JP3029791B2 - Hologram recording / reproduction method, hologram recording / reproduction device, and hologram reproduction light irradiation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION The present invention used a Bi _{1 2} SiO _{2 0} single crystal or the like as a recording material for volume hologram recording and reproducing method of a hologram, it relates to the irradiation device of the apparatus and the reproducing light.

[0002]

2. Description of the Related Art Holography has been applied to interference measurement, optical information processing, and optical elements as a complete wavefront reproducing technique. In order to record a hologram or perform holographic interferometry, a silver halide photosensitive material is generally used at present, and the sensitivity and resolution are excellent. However, when a silver halide photosensitive material is used, a process called development processing is naturally required. For this purpose, Bi ₁₂ SiO
Photorefractive crystals (crystals exhibiting a photo-induced refraction effect) including ₂₀ single crystals are being actively studied as real-time hologram (RH) elements (for example,
"Laser Science Research Report", 1990, Mar. First
Pp. 9 to 9 for holographic recording characteristics of BSO single crystal). These materials only need to apply a voltage,
Since holograms can be recorded and can be reproduced as they are, they have attracted particular attention as materials for real-time hologram elements.

[0003] On the other hand, the dimensions of the hologram are not necessarily required to be large, although there are restrictions depending on the purpose of use in various applications such as interference measurement, optical information processing, and optical elements. However, in three-dimensional display applications, which are expected to be put to practical use recently, it is absolutely necessary to increase the dimensions of the hologram element to some extent. This is because in a three-dimensional display application, it is necessary to utilize the binocular parallax of a person in order to enable the three-dimensional recognition of the person. For this purpose, the dimension of the hologram element is set to a distance between both eyes (about 50 mm). That is because it must be at least.

However, the upper limit of the size of the real-time hologram element is physically limited by the shape and size of the BSO single crystal as a recording member for recording interference fringes.
Specifically, it was at most a dozen mm × a dozen mm. Due to this dimensional limitation, the use of real-time hologram elements is currently limited to only interferometry and optical information processing. However, real-time holograms are a technology that is strongly desired for practical use in the future,
Specifically, application as an output device of a three-dimensional image display system such as a three-dimensional CAD system is expected. Therefore, it is strongly desired to increase the size of the real-time hologram element.

[0005]

SUMMARY OF THE INVENTION The inventor of the present invention has conducted research to solve this problem and produced a large BSO single crystal boule as disclosed in Japanese Patent Application No. 7-245105. From this single crystal boule, for example, 60 m wide
A hologram having a size of at least m was cut out, and the hologram was successfully recorded and reproduced. In addition, Japanese Patent Application Hei 7-
In the specification of Japanese Patent No. 245105, a large-area hologram was produced by joining a plurality of BSO single-crystal plates, and recording and reproduction of the hologram were successfully performed on the hologram.

[0006] However, it has been found that the following problems arise in the course of further research on the real-time hologram by the present inventor. That is, most of the holograms currently put into practical use are silver halide photosensitive materials, but their thickness is about 5 μm to 17 μm, which is extremely thin. However, in contrast, BSO and B ₁₂ SO
_{2 0} photorefractive single crystals such as single crystals and B _{1 2} GeO _{2 0} single crystal is a so-called volume hologram (volume holograms). The thickness of the volume hologram is 0.05 mm or more, usually 0.1 mm
mm / 10 mm. In such a volume hologram, the angle selectivity of the incident angle of the reproduction light is severe. That is, the width of the change in the diffraction efficiency at the incident angle of the reproduction light is several mr.
It is very narrow as ad and diffracts only in a direction that satisfies the so-called Bragg condition.

For example, as schematically shown in FIG. 1, it is assumed that an interference fringe corresponding to the reproduced image 1 is recorded in a hologram 5 having a size or a size capable of utilizing binocular parallax. . When the reproduction light 52 is applied to the main surface 5b of the hologram 5, the reproduction light interferes with the interference fringes in the hologram 5, and the output light 3 is emitted from the main surface 5a at an angle satisfying the Bragg condition. In order to observe the reproduced image 1, it is necessary to position the pupil 4 at a predetermined interval on the main surface 5a side.

However, in order to be able to observe the depth of the reproduced image 1 in the real-time hologram device, it is necessary to use binocular parallax by using the large-sized hologram 5 as described above. It is.
Further, in order to realize a real-time hologram device, it is necessary to use a volume hologram. However, of the emitted light 3 obtained by the volume hologram 5, only the light 3A that actually enters the pupil 4 does not enter the pupil. As a result, it was found that, even if a large-area hologram was used, only the portion 1a of the reproduced image 1 was visible from the pupil, and the portion 1b was not visible at all. In this case, even if reproduction is performed using a large-area hologram, only a very small reproduced image can be observed, and only a small portion of the reproduced image can be observed.

It is an object of the present invention to provide a hologram recording / reproducing apparatus for observing a three-dimensional reconstructed image using binocular parallax using a volume hologram. In the reconstructed image, the area that can be actually observed is enlarged, and preferably, the entire reconstructed image can be observed.

