JP2891659B2 - Hologram element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates relates to a hologram element and a manufacturing method thereof using a Bi _{1 2} SiO _{2 0} single crystal as a recording material of the interference fringes of the hologram.

[0002]

2. Description of the Related Art Holography has been applied to interference measurement, optical information processing, optical elements, three-dimensional displays, etc. as a complete wavefront reproduction technique. Regarding the dimensions of the hologram, in various applications such as interference measurement, optical information processing, and optical elements, elements having large dimensions are not necessarily required, although there are restrictions depending on the purpose of use. However, for 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 a certain extent. Because, in 3D display applications, in order to enable human stereoscopic recognition,
It is necessary to use the binocular parallax of a person, but the dimension of the hologram element must be equal to or more than the distance between the eyes (about 50 mm).

On the other hand, photorefractive crystals such as Bi ₁₂ SiO ₂ single crystals have been actively studied as real-time hologram (RH) elements (see, for example, “Laser Science Research Report”, 1990, Mar.
See pages 1-9, "About the holographic recording characteristics of BSO single crystals." However, the upper limit of the dimension of the real-time hologram element is BS, which is a recording member for recording interference fringes.
It was physically limited by the shape and dimensions of the O single crystal, and specifically, it was at most a dozen mm × a dozen mm.
Because of this dimensional limitation, applications of real-time hologram elements are limited to only interferometry and optical information processing. However, real-time holograms are a technology that is strongly demanded for practical use in the future, and specifically,
There is a long-awaited demand for application as an output device of a three-dimensional image display system such as a three-dimensional CAD system. Therefore, it is strongly desired to increase the size of the real-time hologram element.

[0004] Bi ₁₂ SiO ₂₀ single crystal has a lower thermal conductivity than a general oxide single crystal, so it is difficult to release latent heat accompanying crystallization. For this reason, it has been considered that, during the growth of the crystal, distortion and cracks are likely to occur due to the heat distribution inside the crystal, and it is difficult to increase the size. However, a researcher belonging to the present applicant has disclosed a preferred method of pulling this single crystal by the pulling method (Czochralski method) (“Journal of the Japan Society for Crystal Growth Vo
l. 17 No. 2 (1990) pp. 60-66 ",
JP-A-64-18993, JP-A-1-23439
No. 9).

[0005]

The inventor of the present invention has been working to increase the size of a Bi ₁₂ SiO ₂₀ single crystal by applying the above-mentioned method. Has succeeded in nurturing. However, it is difficult to cut out a large-sized recording member because the single crystal has the following problems. This problem will be described with reference to FIGS. 9A and 9B.

In general, when growing a single crystal, the ease of growth varies depending on the orientation of the growth. Bi
_In the case of a ₁₂ SiO ₂ single crystal, it is known that the orientation of the <100> axis or the <111> axis is the orientation that can be grown. In particular, <10
0> Regarding the axis orientation, a large single crystal was successfully grown. FIG. 9A is a perspective view showing the single crystal 1, and FIG. 9B is a plan view showing the single crystal 1.
The main body 1a of the single crystal 1 has a cylindrical shape, and an upper end 1b having a substantially conical shape is formed at the upper end of the main body 1a. Single crystal body 1 is pulled up to the <100> axis orientation.

[0007] The Bi ₁₂ SiO ₂ single crystal is a crystal that exhibits a photorefractive effect when a voltage is applied.

[Outside 1] It is known that when an external electric field is applied in a direction parallel to the axis, the diffraction efficiency is maximized. In order to cut out a wafer having a main surface (011) from the single crystal body 1 pulled in the direction of the <100> axis, FIGS. 9A and 9B
As shown in (1), cutting the single crystal body 1 in the longitudinal direction to cut out the recording member 15 is a method for obtaining the recording member having the largest area. The pair of main surfaces 15a of the recording member 15 are (011) planes, and the longer side surface 15b is

[Outside 2] The shorter side surface 15c is a (100) plane.

However, Bi ₁₂ SiO ₂₀ single crystal is
The growth rate is remarkably different for each crystal orientation, and a region 2 having a high impurity concentration called a core is generated at the center of the single crystal body 1. The shape of the core portion 2 is substantially cylindrical, and extends in the pulling direction of the single crystal body 1. The diameter of the core portion 2 varies depending on the diameter of the Bi _{1 2} SiO _{2 0} single crystal 1, but the diameter is 80 mm as described above.
When the single crystal body is pulled up, the diameter of the core part 2 reaches about 20 mm.

