JP2001013858A - Computer hologram and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to provide a bright reproduced image while reducing the operation load. SOLUTION: Many unit line segments are defined by a prescribed pitch (h) on the original picture. Many standard points Pmi are defined on the respective unit line segments Am and, at the standard positions, line light sources Lmi which have the length (h) and are parallel to a recording surface 20 are defined. In such a manner, the original picture is expressed as an assembly of the many line light sources. The recording surface 20 is irradiated with a reference light Rϕobliquely from above while forming a prescribed angle ϕ, and the interference fringes between the total line light sources arrayed on the unit line segments Am and the reference light are computed and recorded within a unit region Cm having a width (h). When the wave length λ and the angle ϕ of the light to be used are properly set, the same interference fringe patterns are generated repeatedly and periodically in the direction of Y-axis within the unit region Cm and, therefore, the computing is performed only for the pattern of one cycle, which are duplicated as much as necessary. The interference fringes obtained on the recording surface 20 are binarized, the binary picture is plotted on a medium by means of an electron beam plotting device and an emboss hologram is thus prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hologram, and more particularly, to a method for producing a computer generated hologram formed by forming interference fringes on a predetermined recording surface by calculation using a computer.

[0002]

2. Description of the Related Art In recent years, it has become possible to easily obtain coherent light using a laser, and the commercial use of holograms has become quite widespread. In particular, for cash vouchers and credit cards, from the viewpoint of forgery prevention,
It is becoming common to form holograms on a portion of a medium.

At present, commercially used holograms are obtained by recording an original image on a medium as interference fringes by an optical method. That is, an object constituting an original image is prepared, light from the object and reference light are guided onto a recording surface coated with a photosensitive agent using an optical system such as a lens, and interference fringes are formed on the recording surface. Is adopted. This optical method requires a highly accurate optical system to obtain a clear reproduced image, but is the most direct method for obtaining a hologram, and is the most widely used in industry. Method.

On the other hand, there is also known a method of forming an interference fringe on a recording surface by a calculation using a computer to create a hologram.
Generally, "Computer Synthetic Hologram (CGH: Computer Gen
erated Hologram) ", or simply" computer hologram ". This computer generated hologram is obtained by simulating the process of generating optical interference fringes on a computer, so to speak, the entire process of generating the interference fringe pattern is performed as an operation on the computer. When the image data of the interference fringe pattern is obtained by such a calculation, a physical interference fringe is formed on an actual medium based on the image data.
Specifically, for example, a method has been put to practical use in which image data of an interference fringe pattern created by a computer is given to an electron beam drawing apparatus, and a physical interference fringe is formed by scanning an electron beam on a medium. I have.

With the development of computer graphics technology, the handling of various images on computers is becoming common in the printing industry. Therefore, it is convenient if the original image to be recorded on the hologram can be prepared as image data obtained using a computer. In order to meet such demands, the technology of creating computer holograms has become an important technology, and it is expected that in the future, this technology will replace optical hologram creation methods. For example, Japanese Patent Laid-Open No. 11-
Japanese Patent Application Laid-Open No. H11-24454 discloses a technique for suppressing the occurrence of uneven brightness in a reproduced image, and Japanese Patent Application Laid-Open No. H11-24540 discloses a technique for suppressing the generation of streak noise. Discloses a technique for obtaining a clearer reproduced image, and attempts have been made to improve the quality of the reproduced image. Also, Japanese Patent Application No. 10-22604 discloses a technique for reducing the calculation load, and Japanese Patent Application No. 11-15871 discloses a technique for handling a gradation image. Japanese Patent Application No. 11-17749 discloses a technique for handling a color image.

[0006]

As described above, computer holograms are a field in which great demand is expected in the future. However, at present, there are some problems to be solved for commercial use. I have. For example, one of the important issues to be solved is that a large calculation load is imposed on a computer when calculating interference fringes. At present, it is possible to create a computer hologram with the same quality as an optical hologram by performing an operation over a long period of time using an ultra-high-speed computer with excellent arithmetic processing capability. Such a production method cannot be used commercially. Therefore, in practice, some method must be used to reduce the computational load on the computer by using some method. However, adopting such a technique causes another problem that the reproduced image is darkened as a whole.

Therefore, the present invention reduces the computational load while
An object of the present invention is to provide a method for creating a computer generated hologram capable of obtaining a bright reproduced image.

[0008]

According to a first aspect of the present invention, there is provided a method for producing a computer generated hologram formed by forming interference fringes on a predetermined recording surface by calculation using a computer. Defining an original image, a recording surface for recording the original image, and a reference beam for irradiating the recording surface; defining a number of operation points on the recording surface; Calculating the intensity of the interference wave formed by the object light emitted from the original image and the reference light;
Performing physical interference fringes on the medium based on the intensity of the interference wave obtained for each calculation point, and defining a plurality of reference points distributed on the original image, A line light source passing through a point is defined, and the intensity of an interference wave formed by the object light emitted from the line light source and the reference light is calculated.

(2) The second aspect of the present invention is the above-mentioned first aspect.
In the method for producing a computer generated hologram according to the above aspect, as each line light source, a line light source composed of a line segment having a predetermined length h parallel to the recording surface is defined.

(3) A third aspect of the present invention is the above-mentioned first aspect.
Alternatively, in the method for creating a computer generated hologram according to the second aspect, a plurality of unit line segments are defined on the original image, a plurality of reference points are defined on each unit line segment, and at each of these reference point positions, Line light sources are defined so as to be parallel to each other.