[0010]

According to a hologram recording / reproducing method according to the present invention, a volume hologram made of a material exhibiting a photo-induced refraction effect is irradiated with object light and reference light to record interference fringes. A three-dimensional reconstructed image is obtained by irradiating the volume hologram with reconstructed light, and when observing the three-dimensional reconstructed image using binocular parallax, the wavelength λ ₁ of the object light is used.
Is characterized by reproducing a three-dimensional reproduced image by irradiating the volume hologram with a convergent spherical wave longer than the wavelength λ _{2 of the} reproduction light. Further, the hologram recording / reproducing method according to the present invention is characterized in that a volume hologram made of a material exhibiting a light-induced refraction effect is irradiated with object light and reference light to record interference fringes, and the reproduced light is applied to the volume hologram. When a three-dimensional reconstructed image is obtained by irradiating light, and the three-dimensional reconstructed image is observed using binocular parallax, the wavelength λ ₁ of the object light is shorter than the wavelength λ _{2 of the} reconstructed light, Irradiating a diffused spherical wave to reproduce the three-dimensional reproduced image.

The present invention also relates to a hologram recording / reproducing apparatus for observing a three-dimensional reconstructed image using binocular parallax, wherein the volume hologram is made of a material exhibiting a light-induced refraction effect. A mechanism for irradiating object light to the object, a mechanism for irradiating reference light to the volume hologram,
A mechanism for irradiating the volume hologram with a convergent spherical wave as the reproduction light, wherein the wavelength λ _{1 of the} object light is longer than the wavelength λ _{2 of the} reproduction light, and the volume hologram is irradiated with the convergent spherical wave. It is characterized by reproducing a three-dimensional reproduced image. Further, the present invention is a hologram recording and reproducing apparatus for observing a three-dimensional reproduced image using binocular parallax,
A volume hologram made of a material exhibiting a light-induced refraction effect,
A mechanism for irradiating the volume hologram with object light,
A mechanism for irradiating the volume hologram with reference light, and a mechanism for irradiating the volume hologram with a diffuse spherical wave as reproduction light, wherein the wavelength λ _{1 of the} object light is shorter than the wavelength λ _{2 of the} reproduction light In addition, a three-dimensional reproduced image is reproduced by irradiating a volume hologram with a diffusion spherical wave.

Further, the present invention is an apparatus for irradiating a reproduction light to a volume hologram, comprising a reproduction light source for generating the reproduction light, and lens means for converting the reproduction light into a spherical wave. This lens means comprises a lens array in which condenser lenses are arranged one-dimensionally or two-dimensionally.

Examples of the material having the light-induced refraction effect include a photorefractive crystal and an organic liquid crystal material having a light-induced refraction effect, but these materials are not particularly limited. However, at the moment, Bi _{1 2}
SiO ₂₀ single crystal, Bi ₁₂ GeO ₂₀ single crystal, LiN
A bO ₃ single crystal or the like is preferable, and among them, a Bi ₁₂ SiO ₂₀ single crystal having high sensitivity of the photo-induced effect is particularly preferable.

[0014] Volume holograms are typically 0.1 m thick.
m means a hologram of not less than m, and the upper limit of this thickness is usually 10 mm.

In order to form a volume hologram, it is necessary to form an electrode on a material exhibiting a light-induced refraction effect so that a predetermined drive voltage can be applied to the hologram. As this electrode, any of a transparent electrode and an opaque electrode can be used. As a material of such a transparent electrode,
Examples include a tin oxide film and an indium tin oxide film. Examples of the material of the opaque electrode include a conductive adhesive called a metal paste containing a conductive material such as silver powder, and a metal film of aluminum, gold, chromium, titanium, or the like.

The object light, reference light, and reproduction light that can be used for recording and reproducing the hologram are not particularly limited. However, the wavelength of the object light must be within the wavelength range where the volume hologram exhibits the photoconductive effect, and the wavelength of the reproduction light must be within the wavelength range where the volume hologram does not exhibit the photoconductive effect. Therefore, the range of the wavelength of the object light is different from the range of the wavelength of the reproduction light. For example, Bi
_When using a ₁₂ SiO ₂ single crystal, an argon ion laser beam having a wavelength of 488 nm, which exhibits a photoconductive effect, can be preferably used as object light.
Helium neon laser light having a wavelength of 633 nm, in which Bi ₁₂ SiO ₂₀ single crystal does not exhibit a photoconductive effect, can be preferably used.

Hereinafter, the operation of the present invention will be described in more detail. For example, when a Bi ₁₂ SiO ₂₀ single crystal is used, the thickness of the hologram is several mm.
A diffraction image is obtained by g diffraction. Further, for the above-mentioned reason, the wavelength of the object light to the volume hologram and the wavelength of the reproduction light are greatly different. The present inventor has studied under these conditions, and as a result, has found the following. That is, in the apparatus as shown in FIG. 1, the reproduction light is a parallel light, and therefore, the outgoing lights 3 and 3A are also parallel lights. When a silver halide photosensitive material is used as a hologram, no further study has been made since diffracted light can be obtained from the surface of the hologram in all directions.

