JP4154738B2 - Two-layer hologram - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hologram that is difficult to duplicate and imitate, has a high security effect (forgery prevention effect), and also has an effect of concealing recorded information.
[0002]
[Prior art]
Conventional holograms having a single layer structure are widely used, and a type in which a plurality of different element holograms are formed in the same plane is also known.
On the other hand, there is a hologram having a multilayer structure (a type in which relief holograms are formed on both sides).
[0003]
However, there is no report yet on a known technique that considers coherent characteristics between diffracted light from each hologram of a multilayer (or different element holograms in the same plane).
Therefore, the diffracted light from the existing hologram has been handled as an independent diffracted light of each hologram.
[0004]
[Problems to be solved by the invention]
An object of the present invention is to propose a hologram that cannot be accurately reproduced unless specific reproduction illumination light is used, utilizing the coherent characteristics of the reproduction illumination light used during wavefront reproduction of the hologram.
[0005]
[Means for Solving the Problems]
A hologram according to claim 1 of the present invention comprises:
In a hologram that is a medium for reproducing the wavefront of light,
It consists of two holograms that are almost parallel to each other.
Each layer has a plurality of element holograms so that the optical path difference of the diffracted light from the plurality of element holograms in that layer is within a distance range in which the coherence degree of the light source used for reproduction is high,
The optical path difference of the diffracted light from the two-layer hologram determined depending on the distance between the two layers is in a distance range where the coherence degree of the light source is low.
[0006]
The hologram of claim 2
In a hologram that is a medium for reproducing the wavefront of light,
It consists of two holograms that are almost parallel to each other.
Each layer has a plurality of element holograms so that the optical path difference of the diffracted light from the plurality of element holograms in that layer is within a distance range in which the coherence degree of the light source used for reproduction is high,
The optical path difference of the diffracted light from the element holograms of each layer determined depending on the distance between the two layers is in a distance range where the coherence degree of the light source is high.
[0007]
The hologram according to claim 3 is characterized in that each of the two-layer holograms is a transmission hologram.
[0008]
The hologram of claim 4 is characterized in that each of the two-layer holograms is a reflection hologram.
[0009]
The hologram of claim 5 is characterized in that the element holograms are spatially separated in at least one of the two hologram layers.
[0010]
The hologram of claim 6 is characterized in that the element hologram is a surface relief type hologram.
[0011]
The hologram of claim 7 is characterized in that two layers of holograms are respectively formed on the front and back of a single substrate.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
The first and second embodiments are dependent on claim 1, and the third and fourth embodiments are dependent on claim 2.
[0013]
<Embodiment 1>
FIG. 1 is an explanatory diagram showing a reproduction state of a reflection hologram.
Incident light having a certain coherence characteristic is incident on the hologram, a part of which is incident on the element holograms 1 and 2 in the hologram layer A, and emits diffracted light A1 and A2.
Since the element holograms 1 and 2 are arranged so that the optical path difference of the diffracted light from them is within the distance range where the coherence degree of the light source used for reproduction is high, the diffracted lights A1 and A2 have a high degree of coherence. There is a relationship.
Each layer has a plurality of element holograms so that the optical path difference of the diffracted light from the plurality of element holograms in that layer is within a distance range in which the coherence degree of the light source used for reproduction is high,
[0014]
In the observation plane of the figure, the square of the coherent sum (FIG. 3 (4)) of the complex amplitude distribution (shown in FIGS. 3 (1) and (2)) of the diffracted lights A1 and A2 from the hologram layer A (= Intensity).
[0015]
On the other hand, in the hologram layers A and B, the distance twice the distance d is set to an optical distance at which the degree of coherence between the diffracted lights from both layers becomes low. The light (A1, A2) and the diffracted light B from the hologram layer B (the complex amplitude distribution shown in FIG. 4 (3)) have a low coherence degree (incoherent).