(4) The fourth aspect of the present invention is the above-described third aspect.
In the method for creating a computer generated hologram according to the aspect, a plurality of cut surfaces are defined so as to be parallel to each other at a predetermined pitch h, and each unit line segment is defined as a contour line of a cut surface obtained by cutting the original image at each cut surface. For each reference point on these unit line segments, a line light source having the same length h as the predetermined pitch h is defined so as to be perpendicular to each cut plane.

(5) The fifth aspect of the present invention is the above-mentioned first aspect.
In the method for producing a computer generated hologram according to the fourth to fourth aspects, the wavelength and irradiation angle of the reference light are set so that the same interference fringe pattern is periodically and repeatedly generated on the recording surface, and a plurality of n sets of the same interference The fringe patterns are arranged adjacent to each other, and the other (n-1) sets of the same interference fringe patterns are created using the result of the intensity calculation performed to create one set of interference fringe patterns. It was made.

(6) The sixth aspect of the present invention is the above-mentioned fifth aspect.
In the method for creating a computer generated hologram according to the aspect, physical interference fringes are created on the recording medium of the hologram using a large number of pixels, and an integral multiple of the repetition period d of the interference fringe pattern is equal to the pixel size L. It is set so as to be an integral multiple (however, d / L ≧ 2).

(7) A seventh aspect of the present invention is the above-mentioned first aspect.
In the method for creating a computer generated hologram according to the sixth to sixth aspects, an original image is defined on an XYZ three-dimensional coordinate system, and a recording surface is defined on an XY plane of the coordinate system. And set the direction of the reference light to
The recording medium is parallel to the YZ plane and obliquely enters the recording surface.

(8) The eighth aspect of the present invention is the above-mentioned first aspect.
According to a seventh aspect of the present invention, a medium for a computer generated hologram is prepared by the method for generating a computer generated hologram.

(9) According to a ninth aspect of the present invention, in a computer-generated hologram medium in which an original image is recorded as interference fringes on a predetermined medium by using a calculation using a computer, a plurality of units are provided on the medium. Regions are defined, each unit region is associated with a specific region on the original image, and within each unit region,
Information on line light sources parallel to each other arranged in a corresponding specific area on the original image is recorded.

(10) According to a tenth aspect of the present invention, in a computer-generated hologram medium in which an original image is recorded as interference fringes on a predetermined medium by using a calculation using a computer, a plurality of units are provided on the medium. Define the area, and each unit area:
In each unit area, the same interference fringe pattern is periodically and repeatedly recorded, and at least for the same unit area, the information is repeatedly recorded. The interference fringes are continuous at the boundaries of the interference fringe patterns.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

§1. Basic Principle of Computer-Generated Hologram FIG. 1 is a principle diagram showing a general method of creating a hologram, and shows a method of recording an original image 10 on a recording surface 20 as interference fringes. Here, for convenience of explanation, an XYZ three-dimensional coordinate system is defined as shown in FIG.
It is assumed that it is placed on the Y plane. When the optical method is used, an object to be recorded is prepared as the original image 10. The object light O emitted from an arbitrary point P on the original image 10 travels toward the entire recording surface 20. On the other hand, the recording surface 20 is irradiated with the reference light R, and interference fringes between the object light O and the reference light R are recorded on the recording surface 20.

In order to create a computer generated hologram at the position of the recording surface 20, the original image 10, the recording surface 20, and the reference light R are defined as data on a computer, and the recording surface 2 is defined.
What is necessary is just to calculate the interference wave intensity at each position on 0. Specifically, for example, as shown in FIG.
, PN, and the object light O1, O2 from each point light source is treated as a set of point light sources P1, P2, P3,.
O3,..., Oi,.
y), and the reference light R is applied to the calculation point Q (x,
y), and the calculation for obtaining the amplitude intensity at the position of the calculation point Q (x, y) of the interference wave generated by the interference between the N object lights O1 to ON and the reference light R is performed. Just do it. The calculation is usually performed on the object light and the reference light as monochromatic light. On the recording surface 20, a large number of calculation points corresponding to the required resolution are defined, and the calculation of the amplitude intensity is performed for each of these calculation points. A distribution will be obtained.

If a physical shading pattern or emboss pattern is formed on an actual medium based on image data showing such an intensity distribution, a hologram in which the original image 10 is recorded as interference fringes can be created. As a technique for forming high-resolution interference fringes on a medium, drawing using an electron beam drawing apparatus is suitable. An electron beam lithography apparatus is widely used for purposes such as drawing a mask pattern of a semiconductor integrated circuit, and has a function of scanning an electron beam with high accuracy. Therefore, if the image data showing the intensity distribution of the interference wave obtained by the calculation is given to the electron beam drawing apparatus and the electron beam is scanned,
An interference fringe pattern according to this intensity distribution can be drawn. However, a general electron beam drawing apparatus has only a function of drawing a binary image by controlling drawing / non-drawing. Therefore, a binary image may be created by binarizing the intensity distribution obtained by the calculation, and the binary image data may be provided to the electron beam drawing apparatus.

