light L2. If the reproduction hologram 2 is of a transmission type, a three-dimensional hologram image can be obtained by observing it from the viewpoint 5a, and if it is a reflection type, from the viewpoint 5b. In this way, when a hologram stereoscopic image is reproduced using the Lippmann hologram 2, a clear reproduced image can be obtained even when illuminated with white light. This is explained by the following two reasons.

The first reason is that even if the illumination light L1 is white light, the reproduced illumination light L2 diffracted from the Lippmann hologram 1 becomes close to monochromatic light with a narrow wavelength range. This is explained by Bragg's reflection condition. Now, if the interval between the interference fringes of the Lippmann hologram 1 is dl and the angle of incidence of the illumination light L1 with respect to this interference fringe is θ, then the wavelength λ of the first-order diffracted light from the Lippmann hologram 1 is expressed as λ-2dsinθ (1) Ru.

That is, the reproduction illumination light L2 is composed of light having a wavelength that satisfies the above equation. In reality, completely monochromatic light as shown in the above formula cannot be obtained due to chromatic dispersion, and the light has a certain wavelength width, but compared to the white light of illumination light L1, the reproduced illumination light L2 is extremely It becomes light with a narrow wavelength range. Therefore, a clear reproduced image can be obtained even when illuminated with white light.

The second reason is that if the Lippmann hologram 1 is formed under predetermined conditions, it is possible to compensate for the chromatic dispersion of the reproduction illumination light L2. As described above, the reproduction illumination light L2 is not completely monochromatic light. When the reproduction hologram 2 is irradiated with light of such various wavelengths from the same direction, the diffracted light will go in various directions depending on the wavelength. Therefore, chromatic dispersion occurs and the reproduced image becomes blurred. However, since the diffracted light from the Lippmann hologram 1 goes in different directions depending on the wavelength, the reproduction illumination light L2 is directed toward the reproduction hologram 2.
will be incident at different angles for each wavelength.

Therefore, by appropriately setting the incident angle for each wavelength so that the final diffracted light from the reproduction hologram 2 does not have wavelength dependence, it is possible to compensate for chromatic dispersion.

The conditions for compensating for this chromatic dispersion will be explained in detail below. Now, the Lippmann hologram 1 is the second one.
It shall be formed as shown in the figure. That is, light of wavelength λ is applied to the photosensitive original plate 1' at an incident angle θ. 1 (corresponding to the object beam) and an incident angle θ, 1 (corresponding to the reference beam), and the interference fringes thereof are recorded to form the Lippmann hologram 1.

When the Lippmann hologram 1 formed in this way is illuminated with light of wavelength λ at an incident angle θc1 as shown in FIG. ) % Formula % If the lighting is as follows, equation (2) becomes the following equation.

On the other hand, it is assumed that the reproduction hologram 2 is formed as shown in FIG. That is, the wavelength λ is applied to the photosensitive original plate 2'.
The object light with incident angle θ. 2, and a reference beam of the same wavelength λ is irradiated at an incident angle θr2, and the interference fringes of both are recorded and used as a reproduction hologram 2. When the reproduction hologram 2 thus formed is illuminated with reproduction light of wavelength λ at an incident angle θc2 as shown in FIG.
The output angle θ12 of the first-order diffracted light from the reproduction hologram 2 is expressed by equation (5).

Now, θo2−θ. 1(B) The reproduction hologram 2 is formed so that θr2−θrl (7), and when the first-order diffracted light of the Lippmann hologram 1 is used as the reproduction illumination light of the reproduction hologram 2, θ. 2-θ,,
Assuming that the optical system is arranged so as to satisfy the condition (8), the equation (5) becomes the following equation.

−5inθol (9) Therefore, θ1□−θ. 1(10), and the diffraction angle θI2 of the first-order diffracted light from the reproduction hologram 2 loses the wavelength dependence of the reproduction illumination light, and chromatic dispersion is compensated.

〔Example〕

Hereinafter, the present invention will be explained in detail based on some examples.

Example 1 First, a Lippmann hologram 1 was produced based on the principle shown in FIG. A glass dry plate coated with dichromate gelatin was used as the original photosensitive plate 1' which is the basis of the Lippmann hologram 1.

In addition to the above, a silver salt photosensitive material, a photopolymer, etc. may be used as the photosensitive original plate 1'. As a light source, the wavelength is 488n.
m using parallel light from an Ar laser with an incident angle θ. 1
-o@, θ, 1-135@, and irradiated this photosensitive original plate. After exposure, a predetermined development process was performed to produce Lippmann hologram 1.