[0016]
When diffracted light having a high degree of coherence is combined, it is observed as the sum of complex amplitude distributions. (Fig. 3 (1) + Fig. 3 (2) → Fig. 3 (4))
When diffracted light having a low coherence degree is combined, it is observed as the sum of the intensity (square of complex amplitude) distribution of the diffracted light. (Figure 2 (4) square + Figure 3 (3) square → Figure 3 (c))
[0017]
Therefore, on the observation surface, the sum of the intensity distribution of the coherent sum of the diffracted lights A1 and A2 from the hologram layer A and the intensity distribution of the diffracted light B (FIG. 3C) is observed.
[0018]
Since the above holds true even when each layer is composed of a larger number of element holograms, the sum of intensities relative to the coherent sum of diffracted light for each layer is observed on the observation surface.
[0019]
The reproduction conditions described above depend on the spatial arrangement of element holograms in each layer, the distance between the layers, and the coherence characteristics of light used for reproduction.
Therefore, the hologram of the present invention designed for a specific light is observed as described above only with a specific light.
[0020]
For example, for light with a wider distance range with a higher degree of coherence than light with the set coherence characteristics, all of the above diffracted light will be coherently superimposed on the observation surface and will be observed under the above conditions. The intensity distribution (FIG. 3 (b)) is different from the intensity distribution (FIG. 3 (c)).
[0021]
For light with a narrower distance range (or incoherent light) than the light having the set coherence characteristics, the sum of all diffracted light intensities appears on the observation surface (FIG. 3 (a)). ), The observation results are different from those shown in FIG.
Incoherent illumination conditions are general observation conditions such as observation under fluorescent lamp illumination.
[0022]
As described above, a correct observation result with the hologram of the present invention cannot be obtained except for reproduction light having a set coherence characteristic.
[0023]
Here, the hologram of the present invention under appropriate conditions (conditions of illuminating at an angle set by a light source of a specific wavelength having a designed degree of coherence and observing / measuring on an observation plane at a set distance) The authenticity of the hologram can be determined by visually reading or mechanically reading the intensity distribution reproduced from the detector.
[0024]
On the other hand, if the proper conditions are not known, it is impossible to accurately reproduce the hologram, and it can be seen that it has high information concealment.
[0025]
In addition, when attempting to forge the hologram of the present invention, mechanical duplication such as taking a mold is difficult because of the two-layer structure. Furthermore, each surface of the two layers of the hologram of the present invention may be covered with a resin or the like so that it cannot be molded, and in this case, mechanical replication is substantially impossible.
[0026]
On the other hand, when optically replicating the hologram of the present invention, it is generally difficult to expose (reproduce) the hologram without using light having a high degree of coherence. In this case, all the element holograms have a coherent relationship. The reproduction results are completely different.
[0027]
<Embodiment 2>
FIG. 2 is an explanatory view showing a reproduction state of the transmission hologram of the present invention.
The function of the hologram is almost the same as that of the first embodiment, and the distance d between the two layers needs to be set to an optical distance at which the degree of coherence of the diffracted light from the hologram of each layer is low.
[0028]
In the two-layered holograms of the first and second embodiments, as shown in the drawing, a substrate having a thickness equal to the distance d between two layers (in the case of transmission type) or twice as long as d (in the case of reflection type) is used. For example, it is possible to form two hologram layers on the front and back of the substrate, resulting in a simple structure.
Strictly speaking, this theory is correct only when the refractive index of the substrate n = 1. When n is not 1, the optical distance is n times, so the thickness of the substrate needs to be d / n.
[0029]
In the above case, when both the incident light and the diffracted light are nearly perpendicular, d or 2d is an optical path difference, so the distance d can be designed easily.
Even in cases other than the above, an appropriate distance d that satisfies the first and second embodiments can be set by calculating the difference in the optical path length by considering the directions of the incident angle and the diffraction angle.
[0030]
Thus, in the present invention, since the optical distance can be shortened in the case of the reflection type hologram, there is an advantage that the hologram substrate can be made thin.
In the case of a transmission hologram, since it can be used without performing a surface treatment such as forming a reflection film with a surface relief hologram, it can be carried out simply and at low cost.