On the other hand, the present inventor tried to use a spherical wave as the reproduction light. As a result, it has been found that the range of the reproduced image that can be observed by the human eye is significantly increased, and in particular, the entire reproduced image emitted from the hologram can be observed. Thus, the present invention has been completed.

The present inventor has further studied this system,
We succeeded in specifying the reason why the observable area of the reproduced image was expanded by adopting the spherical wave, and in particular, the specific conditions under which the entire reproduced image could be observed. FIG. 2 is a block diagram schematically showing the apparatus of the present invention, FIG. 3A is a schematic diagram for explaining the irradiation state of the object light and the reference light, and FIG. It is a schematic diagram for explaining the irradiation state of the reproduction light.

The volume hologram 5 was set at a predetermined position.
A laser beam having a wavelength λ ₁ is emitted from a light source 10, and the laser beam is split into two by a half mirror 11. One of the split laser beams passes through the mirror 12, the lens 16, and the diffusion plate 17, is scattered by the diffusion plate 17, and passes through the transparent film 18 on which the original image is printed. The light emitted from the film 18 is used as the object light 15, which is applied to the hologram 5.

On the other hand, of the laser light emitted from the light source 10, the light reflected by the half mirror 11 passes through the condenser lens 13 and the collimator lens 14, and as the reference light 2, the light irradiation surface or main surface of the hologram 5. 5b. The object light 15 and the reference light 2 intersect each other at an intersection angle θ as shown in FIG. Thus, the original image is recorded in the hologram 5 as interference fringes.

The object light 15 is transmitted to the small-diameter pupil 4 (FIG. 3B).
(See FIG. 2), and is light condensed at one point T. The reference light 2 is a collimated light. Pupil (ie observation point)
Is T. Let L be the distance between the convergence point T and the hologram 5. When the y-axis extending in the horizontal direction with respect to the main surfaces 5a and 5b of the hologram 5 is set, the intersection point when the perpendicular is lowered from the converging point T to the y-axis is O, and this intersection point O and the converging point T The axis connecting is referred to as the x-axis.

In the following, the conditions of the reproduction light that can reproduce the interference fringes will be considered. A laser beam 8 is emitted from a light source 6 and transmitted through a condenser lens 7 to irradiate a hologram 5 with reproduction light 9 composed of a spherical wave. The incident angle of the reproduction light needs to satisfy the Bragg diffraction condition with respect to the interference fringes recorded in the element. Here, the incident angle of the reproduction light 9 incident on each point on the hologram 5 is φ (y). The diffracted light 37 for reproducing the interference fringes forms an image at a point at a distance L from the hologram 5. The wavelength of the object light is λ ₁ and the wavelength of the reproduction light is λ ₂ . When recording interference fringes, the wave vector of the object light 15 is k ₁ , the wave vector of the reference light 2 is k ₂ , the wave vector of the reproduction light is k _3, and the wave vector of the interference fringes is kf.

The wave vectors k ₁ , k ₂ , k ₃ and kf
Satisfies the following relationship at each point on the y-axis.

K ₁ = (− L / (L ² + y ² ) ^{−1 /} 2λ ₁ , −y / (L ² + y ² ) ^{−1 /} 2λ ₁ ) (2) k ₂ = (−cos θ / λ ₁ , sin θ / λ ₁ ) (3) kf = k ₁ −k ₂ (4) k ₃ = (− cos φ (y) / λ ₂ , sin φ (y) / Λ ₂ ) (5)

The Bragg condition between the wave vector k ₄ diffracted light with wave vector k ₃ of the reproduction light, the formula (6),
It is as (7).

( ₄ ) k ₄ = k ₃ + kf (6) | k ₄ | = | k ₃ | = 1 / λ ₂ (7)

From equations (6) and (7), equation (8) is obtained.

## EQU3 ## 2k ₃ kf + | kf | ² = 0 (8)

Equations (2) to (5) were substituted into equation (8). Here, the distance L of the observation point from the hologram is y
And developed around the origin O with θ to φ to 0 to obtain the equation (9).

Equation 4] ^{-2 (1-φ 2/2} ) ^{[1-θ 2 / 2- (1-} (y / L) 2/2) ] / λ ₁ λ ₂ -2φ [θ + (y / L) / lambda ₁ lambda _2] +2 [1 + θy / L- (1- θ 2/2) (1- (y / L) 2/2) ] ^{_{/ λ 1 2 = 0 ···· (}} 9)

When the equation (9) is arranged for φ (y),
Equation (1) is obtained.

(5) φ (y) = (λ ₂ / λ ₁ ) · (θ + y / L) / 2 + (θ−y / L) / 2 · (1)

Equation (1) is consistent with a spherical wave in a range where y is sufficiently smaller than L. This range is specifically within the range of y: L = 1 or less: 10. However, in the range of y: L = 1 or less: 4,
It was confirmed that at least a substantially good reproduced image was obtained. If the distance of the observation point from the hologram is L, the entire reproduced image reproduced by the diffracted light 37 can be observed with the pupil. However, even if the actual observation point slightly fluctuates from this distance, the whole image can be observed within the allowable range of the pupil size. The allowable range of this distance was 30% or less. However, even if the position of the observation point deviates from this allowable range, the range of the diffracted light incident on the pupil is relatively large as compared with the conventional example as shown in FIG. The range that can be observed by the pupil is relatively large.

