JP2002074292A - Hologram information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of the picture quality of a picture reproduced from a hologram due to the diffraction of light propagating in a clad layer, and to suppress the generation of a reading error of information recorded in the hologram. SOLUTION: In this hologram information recording medium (hologram card) 5 constituted so that layers (core layers) 1 whose each refractivity is high and layers (clad layers) 2 whose refractivity is low are alternately laminated, light(waveguide light) 6 propagating while being enclosed near the layer whose refractivity is high interposed between the two layers whose refractivity is low is diffracted by a hologram 7, the layers whose refractivity is low are formed of light absorbing materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a read-only hologram information recording medium, and more particularly to a read-only hologram information recording medium suitable for use as a portable memory card, such as a magnetic card or an IC card. .

[0002]

2. Description of the Related Art Hitherto, a read-only multiplex hologram card (hereinafter abbreviated as a hologram card) has been devised as an information recording medium which can be carried in a pocket, is inexpensive and has a low risk of forgery. FIG. 1 is a view for explaining the sectional structure of a hologram card and the principle of information reproduction. In the figure, the hologram card 5 is characterized by a structure in which layers having a high refractive index (referred to as core layer 1) and layers having a low refractive index (referred to as clad layer 2) are alternately laminated. As shown in FIG. 1, when the laser beam 4 narrowed down by the lens 3 is applied to the side end face of the hologram card 5, the laser beam 4 is confined in the vicinity of the core layer 1 and proceeds in the hologram card 5. I do.

This light is referred to as guided light 6, and a region near the core layer 1 where the light energy of the guided light 6 is concentrated is referred to as a slab waveguide or simply a waveguide. One waveguide includes one core layer 1 and a part of the adjacent cladding layer 2. The hologram card 5 has another feature that each waveguide includes a hologram. The guided light 6 propagating through the waveguide is
The light is scattered out of the waveguide by the scattering factor 7 that has been created in advance, and the scattering factor 7 is designed so as to function as a hologram as a whole. Alternatively, the light travels downward and forms an image within one plane outside the hologram card 5. This light is referred to as a diffracted light 8, the image is referred to as a reproduced image (hologram image) 9, and the plane connecting the images is referred to as an image forming plane 10.

The hologram image 9 contains information on the hologram in the waveguide, and the information is read out by observing this image with an image pickup device such as a CCD. Furthermore, if the focusing of the laser beam 4 by the lens 3 is appropriate, the guided light can be propagated to only one of the waveguides, so that the hologram information created in each waveguide can be read out independently. Can be.

[0005]

However, in the conventional hologram information recording medium, a part of the incident light does not enter the core layer, leaks to the cladding layer, and propagates through the cladding layer as it is. This light is diffracted out of the card by the hologram, and is diffracted from the core layer and overlaps with the light that generates the originally intended image, and as a result, causes noise and degrades the quality of the reproduced image, or There is a problem that a reading error occurs with a high probability when reading information by observation. The present invention has been made in view of such circumstances, and prevents the deterioration of the image quality of an image reproduced from a hologram caused by diffraction of light propagating through a cladding layer, or reads out information recorded on a hologram. It is an object of the present invention to provide a hologram information recording medium capable of suppressing occurrence of an error.

[0006]

In order to achieve the above-mentioned object, the present invention is directed to a high refractive index layer and a low refractive index layer which are alternately laminated, and the two low refractive index layers are laminated on each other. The low-refractive-index layer is formed of a light-absorbing material in a hologram information recording medium in which light that is sandwiched and propagated by being confined in the vicinity of the high-refractive-index layer is diffracted by a hologram. It is characterized by.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, when a laser beam 4 is introduced into a specific core layer 1 of a hologram card 5 using a lens 3, it is difficult to introduce 100% of incident light into the core layer 1. The part leaks to the cladding layer 2. The leaked light spreads over the entire hologram card 5, but is totally reflected on the surface of the hologram card 5 due to a difference in refractive index between the air and the cladding layer 2. Therefore, unless a special method is used, this light is transmitted to the hologram card 5 as shown in FIG.
Propagating forever while trapped inside. Hereinafter, this light is referred to as clad propagation light 11.

When the clad propagation light 11 reaches the region where the hologram 7 is provided, the guided light 6 is diffracted by the hologram 7 in the same manner as the diffraction, and travels in a direction substantially perpendicular to the surface of the hologram card 5. Cladding propagation light 1
The diffracted light 13 from 1 is similar to the diffracted light 12 from the guided light 6, and is also light that generates an image similar to a hologram image in the image plane. However, the direction in which the diffracted light travels depends on the propagation constant of the light. Since the refractive index of the cladding layer 2 is slightly smaller than the refractive index of the core layer 1, the propagation constant of the clad propagation light 11 is smaller than the propagation constant of the guided light 6 of the core layer 1.