Next, a reproduction hologram 2 was produced based on the principle shown in FIG. The same photosensitive original plate 2' and light source as the source of the reproduction hologram 2 were used for producing the Lippmann hologram 1. Therefore, the reference light used for producing this reproduction hologram has a wavefront that is equivalent or conjugate to the reference light used for producing the above-mentioned Tubman hologram. As shown in FIG. 6, reference light L3 was irradiated onto the subject 6 from the opposite side to form a reflective Fresnel hologram. The reference light L3 is a parallel light beam, and the incident angle θr2''
It was set to 135°. Also, the average incident angle θ of the object light L4 from the subject 6. 2-0° (this allows the above equation (
0), the conditions of (7) are satisfied). In addition, the subject 6 and the photosensitive original plate 2 that constitutes the reproduction hologram
The distance between the photosensitive original plate 2' and the photoresist plate 2' was 150 mm.In addition to the photosensitive original plate 2', a relief hologram recorded using a photoresist or the like, or a copy thereof, can also be used.

The Lippmann hologram 1 and reproduction hologram 2 produced as described above were arranged as shown in FIG. 1, and the holograms were reproduced. - The Lippmann hologram 1 and the reproduction hologram 2 are arranged in parallel as shown in FIG. 1 (thereby, the condition of the above-mentioned equation (8) is satisfied).

A spotlight with a tungsten lamp is used as the light source 3, and the illumination light from the light source 3 is collimated by the optical system 4 to illuminate the Lippmann hologram 1 at an incident angle θcl''°. The reproduction hologram 2 was illuminated with the -order diffracted light from the hologram 2, and a clear green-blue reproduced image of the object was obtained when observed from the viewpoint 5b. Lippmann hologram 1 is
Because the diffraction efficiency was higher than that of a diffraction grating, a bright reconstructed image was obtained. Note that when the reproduction hologram 2 was simply illuminated with a spotlight, the obtained reproduced image of the object was unclear and it was difficult to grasp the detailed shape.

In addition, the light source 3 for reproduction includes sunlight, mercury lamp, and L.
Although an ED or the like can be used, it is generally preferable to use a white point light source. Further, in FIG. 1, an optical system may be provided between the Lippmann hologram 1 and the reproduction hologram 2 to control the optical path of L2.

Example 2 Lippmann hologram 1 was produced in the same manner as in Example 1. For the reproduction hologram 2, an 8E56HD plate made by Agfagewald, which is suitable for transmission holograms, was used as the original photosensitive master plate 2, and the light source was an A light source with a wavelength of 488 nm, as in the production of Lippmann hologram 1.
An r+ laser was used. As shown in FIG. 7, reference light L3 was irradiated from the same side as the subject 6 to form a transmission type Fresnel hologram. The reference light L3 was a parallel light beam and had an incident angle θ of 2-45°. In addition, the object light L from the subject 6
The average angle of incidence θ of 4. 2-0 @ closed. Note that the distance between the subject 6 and the photosensitive original plate 2'' was 200 mm.

The Lippmann hologram 1 and reproduction hologram 2 produced as described above were arranged as shown in FIG. 1, and the holograms were reproduced. A spotlight is used as the light source 3, and the illumination light from this light source 3 is collimated by an optical system 4 to illuminate the Lippmann hologram 1, and the -order diffracted light from this illuminates the reproduction hologram 2, which is observed from the viewpoint 5a. As a result, a clear green-blue reconstructed image of the subject was obtained. Note that when the reproduction hologram 2 was simply illuminated with a spotlight, the obtained reproduced image of the object was extremely unclear and the shape could not be grasped at all.

Example 3 In this example, an image hologram is used as the reproduction hologram 2. That is, as shown in FIG. 8, an optical system 7 is provided between the subject 6 and the photosensitive original plate 2.
An image of a subject 6 is formed on a photosensitive original plate 2', and a reproduction hologram 2 is produced. Other conditions are the same as in Example 2.

The reproduced image of the obtained image hologram was extremely clear and completely free of blur.

Example 4 This example is slightly different from the previous three examples. That is, all the above-mentioned embodiments are based on formula (3).

Although various conditions were set to satisfy conditions (6), (7), and (8), in the case of this example, similar results were obtained under conditions different from these. .

First, when producing Lippmann hologram 1, θr1≠
180°, θo1≠45@, and when producing the reproduction hologram 2, θr2≠45@ or 135@, θo2≠
It is set to 0@. Then, at the time of reproduction, if the Lippmann hologram 1 and the reproduction hologram 2 are arranged so that the angle formed by them is 45@ as shown in FIG. The wavelength dispersion of the first-order diffracted light from the hologram 2 is eliminated, and the same effects as in each of the above embodiments can be obtained.