By differentiating equation (1) with y, the following equation (1) is obtained.
0) is obtained.

Dφ / dy = (λ ₂ / λ ₁ -1) / 2L (10)

Therefore, when the wavelength λ _{2 of the} reproduction light is larger than the wavelength λ _{1 of the} object light (λ ₂ > λ ₁ ), (10)
The slope of the equation is positive. This means that the reproduction light 9 satisfying the Bragg condition is a diffuse spherical wave. When the wavelength λ _{1 of the} object light is larger than the wavelength λ _{2 of the} reproduction light (λ ₁ > λ ₂ ), the slope of the equation (10) becomes positive. This means that the reproduction light 9 satisfying the Bragg condition is a convergent spherical wave.

In the apparatus shown in FIGS. 2 and 3, since the positions of the light source 6 and the condenser lens 7 are fixed, the focal point of the diffracted light is also constant. For this reason, the pupil 4 is set to the diffracted light 37
Is moved to a certain point where light is condensed (a point at a distance L)
It must be moved at least close to it as described above. Also, in FIG. 3B, a diffused spherical wave is irradiated as reproduction light.
Needs to be smaller than the distance P between the condenser lens 7 and the volume hologram 5 shown in FIG. 2 to focus once before the volume hologram 5. On the other hand, in order to irradiate a convergent spherical wave as reproduction light, a condenser lens 7 is required.
Must be larger than the distance P between the condenser lens 7 and the volume hologram 5 shown in FIG.

The inventor has further encountered the following problem.
That is, in the hologram recording / reproducing apparatus described above, the entire reconstructed image can be observed. For this purpose, the viewpoint of the observer, that is, the position of the pupil 4 is arranged in a certain range of space. There is a need. However, when observing with an actual device, it is necessary to arrange the observation point in the space of the specific range at the beginning of the observation, and if the position of the pupil moves during the observation, the reproduced image will not be visible. Disappears. In view of the above, the present inventor has provided a volume hologram including a detection device that detects an observation point of a reproduced image in a reproduction stage, and a drive mechanism that moves a focal point of reproduction light in accordance with a signal from the detection device. , And the y-axis is set in a direction parallel to the principal surface of the volume hologram. When the intersection of the y-axis and the perpendicular drawn from the observation point to the y-axis is O, and the distance between the observation point and the y-axis is L, the volume of the reproduced light at a position y away from the intersection O on the volume hologram. The drive mechanism can move the focal point of the reproduction light so that the angle of incidence φ (y) to the hologram substantially satisfies the expression (1).

This embodiment will be further described. The recording of interference fringes on the volume hologram 5 is shown in FIGS.
It is assumed that the operation is performed as shown in FIG. FIG. 4 schematically shows the configuration of the reproducing apparatus. The intersection angle between the object light and the reference light when irradiating the volume hologram 5 is defined as θ. Observation point 4
Let L be the distance between the volume hologram 5. Let Q be the center point of the volume hologram 5. The y axis is set around Q. The point of intersection of the y-axis with the perpendicular drawn down from the observation point to the y-axis is denoted by O. The x axis is set in a direction perpendicular to this. In the present embodiment, the mechanism 20 that irradiates the spherical hologram 9 as reproduction light to the volume hologram 5 includes the laser light source 6 and the condenser lens 7. Here, the X-axis is set in the traveling direction of the spherical wave 9 around the center point Q, and the Y-axis is set in a direction perpendicular to this. In FIG. 4, the inclination angle of the X-axis with respect to the x-axis is shown much larger than the actual inclination angle for convenience of explanation.

The detection device for detecting the observation point of the reproduced image includes an image pickup tube 31, an image processing device 32, a display 33, and a drive control device 34. It is assumed that the pupil 4 is located at a point (L, y ₀ ) on the (x, y) coordinates. The position of the pupil 4 is detected by the image pickup tube 31 and sent to the image processing device 32 to detect the coordinates. The position of the pupil is displayed on the display 33 as necessary. The signal of the coordinates is sent to the drive control device 34. The drive control device 34 is connected to a drive device (not shown in FIG. 4) for moving the focal point of the reproduction light, and controls the drive device. In the present embodiment, the entire mechanism 20 is moved in the directions of the X axis and the Y axis by this driving device, thereby changing the coordinates (X ₀ , Y ₀ ) of the condenser lens 7.