FIG. 3 is a conceptual diagram of such a binarization process. By the above calculation, each calculation point Q on the recording surface 20
(X, y) defines a predetermined amplitude intensity value. Therefore, a predetermined threshold value (for example, an average value of all the amplitude intensity values distributed on the recording surface 20) is set for the amplitude intensity value, and a calculation point having an intensity value equal to or more than the threshold value is set to A pixel value “1” is given, and a pixel value “0” is given to a calculation point having an intensity value less than the threshold value, and each calculation point Q (x, y) is set to “1” or “0”. Is converted into a pixel D (x, y) having a pixel value of
A binary image consisting of a set of (x, y) is obtained. By giving the data of this binary image to the electron beam drawing apparatus and performing drawing, the interference fringes can be drawn as a physical binary image. Actually, based on the physically drawn interference fringes, for example, an embossed plate is created, and embossing is performed using the embossed plate, thereby forming a hologram in which the interference fringes are formed as an uneven structure on the surface. Can be mass-produced.

§2. Conventional to reduce the computational burden
Proposed method The basic principle of creating a computer generated hologram is as described above. However, in order to obtain a reproduced image with high quality, it is necessary to increase the resolution of the interference fringes recorded on the recording surface 20 and the resolution of the original image 10 itself.
In other words, it is necessary to increase the number of calculation points Q defined on the recording surface 20 and increase the number of point light sources P constituting the original image 10, and the calculation load on the computer increases according to the product of the two. Will do. For this reason, it is difficult to commercially use a computer generated hologram created by such a method in consideration of the processing capability of a general computer at present.

Therefore, for example, Japanese Patent Application No. Hei 10-2260
No. 4 discloses a practical method for reducing the computational load. Here, this method will be briefly described.

Now, as shown in FIG.
A plurality of M unit line segments A1,..., Am-1, Am, Am + 1,.
..., AM is defined. Actually, a plurality of cut planes may be defined so as to be parallel to each other at a predetermined pitch h, and each unit line segment may be defined as a contour line of a cut surface obtained by cutting the original image at each cut plane. In the case of recording an arbitrary-shaped solid or the like as an image, since the original image 10 has an arbitrary curved surface, the unit line defined on the arbitrary curved surface forms a “curve segment”. Therefore, the term “unit line segment” in this specification is used to mean not only “straight line segment” but also “curved line segment”. After the M unit line segments are defined in this way, subsequently, a plurality of reference points are defined on each unit line segment. For example, FIG. 4A shows an example in which N reference points Pm1,..., Pmi,..., PmN are defined on the m-th unit line segment Am. The reference points may be arranged at a predetermined pitch on a unit line segment, for example.

On the other hand, as shown in FIG.
On the top, M projection line segments B1,..., Bm-1, Bm, B
, BM (indicated by broken lines in the figure) are defined. These projected line segments are respectively defined as unit line segments A1,..., Am-1, Am, Am + 1,.
M is a projection image obtained when the recording surface 20 is projected onto the recording surface 20, and corresponds to a cut edge when the recording surface 20 is cut by the above-described cutting surface. Then, each projection line segment is moved up and down by a width of h / 2 in the direction perpendicular to the projection line segment by cutting at + h / 2 and − (FIG. 4B). ), A band-shaped unit area C1,..., Cm-1, Cm, Cm + 1,.
To form In FIG. 4B, the m-th unit area Cm formed by moving the m-th projection line segment Bm up and down is hatched. As a result, M unit line segments A1,..., Am-1, Am, A on the original image 10
, AM, and M unit areas C on the recording surface 20
, Cm-1, Cm, Cm + 1,..., CM correspond one-to-one.

In order to record the information of the original image 10 on the recording surface 20, as described above, the positions of a large number of calculation points Q defined on the recording surface 20 are determined based on the number of operation points Q defined on the original image 10. Then, the intensity of the interference wave between the object light from the point light source P and the reference light R is calculated. Therefore, each unit line segment A
,..., Am−1, Am, Am + 1,..., AM, point light sources are defined at respective reference point positions, and the intensity calculation of the interference wave between the object light and the reference light R from these point light sources is performed. At this time, for the calculation point Q in the m-th unit area Cm, N reference points Pm1,..., Pmi,..., PmN on the corresponding m-th unit line segment Am The calculation is performed in consideration of only the object light from the upper point light source. That is, as for the calculation points in the hatched area in FIG. 4B, only the information on the point light sources on the N reference points Pm1,..., Pmi,. Will be recorded.

FIG. 5 is a view showing a system necessary for recording as viewed from the back side of the recording surface 20 for explaining the above basic principle. Here, an XYZ three-dimensional coordinate system is defined, and the recording surface 20 is placed on the XY plane. For convenience of explanation, the original image 10 is m-th
Only the m-th unit line segment Am is shown, and on the recording surface 20, the m-th unit region Cm (hatched elongated rectangular region having a width h around the m-th projection line segment Bm) ) Are only shown. A number of reference points are defined on the unit line segment Am, and interference fringes between the object light from the point light source defined at these reference point positions and a predetermined reference light are defined on the recording surface 20. It is recorded at each calculation point on the unit area Cm. In the calculation for recording such interference fringes, focusing on individual point light sources, a certain reference point Pm
It can be said that the calculation is such that the spread angle in the Y-axis direction of the object light (indicated by a dashed line in the figure) emitted from the point light source on i is limited to a predetermined angle ξ shown in FIG. In this example,
Since the spread of the object light in the X-axis direction is not limited, all the reference points Pm1, Pm2,
The object light emitted from Pm3,..., Pmi,..., PmN is applied to a rectangular unit area Cm having a width equal to the width of the recording surface 20 and a height h having a dimension h determined according to the angle ξ. Will be.

