Abstract:
A color hologram recording medium  2  includes volume hologram recording mediums  14 R,  14 G and  14 B for diffracting light of wavelengths different from each other. Reconstruction patterns  1 R,  1 G and  1 B of the volume hologram recording mediums  14 R,  14 G and  14 B are recorded so that the reconstruction patterns  1 R,  1 G and  1 B are reconstructed at reconstruction positions different from each other. Thus, the color hologram recording medium  2  can have a wide variety of designs and artistic characters that the recorded color reconstruction patterns vary depending on watched directions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a color hologram recording medium, more specifically to a color hologram recording medium which includes volume holograms containing reconstruction patterns recorded in a plurality of wavelengths, and can have a large variety of designs and artistic characters. 
     2. Related Art 
     It is conventionally known that a color hologram recording medium includes volume holograms containing reconstruction patterns of three colors, R (red), G (green) and B (blue). The volume holograms are multi-recorded or overlapped for additive color mixing. It is also known that a color hologram recording medium includes R picture elements or dots, G picture elements or dots and B picture elements or dots which are juxtaposed with one another for additive color mixing resorting to area ratios among them. It has been also proposed by the inventors of the present invention in Japanese Patent Application No. 190970/1997 (Japanese Patent Laid-Open Publication No. 133611/1998) that neutral tints are provided by dot area ratios in such color hologram recording mediums. 
     However, in the conventional color hologram recording mediums, the volume holograms contain reconstruction patterns of the respective colors so that the reconstruction patterns are reconstructed in the same plane. Accordingly, the conventional color hologram recording mediums cannot provide a variety of designs and artistic characters that, for example, recorded color reconstruction patterns vary depending on watched directions. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in light of such disadvantage of the conventional color hologram recording mediums. An object of the present invention is to provide a color respective colors recorded so that the reconstruction patterns of the respective colors can be reconstructed at positions different from each other. Accordingly to the present invention, a wide variety of designs and artistic characters that, for example, the recorded color reconstruction patterns vary depending on watched directions can be provided. 
     The color hologram recording medium according to the present invention includes a plurality of volume holograms respectively including reconstruction patterns independent from each other, for diffracting light of wavelengths different from each other. The reconstruction patterns of the volume holograms are reconstructed at positions, which are different from each other. 
     In the above-described color hologram recording medium, it is preferable that the volume holograms are multi-recorded in a recording sensitive material. Also, it is preferable that each of the volume holograms is recorded in each of a plurality of sensitive materials to be laid one on another. 
     In the above-described color recording medium, it is preferable that the reconstruction patterns of the volume holograms are plane patterns. Also, it is preferable that the plane patterns are parallel with each other. In addition, it is preferable that the volume holograms are reflection/scattering holograms. 
     In the above-described color recording medium, it is preferable that the reconstruction patterns of the volume holograms are partially overlapped on each other so as to exhibit a neutral tint by additive color mixing of the reconstruction patterns in case that the volume holograms are observed in at least one direction. Also, it is preferable that at least one of the volume holograms has the reconstruction pattern formed in dots. 
     The process for fabricating the color hologram recording medium according to the present invention includes the step of preparing a plurality of first original plates respectively recording volume holograms which diffract light of wavelengths holograms recorded in the first original plates into second original plates, which are respectively spaced from the first original plates by distances which are different from each other; and the step of multi-recording the volume holograms recorded in the second original plates into a recording sensitive material to fabricate a color hologram recording medium. 
     The process for fabricating the color hologram recording medium according to the present invention includes the step of preparing a plurality of first original plates respectively recording volume holograms which diffract light of wavelengths different from each other; the step of recording the volume holograms recorded in the first original plates into second original plates which are respectively spaced from the first original plates by distances which are different from each other; the step of recording the volume holograms recorded in the second original plates respectively into recording sensitive materials spaced from the second original plates by a prescribed distance; and the step of laying the respective recording sensitive materials one on another to fabricate a color hologram recording medium. 