Here, within a range where the width of the volume hologram is sufficiently smaller than L, y ₀ and Y ₀ can be treated as the same. That is, y _{0 of the} observation point 4
Is changed, the entire mechanism 20 is moved so that Y ₀ becomes the same as y ₀ . At the same time, by moving the coordinates X ₀ of the condenser lens 7, changing the distance from the intersection O of the focal point of the condenser lens 7. This makes it possible to control the incident angle φ (y) of the reproduction light on the volume hologram at a position y away from the intersection O on the volume hologram 5. At this time, the coordinate X ₀ of the condenser lens 7 is moved so that the incident angle φ (y) satisfies the above equation (1). This relational expression is built in the processor 32, and can control the coordinates (X ₀ , Y ₀ ) in real time.

In this embodiment, detection of the observation point 4
When calculating the coordinates (X ₀ , Y ₀ ) and driving the mechanism 20 is one cycle, it is preferable to execute 30 cycles or more per second in order to prevent flickering of the reproduced image.

FIG. 5 is a perspective view showing an example of the mechanism 20 having the driving device. Laser light source 6 is holder 2
The lens 21 is fixed on the pedestal 23 by the holder 21. The pedestal 23 is slidably supported on a moving rail 25, and the pedestal 23 is attached to a feed screw 24. The feed screw 24 is rotated by the pulse motor 50A to move the pedestal 23 in the Y-axis direction. All of these mechanisms are further supported on the moving rail 27,
And it is attached to the feed screw 26. The rail 27 and the feed screw 26 are attached to a support 28. The feed screw 26 is rotated by the pulse motor 50B to move the pedestal 23 in the X-axis direction.

In the mechanism 20, the laser light source 6 and the condenser lens 7 are simultaneously moved. However, it is also possible to mount the laser light source 6 and the condenser lens 7 on separate driving devices and move them separately.

As the condenser lens, various lenses used in micro optics can be used. However, a gradient index rod lens (GRIN) lens (distributed index rod lens) is particularly preferred.

Further, the present inventor has described a real-time hologram recording / reproducing apparatus as described above, wherein a mechanism for irradiating the volume hologram with a spherical wave as a reproducing light is a reproducing light source for generating a reproducing light, In the case where a lens means for converting the light into a spherical wave is provided, it has been conceived to use a lens array in which condenser lenses are arranged one-dimensionally or two-dimensionally.

First, such a microlens array will be described. A linear or planar object is cut by cutting a gradient index rod lens under the same-magnification positive-rate imaging conditions, arranging the polished ones in a one-dimensional array or a two-dimensional matrix, and fixing. It can be transmitted as a 1: 1 image. Such a lens array is described in, for example, "Micro Optics and Packaging Technology", Koichi Nishizawa, "Journal of the Circuit Packaging Society", Vol. 10, No. 5, 1995, pp. 315-319.

FIG. 6 is a block diagram showing a hologram reproducing apparatus according to this embodiment. The laser light 8 emitted from the laser light source 6 is once focused by the condenser lens 38 and is applied to the collimator lens 39 as a diffused spherical wave. The collimated light from the lens 39 is irradiated on the microlens array 40 and then on the hologram 5. FIG. 7 shows such a microlens array 40.
It is a top view which shows an example of 1 typically. A predetermined number of micro lenses 42 are provided on a support plate 41 made of aluminum or the like.
Are arranged and fixed in a matrix.

When such a reproducing light irradiation mechanism is used,
First, as shown in FIG.
In each of A, 42B, 42C, 42D, and 42E, a laser beam 8 from a light source is collected at a focal point 43A. As a result, a diffused spherical wave 44A is emitted from the focal point 43A. The angle of incidence φ (y) of the diffused spherical wave 44A on the volume hologram is determined by the position of the focal point 43A, that is, is determined to be constant by the focal length of each microlens.

However, at the same time, for example, FIG.
As shown in FIG.
Outgoing light 44B transmitted through the respective microlenses 42C of the microlenses 42B and 42D on both sides of 2C.
Is light that spreads outward around the microlens 42C, and the focus of this light is generated at 43B. Thereby, the incident angle φ (y) of the reproduction light to the volume hologram 5
Changes. Further, for example, as shown in FIG. 8B, of the laser beam 8, the micro lenses 42B or 42 of the outer micro lenses 42A and 42E, respectively.
The outgoing light 44C transmitted through the D side is converted into a micro lens 42C.
Is the light that spreads out from the center, and the focal point of this light is generated at 43C. The focal point 43C occurs at a position farther from the microlens array than the focal point 43B. As a result, a large number of diffused spherical waves having various focal lengths are simultaneously generated and irradiated on the volume hologram 5.

For example, as shown in FIG. 8C, outgoing light 46A of the laser beam 8 that has passed through the microlenses 42A and 42E of the microlenses 42B and 42D on both sides of the microlens array 42C, respectively.
It becomes light converging around the micro lens 42C,
This light focus is generated at 45. Out of the laser light 8, the outgoing light 46B that has passed through the outside of each of the microlenses 42A and 42E that is further outside when viewed from the microlens array 42C also becomes light converging around the microlens 42C. The focal point is generated at a position farther from the microlens array than the focal point 45. In these cases, by disposing the volume hologram 5 between the microlens array and the focal point 45, it is possible to simultaneously irradiate the volume hologram 5 with a large number of converging spherical waves having various focal lengths.

