Fingerprint recognition device using a hologram

A fingerprint recognition device which is capable of improved recognition through the generation of an accurate distortion-free image of a fingerprint, the fingerprint recognition device comprising:

• a laser for emitting a laser beam along a first optical axis,
• a collimator disposed or the first optical axis for collecting the laser beam and directing the laser beam along and parallel with the first optical axis,
• a tetragonal prism having first and second parallel surfaces thereon and a third surface which is inclined to the first and second surfaces, the second prism surface being adapted to receive a finger thereon whose fingerprint it is desired to be recognized,
• the laser beam which is directed along the first optical axis being incident on and perpendicular to the first prism surface so that the collimated laser beam passes through the first prism surface to the second prism surface where it is diffused by the fingerprint thereon so as to form an image of the fingerprint within the tetragonal prism at a first image plane, which image plane is inclined to the second prism surface,
• the diffused laser beam being deflected by the second prism surface so to pass through the first image plane and orthogonally through the third prism surface along a third optical axis,
• a hologram disposed along the third optical axis so as to intercept the diffused laser beam from the first image plane, the hologram being disposed parallel to the first image plane and producing a distortion-free virtual image of the fingerprint at a second image formation plane, a central point of the virtual image and the intersection of the third optical axis with the hologram define a second optical axis,
• an image-forming lens aligned on the second optical axis for viewing the virtual image of the fingerprint through the hologram and for forming a real distortion-free image of the fingerprint,
• an area CCD disposed along and perpendicular to the second optical axis at the plane of the real distortion-free image formed by the image-forming lens to convert that fingerprint image into electrical signals, and
• a circuit connected to the area CCD for amplifying and analyzing these electrical signals, whereby improved fingerprint identification is accomplished because the area CCD is presented with a distortion-free image produced by the hologram.