JP3425166B2 - Confirmation method using hologram - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for confirming whether a hologram is right or wrong.

[0002]

2. Description of the Related Art Conventionally, holograms have been used as a means for confirming the authenticity by attaching them to parts of certificates, securities, credit cards and the like. Conventionally, what is called a machine-readable hologram is used as a confirmation means using such a hologram. This method prepares multiple holograms that diffract in different directions by changing the pitch of interference fringes, makes light incident on each hologram, and reads the multiple diffracted light produced by the holograms with a one-dimensional sensor. is there. The diffracted light at this time has a different number and pattern of diffracted light depending on the information recorded in the hologram. The reading device stores this number and pattern in advance and checks whether the stored information matches the hologram information. It judges by collating. Further, in the authenticity confirmation method of a forgery prevention hologram such as a credit card or rental video package, the hologram is actually inspected with the naked eye.

[0003]

However, the conventional machine-readable double hologram has a simple diffracted light pattern, and whether a diffracted light is received or not by using a one-dimensional sensor composed of a plurality of light receiving elements. Since the verification is based on value information, the method of authenticity verification is too simple and there is a problem in preventing forgery. Further, the conventional method using a forgery-preventing hologram such as a package of a credit card or a rental video has a problem in terms of work efficiency and accuracy because the authenticity can be confirmed only by visual inspection.

The present invention is intended to solve the above-mentioned problems, and it is possible to dramatically improve the reliability of anti-counterfeiting, and use a hologram that can improve the efficiency and accuracy of the authenticity confirmation work. The purpose is to provide a method.

[0005]

FIG. 1 is a diagram showing an example using linearly polarized light. In the figure, 1 is an object light, 2 and 3 are reference lights, 4 is a hologram photosensitive material, 5 and 6 are reproduction illumination light, 7 is reproduction image light, 8 is a prism, and 9 and 10 are detectors.

To explain the recording with reference to FIG. 1A, the object light 1 is linearly polarized light and has an inclination of θ with respect to the main axis. The object light 1 and the reference lights 2 and 3 whose polarization directions are orthogonal to each other are caused to interfere with each other in the hologram photosensitive material 4 to create a hologram. The reference light is composed of X-polarized light and Y-polarized light, and the X-direction component and the Y-direction component of the object light 1 are recorded by interfering with the X-polarized light and the Y-polarized reference light, respectively.

When the X-polarized light 5 and the Y-polarized light 6 are irradiated as reproduction illumination light from the same direction as the reference light onto the hologram 4 thus created, as shown in FIG. Reconstructed image light 7 that is linearly polarized light inclined by θ with respect to the principal axis is obtained as diffracted light. For example, if the reproduced image light 7 is P-polarized light and S-polarized light, it can be divided into orthogonal polarization components by a prism 8 tilted by Brewster's angle θ _B , and detected by detectors 9 and 10, and intensity components are detected. The polarization angle of the object light can be detected by determining the ratio of Therefore, it is possible to determine the authenticity of the hologram by holding the polarization angle of the object light as reference data in advance and comparing it with this.

In the above description, the object light having one polarization direction has been described, but the light transmitted through the mask of the polarizing plates arranged in various patterns in various polarization directions is used as the object light. When an interference pattern is recorded on the hologram light-sensitive material using the X-polarized light and the Y-polarized light shown in (a) as reference light,
Since patterns having different polarization directions can be reproduced at the time of reading a hologram, it is possible to further enhance the anti-counterfeiting effect by preliminarily holding each pattern as reference data and collating with it.

2 and 3 are views showing a recording / reproducing optical system using circularly polarized light. In the figure, 20 is a λ / 4 plate, 21 is object light, 22 and 23 are reference lights, 24 is a hologram sensitive material,
25 and 26 are views showing reproduction illumination light, 27 is a λ / 4 plate, 28 is a polarizing plate, 29 is a screen and a light receiving part.

First, the hologram recording will be described with reference to FIG. 2. The object light 21 is light polarized in one direction. The λ / 4 plate 20 is divided into, for example, four regions as shown in the drawing. The regions 20a and 20d have a fast axis of 45 ° with respect to the vibration direction of the object light, and the regions 20b and 20c have a slow axis of 45 °. To form a mask. Therefore, when the object light 21 passes through the λ / 4 plate 20, right circularly polarized light is emitted from the regions 20a and 20d.
Left circularly polarized light is obtained from b and 20c, respectively. The circularly polarized light and the reference lights 22 and 23 polarized in one of the X and Y directions are interfered with each other in the hologram photosensitive material and recorded.

