Importance

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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.

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First Claim