Thus, even if the position of the observation point 4 is variously changed, a reproduced image corresponding to the position can be seen from the observation point 4.

In the micro lens array, the pitch d of the micro lenses is preferably 5 mm or less, more preferably 3 mm or less. If the pitch d is too large relative to the size of the pupil when the observer changes the viewpoint position (observation point), a phenomenon in which the reproduced image flickers easily occurs. Such flicker can be prevented. When the intersection angle between the optical axis of the object light and the optical axis of the reference light is θ, and the focal length of the microlens is f, it is preferable to use a microlens array satisfying d / 2θ <f. By setting d / 2θ <f, the reproduced light does not directly enter the pupil of the observer, and the contrast of the reproduced image can be further improved.

[0049]

[Example 1]

(Production of hologram recording / reproducing apparatus) A boule of Bi ₁₂ SiO ₂ single crystal having a diameter of 80 mm and a length of 100 mm was produced. As a crucible, diameter 150mm, height 150m
A platinum crucible having a cylindrical shape of m was used. In the crucible,
14 kg of a sintered body of Bi ₁₂ SiO ₂₀ was accommodated and heated to 900 ° C. to generate a melt. By using a platinum after-heater, a temperature gradient of up to 10 mm above
The temperature was adjusted to 75 ° C./cm, and the subsequent temperature gradient up to 150 mm was adjusted to 10 ° C./cm. The lifting speed was 1 to 1.5 mm / hour, and the rotation speed of the lifting shaft was 10 rpm. The properties of the obtained single crystal are shown in Table 1 below.

[0050]

Table 1 Lattice constant 10.103 × 10 ^-10 m Density 9.2 g / cm ³ Dielectric constant 56 (100 kHz) Refractive index 2.53 (λ = 633 nm) Dark resistance 10 ¹⁴ Ω · cm Photoconductivity 10 ⁸ Ω · cm (λ = 458nm, 2.5mW / cm 2) half wave voltage 3900V (λ = 633nm) Verdet constant ^{3.67 × 10 - 3 / Oe ·} cm (λ = 633nm) 9.33 × 10 - 4 / Oe · cm (λ = 1150nm)

From this boule, a diameter of 80 mm and a thickness of 3 m
m volume hologram 5 was cut out. The pair of main surfaces of the hologram 5 are polished by a plane polishing machine, and each flatness is set to 0.6.
μm. Next, a transparent electrode film made of indium phosphide was formed on the end face of the volume hologram 5 by a sputtering method.

(Hologram Recording and Reproduction Experiment) FIG.
Using the apparatus shown in FIGS. 3 to 3, hologram recording and reproduction experiments were performed. Argon ion laser light having a wavelength of 488 nm was used as the object light. θ was set to 10 °.
Helium-neon laser light having a wavelength of 633 nm was used as reproduction light. Reproduction light was made to enter the center point Q of the volume hologram 5. The focal length f of the condenser lens 7 was set to 40 mm. According to the above-mentioned formula (1), the dimensions of each part were set as follows. That is, the distance L between the observation point 4 and the volume hologram 5 is set to 300 mm, the distance between the condenser lens 7 and the volume hologram 5 is set to 2059 mm, and the incident angle of the reproduction light with respect to the center of the volume hologram 5 is set to 1
1.49 °.

The viewpoint was fixed at the above position of the volume hologram 5 and the reproduced image was observed. As a result, it was found that the reproduced image was reproduced at a position corresponding to the original image, whereby the depth in the original image was reproduced also in the reproduced holography. This image is shown in FIG. The depth of the holography could be confirmed using binocular parallax. in this way,
According to the present invention, using the binocular parallax, the depth and stereoscopic effect of the original image can be faithfully reproduced and confirmed.
We succeeded in providing a three-dimensional display using real-time holograms.

It should be noted that the image recorded in the volume hologram in this manner has a voltage of 0 V applied to the volume hologram.
In this state, the volume hologram could be erased by irradiating the entire surface of the light irradiation surface with uniform blue light.

Example 2 A volume hologram 5 was produced in the same manner as in Example 1. Using the hologram recording and reproducing apparatus shown in FIGS. 4 and 5, hologram recording and reproducing experiments were performed. Argon laser light having a wavelength of 488 nm was used as object light. θ was set to 10 °. Helium-neon laser light having a wavelength of 633 nm was used as reproduction light. The focal length f of the condenser lens 7 was set to 40 nm. The incident angle of the reproduction light with respect to the center of the volume hologram 5 was set to 11.49 °.

The position of the mechanism 20 was controlled according to the equation (1). Specifically, a change in the position of the pupil is detected, and Y ₀ = y
₀ , and X = x (mm) × 6.73 + 40 (mm)
The position of the mechanism 20 was controlled so that As a result, it was found that the reproduced image was reproduced at a position corresponding to the original image, whereby the depth in the original image was reproduced also in the reproduced holography. Then, x = 100 mm to 500 mm, y = −100 mm to
Within the range of +100 mm, a three-dimensional reproduced image could be confirmed well.