The physical properties of the core 2 are described in IEICE Technical Report Vol. 87 No. 373, IEICE Technical Report CPM 87-103-110 (published February 17, 1988, IEICE)
Pp. 27 to “On the optical quality involved in the facet growth of Bi ₁₂ GeO ₂₀ single crystal”.
According to this, Bi ₁₂ GeO ₂₀ , Bi ₁₂ SiO
When growing a ₂₀ single crystal, a facet is usually generated, and incorporation of impurities and crystal defects occur in this facet.

In this facet, the lattice constant, light absorption characteristics, and photoconductivity are different from those of other parts (off facet, normal part), and the crystal is distorted due to the mismatch of the lattice constant. It has been. It has also been found that the facet and the off-facet have different colors, and that the facet has a higher absorption at 400 to 500 nm. Thus, facets have been found to be optically inhomogeneous and are disclosed to be particularly problematic in photovoltaic sensors.

Such a facet is the core part 2 in FIG. 9, but in order to manufacture a recording member of a real-time hologram element, as shown in FIGS. May be cut out so as not to be included in the recording member 15. However, when the recording member 15 is cut out in this way, the dimensions of the recording member 15 are reduced. In particular, if the diameter of the single crystal body 1 is about 80 mm, which is the maximum value currently achievable, and the diameter of the core is 20 mm, it is difficult to make the size of the recording member 15 50 mm or more. Therefore, it cannot be used as a recording member of the real-time hologram element.

An object of the present invention is to make it possible to increase the size of a recording member of a hologram element made of Bi ₁₂ SiO ₂₀ single crystal when manufacturing the same, and at the same time, to manufacture the hologram element as a hologram element. The purpose is to prevent performance degradation.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a hologram element comprising a recording member and an electrode for applying a voltage to the recording member, wherein the hologram element is formed by a Bi ₁₂ SiO _The recording member is cut out of a single crystal having 20 cores and a single crystal having a core portion and a normal portion extending in the direction of the pulling axis of the single crystal, and the core portion And a normal portion are included in the recording member.

Further, the present invention is a single crystal composed of Bi _{1 2} SiO ₂₀ single crystal grown by the Czochralski method, have a core part and a normal portion extending in the direction of the pulling axis of the single crystal body The method according to the hologram element manufacturing method, wherein the recording member of the hologram element is cut out from the single crystal body, and the recording member is cut out such that the core part and the normal part are included in the recording member. is there.

The present inventor has found that Bi ₁₂ S
The optical characteristics of the core portion (facet) in the iO ₂₀ single crystal are different from those of the normal portion (off facet),
According to the common knowledge of those skilled in the art that the recording member is optically inhomogeneous, the recording member is cut away from the core portion as shown in FIGS. 9A and 9B. However, contrary to this common sense, the present inventor cut out the recording member so as to include the core portion, and using this recording member, as will be described later, the diffraction efficiency of each portion of the core portion and the normal portion. The sensitivity was measured.

As a result, it was confirmed that there was no surprising difference in diffraction efficiency between the core portion and the normal portion. Furthermore, the present inventor has performed recording and reproduction of each image of a binary image and an analog image using this recording member, and as a result, there is no difference between the two and a good image is developed in any case. Was found. As a result, when cutting the recording member from the single crystal, the recording member can be cut so as to include the core portion, and the dimensions of the recording member have been successfully increased.

[0017]

Here, the single crystal can be pulled toward the <100> axis orientation and the <111> axis orientation. However, in order to obtain a particularly large single crystal, the <1>
00> It is preferable to raise in the axial direction. A particularly preferred lifting method will be described later. When the recording member is pulled up along the <100> axis, the main surface of the recording member is (01)
1) It is preferable that the recording material is cut out so as to form a surface. In this case, the recording member having the largest area can be cut out. In addition, the recording member can be cut out such that the main surface thereof becomes the (100) plane. In this case, the single crystal can be cut out perpendicular to the pulling axis direction.

FIG. 1A is a perspective view for explaining a cutting method according to an embodiment of the present invention, and FIG.
Is a plan view of the single crystal body 1. FIG. Main body 1 of single crystal 1
a has a columnar shape, and a substantially conical upper end 1b is formed at the upper end of the main body 1a. The single crystal 1 has a <10
0> axis direction. A core portion 2 is formed at the center of the single crystal body 1, and a normal portion 24 is formed so as to surround the core portion 2.