On the other hand, the reference light Rφ is a plane wave that travels along a plane parallel to the YZ plane when an XYZ three-dimensional coordinate system is defined as shown in FIG.
Is light emitted from obliquely above. of course,
The irradiation direction of the reference light Rφ may theoretically be incident from any direction, but in practice, as shown in the illustrated example,
It is preferable to be parallel to the YZ plane and to enter the recording surface 20 from obliquely above. This is because when a hologram recorded on the recording medium 20 is used as a forgery prevention mark for a credit card or the like, it is often observed using reproduction illumination light obliquely from above. The hologram created using such reference light Rφ can present an optimum reproduced image under reproduction light emitted from obliquely above, such as light from ceiling illumination.

If an original hologram image is to be recorded, it is necessary to perform a calculation for each calculation point in consideration of object light from all point light sources on the original image 10 shown in FIG. However, according to the above-described method, since the calculation only needs to take into account the object light from the point light source located on one unit line segment, the calculation load is greatly reduced.

The width h (vertical width) of each unit area defined on the recording surface 20 in the Y-axis direction is a dimension that cannot be visually recognized (a resolution higher than the resolution of the naked eye is realized). It is preferable to set it to the size that can be achieved. This is because, when the width h is set to a visually recognizable dimension, the boundary line of each unit area is recognized by the naked eye when the entire recording surface 20 is observed, and a horizontal stripe pattern is generally formed. This is because they may be observed. For example, when h is set to about 1 mm (a dimension that can be visually recognized sufficiently), the width of the reproduced image is 1 mm.
mm horizontal stripes will be observed in an overlapping manner. Specifically, h <100 μm or less, more preferably h <50 μm
With the following setting, in most cases, the horizontal stripe pattern is not recognized. On the other hand, since the width of the unit area in the X-axis direction is equal to the width of the recording surface 20, the unit area naturally has a visually recognizable dimension.

§3. Production of computer generated hologram according to the present invention
The method of forming a computer generated hologram according to the present invention is a method obtained by further improving the method described in §1 and §2 described above, and its basic concept is to perform an operation using a line light source instead of a point light source. On the point. For example, in the method shown in FIG.
A point light source is defined on the reference point Pmi, and interference fringes between the object light from the point light source and the reference light Rφ are recorded. In general,
The light from the point light source is light that spreads so that the wavefront becomes spherical. When the object light traveling from the point light source located on the reference point Pmi is projected on the XZ plane or the YZ plane, one point is shown in FIG. A projected image as indicated by the chain line is obtained. Therefore, originally, the object light from the point light source reaches the entire surface of the recording surface 20, but in the method described in §2, as shown in FIG. Since the calculation is performed with the spread angle limited to the predetermined angle 所 定, the object light from the point light source on the reference point Pmi reaches only within the unit area Cm.

On the other hand, in the present invention, many line light sources are defined on the original image 10. For example, as shown in FIG. 7, a line light source Lmi is defined on a reference point Pmi,
Consider a case where interference fringes between the object light from the line light source Lmi and the reference light Rφ are recorded on the recording surface 20. here,
The line light source Lmi is assumed to be composed of a line segment having a length h that is parallel to the recording surface 20. More specifically,
In the example shown in FIG. 7, the line light source Lm is set so as to be parallel to the Y axis.
i is defined, and the center of the line light source Lmi is the reference point P
mi position. Here, since the XYZ three-dimensional coordinate system is defined such that the unit line segments Am and Bm are parallel to the X axis and the recording surface 20 is on the XY plane, the line light source Lmi is parallel to the Y axis. . Line light source Lmi
Is a linear light emitting element having a uniform intensity, and its intensity value may be determined based on, for example, a pixel value of the reference point Pmi on the original image 10. In general, the light from the line light source is light that spreads so that the wavefront becomes cylindrical. When the object light traveling from the line light source Lmi on the reference point Pmi is projected on the XZ plane, a dashed line in FIG. Although a projected image as shown in the figure is obtained, when this is projected on the YZ plane, a projected image as shown by a chain line in FIG. 8 is obtained.

In other words, when observing the system shown in FIG. 7 from above, the object light from the line light source Lmi spreads radially as shown in FIG. When observed, the object light from the line light source Lmi becomes light traveling in the horizontal direction as shown in FIG. After all,
The object light from the line light source Lmi reaches only the unit area Cm having the width h in the Y-axis direction without any restriction on the spread angle. In this way, for each calculation point in the unit area Cm, the intensity of the interference wave between the object light from the line light source Lmi and the reference light Rφ is calculated, and the interference fringes are recorded in the unit area Cm. Become.

In FIG. 7, for convenience of illustration, the line light source Lmi defined on the i-th reference point Pmi on the unit line segment Am
Although only the manner in which the interference fringes between the object light and the reference light Rφ are recorded in the unit area Cm is shown, in fact, N reference points Pm1 to PmN are formed on the unit line segment Am. Are defined and the line light sources Lm1 to Lm1
mN is defined (each line light source has a length h and is arranged in a direction parallel to the Y axis so that its center is on the unit line segment Am). Therefore, in the unit area Cm, interference fringes between the object light from the N line light sources Lmi to LmN and the reference light Rφ are recorded in an overlapping manner.

Further, as shown in FIG.
Above, M unit line segments A1 to AM are defined so as to be parallel to each other with a predetermined pitch h (all become line segments or curve segments parallel to the XZ plane), and all of them are , A plurality of reference points are defined on each of the unit line segments, and a line light source perpendicular to each of the unit line segments (parallel to the Y axis) is defined for each of the reference points. Therefore, all the M unit areas C1 shown in FIG.
To CM, corresponding unit line segments A1 to AM
The interference fringes between the object light and the reference light from the line light source defined at the plurality of reference points are recorded.