     According to the present invention, the reconstruction patterns of the volume holograms are multi-recorded or overlapped on each other so that the reconstruction patterns can be reconstructed at positions different from each other. Therefore, the reconstruction patterns are visible separately at positions which are depth-wise different from one another. The general pattern of the reconstruction patterns, and the shapes and the layout of the tint regions, that is the overlapped regions between the reconstruction patterns, change when an observation position is displaced. Thus, the color hologram recording medium having a wide variety of designs and artistic characters can be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     By referring now to the accompanying drawings, preferred embodiments of the present invention will be described in detail. 
     In the drawings, 
     FIG. 1 is a plan view of the color hologram recording medium according to an embodiment of the present invention, which shows a recorded pattern thereof; 
     FIG. 2 is a plan view of a mask pattern for R used in fabricating the color hologram recording medium; 
     FIG. 3 is a view of assistance in explaining the step of deactivating a part of a recording sensitive material during the process for fabricating the color hologram recording medium shown in FIG. 1; 
     FIG. 4 is a view of assistance in explaining the step of forming an R diffraction first original plate during the process for fabricating the color hologram recording medium shown in FIG. 1; 
     FIG. 5 is a view of assistance in explaining the step of forming an R diffraction second original plate during the process for fabricating the color hologram recording medium shown in FIG. 1; 
     FIG. 6 is a view of assistance in explaining the step of forming an R diffraction volume hologram during the process for fabricating the color hologram recording medium shown in FIG. 1; 
     FIG. 7 is a view of assistance in explaining the step of forming a G diffraction volume hologram during the process for fabricating the color hologram recording medium shown in FIG. 1; 
     FIG. 8 is a view of assistance in explaining the step of forming a B diffraction volume hologram during the process for fabricating the color hologram recording medium shown in FIG. 1; 
     FIG. 9 is a view of assistance in explaining an image reconstructing position of the completed color hologram recording medium according to the embodiment of the present invention; and 
     FIGS. 10A and 10B are views of assistance in explaining variations of patterns given when the color hologram recording medium shown in FIG. 9 is observed at different view points. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To simplify the explanation of the present invention, in the present embodiment, as shown in FIG. 1, the color hologram recording medium  2  containing circular reconstruction patterns  1 R,  1 G and  1 B of R (red), G (green) and B (blue) is fabricated by multi-recording or overlapping a plurality of volume holograms which diffract light of the wavelengths of R, G and B. The circular reconstruction patterns  1 R,  1 G and  1 B are superimposed on each other as shown in FIG.  1 . In FIG. 1, reference numeral  1 Y represents a region where R and G are added and mixed to appear yellow (Y); reference numeral  1 C represents a region where G and B are added and mixed to appear cyan (C); reference number  1 M represents a region where R and B are added and mixed to appear magenta (M); and reference numeral  1 W represents a region where G and B are added and mixed to appear white (W). 
     First, a process for forming an R diffracting volume hologram presenting the circular R pattern  1 R will be explained. A mask pattern plate  3 R for R having a shield portion  1 R′ corresponding to the pattern  1 R as shown in FIG. 2 is prepared. As shown in FIG. 3, the mask pattern plate  3 R is laid on a hologram recording material  6  which includes a transparent substrate  5  and a recording sensitive material  4  for the volume hologram. The recording sensitive material  4  is formed of a photopolymer or others and applied to the transparent substrate  5 . UV radiation  7  is applied to the recording sensitive material  4  from the side of mask pattern plate  3 R to photosensitize the recording sensitive material  4 , whereby a region  4   b  of the recording sensitive material  4  other than the circular R pattern  1 R is deactivated with a region  4   a  of the volume hologram recording sensitive material  4  corresponding to the pattern  1 R remaining photosensitive. 
     Then, as shown in FIG. 4, a reflection/scattering plate  8  is positioned in close contact with or near the backside of the hologram recording material  6  with the region  4   b  of the recording sensitive material  4  deactivated. Light  9 R of the R recording material  6  at a prescribed incident angle θ, passes through the recording sensitive material  4  to be reflected/scattered on the reflection/scattering plate  8 . The light reflected/scattered on the reflection/scattering plate  8  interferes with the incident light (the light  9 R of the R wavelength) in the photosensitive region  4   a  of the recording sensitive material  4 . Thus, an R diffracting first original plate  10 R for reflecting/scattering/diffracting light of the R wavelength is formed (see FIG.  5 ). The reflection/scattering plate  8  may be a usual reflection plate but may be a hologram scattering plate. 