The single crystal 1 is cut in the longitudinal direction, and the recording member 3 is cut.
Is cut out. The pair of main surfaces 3a of the recording member 3 are (011) planes, and the longer side surface 3b is

[Outside 3] The shorter side surface 3c is a (100) plane. As shown in FIG. 1C, the recording member 3 includes an elongated core portion 20 at the center thereof, and normal portions 21 on both sides of the core portion 20. This makes it possible to cut out a recording member having an extremely large area, which has not been achieved in the past.

FIG. 2 (a) shows a single crystal 1 to a recording member 4;
FIG. 9 is a perspective view for describing a method of cutting out the direction perpendicular to the <100> axis. A pair of main surfaces 4a of the recording member 4 are oriented in the <100> axis direction.
b is

[Outside 4] The side surface 4c faces the <011> axis direction. As shown in FIG. 2B, a central portion of the recording member 4 includes a circular core portion 22.
The normal part 23 remains so as to surround the core part 22.

Next, Bi particularly suitable for the present invention is described.
_A method for producing a ₁₂ SiO ₂ single crystal and its characteristics will be described. FIG. 3 is a cross-sectional view schematically showing a single crystal pulling apparatus that can be suitably used in this manufacturing method. Inside the refractory 10, a crucible 12 preferably made of platinum is housed and installed, and the crucible 12 houses a melt 11 therein. High-frequency coil 8 surrounding refractory 10
Is provided, and the material in the crucible is melted by generating heat.

A refractory 6 is further provided on the upper side of the refractory 10, and an after heater 7 made of platinum is provided in the refractory 6.
Is installed. The pulling shaft 5 is inserted into the window 6 a of the refractory 6, and the lower end of the pulling shaft 5 is connected to the single crystal 9. While rotating the pulling shaft 5 as shown by the arrow B, it is pulled upward as shown by the arrow A to grow the single crystal body 9. 13 is a spacer.

The conditions for growing the single crystal are as follows:
It is preferable to use the conditions described in Japanese Patent Application No. 1-234399. That is, the temperature gradient from the surface of the melt of the crucible containing the raw material to 10 mm above in the pulling direction of the single crystal body is set to 50 to 75 ° C./cm, and the temperature gradient from then to 150 mm is set to 10 mm. ° C / cm
Hereinafter, the temperature is preferably set to 1 ° C./cm or more. Further, the heating temperature of the melt is preferably set to 850 to 950 ° C., and by installing a load cell on the pulling shaft,
Preferably, the diameter of the single crystal is automatically controlled.

Further, it is preferable to grow in an oxidizing atmosphere, the pulling speed is preferably 0.3 mm / hour to 4 mm / hour, and the rotation speed of the pulling shaft is 5 to 2 mm.
It is preferably set to 0 rpm. Under such growth conditions, a Bi ₁₂ SiO ₂₀ single crystal having the following characteristics can be obtained, and the present invention can be particularly suitably applied thereto.

[0025]

TABLE 1 lattice constant 10.0~10.2 × 10 ^{- 1 0} m density 9.1~9.3g / cm ³ permittivity 54-58 (100kHz) refractive index 2.4 to 2.6 (lambda = 633 nm) Dark resistance 0.5-5 × 10 ¹⁴ Ω · cm Photoconductivity 0.5-5 × 10 ⁸ Ω / cm (λ = 458)
nm, 2.5 mW / cm ² ) Verde constant 3.4 to 4.0 × 10 ⁻³ Oe · cm (λ
= 633 nm)

The principle of the hologram using the Bi ₁₂ SiO ₂₀ single crystal is described in the above-mentioned document “Holographic phase characteristics of BSO single crystal”, which can be used as a phase type volume hologram. .
When manufacturing this hologram, electrodes are formed on two side surfaces of the recording member, and a power supply is connected to each of these electrodes.
As a material for such an electrode, an ITO vapor-deposited film, a conductive adhesive in which a conductive material such as silver powder is contained in an adhesive, or the like is preferable.

As shown in FIGS. 1A and 1B,
When the main surface 3a of the recording member 3 faces the <011> axis, each electrode is

[Outside 5] Preferably, it is formed on the surface 3b. Then, the object light is made incident in a direction perpendicular to the main surface 3a, and at the same time, the reference light is made incident to write an image in the hologram element. Then
The reproduction light is irradiated onto the main surface from the same direction as the reference light to reproduce the written image.