§4. Advantages of using a linear light source As described above, the conventional method described in §1 and §2 and the §
The fundamental difference from the method according to the present invention described in 3 is that the former records information about a point light source arranged on each reference point, while the latter records information on each reference point. The point is that information about the line light source is recorded. By using a linear light source instead of a point light source,
It has been found that two advantages can be obtained. The first advantage is that a brighter reproduced image can be obtained, and the second advantage is that the calculation load for obtaining interference fringes can be reduced. Hereinafter, these two advantages will be described in order.

The reason for obtaining a bright reproduced image, which is the first merit, can be considered as follows. Now, consider a point light source model shown in FIG. 9 and a line light source model shown in FIG. The point light source model shown in FIG. 9 is a model for reproducing a computer generated hologram (the method of FIG. 5) in which an original image is recorded using the conventional point light source described in §2, and a line light source model shown in FIG. Is a model for reproducing a computer generated hologram (method of FIG. 7) in which an original image is recorded using the line light source according to the present invention described in §3. Both models show side views as viewed from the lateral direction. The original image is placed on the left side of the recording surface 20, and the reference light R is also placed on the left side.
Irradiation with φ (indicated by a dashed line) records interference fringes, and the reproduction state when the interference fringes are observed from a viewpoint E on the right side of the recording surface 20 is shown. At the time of reproduction, the illumination light for reproduction is irradiated from the same direction as the reference light Rφ (actually, the illumination light for reproduction is often irradiated from the right side of the recording surface 20; The illumination light is emitted from a direction having a mirror image relationship with the reference light Rφ when the recording surface 20 is a mirror surface).

Now, let us consider a part of the original image reproduced based on the interference fringes recorded in the area (unit area Cm) of the width h of the recording surface 20, as shown in FIG. In the case of the light source model, the point light source on the reference point Pmi is reproduced, whereas in the case of the line light source model shown in FIG. 10, the line light source Lmi is reproduced. In the former case, the object light O (shown by a solid line) spreads from the reference point Pmi.
Since the reproduction light (indicated by a broken line) directed to the viewpoint E is on an extension of this object light, the reproduction light becomes light spreading vertically as shown in FIG. However, in the latter case, the object light O
(Indicated by a solid line) proceeds in parallel from the line light source Lmi. Playback light (also indicated by a broken line) that also goes to the viewpoint E
Is on an extension of this object light, and as shown in FIG. 10, the reproduction light is light that travels in parallel. After all, in the point light source model shown in FIG. 9, the reproduction light tends to be dispersed vertically, whereas in the line light source model shown in FIG.
Such reproduction light dispersion will not occur. For this reason, as shown in the figure, as far as the viewpoint E is located in the traveling direction of the reproduction light, the latter has a greater amount of reproduction light gathered at the viewpoint E than the former, and appears brighter. Become.

However, if the position of the viewpoint E is changed, the merit turns into a demerit. For example, if the position of the viewpoint E is moved upward from the position shown in the figure and the image of the light source is observed obliquely from above, if the latter, the reproduced light does not reach the viewpoint E at all, and the reproduced image is completely invisible. On the other hand, in the former case, in the former, a part of the reproduction light reaches the viewpoint E, and the reproduced image is somewhat visible.
In other words, in the point light source model shown in FIG. 9, the observation range of the image in the vertical direction is set wide, whereas in the line light source model shown in FIG. 10, the observation range of the image in the vertical direction is set narrow. It will be.

However, considering the use of a credit card as a forgery prevention mark or the like, it is generally considered that the observation is frequently performed with the viewpoint E positioned vertically above the recording surface 20, so that the observation range is narrow. Even if this happens, it can be said that the line light source model shown in FIG. 10 that can obtain the brightest reproduced image when observed with the viewpoint E placed vertically above is more preferable. This is the first advantage of the present invention.

The second advantage, that is, "the calculation load for obtaining interference fringes can be reduced" is as follows. First, compare FIG. 11 and FIG. FIG. 11 is a schematic diagram of an interference fringe pattern recorded in one unit area in the point light source model shown in FIG. 9, and FIG. 12 is a schematic diagram of a pattern recorded in one unit area in the linear light source model shown in FIG. FIG. 2 is a schematic view of a pattern of interference fringes to be performed (both schematically show interference fringe patterns and do not show actual interference fringes). Comparing the two, the pattern shown in FIG. 12 can be divided into four parts in the vertical direction, and when such division is made, the same interference fringe pattern is formed in each divided area. You can see that there is. That is, the interference fringe patterns in the four divided regions having the vertical width d are all identical patterns. Even if the pattern shown in FIG. 11 is divided into four in the vertical direction to form divided regions, the patterns in each divided region are not the same.

As shown in FIG. 12, if it is known in advance that the same interference fringe pattern is repeatedly arranged adjacently on the recording surface with a period d, the calculation load for obtaining the interference fringes can be reduced. It is. That is, if it is known in advance that a plurality of n sets of the same interference fringe patterns are arranged adjacent to each other, the result of the intensity calculation performed to create one set of the interference fringe patterns is used to obtain another (n). -1) Since a set of identical interference fringe patterns can be created, the number of calculations can be reduced to 1 / n. For example, in the example shown in FIG. 12, it is known in advance that a plurality of four sets of the same interference fringe patterns are arranged adjacently with a period d. Need not be performed. For example, an interference fringe operation is performed on one set of divided regions having a width d (a quarter of the entire region), and the remaining three sets of divided regions are calculated by the first set of operations. It is sufficient to duplicate and arrange the obtained interference fringe pattern. If the same interference fringe pattern can be duplicated and used in this way, it is possible to obtain not only the advantage of reducing the calculation load but also the additional advantage of reducing the total data amount required for pattern drawing. Due to this advantage, when drawing an interference fringe pattern using an electron beam drawing apparatus or the like, the data transfer efficiency is significantly improved.