[0031]
If the element holograms are close to each other in the hologram layer A, only the component of the light transmitted through the hologram layer A (the zero-order diffracted light from the element hologram of the hologram A) is incident on the element hologram of the hologram layer B. Thus, the amount of light contributing to the reproduction of the element hologram of the hologram layer B is reduced.
[0032]
However, by disposing the element holograms spatially apart, it is possible to reproduce the element hologram of the hologram layer B by incident light that passes through the region where the element hologram does not exist in the hologram layer A (is hardly attenuated). Therefore, the light utilization efficiency can be increased, and the intensity ratio of the diffracted light from the holograms in both layers can be optimized.
[0033]
By increasing the transmittance of the spatial region where the element hologram does not exist in the hologram layer A, this effect becomes more remarkable. In the case of the reflection type hologram as in the first embodiment, the above discussion is also effective when the diffracted light from the hologram layer B passes through the hologram layer A.
[0034]
The spatial arrangement of the element holograms in the hologram layer B is important for efficiently transmitting each diffracted light from the hologram layer A in the case of the transmission hologram as in the second embodiment.
[0035]
Therefore, by disposing the element holograms spatially apart, the coherence characteristic becomes clear, and authenticity determination becomes easier.
[0036]
<Embodiment 3>
FIG. 4 is an explanatory diagram showing a reproduction state of the reflection hologram.
Incident light having a certain coherent characteristic is incident on the hologram, a part of which is incident on the element holograms 1 and 2 in the hologram layer A, and emits diffracted light A1 and A2.
[0037]
Since the element holograms 1 and 2 are arranged so that the optical path difference of the diffracted light from them is within the distance range where the coherence degree of the light source used for reproduction is low, the diffracted lights A1 and A2 have a low coherence degree. There is a relationship.
Therefore, the sum of the incoherent intensity distributions of the diffracted lights A1 and A2 from the hologram layer A is observed on the observation surface.
That is, the sum of the square of the complex amplitude of the diffracted light A1 (FIG. 6 (1)) and the square of the complex amplitude of the diffracted light A2 (FIG. 6 (2)) corresponds to the sum of the incoherent intensity distributions. .
[0038]
On the other hand, the diffracted light from the hologram of the hologram layer A and the diffracted light from the hologram of the hologram layer B have an optical distance (distance d of 2) so that the degree of coherence between the diffracted lights from both layers is high. Double distance), the diffracted light (A1, A2) from the hologram layer A and the diffracted light B3 from the hologram layer B on the observation surface have a high coherence relationship (coherent).
[0039]
Accordingly, the observation surface is observed as a coherent sum of the incoherent intensity distribution of the diffracted lights A1 and A2 from the hologram layer A and the diffracted light B.
[0040]
In other words, the coherent sum (FIG. 6 (4)) of the complex amplitude of the diffracted light A1 (FIG. 6 (1)) and the complex amplitude of the diffracted light B (FIG. 6 (3)) and the diffracted light A2 Observed as the sum of coherent intensity distributions. (Fig. 6 (4) square + Fig. 6 (2) square → Fig. 6 (c))
[0041]
Since the above holds true even when each layer is composed of a larger number of element holograms, the sum of intensities relative to the coherent sum of diffracted light for each layer is observed on the observation surface.
[0042]
The above reproduction conditions depend on the spatial arrangement of the element holograms in each layer, the distance between each layer, the coherence characteristics of the light used for reproduction, and the incident angle of the reproduction light on the hologram.
Therefore, the hologram of the present invention designed for a specific light is observed as described above only with a specific light.
[0043]
For example, for light with a wider distance range with a higher degree of coherence than light with the set coherence characteristics, all of the above diffracted light will be coherently superimposed on the observation surface and will be observed under the above conditions. The intensity distribution (FIG. 6 (b)) is different from the intensity distribution (FIG. 6 (c)).