As the object light and the reference light, Bi ₁₂ S
Argon ion laser light having a wavelength of 488 nm, in which the iO ₂₀ single crystal exhibits a photoconductive effect, can be preferably used, and helium neon laser having a wavelength of 633 nm, in which the Bi ₁₂ SiO ₂₀ single crystal does not exhibit a photoconductive effect, can be used as reproduction light. Light can be preferably used.

[0029]

EXAMPLES (Example 1) A recording member 3 was cut out by the method shown in FIG. 1, and a hologram element was prepared using the recording member 3, and its recording and reproduction characteristics were tested. Specifically, the single crystal body 1 having a diameter of 80 mm and a length of 100 mm was manufactured according to the above-described manufacturing method described with reference to FIG. As a crucible, diameter 150mm,
A cylindrical platinum crucible having a height of 150 mm was used.
In a 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, it is possible to increase the number of 10
The temperature gradient up to 150 mm was adjusted to 50-75 ° C./cm, followed by the temperature gradient up to 150 mm at 10 ° C./cm. In addition, the lifting speed is 1 to
1.5 mm / hour and the rotation speed of the pulling shaft is 10 r
pm. The properties of the obtained single crystal are shown in Table 2 below.

[0031]

Table 2 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 single crystal body 1, FIGS. 1 (a) and 1 (b)
As shown in FIG.
The recording member 3 of (c) was cut out. From this recording member, a flat sample of 8 mm × 8 mm × 3 mm in size was cut out by a peripheral knife grinder, and each main surface 3a of the sample was optically polished.

[Outside 6] Electrodes were formed on the two side surfaces 3b in the axial direction with a conductive resin, and a hologram element was formed.

The main surface was irradiated with an interference fringe of 130 lp / mm by an argon ion laser beam having a wavelength of 488 nm, and the diffraction efficiency of a 633 nm wavelength helium neon laser beam incident under Bragg diffraction conditions was measured. In FIG.
This measurement result is shown. In FIG. 4, the horizontal axis is the intensity of the writing light, the vertical axis is the diffraction efficiency, the white circles are the characteristics of the normal part, and the black circles are the characteristics of the core part. As can be seen from FIG. 4, it was surprisingly found that there was no difference in diffraction efficiency between the core portion and the normal portion.

Example 2 A recording member 3 was cut out from the single crystal 1 produced in Example 1 in the same manner as in Example 1. The dimensions of this recording member are 70 mm x 70 mm x 3 mm
And A pair of side surfaces 3b of the recording member 3 [

[Outside 7] On the surface in the axial direction] using a conductive resin. 7
The dimension of 0 mm x 70 mm is the distance between the eyes (usually 50 mm
), The reconstructed image can be observed using binocular parallax.

The main surface 3a was irradiated with 130 lp / mm interference fringes by argon ion laser light having a wavelength of 488 nm, and the diffraction efficiency of helium neon laser light having a wavelength of 633 nm satisfying the Bragg diffraction condition was measured. The applied voltage between the pair of electrodes was DC 20 kV. FIG. 5 shows the measurement results of the sensitivity characteristics of the diffraction efficiency.

In FIG. 5, the horizontal axis is the intensity of the writing light, and the vertical axis is the diffraction efficiency. As can be seen from FIG.
By irradiating light having an energy of 4 mJ / cm ² or more, a diffraction efficiency of 0.5% was obtained.

Then, in order to confirm the uniformity of each point on the hologram element, the diffraction efficiency at each point of the element was measured. FIG. 6 shows the measurement results. In FIG.
The horizontal axis shows the distance of each point on the main surface 3a from the side surface 3b, and the vertical axis shows the diffraction efficiency at each point. As can be seen from FIG. 6, there was no difference in diffraction efficiency between the normal part and the core part, and almost uniform diffraction efficiency was obtained at any position. This is also consistent with the result of Example 1 described above.

(Example 3) Using the hologram element prepared in Example 2, an experiment for reproducing a binary image and an analog image was performed. That is, each original image was written on a transmission film, and the transmission film was irradiated with scattered light having a wavelength of 488 nm, and the scattered light transmitted through the transmission film was used as each object light. The object light was incident on the main surface 3a in the vertical direction, and at the same time, the collimated reference light was irradiated on the main surface 3a, and each image was hologram-recorded. The dimensions of the transmission film on which the original image was recorded were 100 mm x 100 mm,
Each transmission film is 600 mm from the main surface of the hologram element.
It was installed at a remote location. Then, the main surface was irradiated with reproduction light having a wavelength of 633 nm to reproduce the hologram.

