JP2006023675A - Hologram recording medium, hologram recording device, and hologram recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording medium that is difficult to fabricate and alter and in which recordable transmission volume hologram is recorded using a simple device constitution, and to provide a hologram recording device and a hologram recording method for recording the transmission volume hologram difficult to fabricate and alter in the simple device constitution on demand. <P>SOLUTION: When scattered light is irradiated in a spatial light modulator 14 displaying images, the irradiated scattered light is intensity-modulated, in response to values of each pixel of digital data images, and a mask-shaped speckle pattern is irradiated on an optical recording sheet 16. Refractive index dispersion, corresponding to the speckle pattern, is formed in the inside of the optical record sheet 16 by the irradiation of the speckle pattern. The irradiation of the speckle pattern is equivalent to that which has irradiated the object light and reference light from the same side of the optical record sheet 16, The transmission type volume hologram is recorded in a part mask-exposing the optical recording sheet 16. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording medium, a hologram recording apparatus, and a hologram recording method, and in particular, a hologram recording medium on which a transmission type volume hologram is recorded, and a hologram recording apparatus and a recording method for manufacturing the hologram recording medium, , Regarding.

  Forgery and alteration of ID cards and credit cards have become a social problem. This is due to the fact that the hologram seal affixed to prevent counterfeiting can be duplicated due to the development of duplication technology.

  A conventional hologram seal is a duplicate of a master hologram, and a rainbow hologram with surface irregularities is generally used. For example, a press mold is produced from a relief master hologram having a concavo-convex pattern, and the same pattern is heated and pressed using this mold to produce a large number of hologram stickers, which are attached to a display medium such as a card. . However, with the current technology, it is relatively easy to duplicate the concavo-convex pattern. For this reason, the forgery prevention effect by a hologram seal is decreasing day by day.

  On the other hand, the hologram that is most difficult to forge / modify is a volume hologram represented by a Lippmann hologram or the like. This volume hologram is very difficult to counterfeit because it forms a refractive index grating in a material such as a photopolymer rather than surface irregularities.

In recent years, a method for printing a hologram on demand has been proposed to make counterfeiting difficult (Patent Document 1). In this method, for example, since a hologram corresponding to individual information such as an ID number and a manufacturing number is applied to a display medium such as a card, the card can be prevented from being altered and the safety can be further improved. On-demand holograms are usually printed on a display medium using a hologram transfer foil ribbon (Patent Document 2).
JP 2000-263910 A JP 2000-2111257 A

  However, for volume hologram recording, it is necessary to irradiate the object beam and the reference beam at the same time, so the apparatus becomes large, and a vibration isolator is necessary for hologram recording by two-wave interference. There is.

  Moreover, since the on-demand hologram uses a hologram transfer foil ribbon, it has the following problems. In other words, by using a hologram that is not printed on the display medium and remains on the transfer foil ribbon, a third party may be able to create a similar hologram. Need to manage. Further, since the transfer foil ribbon is a relief hologram, it can be forged by examining the shape of the unevenness.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a hologram recording in which a transmission type volume hologram that is difficult to forge and alter and can be recorded with a simple device configuration is recorded. To provide a medium.

  Another object of the present invention is to provide a hologram recording apparatus and a hologram recording method capable of recording on-demand a transmission-type volume hologram that is difficult to forge or alter with a simple apparatus configuration.

  In order to achieve the above object, the hologram recording medium of the present invention is characterized by comprising a recording layer in which a large number of small areas in which speckle patterns are recorded as transmission volume holograms are two-dimensionally arranged.

  The hologram recording apparatus of the present invention spatially modulates a laser light source that emits laser light, a diffuser that diffuses laser light emitted from the laser light source, and diffused light obtained by the diffuser. And a spatial light modulator that irradiates the optical recording medium with the modulated diffused light.

  Further, the hologram recording method of the present invention spatially modulates the diffused light obtained by diffusing the laser light, and irradiates the optical recording medium with the modulated diffused light to record the transmission type volume hologram. It is characterized by.

  As described above, according to the hologram recording medium of the present invention, it is possible to provide a hologram recording medium on which a transmission type volume hologram that is difficult to forge and alter and can be recorded with a simple device configuration is recorded. Is obtained.