[0044]
For light with a narrower distance range (or incoherent light) than the light having the set coherence characteristic, the sum of all diffracted light intensities appears on the observation surface (FIG. 6 (a)). ), The observation results are different from those shown in FIG.
[0045]
<Embodiment 4>
FIG. 5 is an explanatory view showing the reproduction state of the transmission hologram of the present invention.
The function of the hologram is almost the same as in the third embodiment, and the distance d between the two layers needs to be set to an optical distance at which the degree of coherence of the diffracted light from the hologram of each layer is high. This is the same as in the third embodiment.
[0046]
In the two-layered holograms of the third and fourth embodiments, as shown in the drawing, a substrate having a thickness equal to the distance d between two layers (in the case of a transmission type) or twice as long as d (in the case of a reflection type) is used. For example, it is possible to form two hologram layers on the front and back of the substrate, resulting in a simple structure.
Strictly speaking, this theory is correct only when the refractive index of the substrate n = 1. When n is not 1, the optical distance is n times, so the thickness of the substrate needs to be d / n.
[0047]
In the above case, when both the incident light and the diffracted light are nearly perpendicular, d or 2d is an optical path difference, so the distance d can be designed easily.
Even in cases other than the above, an appropriate distance d that satisfies Embodiments 3 and 4 can be set by calculating the difference in the optical path length by considering the directions of the incident angle and the diffraction angle.
[0048]
If the element holograms are close to each other in the hologram layer A, only the component of the light transmitted through the hologram layer A (the zero-order diffracted light from the element hologram of the hologram A) is incident on the element hologram of the hologram layer B. Thus, the amount of light contributing to the reproduction of the element hologram of the hologram layer B is reduced.
[0049]
However, by disposing the element holograms spatially apart, it is possible to reproduce the element hologram of the hologram layer B by incident light that passes through the region where the element hologram does not exist in the hologram layer A (is hardly attenuated). Therefore, the light utilization efficiency can be increased, and the intensity ratio of the diffracted light from the holograms in both layers can be optimized.
[0050]
By increasing the transmittance of the spatial region where the element hologram does not exist in the hologram layer A, this effect becomes more remarkable. In the case of a reflection hologram as in the third embodiment, the above discussion is also effective when diffracted light from the hologram layer B passes through the hologram layer A.
[0051]
The spatial arrangement of the element holograms in the hologram layer B is important for efficiently transmitting each diffracted light from the hologram layer A in the case of the transmission hologram as in the fourth embodiment.
[0052]
Therefore, by disposing the element holograms spatially apart, the coherence characteristic becomes clear, and authenticity determination becomes easier.
[0053]
As described above, in Embodiments 1 to 4, the light to be handled as the complex amplitude is expressed only by “amplitude”, but in reality, “phase” needs to be considered.
In the above description, by giving a sign to the amplitude, it has been handled simply as a representation of only the state where the phase is 0 (amplitude corresponds to positive) and π (amplitude corresponds to negative). When an arbitrary phase is actually considered, in the above discussion, in the case of coherent superposition, it should be handled as a sum of complex amplitudes that also consider the phase.
In the case of incoherent, the square of the amplitude becomes the intensity of light, and the same handling as described above may be performed.
[0054]
【The invention's effect】
According to the present invention, a hologram that cannot be accurately reproduced unless specific reproduction illumination light is used in accordance with the coherence characteristics (and coherence characteristics between element holograms) of the reproduction illumination light used when reproducing the wavefront of the hologram. Is provided.
[0055]
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a reproduction state of a reflection hologram of the present invention.
FIG. 2 is an explanatory diagram showing a reproduction state of a transmission hologram according to the present invention.
