Optical: systems and elements – Holographic system or element – For synthetically generating a hologram
Reexamination Certificate
2002-12-17
2004-11-02
Boutsikaris, Leo (Department: 2872)
Optical: systems and elements
Holographic system or element
For synthetically generating a hologram
C359S002000, C359S022000, C359S032000, C283S086000
Reexamination Certificate
active
06813048
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a hologram-recorded medium and a process for the fabrication of the same, and more particularly to a process for the fabrication of a computer-generated hologram in which interference fringes are formed on a given recording surface by computer-aided computation and a hologram-recorded medium obtained by the same.
In recent years, coherent light has been easily obtainable by use of lasers, and holograms have been widely commercialized as well. Especially for notes and credit cards, the formation of holograms on portions of their media has become popular for anti-counterfeiting purposes.
Today's commercially available holograms are obtained by recording original images on media in form of interference fringes, using optical techniques. That is, an object that forms an original image is first provided. Then, light from this object and reference light are guided through an optical system such as a lens onto a recording surface with a photosensitive agent coated thereon to form interference fringes on the recording surface. Although this optical technique requires an optical system of some considerable precision for the purpose of obtaining sharp reconstructed images, it is the most straightforward method for obtaining holograms and so becomes most widespread in industry.
On the other hand, techniques for forming interference fringes on a recording surface by computer-aided computations for the fabrication of holograms, too, have been known to those skilled in the art. A hologram fabricated by such techniques is generally called a computer-generated hologram (CGH for short) or referred to simply as a computer hologram. This computer hologram is obtained by computer simulation of a process of generation of optical interference fringes, which process is all performed through computer-aided computations. Once image data on an interference fringe pattern have been obtained by such computations, physical interference fringes are formed on an actual medium. A specific technique has already been put to practical use, in which image data on a computer-generated interference fringe pattern are given to an electron beam lithographic system, so that the data are scanned by electron beams on a medium thereby forming physical interference fringes on the medium.
While keeping pace with recent developments of computer graphics, computer-aided processing of various images is being generalized in the printing industry. For the original images to be recorded in holograms, too, it is thus convenient to provide them in the form of image data. In consideration of such demands, techniques for generating computer holograms are of growing importance, and expected to take over optical hologram fabrication methods at some future time.
As explained above, significantly important commercial exploitations of holograms are to use them as anti-counterfeiting means for notes, credit cards or the like. To further enhance the anti-counterfeiting effect in such applications, it is effective to record a plurality of original images in the form of holograms. For instance, if the first original image comprising a pattern of size large enough for visual perception and the second original image comprising a pattern of visually unperceivable size are recorded on the same recording medium, then authentication can be carried out by observing the first original image. For the purpose of stricter authentication, it is possible to observe the second original image under loupes, microscopes or the like, thereby making more precise authentication. If micro-characters having a maximum size of up to 300 &mgr;m are used for the second original image, they visually looks just like a simple striped pattern, but they can be perceived as characters under loupes, microscopes or the like.
In commercial applications, holograms are used as ornamental materials for commodities, for instance, in the form of cards, key holders, and ornamental articles. In such applications, too, it is effective to record a plurality of original images thereby improving the decorative effects of the holograms. For instance, if the first original image that is a master motive and the second original image functioning as a background pattern are recorded on the same recording medium, it is then possible to obtain a great-looking 3D appearance at the time of viewing. It is understood that three or more original images may be recorded as holograms in the same recording medium.
However, illumination environments for reconstruction of commercially exploited hologram-recorded media are usually far from ideal. By definition, the illumination environment ideal for reconstruction is an environment wherein a hologram is irradiated with illumination light comprising the same monochromatic light as used for recording reference light from the same direction as applied for recording. In the real world, however, hologram images are hardly reconstructed in such an ideal illumination environment. That is, in daily life, hologram images are reconstructed in illumination environments having a broad range of wavelengths, e.g., under sunbeams in outdoor conditions and under electric bulbs within rooms, and so reconstructed images are much inferior in sharpness to ideal reconstructed images. For this reason, when images are reconstructed from a hologram-recorded medium with a plurality of original images recorded therein, plural reconstructed images are prima facie obtainable, but individual reconstructed images lack sharpness, providing generally blurred, flat images. Especially with a hologram fabricated in such a way that a plurality of original images having master-slave relations are recorded with some intents, e.g., a hologram having a combined master motive and background pattern, they are observed in a fused state where the master-slave relations are little identified.
SUMMARY OF THE INVENTION
It is thus the primary object of the present invention to provide a computer-generated hologram that enables a plurality of original images to be viewed with master-slave relations as intended even when a hologram image is reconstructed in daily illumination environments, and a process for the fabrication of the same.
(1) According to the first embodiment of the present invention, there is provided a process of the fabrication of a computer-generated hologram with interference fringes recorded on a given recording surface by computer-aided computations, which comprises steps of:
defining 2 to K original images, a recording surface for recording the original images and reference light with which the recording surface is irradiated and which corresponds to the 2 to K original images,
defining a multiplicity of sample light sources on each original image,
defining a given angle of spreading for object light emitted from individual sample light sources,
determining an area on the recording surface, at which object light emitted from all sample light sources defined on one original image arrive with a limited angle of spreading, as a recording area corresponding to said one original image, thereby defining recording areas corresponding to each of the K original images,
assigning priorities to a plurality of recording areas when the plurality of recording areas overlap one another on the recording surface, so that a recording area having higher priority is preceded over the rest with respect to an overlapping portion, thereby eliminating the overlapping portion,
defining a multiplicity of computation points on the recording surface so that on each computation point, the intensity of interference fringes formed by reference light and object light emitted from sample light sources on the original image corresponding to the recording area to which said computation point is allocated and from which the overlapping has been eliminated is found by computation, and
forming interference fringes comprising a distribution of intensities of interference fringes found on each computation point as a hologram on the recording surface.
(2)
Boutsikaris Leo
Dai Nippon Printing Co. Ltd.
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