  Further, according to the hologram recording apparatus and the hologram recording method of the present invention, it is possible to record an on-demand transmission volume hologram that is difficult to forge and alter with a simple apparatus configuration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  First, the configuration of the hologram recording apparatus according to the present embodiment will be described. As shown in FIG. 1, the hologram recording apparatus includes a laser light source 10 that emits laser light that is coherent light. A plate-like diffuser 12 that diffuses and transmits incident laser light is disposed on the laser light emission side of the laser light source 10. A spatial light modulator 14 that modulates light diffused by the diffuser 12 (diffused light) according to a recording signal and generates recording light is disposed on the laser beam emission side of the diffuser 12. The spatial light modulator 14 is connected to a personal computer (not shown) that drives and controls the spatial light modulator 14.

  When recording a hologram using the above hologram recording apparatus, the optical recording sheet 16 for recording the hologram has a spatial light modulator such that the surface on which recording light is incident faces the spatial light modulator 14. 14 is arranged in the vicinity. The shorter the distance between the spatial light modulator 14 and the optical recording sheet 16, the better. For example, it is 0 to 3 mm, preferably 0 to 0.5 mm. The recording material used for the optical recording sheet 16 will be described later.

  As the laser light source 10, a laser light source that emits laser light in the visible region having a wavelength of 400 nm to 780 nm can be used depending on the purpose. The spectrum of scattered / diffracted light from the generated hologram is distributed around the recording wavelength. That is, the hologram reproduces a color close to the recording wavelength. Accordingly, when it is desired to form a red hologram, for example, a wavelength of 580 nm or more may be used, and a wavelength of 500 to 580 nm for green and 500 nm or less for blue may be used.

  As the diffuser 12, a transmissive diffusion plate having at least one surface roughened like rubbed glass can be used. For example, sand numbers # 240 to # 1500 of “Frost type diffuser plate” manufactured by Sigma Koki Co., Ltd. can be used. The spatial light modulator 14 is composed of, for example, a liquid crystal display element that displays a binary two-dimensional digital data image generated according to a recording signal.

  In the above hologram recording apparatus, the laser light emitted from the laser light source 10 is transmitted and diffused by the diffuser 12 and applied to the spatial light modulator 14. When coherent light such as laser light is transmitted through the diffuser 12, light scattered at each point on the rough surface of the diffuser 12 (diffused light) interferes randomly and diffused light is obtained as shown in FIG. A speckled pattern called a speckle pattern is generated inside.

  The diffused light irradiated on the spatial light modulator 14 is modulated in accordance with the recording signal and irradiated on the optical recording sheet 16. This spatial light modulator 14 functions as a so-called programmable mask. That is, as shown in FIG. 3, when the diffused light is irradiated to the spatial light modulator 14 on which the image is displayed, the irradiated diffused light is converted into each pixel of the digital data image (character “X” in FIG. 3). The optical recording sheet 16 is irradiated with a speckle pattern having a mask shape.

  Due to the speckle pattern irradiation, a refractive index distribution corresponding to the speckle pattern is formed inside the optical recording sheet 16. This speckle pattern irradiation is equivalent to irradiation of object light and reference light from the same side of the optical recording sheet 16, and a transmission type volume hologram is formed in the mask-exposed portion of the optical recording sheet 16. To be recorded.

  In the above hologram recording apparatus, an example using a spatial light modulator (programmable mask) controlled by a computer has been described. However, even if a mask such as a transparent film on which a binary image is printed is used, the diffused light Modulation can be performed.

  Next, the optical recording sheet 16 will be described. The optical recording sheet 16 can be used by being mounted on the substrate surface. When the optical recording sheet 16 is mounted on a substrate and used, the optical recording sheet and the substrate can be collectively referred to as an “optical recording medium”. Examples of the substrate on which the optical recording sheet 16 is mounted include sheet-like substrates such as paper and resin films in addition to plate-like substrates such as plastic cards. Further, recording may be performed with the optical recording sheet 16 mounted on the substrate surface, or the optical recording sheet 16 on which a hologram has been recorded in advance may be mounted on the substrate surface.