     Next, as shown in FIG. 5, the R diffracting first original plate  10 R formed in the arrangement shown in FIG. 4 is turned upside down. A spacer transparent plate  11  is laid on the substrate  5 , and another hologram recording material  6  is laid on the spacer transparent plate  11 . Light  12 R of the R wavelength (the same wavelength as that of the light  9 R) is applied to the hologram recording material  6  at the same incident angle θ as that for forming the R diffraction first original plate  10 R. At this time, the light  12 R of the R wavelength passes through the hologram recording material  6  and the spacer transparent plate  11 , and scattered/diffracted light is generated backward with respect to the volume hologram region  4   c . The scattered/diffracted light and the incident light (the light  12 R of the R wavelength) interfere with each other in the recording sensitive material  4  of the hologram recording material  6 . Thus, an R diffraction second original plate  13 R for reflecting/scattering/diffracting light of the R wavelength is formed (see FIG.  6 ). 
     Then, as shown in FIG. 6, the R diffracting second original plate  13 R formed in the arrangement shown in FIG. 5 is turned upside down, and a volume hologram recording sensitive material  14  of a photopolymer or others is positioned at a prescribed distance from the substrate  5 . Light  15 R of the R wavelength (the same wavelength as that of the light  9 R and the light  12 R) is applied to the volume hologram recording sensitive material  14  second original plate  13 R. At this time, the light  15 R of the R wavelength is diffracted by the R diffracting second original plate  13 R, and the diffracted light forms an image at a position (image forming position  16 R) corresponding to the relative position of the R diffracting first original plate  10 R at the time that the R diffraction second original plate  13 R is formed. In the arrangement shown in FIG. 5, when a thickness of the substrate  5  of the hologram recording material  6  is 2 mm, and a thickness of the spacer transparent plate  11  is 10 mm, the image forming position  16 R is at a 14 mm distance from the hologram surface of the R diffracting second original plate  13 R. At the image forming position  16 R, the diffracted light is incident only on a region  1 R″ corresponding to the circular R pattern  1 R. 
     Here, a layout position of the volume hologram recording sensitive material  14  is spaced by 10 mm from the hologram surface of the R diffracting second original plate  13 R as shown in FIG.  6 . In this arrangement, the diffracted light from the volume hologram of the R diffracting second original plate  13 R to the region  1 R″ corresponding to the circular R pattern  1 R interferes with the incident light  15 R in the volume hologram recording sensitive material  14 . Thus, an R diffracting volume hologram with the circular R pattern  1 R ( 1 R″) recorded is formed in the volume hologram recording sensitive material  14 . The thus-recorded R diffracting volume hologram recording body is represented by reference numeral  14 R (see FIG.  9 ). The R diffracting volume hologram recording body is a volume hologram which reconstructs and displays the circular R pattern  1 R at a position spaced by 4 mm upward from the hologram surface when light of the R wavelength is incident on the hologram surface at an incident angle θ. 
     By performing the steps shown in FIGS. 2 to  6 , replacing the wavelength  9 R,  12 R and  15 R of the recording light R by the wavelengths of G and B, a G diffracting first original plate and a G diffracting second original plate  13 G are formed (see FIG.  7 ), and finally a G diffracting volume hologram recording body  14 G which reconstructs and displays the circular pattern  1 G of plate and a B diffracting second original plate  13 B are formed (See FIG.  8 ), and finally a B diffracting volume hologram recording body  14 B which reconstructs and displays the circular pattern  1 B of B is formed (see FIG.  9 ). However, in the arrangement shown in FIG. 5, the spacer transparent plate  11  is 6 mm for forming the G diffracting second original plate  13 G but is not used in forming the B diffracting second original plate  13 B. Then, in the arrangement shown in FIG. 6, image forming positions  16 G,  16 B are positioned with respect to the G diffracting second original plate  13 G and the B diffracting second original plate  13 B are respectively as shown in FIGS. 7 and 8. 