Next, as shown in FIG.
When 4 is irradiated with reproducing illumination light 25 and 26 polarized in the X direction and the Y direction from the same direction as the reference light at the time of recording, λ /
Diffracted light in the right and left circular directions is obtained corresponding to each region of the four plates 20, respectively. When the diffracted light from this hologram is passed through a λ / 4 plate 27 having a fast axis of 45 °, right circularly polarized light,
The left-handed circularly polarized light is linearly polarized light having one polarization direction of X and Y. This linearly polarized light is converted into, for example, the X-direction polarizing plate 2
When the light is passed through 8, the light polarized in the same direction as the polarization direction of the polarizing plate 28 is transmitted, and the light orthogonal to it cannot be transmitted.
In the screen and the light receiving section 29, a light and dark pattern is obtained corresponding to the four areas of the λ / 4 plate 20.
In order to reproduce this pattern, it is not possible to obtain any of the optical elements shown in FIGS. 2 and 3 so that it is possible to dramatically improve the forgery prevention.

In the above description, an example of the pattern in which the λ / 4 plate is divided into four areas has been described, but if the pattern is made more complicated, the anti-counterfeiting effect can be further enhanced.

FIG. 4 and FIG. 5 are views showing an example in which different patterns are recorded and are separated and detected by polarized light. Figure 4
In (a), the mask 31 is illuminated with the object light 30, and the transmitted light and the hologram light sensitive material 33 are irradiated with the reference light 32 at an angle of θ ₁ to record the mask pattern A on the hologram light sensitive material 33. Then, the hologram photosensitive material 33 is irradiated with the object light 40 on the mask 41, and the transmitted light and the hologram photosensitive material are irradiated with the reference light 42 at an angle of θ ₂ to record the mask pattern B. In this way, with respect to the hologram photosensitive material 33 on which the pattern A and the pattern B are recorded by the double exposure, the reference light 50 having polarization directions orthogonal to each other,
When the hologram sensitive material 33 is illuminated as reproduction illumination light from 51 at the angles of θ ₁ and θ _{2 in} the same direction as at the time of recording at 51, diffracted light in polarization directions orthogonal to each other is obtained. When this is separated into orthogonal components by the polarization beam splitter 52, the pattern A is separated by the reproduction light from the θ ₁ direction, and the pattern B is separated by the reproduction light from the θ ₂ direction, which are detected by the screen and the light receiving elements 53 and 54. be able to. In this example, since two patterns can be detected at a time, the reading speed can be doubled, and since the authenticity determination can be performed by comparing the two patterns, the camouflage prevention effect can be enhanced.

Although not shown in the figure, patterns in which the polarization directions are changed are recorded on the hologram.
When a mixed light of P-polarized light and S-polarized light is irradiated, it cannot be seen as white, but if recording is performed so that the pattern can be seen when only P-polarized light is irradiated, the pattern can be reproduced by using the P-polarized light as reproduction light. Therefore, the anti-counterfeiting effect can be obtained as well.

FIG. 6 shows the apparatus configuration of the present invention. The above-described hologram 64 can be detachably set on the reader 60. This hologram is set, reproduction illumination light is emitted by the polarization optical system 61 for illumination installed on the reader side, the diffracted light from 64 is read by the polarization optical system for reading, and the read pattern and a reference pattern that is stored in advance. The discriminator 63 collates and to determine whether they are correct. Needless to say, the present invention is not limited to the above description and can be applied to a prepaid card system, an entrance / exit management system, a credit card forgery prevention, and the like.

[0016]

According to the present invention, the hologram is not read as it is, but the hologram is recorded with not only the phase amplitude intensity but also the polarization direction of the light, and the hologram is read in a predetermined reading device. The correctness is confirmed by.

In order to accurately reproduce the polarization state of the hologram, it is necessary to illuminate each of the two reproduction illumination lights whose polarization directions are orthogonal to each other from the same position as during recording. In addition, by using object light in which two types of right-handed and left-handed circularly polarized light are arranged in a pattern, during reproduction, the light is converted into linearly polarized light orthogonal to each other by a λ / 4 plate in the reading device, and this light is unidirectionally polarized. By passing through the polarizing plate, a bright and dark pattern can be displayed on the screen, and this pattern can be read, so it is extremely difficult to know the information recorded in the hologram, and the counterfeit prevention effect is greatly improved. It is possible.