  4A and 4B are views showing a state in which a small piece of an optical recording sheet 16 of several mm square is attached to the surface of a substrate 18 made of a credit card-sized plastic card. In this example, the optical recording sheet 16 is affixed to the lower right side of the substrate 18 via a reflective layer 20 that reflects the reproduction light reproduced from the recorded hologram.

  The optical recording sheet 16 is made of a recording material capable of writing a volume hologram by changing the refractive index. Examples of such a recording material include a photopolymer. As the photopolymer, for example, a photopolymer disclosed in Japanese Patent No. 2849021 can be used.

  In addition, a photorefractive material or a polarization sensitive material that exhibits photoinduced refractive index change or photoinduced dichroism and maintains these characteristics at room temperature can be used. These photorefractive material and polarization sensitive material can erase a hologram recorded by light irradiation and record a new hologram, that is, rewrite the hologram.

  Among these, a polymer having a photoisomerizable group in the side chain, for example, at least one polymer selected from the group of polyesters having a photoisomerizable group in the side chain, for example, an azobenzene skeleton Material is preferred.

  Azobenzene repeats a trans-cis-trans isomerization cycle upon irradiation with light. Before the light irradiation, a lot of trans azobenzene molecules exist in the optical recording layer. These molecules are randomly oriented and are isotropic in macro. When irradiated with linearly polarized light, azobenzene molecules having an absorption axis in the same direction as the polarization direction are selectively trans-cis isomerized. Molecules relaxed in a trans form having an absorption axis perpendicular to the polarization direction no longer absorb light and are fixed in that state. As a result, anisotropy of absorption coefficient and refractive index, that is, dichroism and birefringence are induced macroscopically. A polymer containing such a photoisomerization group can change the orientation of the polymer itself by photoisomerization and induce a large birefringence. The birefringence induced in this way is stable below the glass transition temperature of the polymer and is suitable for hologram recording.

  For example, a polyester having cyanoazobenzene in the side chain represented by the following chemical formula (see JP-A-10-340479) is suitable as a material for recording a hologram by the above-described mechanism. This polyester can record the polarization direction of signal light as a hologram due to photo-induced anisotropy due to photoisomerization of side chain cyanoazobenzene, and can record holograms at room temperature. Unless recorded, the recorded hologram is retained semi-permanently.

The thickness of the optical recording sheet 16 is preferably in the range of 3 μm to 200 μm from the viewpoint of preventing bulkiness, and more preferably in the range of 10 μm to 100 μm in order to improve the diffraction efficiency. The optical recording sheet 16 is a sheet-shaped product obtained by producing a plate-shaped molded product by injection molding, and then sandwiching the plate-shaped molded product with a pair of releasable resin films and hot pressing under vacuum. Formed. The optical recording sheet 16 is peeled from the resin film, and is used by being cut into small pieces of several mm square (for example, 8 mm square). The heating temperature is preferably a temperature equal to or higher than the Tg of the recording material, and the pressing pressure is preferably 0.01 to 0.1 t / cm ² . As the releasable resin film, for example, a polyethylene terephthalate (PET) film in which a silicone resin is coated on the surface as a release agent can be used.

  The reflective layer 20 is configured by forming a thin film made of a light reflective material having a reflectance of 70% or more with respect to a laser beam used for recording / reproduction on a substrate 18 such as a plastic card. Examples of such a light reflective material include Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Mention may be made of metals such as Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn, Bi, and semimetals or stainless steel. Among these, Au, Ag, Al, or an alloy thereof is preferable, and Al (aluminum) is particularly preferable. Said light reflective material may be used independently, and may be used in combination of 2 or more types.

  The reflective layer 20 can be formed by, for example, vapor-depositing, sputtering, or ion plating the above-described light reflective material on the substrate 18. The thickness of the reflective layer 20 is preferably in the range of 1 nm to 100 μm from the viewpoint of preventing bulkiness, but the thinner the better in this range. In addition, when the reflectance of the substrate itself is high, the reflective layer 20 may be omitted.

  A protective layer is preferably provided on the surface of the reflective layer 20 (the surface of the optical recording sheet 16 when the reflective layer 20 is omitted). The protective layer can be made of a resin material that is transparent and flexible with respect to the laser beam used for recording / reproduction. The thickness of the protective layer is preferably in the range of 1 μm to 200 μm from the viewpoint of preventing bulkiness, and the thinner the better in this range. From the viewpoint of light utilization efficiency, the transmittance of the laser beam used for recording / reproduction of the protective layer is preferably 50% or more, and more preferably 80% or more.

