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Method of reading hologram information
| Details |
Inventors: Yamazaki, Satoshi;
Assignee: Dai Nippon Printing Co., Ltd. (Tokyo, JP)
Primary Examiner: Dzierzynski; Paul M.
Assistant Examiner: Juba, Jr.; John
Attorney, Agent or Firm: Dellett and Walters
A method of photoelectrically reading information recorded in the form of a Fresnel hologram, which makes it possible to eliminate the effect on the reading accuracy of a scratch, a stain, etc., on the hologram surface when the recorded information is reconstructed by applying a light beam having a small diameter to the hologram. The surface of the hologram is illuminated by scanning it with a light beam having a cross-section smaller than the hologram recording region, thereby reconstructing and reading the same recorded information separately from different hologram regions, and thus compensating for momentary disability to reconstruct the recorded information due to a scratch or stain. At the same time, since a light beam having a small beam diameter is used for reconstruction, the depth of focus of the reconstructed image increases, so that the number of restrictions on the installation position of the read sensor decreases. |
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DETAILED DESCRIPTION In view of the above-described circumstances, it is an object of the present invention to provide a hologram information reading method wherein when a hologram is illuminated with a beam of light having a small diameter to reconstruct information recorded thereon, the light beam is moved to scan the hologram surface, thereby eliminating the effect on the reading accuracy of a scratch, a stain, etc.
, on the hologram surface.
To attain the above-described object, the present invention provides a method of photoelectrically reading information recorded in the form of a Fresnel hologram, wherein the hologram surface is illuminated by scanning it with a beam of light having a cross-section smaller than a hologram recording region, thereby reconstructing and reading the same recorded information separately from different hologram regions.
Preferably, the recorded information is a pattern comprising a plurality of parallel bars, for example, and the light beam is moved to scan in a direction parallel to each bar.
Further, the hologram is moved relative to the light beam in a direction intersecting the scanning direction.
The hologram may be provided on a card.
In such a case, it is possible to judge whether the card is genuine or a forgery from the recorded information.
It is also possible to detect zero-order diffracted light from the hologram and to sense a hole punched in the hologram from the interrupting time of the zero-order diffracted light simultaneously with the reading of the recorded information.
According to the present invention, the hologram surface is illuminated by scanning it with a light beam having a cross-section smaller than the hologram recording region, thereby reconstructing and reading the same recorded information separately from different hologram regions.
Therefore, even if there is a scratch or a stain in a specific illuminated region on the hologram, since the beam of illuminating light also illuminates scratch- or stain-free portions in the neighborhood of the specific region before and after it to reconstruct the recorded information, it is possible to compensate for momentary disability to reconstruct the recorded information due to the scratch or stain
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