US 5,629,764 AGranted

Prism fingerprint sensor using a holographic optical element

AssigneeAdvanced Precision Technology, Inc.

InventorsRamendra D. Bahuguna, Thomas M. Corboline

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Abstract

A fingerprint sensor having a holographic phase grating glued on one right angle surface of a prism is described where a light source oriented normally relative to the hypotenuse surface of the prism illuminates an interface of the grating and finger surface. Incident light rays are refracted and absorbed where ridges of the finger surface contact the grating surface, whereas light rays are totally internally reflected in areas between and pores in finger surface ridges not in contact the grating surface. The reflected light rays, diffracted by the holographic phase grating, propagate normally (.perp.) back into the right angle prism where they are reflected normally (.perp.) out the remaining right angle surface of the prism by a second total internal reflection at the internal hypotenuse surface of the prism. The reflected light rays emerging from the sensor contain high contrast, detailed images of the ridges and valleys of the finger surface including pores in the ridges, i.e., a high quality fingerprint image oriented in a plane normal to the optical axis. The holographic phase grating eliminates image distortion due dimensional compression, and there is no necessity for optically correcting astigmatism in the image before capture. Fingerprint images of a quality that allows resolution of pores on the finger surface ridges are reliably obtained making the invented fingerprint sensor ideally suited for providing input to fingerprint recording, recognition and verification systems.

Claims7

Dependent claims

A fingerprint sensor for generating a light waveform image of finger surface ridges, comprising, in combination,

a) a right angled prism having a hypotenuse surface and a first and a second right angle surface,
b) a holographic phase grating plate having a plate surface optically coupled with the first right angle transmission surface of the prism and an exterior plate surface for diffracting light totally internally reflecting from its exterior plate surface to propagate normally (.perp.) back into the prism, wherein a finger is pressed against the exterior plate surface of the holographic phase grating plate providing a finger-surface interface;
c) a source of light illuminating the finger-surface interface through the hypotenuse surface of the prism, the illuminating light being refracted and absorbed in areas where finger surface ridges are in contact with the exterior plate surface, and being totally internally reflected back into the prism in areas corresponding to valleys between and pores in the finger surface ridges not in contact with exterior plate surface of the holographic phase grating plate,
whereby the totally internally reflected light containing a true image of the finger-surface interface is reflected out of the the second right angle transmission surface of the prism by the hypotenuse surface of the prism, the true image of the finger-surface interface being oriented a plane parallel to the the second right angle transmission surface for capture, the areas corresponding to finger surface ridges being dark, the areas corresponding to valleys between and pores in the finger surface ridges being bright.

1 more element

Dependencies are inferred from the claim text.