[0018]

EXAMPLE In order to confirm the effect of the present invention, an experiment for the example shown in FIG. 2 was conducted as follows. First, linearly polarized light of laser light (argon laser 514.5 nm) is arranged in an arbitrary pattern in the fast axis and slow axis (45 °) directions with respect to this polarization direction. 100m
Then, circularly polarized light having a rotation in each of the left and right directions, which matches the pattern, was made to be incident light. Next, two lights having linearly polarized light orthogonal to each other were used as reference lights, and the object lights and the reference lights were caused to interfere with each other in a hologram recording light-sensitive material (DuPont Omnidex 352). Give 30 mJ / cm ² and exposure conditions, followed by irradiation of UV light of 100 mJ / cm ² as developing step and 120
Heating was performed at 2 ° C. for 2 hours.

The above reference light was made to enter the hologram as reproduction illumination light for the hologram thus created. Next, the reproduced image light generated is transmitted through a λ / 4 plate tilted in the direction of 45 ° with respect to the original linearly polarized light of the object light (in this case, the directions of the advanced phase and the delayed phase are arbitrary), and then The original polarization direction of the object light was passed through a polarizing plate that was oriented in one direction (whether it was in the same direction or in the orthogonal direction), and when it was projected on a screen, the λ / 4 plate at the time of recording was It was possible to obtain a light-dark pattern that matches the pattern arranged in a 10 mm square. This experimental result shows that the hologram recorded information about the polarization direction that the object light had.

Subsequently, this hologram was inserted into a dedicated reading device for judging whether the hologram is correct or not, and an experiment was carried out as to whether or not the hologram can be judged whether it is correct or not. An argon laser is built in this reading device, and it is possible to make two reproducing illumination light beams enter the hologram under the same conditions as in the experiment. In order to read the bright and dark patterns that occur, a light receiving element is provided for each pattern and the amount of light for each pattern is detected. Actually installed the hologram created in this device,
When reproduced in the apparatus, the pattern generated by the hologram was compared with the pattern that was also recorded in the reading apparatus, and it was possible to judge whether the pattern was correct or not.

[0021]

As described above, according to the present invention, the polarization of light is used for recording or reproduction and the information on the polarization is used, so that it is possible to further improve the forgery prevention.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system for recording and reproducing linearly polarized light.

FIG. 2 is a diagram showing an example in which circularly polarized light and linearly polarized light are interfered with each other for recording.

FIG. 3 is a diagram showing a reproduction optical system of a hologram recorded by causing circularly polarized light and linearly polarized light to interfere with each other.

FIG. 4 is a diagram showing an optical system for double-exposure recording of different patterns.

FIG. 5 is a diagram showing a reproduction optical system of a hologram in which different patterns are double-exposure recorded.

FIG. 6 is a diagram showing a device configuration of the present invention.

[Explanation of symbols]

1 ... object light, 2, 3 ... reference light, 4 ... hologram sensitive material,
5, 6 ... Playback illumination light, 7 ... Playback image light, 8 ... Prism,
9, 10 ... Detector, 20 ... 1 / 4λ plate, 21 ... Object light,
22, 23 ... Reference light, 24 ... Holographic photosensitive material, 25, 2
6 ... Reproducing illumination light, 27 ... 1/4 λ plate, 28 ... Polarizing plate, 2
9 ... Screen and light receiving part, 60 ... Reader, 61 Playback polarization optical system, 62 ... Reading polarization optical system, 63 ... Discrimination device, 64 ... Hologram.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03H 1/26

Claims (2)

(57) [Claims] 1. A hologram produced by interfering arbitrary linearly polarized object light and two reference lights whose polarization directions are orthogonal to each other in a light-sensitive material has two holograms whose polarization directions are the same as those of the reference light . irradiating a reproduction illumination light, the diffracted light linearly polarized reproduced divided into polarized light components identical orthogonal to the reference light, and detects the polarization direction from the ratio of the intensity component, the
Based on the linear polarization direction of the object light, the detected polarization
A confirmation method using a hologram characterized by matching with the light direction . 2. The linearly polarized light is made incident on a mask in which λ / 4 plates are arranged in a pattern so that the fast axis and the slow axis are 45 ° with respect to the vibration direction, and the light is turned clockwise and left. The circularly polarized light around the light is converted into light arranged in the pattern as the object light, and two reference lights whose polarization directions are orthogonal to each other interfere with each other in the photosensitive material to produce a hologram, and the hologram is
Two reproduction illumination lights having the same polarization directions as the reference light and orthogonal to each other are irradiated, and the substantially circularly polarized reproduction light is λ /
A linearly polarized light through a 4 plate, the polarization of the linearly polarized light
At least one polarization direction is linearly polarized with respect to the light direction
The polarization direction of the object light is detected by detecting the polarization direction from the light-dark pattern through a linear polarizing plate so as to be parallel to the transmission axis of the plate.
A confirmation method using a hologram, characterized in that it is matched with the detected light-dark pattern on the basis of .