     That is, in recording the circular pattern  1 G ( 1 G″) in the G diffracting volume hologram recording sensitive material  14  to form the G diffracting volume hologram recording body, as shown in FIG. 7, an image forming position  16 G of the diffracted light from the G diffracting second original plate  13 G is identical with the position where the volume hologram recording sensitive material  14  is positioned. Accordingly, the G diffracting volume hologram recorded in the volume hologram recording sensitive material  14  body is a volume hologram which reconstructs and displays the circular G pattern  1 G at a position of the hologram surface when light of the G wavelength is incident on the hologram surface at an incident angle θ, 
     In recording the circular pattern  1 B ( 1 B″) in the B diffracting volume hologram recording sensitive material  14  to form the B diffracting volume hologram recording body, as shown in FIG. 8, an image forming position  16 B of the diffracted light from the B diffracting second original plate  13 B is spaced by 4 mm from the B diffracting second original plate  13 B. Accordingly, the B diffracting volume hologram recorded in the volume hologram recording sensitive material  14  is a volume hologram which reconstructs and displays the circular B pattern  1 B at a position spaced by 6 mm downward from the hologram surface when light of the B wavelength is incident on the hologram surface at an incident angle θ. 
     As shown in FIG. 9, three sheets of the thus-formed R volume hologram recording body  14 G and the B diffracting volume hologram recording body  14 B are laid one on another to form one sheet of color hologram recording medium  2 . Otherwise, three sheets of the hologram recording bodies  14 R,  14 G and  14 B are multi-recorded in another sheet of the recording sensitive material to form the color hologram recording medium  2 . When white light  17 , or light containing the R wavelength, the G wavelength and the B wavelength is applied to the thus-formed color hologram recording medium  2  at the same incident angle θ as that for forming the respective volume hologram recording bodies  14 R,  14 G and  14 B, and the color hologram recording medium  2  is observed with the eyes from the side of the incidence, the circular R pattern  1 R is spaced by 4 mm upward from the surface of the color hologram recording medium  2 , the circular G pattern  1 G is visibly reconstructed at the same position as the surface of the color hologram recording medium  2 , and the circular B pattern  1 B is visibly reconstructed at a position deeper by 6 mm than the surface of the color hologram recording medium  2 . That is, the three patterns  1 R,  1 G and  1 B of the different colors are visible separately at positions which are depth-wise different from one another. 
     Accordingly, when the color hologram recording medium  2  is watched at the front, as shown in FIG. 1, the circular R, G and B patterns  1 R,  1 G and  1 B appear, partially overlapping one another. Owing to the additive color mixing, the overlapped region between the patter  1 R and the pattern  1 G appears yellow (Y), the overlapped region between the pattern  1 G and the pattern  1 B appears cyan (C), the overlapped region among the pattern  1 R, the pattern  1 B appears magenta (M), and the overlapped region between the pattern  1 R and the pattern  1 G and the pattern  1 B appears white (W). 
     When an observation position is displaced from the front to the right, as shown in FIG. 10A, with respect to the pattern  1 G of G fixed to the surface of the color hologram recording medium  2 , the pattern  1 R of R positioned in front of the pattern  1 G moves to the left, the pattern  1 B positioned behind the pattern  1 G moving the case shown in FIG. 10A the magenta region  1 M and the white region  1 W disappear. When an observation position is displaced from the front to the left, as shown in FIG. 10B, with respect to the pattern  1 G of G fixed to the surface of the color hologram recording medium  2 , the pattern  1 R of R positioned in front of the pattern  1 G moves to the right, the pattern  1 B positioned behind the pattern  1 G moves to the left. Not only a shape of the general pattern, but also shapes of the respective color regions change. 
     In the above-described embodiment, all the respective color regions are solidly colored throughout their regions (see FIG.  2 ). However, a lightness of a color to be recorded (e.g., R) can be adjusted by forming the shield portion of the mask pattern in a dot pattern having an arbitrary dot area ratio in place of the solid light shield pattern. By adjusting lightness of the respective colors, tints of the regions  1 Y,  1 C,  1 M and  1 W of the additive color mixing can be adjusted. 
     The color hologram recording medium and a process for fabricating the same according to the present invention have been explained above by means of an embodiment thereof, but the present invention covers other various modifications. The hologram of the present invention is not limited to the reflection/scattering volume hologram but may be a transmission/scattering volume hologram or a volume hologram which can reconstruct picture patterns, such as cubic images. Dots used in the present invention may be not only collections of shapes, such as fine circles, rectangles, etc., but also collections of fine stripes.