Next, reproduction of the hologram recorded on the optical recording sheet 16 will be described with reference to FIG. As shown in FIG. 5A, when the optical recording sheet 16 is irradiated with white light, diffused light is reproduced from the speckle pattern recorded on the optical recording sheet 16 as shown in FIG. As shown in FIG. 5C, the reproduced diffused light is reflected by the reflective layer 20 and is emitted to the outside of the optical recording sheet 16. As a result, diffused light is observed in the portion where the speckle pattern is recorded.
-Recording and playback experiments-
An optical recording sheet in which a photopolymer “Omunidex (R)” HRF-800 manufactured by DuPont was formed into a sheet having a film thickness of 15 μm was prepared.

Using an OHP sheet on which a binary image consisting of white letters “X” is printed as a mask, the mask is superimposed on the above optical recording sheet, and laser light having a wavelength of 532 nm and a light quantity of 20 mJ / cm ² is applied to Sigma. Irradiation was performed through “Frost type diffuser plate”, sand number # 500, manufactured by Koki Co., Ltd., and the optical recording sheet was mask-exposed with the obtained diffused light. The exposure amount was 1.2 J / cm ² . After the exposure, the optical recording sheet was heat-treated at 100 ° C. for 120 minutes.

  When the optical recording sheet on which the hologram was recorded was placed on black paper and irradiated with white light, a reproduced image shown in FIG. 6 was obtained. It can be seen that the original image (letter “X”) printed on the OHP sheet as a mask is reproduced. The reconstructed image was visible from a wide range of observation angles.

  As described above, in the present embodiment, since the refractive index distribution corresponding to the speckle pattern, that is, the volume hologram is recorded on the optical recording sheet, it is difficult to forge or alter the recorded hologram. In addition, a reproduced image obtained from a recorded hologram can be viewed from a wide range of viewing angles, and is excellent in visibility.

  In addition, it is possible to record a transmission type volume hologram by irradiating the optical recording sheet with a speckle pattern, and compared with the case where the volume hologram is recorded by irradiating the reference beam and the object beam, the configuration of the hologram recording device Becomes easier.

  Furthermore, since a hologram can be recorded using a mask that displays an arbitrary image, a volume hologram that is difficult to forge or alter can be recorded on demand with a simple apparatus configuration.

It is the schematic of the hologram recording device of this Embodiment. It is explanatory drawing which shows the function of a diffuser. It is a figure which shows intensity distribution of the diffused light modulated by the spatial light modulator. (A) is a figure which shows a mode that the hologram sheet was affixed on the card | curd, (B) is AA arrow sectional drawing of (A). (A)-(C) are sectional drawings along an optical axis which shows a mode that reproduced diffused light is emitted. It is a figure which shows the reproduction | regeneration image reproduced | regenerated from the recorded hologram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Laser light source 12 Diffuser 14 Spatial light modulator 16 Optical recording sheet 18 Substrate 20 Reflective layer

Claims (8)

  A hologram recording medium comprising a recording layer in which a large number of small areas in which a speckle pattern is recorded as a transmission volume hologram are arranged two-dimensionally.   The hologram recording medium according to claim 1, further comprising a reflective layer that reflects the reproduction light transmitted through the recording layer on the reproduction light transmission side of the recording layer.   The hologram recording medium according to claim 1, further comprising a base material for holding the recording layer.   The hologram recording medium according to claim 3, wherein the substrate is a sheet-like substrate.   The hologram recording medium according to claim 4, wherein the sheet-like substrate is made of paper or resin.   The hologram recording medium according to claim 1, wherein a protective layer for protecting the recording layer is formed on a surface of the recording layer. A laser light source for emitting laser light;
A diffuser for diffusing laser light emitted from the laser light source;
A spatial light modulator for spatially modulating the diffused light obtained by the diffuser and irradiating the optical recording medium with the modulated diffused light;
A hologram recording apparatus comprising:   A hologram recording method for recording a transmission volume hologram by spatially modulating diffused light obtained by diffusing laser light and irradiating the optical recording medium with the modulated diffused light.