FIG. 7 shows a reproduced image of the binary image thus obtained, and FIG. 8 shows a reproduced image of the analog image.
Although speckle noise appears, a good image is reproduced. Each of these images could be directly observed with the naked eye. At this time, the position of the reproduced image corresponded to the position where the original film was placed, and the depth was accurately reproduced and confirmed with both eyes. From this experimental result, Bi _{1 2}
It has been confirmed that a hologram element using a SiO ₂ single crystal can be applied to a three-dimensional display.

[0040]

As described above, according to the present invention, when a recording member is cut from a single crystal, the recording member can be cut so as to include a core portion.
We succeeded in increasing the size of the recording member. And
By using this hologram element, a binary image or an analog image can be observed by binocular parallax, and the depth corresponding to the depth of the original image can be directly observed.

[Brief description of the drawings]

1A is a perspective view illustrating a state where a recording member 3 is cut out from a single crystal body 1, and FIG. 1B is a plan view illustrating a state where the recording member 3 is cut out from a single crystal body 1. FIG. FIG. 3C is a front view showing the recording member 3.

FIG. 2A is a perspective view showing a state in which a recording member 4 is cut out from a single crystal body 1, and FIG. 2B is a front view showing the recording member 4.

FIG. 3 is a cross-sectional view schematically showing a production apparatus suitable for producing a Bi ₁₂ SiO ₂₀ single crystal.

FIG. 4 shows a relationship between the write light intensity and the diffraction efficiency in the hologram element when the recording member 3 is cut to produce a small-dimension recording member sample and the hologram element is produced using the sample. It is a graph shown about both a part and a normal part.

FIG. 5 is a graph showing a relationship between writing light intensity and diffraction efficiency in a hologram element when a hologram element is manufactured using the recording member 3;

FIG. 6 is a graph showing a relationship between the position of each point of the hologram element and the diffraction efficiency at each point when the hologram element is manufactured using the recording member 3;

FIG. 7 is a photograph showing a binary image reproduced using a hologram element using a large-sized recording member 3;

FIG. 8 is a photograph showing an analog image reproduced using a hologram element using a large-sized recording member 3;

9A is a perspective view illustrating a state where the recording member 15 is cut out from the single crystal body 1, and FIG. 9B is a plan view illustrating a state where the recording member 15 is cut out from the single crystal body 1. FIG.

[Explanation of symbols]

1 Single crystal produced by the pulling method (Boolean)
2 Core part in single crystal body 3 Large recording member
3a Main surface (011) surface of recording member 3 3b Side surface of recording member 3

[Outside 8] Surface 3c Side surface (100) surface of recording member 3 4 Recording member 4a obtained by cutting single crystal body 1 in the horizontal direction 4a Main surface (100 surface) of recording member 4 4b Side surface of recording member 4

[Outside 9] Surface 4c Side (011) surface of recording member 4 5 Pull-up shaft 7 After heater 8 High frequency coil 11 Melt 12 Platinum crucible 20, 22
Core part in recording member 21, 23 Normal part in recording member 24 Normal part of single crystal 1

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03H 1/02 G03H 1/22 G03H 1/26 G02F 1/05 G02F 1/03 C30B 15/00 C30B 29 / 00 G02B 5/32

Claims (5)

(57) [Claims] 1. A hologram element comprising a recording member and an electrode for applying a voltage to the recording member, wherein the hologram element is a single crystal made of a Bi ₁₂ SiO ₂₀ single crystal grown by a pulling method. Body, the recording member is cut out of a single crystal having a core portion and a normal portion extending in the direction of the pulling axis of the single crystal body, and the core portion and the normal portion are A hologram element, wherein the hologram element is included in the recording member. _{2. The} Bi ₁₂ S grown by the pulling method.
When cutting out the recording member of the hologram element from a single crystal body made of iO ₂₀ single crystal and having a core part and a normal part extending in the direction of the pulling axis of the single crystal body, A method for manufacturing a hologram element, wherein the recording member is cut out such that the core portion and the normal portion are included in the recording member. 3. The method for manufacturing a hologram element according to claim 2, wherein said single crystal is pulled up in the <100> axis direction. 4. The hologram element according to claim 3, wherein the recording member is cut out along the <100> axis such that a main surface of the recording member has a <011> axis orientation. Production method. 5. The recording member according to claim 1, wherein a main surface of said recording member is <10.
4. The method for producing a hologram element according to claim 3, wherein the hologram element is cut out so as to have a 0> axis orientation.