Example 3 A volume hologram 5 was produced in the same manner as in Example 1. Using the hologram recording / reproducing apparatus shown in FIGS. 6 to 8, hologram recording / reproduction experiments were performed. Argon laser light having a wavelength of 488 nm was used as object light. θ was set to 10 °. Helium-neon laser light having a wavelength of 633 nm was used as reproduction light. The incident angle of the reproduction light with respect to the center of the volume hologram 5 was set to 11.49 °. The support plate 41 of the microlens array was an aluminum plate having a size of 120 mm × 120 mm. A distributed refractive index rod lens having a diameter of 2 mm was used as each microlens. Pitch d is 2.4
mm and the number of microlenses was 45 × 45.

As a result, it was found that the reproduced image was reproduced at a position corresponding to the original image, whereby the depth in the original image was reproduced also in the reproduced holography. Then, x = 100 mm or more, y =
Within the range of −60 mm to +60 mm, a three-dimensional reconstructed image was successfully confirmed.

[0059]

As described above, according to the present invention, a device for observing a reproduced image of a hologram using a volume hologram, such as a real-time hologram device, is constituted by diffracted light from the volume hologram. In the reproduced image to be obtained, an area that can be actually observed can be enlarged, and in particular, the entire reproduced image can be observed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a limit of an observable range of a reproduced image in a real-time hologram element.

FIG. 2 is a block diagram schematically showing an apparatus according to an embodiment of the present invention.

3A is a diagram schematically showing a state in which object light and reference light are incident on a volume hologram 5, and FIG. 3B is a diagram in which reproduction light is incident on the volume hologram 5. FIG. It is a figure which shows the state which is performing typically.

FIG. 4 is a block diagram schematically showing a hologram recording / reproducing apparatus according to another embodiment of the present invention.

FIG. 5 is a perspective view showing a reproducing light irradiation device used in the device of FIG. 4;

FIG. 6 is a block diagram schematically showing a hologram recording / reproducing apparatus according to still another embodiment of the present invention.

FIG. 7A is a plan view illustrating an example of a microlens array, and FIG. 7B is a schematic diagram illustrating a traveling direction of a reproduction light imaged in each microlens.

8 (a), (b) and (c) show a traveling direction of each emitted light irradiated from the microlens array to the volume hologram 5 and a position of each focal point corresponding to each emitted light, respectively. It is a schematic diagram for demonstrating a change.

FIG. 9 is a photograph showing a reproduced image of a hologram made observable by the apparatus of the present invention.

[Explanation of symbols]

2 reference light, 4 pupils, 5 volume hologram, 9
Reproduction light, 10 laser light source, 11 half mirror, 15 object light, 17 diffusion plate, 18 transparent film on which original image is printed, 20 mechanism for irradiating reproduction light, 31 image pickup tube, 34 drive control device, 4
0 micro lens array, 42, 42A, 42B,
42C, 42D, 42E micro lens, 43A,
43B, 43C focal point, 44A, 44B, 44C diffusing spherical wave, 46A, 46B converging spherical wave, O intersection point when a perpendicular line is dropped from convergence point T to hologram 5,
x-axis intersection O and the axis connecting the focal point T, as the y-axis intersection O, x-axis perpendicular to the direction of the axis, k ₂ of the reference beam 2 wavevector, k ₃ wave vector of the reproducing light, Kf
Fringe 19 number vector, intersection angle between the reference beam 2 and θ object beam 15, a wavelength of lambda ₁ object beam, a wavelength of lambda ₂ reproduction light

Claims (11)