The reason why the same interference fringe pattern is repeated when a line light source is used will be briefly described with reference to the model shown in FIG. First, the line light source L
From the mi, object light O is emitted from any part in the right direction in the figure. Here, the line light source Lmi is a light source having a uniform intensity in the length direction and is parallel to the recording surface 20, so that any linear light source Lmi in the unit area having the length h on the recording surface 20 Regarding the position, the object light O is irradiated under the same condition, and the amplitude intensity and the phase are exactly the same. In this way, the interference fringe pattern is formed in this unit area even though the object light O is irradiated under exactly the same conditions, because the phase of the reference light Rφ is different in each part.

Now, as a light beam constituting the reference light Rφ,
As shown, five light beams R1 to R5 are considered. Since the reference light Rφ is originally spatially coherent light, the phases of the five light beams are all the same. However, since the light enters the recording surface 20 at an oblique angle φ, the optical path lengths before reaching the recording surface 20 are different from each other, and the phases at the arrival points F1 to F5 are different from each other. For example, the light path length of the light flux R2 is longer than the light path length of the light flux R1 by a predetermined length, and the light flux R
The optical path length of the light flux R3 is longer than the optical path length of No. 2 by a predetermined length. Here, assuming that the difference in the optical path length is exactly one wavelength, the phases of the reference light Rφ are different by 2π at the points F1 and F2, and also at the arrival points F2 and F3. The phases will differ by 2π. After all, the phase of the reference light Rφ is shifted by 2π between the five arrival points F1 to F5. For this reason, the same interference fringe pattern having a period d appears four times repeatedly on the recording surface 20, and an interference fringe pattern as shown in FIG. 12 is obtained.

On the other hand, when a point light source is used, the phase of the reference light Rφ on the recording surface 20 is repeated at a period d as shown in FIG. Therefore, no repetitive pattern is obtained in the entire unit section having the width h.

The repetition period d of the interference fringe pattern obtained when a line light source is used can be obtained in advance by the equation shown in FIG. That is, as shown in the upper part of FIG. 13, the irradiation angles of the object light O and the reference light R are considered, and the recording surface 2
With the normal direction set on zero as a reference for the angle, the traveling angle of the object light O is represented by θo, the traveling angle of the reference light R is represented by θr,
If the wavelength of the light used (object light and reference light) is λ,
Repetition period d of interference fringe pattern appearing on recording surface 20
Is determined by d = λ / | sin θr−sin θo |, as shown in the lower part of FIG. Since the object light O travels rightward in the figure toward the viewpoint E, θo = 0 always.
In the above example, θr = φ. Of course, if the repetition period d becomes longer than the length h of the linear light source, a repetition pattern can no longer be obtained. Therefore, in order to obtain a repetitive pattern in order to reduce the calculation load, it is necessary to set the wavelength λ of the light to be used and the irradiation angle θr of the reference light to appropriate values so that d <h. More preferably, if h is an integer multiple of d, the same interference fringe pattern may be duplicated on the recording surface 20 an integral number of times, thus further reducing the computational load (h If not an integer multiple of d, for example, h is d
3.7 times the same interference fringe pattern, the same interference fringe pattern is duplicated only twice, and then the width of the pattern is reduced to 7/1.
A process of duplicating only the 0 part is required, which makes the process somewhat complicated).

In setting the repetition period d, there is another point to be noted. That is, the size of a pixel when recording interference fringes on a physical medium is taken into consideration. As described above, when actually recording an interference fringe pattern obtained by calculation on a physical medium, an electron beam lithography apparatus or the like is used. In such a drawing apparatus, since the interference fringe pattern is drawn as a set of rectangular pixels, it is better to set the period d of the interference fringe pattern to be an integral multiple of the size of this pixel. convenient. For example, λ = 633 nm, θr = 45 °, θ
If o = 0 °, then d = 895.
19 …… nm. If such an irregular dimension value appears, there is a problem in performing drawing with a general electron beam drawing apparatus.

For example, if the sampling interval of the electron beam lithography system used is 200 nm, the interference fringe pattern created using this lithography system has a size of 200 nm.
It is rendered as a set of m pixels. Therefore, if the period d is an integral multiple of 200 nm, it is very convenient for performing drawing. As an example,
If the period d is set to four times the sampling interval 200 nm, d may be set to 800 nm. In this way, if the period d is determined first and the above equation is applied, for example, λ = 565.865 nm, θr = 45 °, θo
= 0 ° can be set. Here, the wavelength λ is an odd value. Actually, there may not be a light source having such a wavelength, but in the case of a computer generated hologram, the wavelength λ is a mere numerical value used for calculation. There is no problem at all.

FIG. 14 is a diagram showing an interference fringe pattern actually drawn under such conditions. Due to the restrictions of the electronic application, the detailed portion of the figure cannot be clearly expressed, but it can be recognized to some extent that the same interference fringe pattern is repeated with a period d. FIG. 15 shows the cycle d.
FIG. 6 is a diagram extracting and showing only one interference fringe pattern corresponding to FIG. Here, d = 800 nm, h = 8 μm, and the sampling interval is 200 nm. Therefore, the interference fringe pattern for one cycle shown in FIG. 15 is composed of four pixels arranged in the vertical direction, and the interference fringe pattern for one unit area shown in FIG. 10 times. Of course, the calculation for obtaining the interference fringe pattern only needs to be performed for the pattern for one cycle shown in FIG. 15, and for the remaining nine cycles, the processing for duplicating the pattern may be performed.