FIG. 3 is an explanatory diagram showing complex amplitude distribution / intensity distribution of diffracted light from the holograms according to Embodiments 1 and 2 (and superimposing them), (1) is an element hologram 1 of layer A (2) is the complex amplitude distribution of the diffracted light from the element hologram 2 of layer A, (3) is the complex amplitude distribution of the diffracted light from the element hologram 3 of layer B, (4) Is the complex amplitude distribution for the coherent sum of the diffracted light from the element holograms 1 and 2 of layer A, (a) is the sum of the intensities of the diffracted light from the element holograms 1, 2 and 3 (the square of the complex amplitude) Distribution, (b) Distribution of intensity (square of complex amplitude) for coherent sum of diffracted light from element holograms 1, 2, 3, and (c) Appropriate illumination of holograms according to first and second embodiments This is the intensity distribution of the reproduction light detected only when it is detected.
FIG. 4 is an explanatory diagram showing a reproduction state of the reflection hologram of the present invention.
FIG. 5 is an explanatory diagram showing a reproduction state of a transmission hologram according to the present invention.
FIG. 6 is an explanatory view showing complex amplitude distribution / intensity distribution of diffracted light from a hologram according to Embodiments 3 and 4 (and superimposing them), (1) is an element hologram 1 of layer A (2) is the complex amplitude distribution of the diffracted light from the element hologram 2 of layer A, (3) is the complex amplitude distribution of the diffracted light from the element hologram 3 of layer B, (4) Is the complex amplitude distribution for the coherent sum of the diffracted light from the element holograms 1 and 2 of layer A, (a) is the sum of the intensities of the diffracted light from the element holograms 1, 2 and 3 (the square of the complex amplitude) Distribution, (b) Distribution of intensity (square of complex amplitude) for coherent sum of diffracted light from element holograms 1, 2, 3, and (c) Appropriate illumination of holograms according to embodiments 3 and 4 This is the intensity distribution of the reproduction light detected only when it is detected.
[0056]
[Explanation of symbols]
1 Element hologram 1 of hologram layer A
2 ... Element hologram 2 of hologram layer A
3 ... Element hologram 3 of hologram layer B

Claims (7)

In a hologram that is a medium for reproducing the wavefront of light,
It consists of two holograms that are almost parallel to each other.
In each layer, the optical path difference (| diffracted light A1−diffracted light A2 |) of diffracted light from a plurality of element holograms in the layer is within a distance range where the coherence degree of the light source having the coherence characteristics used for reproduction is high. Have multiple element holograms,
The optical path difference (| diffracted light A1− (diffracted light B + d / cos θ) | and | diffracted light A2− (diffracted light B + d / cos θ) |) of the diffracted light from the two-layer hologram determined depending on the distance between the two layers. The two-layer structure hologram is in a distance range where the coherence degree of the light source is low.
In addition, d shows the space | interval of two layers, (theta) shows the incident angle of incident light (angle which the incident light makes with respect to the normal line standing at the incident point). In a hologram that is a medium for reproducing the wavefront of light,
It consists of two holograms that are almost parallel to each other.
In each layer, the optical path difference (| diffracted light A1−diffracted light A2 |) of the diffracted light from a plurality of element holograms in the layer is within the distance range where the coherence degree of the light source having the coherence characteristics used for reproduction is low. Have multiple element holograms,
The optical path difference (| diffracted light A1− (diffracted light B + d / cos θ) | and | diffracted light A2− (diffracted light B + d / cos θ) |) of the diffracted light from the two-layer hologram determined depending on the distance between the two layers. The two-layer hologram is in a distance range where the coherence degree of the light source is high.
In addition, d shows the space | interval of two layers, (theta) shows the incident angle of incident light (angle which the incident light makes with respect to the normal line standing at the incident point).   The two-layer hologram according to claim 1 or 2, wherein each of the two-layer holograms is a transmission hologram.   The two-layer hologram according to claim 1 or 2, wherein each of the two-layer holograms is a reflection hologram.   The two-layer hologram according to any one of claims 1 to 4, wherein element holograms are arranged spatially separated in at least one of the two-layer holograms.   6. The two-layer hologram according to claim 1, wherein the element hologram is a surface relief hologram.   7. The two-layer hologram according to claim 1, wherein two-layer holograms are respectively formed on the front and back of a single substrate.

Images