Effects of Examples (1) Reproduction of Fresnel holograms conventionally required laser light, and therefore lacked versatility for use in general display devices. However, the above-mentioned Example 1.2
According to the method shown in , a clear reproduced image can be obtained using a white light source.

(2) Reproduction of image holograms has traditionally been performed using a white light source, but with one conventional reproduction method, the reproduced image at a position far from the hologram surface was blurred, and a clear image could not be obtained. , according to the method shown in Example 3 above,
A clear reproduced image can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the Lippmann hologram is irradiated with white light, and the diffracted light from the Lippmann hologram is irradiated as reproduction illumination light to the reproduction hologram to obtain a reproduced image. It becomes possible to obtain a clear reproduced image.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of a hologram reproducing method and a reproducing apparatus according to the present invention, FIG. 2 is a diagram showing a method for manufacturing the Lippmann hologram shown in FIG. 1, and FIG. 3 is a diffraction diagram of the Lippmann hologram shown in FIG. 1. Figure 4 is a diagram showing the manufacturing method of the reproduction hologram shown in Figure 1, Figure 5 is a diagram showing the diffraction characteristics of the reproduction hologram shown in Figure 1, Figure 6 is a diagram showing the characteristics.
FIG. 7 is a diagram showing a method for manufacturing a reflection Fresnel hologram for reproduction according to the present invention, FIG. 7 is a diagram showing a method for manufacturing a transmission Fresnel hologram for reproduction according to the present invention, and FIG. FIG. 9 is a diagram illustrating a method of manufacturing a transmission image hologram for reproduction, and is a diagram illustrating conditions for arranging each hologram in a hologram reproduction apparatus according to an embodiment of the present invention. 1... Lippmann hologram, 1-... Photosensitive original plate, 2
...Reproduction hologram, 2゛...Photosensitive original plate, 3...
・Light source, 4...Optical system, 5a, 5b...Viewpoint, 6.
...Show object, 7...Optical system, Ll...Illumination light, L2
...Reproduction illumination light, L3...Reference light, L4...Object light. Applicant's agent Sato -Yuman 1 Figure 2 Figure 3 Figure 6 Figure 7 68 Figure 9

Claims (1)

[Scope of Claims] 1. In a hologram reproduction method in which a reproduction hologram in which a three-dimensional image is recorded is reproduced using white light, white light is irradiated onto the Lippmann hologram, and diffracted light from the Lippmann hologram is used as reproduction illumination. A method for reproducing a hologram, characterized in that a reproducing hologram is irradiated with light to obtain a reproducing image. 2. Claim 1, characterized in that the first-order diffracted light from the Lippmann hologram is used as reproduction illumination light.
How to reproduce a hologram as described in section. 3. The wavelength dispersion that occurs in the first-order diffracted light from the Lippmann hologram compensates for the wavelength dispersion that occurs in the first-order diffracted light from the reproduction hologram, so that the diffraction angle of the first-order diffracted light from the reproduction hologram does not have wavelength dependence. A method for reproducing a hologram according to claim 2, characterized in that: 4. A reproduction hologram with a three-dimensional image recorded thereon, a white light source for illuminating the reproduction hologram, and a system that receives light from the white light source and emits only light in a limited wavelength range as diffracted light. A hologram reproducing apparatus comprising: a Lippmann hologram that irradiates the reproducing hologram, and forming a reproduced image using diffracted light from the reproducing hologram. 5. The hologram reproducing apparatus according to claim 4, wherein the reproducing hologram and the Lippmann hologram have exposure patterns using light having the same wavelength and equivalent or conjugate wavefronts. 6. The reproduction hologram and the Lippmann hologram are arranged parallel to each other, and both have patterns consisting of interference fringes of two types of light beams, and the conditions regarding the incident angles of the two types of light beams are: 6. The hologram reproducing apparatus according to claim 5, wherein the reproducing hologram and the Lippmann hologram are both equal. 7. The reproduction hologram has a luminous flux with an incident angle of 0° and an incident angle of 4
The Lippmann hologram has a pattern formed by interference fringes with a light beam of 5° or 135°, and the Lippmann hologram has an incident angle of 4
The reproduction hologram and the Lippmann hologram are arranged at an angle of 45° to each other, and the pattern is formed by interference fringes between a light beam of 5° and a light beam of 180°, and 6. The hologram reproducing apparatus according to claim 5, wherein said light is irradiated onto said Lippmann hologram at an incident angle of 45 degrees.