At this time, as shown in FIG. 2, the diffracted light 13 from the clad propagation light 11 is directed in a direction opposite to the direction of propagation of the diffracted light 12 from the guided light 6 in the core layer 1. It proceeds in a slightly inclined direction (the inclination angle θ ₀ is typically 1 ° or less). Therefore, in the image plane, FIG.
As described above, the target reproduced image 9 and the image slightly displaced in the direction opposite to the waveguide direction are observed overlapping. Also,
Since the diffracted light 13 from the clad propagation light 11 and the diffracted light 12 from the guided light 6 in the core layer 1 interfere with each other, FIG.
As shown in (b), the image may be observed after being modulated into a stripe pattern. In any case, the image must be degraded, and a read error has occurred with a high probability when trying to read information from the observed image.

As described above, since this problem is caused by the clad propagation light, it can be solved by removing the clad propagation light. As can be seen from FIG.
Although the clad propagation light 11 also travels through the core layer 1, it almost propagates in the clad layer 2. Therefore, the present invention solves the problem by eliminating the clad propagation light 11 by forming the clad layer 2 of the hologram card 5 as a hologram information recording medium using a light absorbing material. Since the core layer 1 does not use a light absorbing material for the attenuation of the clad propagation light 11,
The guided light 6 of the core layer 1 propagates without being greatly affected, and a reproduced image originally intended can be generated.

In addition to the method of attenuating the clad propagation light generated as in the present invention, there is also a method of preventing the clad propagation light from being generated. A certain effect can be expected by adjusting the intensity pattern of the incident light on the hologram card 5 for reproducing the hologram, precisely processing the incident end face of the hologram card 5, and further precisely positioning. However, due to the limitation of accuracy, a very large effect cannot be expected, and it is considered that the present invention is superior in simplicity and the magnitude of the effect.

An example of a hologram information recording medium according to an embodiment of the present invention will be described below. In the present embodiment, two types of hologram cards were manufactured using an ultraviolet curable resin for both the core layer and the clad layer. In one of the hologram cards, a light-absorbing material was mixed with a resin material when forming the cladding layer. As a result, the wavelength of the semiconductor laser as a light source used for hologram reproduction is 680 nm.
In this case, a cladding layer having an absorption coefficient of 56 dB / cm was obtained. The clad layer of the other hologram card was not subjected to such a treatment. Other manufacturing conditions such as hologram and layer thickness were all equal.

The distance from the incident end of the hologram card to the hologram area was set to about 10 mm. When light was incident from the incident end of the hologram card and reproduction was performed, a hologram card in which a light-absorbing material was not mixed when the clad layer was manufactured, the reproduced image due to diffraction from the guided light of the core layer was not obtained. By the side, although the strength is weak,
It was observed that an image was generated by diffraction from the clad propagation light. The intensity was 3% of the intended reproduced image. However, in the case of a hologram card in which a light-absorbing material is mixed when the clad layer is manufactured, the diffraction image from the clad propagation light is within the range of the measurement error (0.5% of the intended reproduced image light intensity). Was not observed, and it was confirmed that the present invention was effective.

[0014]

As described above, according to the present invention, a layer having a high refractive index and a layer having a low refractive index are alternately laminated, and sandwiched between the two layers having a low refractive index. In the hologram information recording medium in which the light confined in the vicinity of the high refractive index layer and propagated is diffracted by the hologram, the low refractive index layer is formed of a light absorbing material. In the card, the deterioration of the reproduced image due to the diffraction from the clad propagation light can be prevented, or the occurrence of errors can be significantly suppressed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the structure of a hologram card and the principle of information reproduction.

FIG. 2 is an explanatory view showing a diffraction state of clad propagation light when light for reproduction is incident on a hologram card.

FIG. 3 is an explanatory view showing a state in which the quality of a reproduced image is degraded at the time of hologram reproduction caused by diffraction of clad propagation light.

[Explanation of symbols]

 Reference Signs List 1 core layer 2 clad layer 3 lens 4 laser beam 5 hologram card 6 guided light 7 scattering factor (hologram) 8 diffracted light 9 hologram image 10 imaging plane 11 clad propagating light 12, 13 diffracted light

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ikuo Yagi 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Akiyuki 2-chome Otemachi, Chiyoda-ku, Tokyo No. 3-1 Nippon Telegraph and Telephone Corporation F-term (reference) 2C005 HA26 JB08 KA31 2K008 AA13 CC01 DD02 EE04 5B035 AA00 BA05 BB05 BC00 5C082 AA37 MM10

Claims (1)

[Claims] 1. A high-refractive-index layer and a low-refractive-index layer are alternately stacked, and are confined in the vicinity of the high-refractive-index layer sandwiched between the two low-refractive-index layers. A hologram information recording medium in which propagating light is diffracted by a hologram, wherein the low refractive index layer is formed of a light absorbing material.