The period d does not necessarily need to be an integral multiple of the pixel size of the drawing apparatus, and may be set so that twice the period d is an integral multiple of the pixel size. For example, in the above example, the period d is set to 800 nm for the pixel size of 200 nm, but the period d is set to 700 nm.
Can also be set to If d = 700 nm, the period d itself is not an integral multiple of the pixel size, but 1400 nm, which is twice the period d, is equal to the pixel size 200.
Since this interference fringe pattern is an integral multiple of nm, if this interference fringe pattern is handled as a pattern having a period of 2d, no problem will occur when performing drawing. As a result, it is sufficient to set such that the integral multiple of the period d is an integral multiple of the pixel size. However, an interference draft cannot be recorded unless the period d is set to be twice or more the pixel size L by the sampling theorem.

§4. Computer hologram medium according to the present invention
As described above, according to the computer generated hologram of the present invention, the first advantage that a bright reproduced image can be obtained and the second advantage that the calculation load at the time of creation can be reduced can be obtained. . Here, the configuration of the computer generated hologram medium itself capable of producing such advantages will be described.

First, a plurality of unit areas are defined in the computer generated hologram medium, and each unit area corresponds to a specific area on the original image.
For example, in the case of a medium having a recording surface 20 as shown in FIG. 4B, a total of M unit areas C1 to CM are defined, and each unit area is a specific area on the original image 10, That is, it corresponds to an area corresponding to the unit line segments A1 to AM. In each unit area, information on a line light source arranged in parallel with the medium is recorded in a corresponding specific area on the original image. For example, FIG.
In the m-th unit area Cm shown in FIG.
Information on the line light sources (parallel to the recording surface 20) arranged at the reference points Pm1 to PmN on the corresponding unit line segment Am is recorded. In this way, when the information of the line light source is recorded, as described with reference to the model of FIG. 10, the effect that the reproduction light is gathered at the position of the viewpoint E without dispersion is obtained, and thus the entire light is bright. A reproduced image will be obtained.

Focusing on the merit of reducing the computational load at the time of creation, the same interference fringe pattern having a period d periodically appears in each unit area of the computer generated hologram as shown in FIG. It will be recorded repeatedly. Moreover, the interference fringes are not simply recorded repeatedly, and the interference fringes are continuous at the boundaries of the repeatedly recorded interference fringe patterns as far as the unit area is concerned. That is, the interference fringe pattern shown in FIG. 12 is a continuous pattern over the width h, and is also a continuous pattern at the boundary portion for each repetition period d. This means that the information amount of the original image is not reduced as a result of performing the processing for reducing the calculation load. In other words, FIG.
In the above, even when the calculation is actually performed on all the calculation points in the full width h to form the interference fringe pattern, the calculation is actually performed only on the calculation points in the quarter of the full width h corresponding to the period d. Even if an interference fringe pattern is formed and copied to obtain an interference fringe pattern for the entire width h, exactly the same result can be obtained.

The above-mentioned publications disclose various methods for reducing the computational load when creating a computer generated hologram. However, in the conventionally disclosed method,
Since the amount of information of the original image is reduced by the measure for reducing the calculation load, a problem that the quality of the reproduced image is deteriorated is unavoidable. According to the method of the present invention, the same reproduced image quality can be obtained with or without taking measures to reduce the computational burden.

As described above, the present invention has been described based on the illustrated embodiments. However, the present invention is not limited to these embodiments, and can be implemented in various other forms. For example, the original image used in the present invention may be a two-dimensional image or a three-dimensional image. Of course, the present invention can be applied to a method of recording a gradation image or a color image (the method described in each of the above-mentioned publications). In the above embodiment, each line light source is set to be parallel to the recording surface. However, for the purpose of obtaining a merit of obtaining a bright reproduced image, each line light source is not necessarily parallel to the recording surface. do not have to. However, it is preferable that each line light source be parallel to each other. In practice, it is preferable to obtain the brightest reproduced image when observed from above and perpendicular to the recording surface. From this viewpoint, it is preferable to set each line light source parallel to the recording surface. Is preferred. Further, the present invention relates to the above-mentioned Japanese Patent Application No.
The method is also applicable to the method disclosed in the specification of JP-A-1-15711, and in this case, the original image can be recorded and reproduced as an image having a gradation.

[0057]

As described above, according to the method for producing a computer generated hologram according to the present invention, a bright reproduced image can be obtained while reducing the computational load at the time of production.

[Brief description of the drawings]

FIG. 1 is a principle diagram showing a general method of creating a hologram, and shows a method of recording an original image 10 on a recording surface 20 as interference fringes.

FIG. 2 is a diagram showing a method of calculating the intensity of an interference wave at an arbitrary point Q (x, y) on a recording surface based on the principle shown in FIG.

FIG. 3 is a conceptual diagram illustrating a process of binarizing an intensity distribution image obtained by calculation to obtain a binary image.

FIG. 4 is a diagram showing a unit line segment defined on an original image 10 and a unit area defined on a recording surface 20, in one embodiment of a method for creating a computer generated hologram according to the present invention.

FIG. 5 is a perspective view showing a conventional method of recording object light from a point light source on an original image on a recording surface 20.