(57) [Claims] 1. A three-dimensional volume hologram made of a material exhibiting a photo-induced refraction effect is irradiated with object light and reference light to record interference fringes, and the volume hologram is irradiated with reproduction light. A reconstructed image is obtained, and this three-dimensional reconstructed image is
Recording / reproduction of hologram for observation using eye parallax
A method, wavelength lambda ₁ of the object beam is the wavelength of the reproduction light lambda
Than ₂ rather long, characterized in that by irradiating a convergent spherical wave with respect to the volume hologram to reproduce the three-dimensional reconstructed image, recording and reproducing method of a hologram. 2. An angle of intersection between the object light and the reference light when irradiating the volume hologram is set to θ, a y-axis is set in a direction parallel to a main surface of the volume hologram, and an observation point of a reproduced image is set. When the distance between the vertical axis drawn from the observation point to the y-axis and the y-axis is defined as O, the distance between the observation point and the y-axis is defined as L, and the distance from the intersection O on the volume hologram is y. Wherein the focal point and the observation point of the reproduction light are positioned such that the incident angle φ (y) of the reproduction light on the volume hologram substantially satisfies the following expression (1). A method for recording and reproducing a hologram according to claim 1. φ (y) = (λ ₂ / λ ₁ ) · (θ + y / L) / 2 + (θ
-Y / L) / 2 (1) 3. A three-dimensional volume hologram made of a material exhibiting a light-induced refraction effect is irradiated with object light and reference light to record interference fringes, and the volume hologram is irradiated with reproduction light. A reconstructed image is obtained, and this three-dimensional reconstructed image is
Recording / reproduction of hologram for observation using eye parallax
A method, wavelength lambda ₁ of the object beam is the wavelength of the reproduction light lambda
Rather shorter than _2, characterized by reproducing the three-dimensional reconstruction image by irradiating a diffused spherical wave with respect to the volume hologram recording and reproducing method of a hologram. 4. An observation point for a reproduced image, wherein an intersection angle between the object light and the reference light when irradiating the volume hologram is θ, a y-axis is set in a direction parallel to a main surface of the volume hologram, When the distance between the vertical axis drawn from the observation point to the y-axis and the y-axis is defined as O, the distance between the observation point and the y-axis is defined as L, and the distance from the intersection O on the volume hologram is y. Wherein the focal point and the observation point of the reproduction light are positioned such that the incident angle φ (y) of the reproduction light on the volume hologram substantially satisfies the following expression (1). A hologram recording / reproducing method according to claim 3 . φ (y) = (λ ₂ / λ ₁ ) · (θ + y / L) / 2 + (θ
-Y / L) / 2 (1) 5. A three-dimensional reconstructed image is observed using binocular parallax.
A hologram recording / reproducing apparatus for: a volume hologram made of a material exhibiting a light-induced refraction effect;
A mechanism for irradiating the volume hologram with object light,
A mechanism for irradiating the volume hologram with reference light,
A mechanism for irradiating the volume hologram with a convergent spherical wave as reproduction light , wherein the wavelength λ _{1 of the} object light is
Longer than the wavelength λ _{2 of the} reproduction light,
A hologram recording / reproducing apparatus, which reproduces the three-dimensional reproduced image by irradiating a convergent spherical wave . 6. A volume hologram is illuminated with a detection device for detecting an observation point of a reproduced image, and a drive mechanism for moving a focal point of the reproduction light in accordance with a signal from the detection device. The intersection angle between the object light and the reference light
A distance between the observation point and the volume hologram is L, a y-axis is set in a direction parallel to the main surface of the volume hologram, and a perpendicular line lowered from the observation point to the y-axis and the volume hologram When the point of intersection with O is O, the angle of incidence φ (y) of the reproduction light on the volume hologram at a position y away from the point of intersection O on the volume hologram substantially satisfies the following expression (1). 6. The hologram recording / reproducing apparatus according to claim 5 , wherein the drive mechanism is configured to move the focal point of the reproduction light. φ (y) = (λ ₂ / λ ₁ ) · (θ + y / L) / 2 + (θ
-Y / L) / 2 (1) 7. A mechanism for irradiating a spherical wave as reproduction light to the volume hologram, comprising: a reproduction light source for generating the reproduction light; and lens means for converting the reproduction light to the spherical wave. 7. The hologram recording / reproducing apparatus according to claim 5 , wherein the lens means comprises a lens array in which condensing lenses are arranged one-dimensionally or two-dimensionally. 8. A three-dimensional reproduced image is observed using binocular parallax.
A hologram recording / reproducing apparatus for: a volume hologram made of a material exhibiting a light-induced refraction effect;
A mechanism for irradiating the volume hologram with object light,
A mechanism for irradiating the volume hologram with reference light,
A mechanism for irradiating the volume hologram with a diffuse spherical wave as reproduction light , wherein the wavelength λ _{1 of the} object light is
Shorter than the wavelength λ _{2 of the} reproduction light,
A hologram recording / reproducing apparatus, which irradiates a diffuse spherical wave to reproduce the three-dimensional reproduced image . 9. A volume detection device for irradiating the volume hologram with a detection device for detecting an observation point of a reproduced image, and a drive mechanism for moving a focal point of the reproduction light in accordance with a signal from the detection device. The intersection angle between the object light and the reference light
A distance between the observation point and the volume hologram is L, a y-axis is set in a direction parallel to the main surface of the volume hologram, and a perpendicular line lowered from the observation point to the y-axis and the volume hologram When the point of intersection with O is O, the angle of incidence φ (y) of the reproduction light on the volume hologram at a position y away from the point of intersection O on the volume hologram substantially satisfies the following expression (1). 9. The hologram recording / reproducing apparatus according to claim 8 , wherein the drive mechanism moves the focal point of the reconstructed light. φ (y) = (λ ₂ / λ ₁ ) · (θ + y / L) / 2 + (θ
-Y / L) / 2 (1) 10. A mechanism for irradiating a spherical wave as reproduction light to the volume hologram, comprising: a reproduction light source for generating the reproduction light; and lens means for converting the reproduction light to the spherical wave. 10. The hologram recording / reproducing apparatus according to claim 8 , wherein the lens means comprises a lens array in which condensing lenses are arranged one-dimensionally or two-dimensionally. 11. An apparatus for irradiating a reproduction light to a volume hologram, comprising: a reproduction light source for generating the reproduction light; and lens means for converting the reproduction light into a spherical wave. The means may include a one-dimensional or two-dimensional condenser lens.
A hologram reproduction light irradiation device, comprising a lens array arranged in a three-dimensional manner.