FIG. 6 is a diagram showing a traveling direction of object light emitted from a point light source.

FIG. 7 is a perspective view showing a method of the present invention for recording object light from a line light source on an original image on a recording surface 20;

FIG. 8 is a diagram showing a traveling direction of object light emitted from a line light source.

FIG. 9 is a side view showing a traveling direction of reproduction light when an interference fringe between an object light and a reference light from a point light source is recorded.

FIG. 10 is a side view showing a traveling direction of reproduction light when an interference fringe between an object light from a line light source and a reference light is recorded.

FIG. 11 is a plan view showing an example of an interference fringe pattern generated by object light and reference light from a point light source.

FIG. 12 is a plan view showing an example of an interference fringe pattern generated by object light and reference light from a line light source.

FIG. 13 is a principle diagram showing that an interference fringe pattern generated by object light and reference light from a line light source is a periodic pattern.

FIG. 14 is a plan view showing an example of an interference fringe pattern for one unit area recorded by the method according to the present invention.

FIG. 15 is a plan view showing only one cycle of the interference fringe pattern shown in FIG. 14;

[Explanation of symbols]

10: Original image 20: Recording surface A1, Am-1, Am, Am + 1, AM: Unit line segment on original image B1, Bm-1, Bm, Bm + 1, BM: Projected line segment on recording surface C1, Cm- 1, Cm, Cm + 1, CM: unit area D (x, y): pixels constituting a binary image d: repetition period of interference fringe pattern E: viewpoint F1 to F5: arrival point of reference light h: vertical of unit area Width / pitch of unit line Lmi: Line light source O, O1, Oi, ON: Object light P, P1, Pi, PN, Pm1, Pmi, PmN: Point light source / reference point Q (x, y): Calculation point R , Rφ: Reference light (reproducing light) R1 to R5: Light flux of reference light θo: Irradiation angle of object light θr: Irradiation angle of reference light φ: Incident angle of reference light ξ: Spread angle λ of object light in Y-axis direction ... wavelengths of object light and reference light

Claims (10)

[Claims] 1. A method for creating a computer generated hologram formed by forming interference fringes on a predetermined recording surface by a calculation using a computer, comprising: a predetermined original image; and a recording surface for recording the original image. Defining a reference light to be irradiated on the recording surface, defining a number of calculation points on the recording surface, and for each calculation point, an object light emitted from the original image; Calculating the intensity of the interference wave formed by the reference light; and forming physical interference fringes on the medium based on the intensity of the interference wave obtained for each calculation point. Defining a plurality of reference points distributed on the original image, defining a line light source passing through each reference point, the object light emitted from this line light source, and the interference light formed by the reference light It is characterized by calculating the intensity How to create a computer-generated hologram that. 2. A method according to claim 1, wherein each line light source has a predetermined length h parallel to a recording surface.
A method for creating a computer generated hologram, comprising defining a line light source composed of the following line segments. 3. The method according to claim 1, wherein a plurality of unit segments are defined on the original image, and a plurality of reference points are defined on each unit segment. A method for creating a computer generated hologram, wherein linear light sources are defined so as to be parallel to each other at respective reference point positions. 4. The method for creating a computer generated hologram according to claim 3, wherein a plurality of cut surfaces are defined so as to be parallel to each other at a predetermined pitch h, and a cut surface obtained by cutting an original image at each of the cut surfaces is defined. A unit line segment is defined as an outline, and a line light source having the same length h as the predetermined pitch h is defined so as to be perpendicular to each of the cut planes with respect to each reference point on the unit line segment. A method for producing a computer generated hologram. 5. The method for producing a computer generated hologram according to claim 1, wherein the wavelength and the irradiation angle of the reference light are set such that the same interference fringe pattern is periodically repeated on the recording surface. Then, a plurality of n sets of the same interference fringe patterns are arranged adjacent to each other, and the result of the intensity calculation performed to create one set of the interference fringe patterns is used. A method for creating a computer generated hologram, wherein the same interference fringe pattern is created. 6. The method for creating a computer generated hologram according to claim 5, wherein a physical interference fringe is formed on a hologram recording medium using a large number of pixels, and an integer of a repetition period d of the interference fringe pattern. A method for creating a computer generated hologram, wherein the magnification is set to be an integral multiple of the pixel size L (where d / L ≧ 2). 7. The method according to claim 1, wherein an original image is defined on an XYZ three-dimensional coordinate system, and a recording surface is defined on an XY plane of the coordinate system. , Each line light source is Y
A method for producing a computer generated hologram, wherein the direction is set so as to be parallel to an axis, and the direction of the reference light is parallel to the YZ plane and obliquely enters the recording surface. 8. A medium for a computer generated hologram created by the method according to claim 1. 9. A computer-generated hologram medium in which an original image is recorded as interference fringes on a predetermined medium by using a calculation using a computer, a plurality of unit areas are defined on the medium, and each unit area is Each corresponds to a specific area on the original image, and in each unit area, information on mutually parallel line light sources arranged in the corresponding specific area on the original image is recorded. A computer generated hologram medium. 10. A computer-generated hologram medium in which an original image is recorded as interference fringes on a predetermined medium by using a calculation using a computer, a plurality of unit areas are defined on the medium, and each unit area is defined by each unit area. , Information about a specific area on the original image is recorded.In each unit area, the same interference fringe pattern is periodically and repeatedly recorded. A medium for a computer generated hologram, wherein interference fringes are continuous at boundaries of recorded interference fringe patterns.