Importance

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Abstract

A miniaturized fingerprint sensor has a holographic phase grating glued to a base surface of a trapezoidal prism which operates on light totally internally reflecting from a finger-coverslip interface protecting the exterior surface of the grating, diffracting the reflected light to propagate back through the base surface and out the top parallel surface of the prism in a converging beam having an optical axis normally oriented (.perp.) with respect to such parallel base and top surfaces of the prism. A mirror folds the emerging converging light beam directing it into a camera system. The converging light beam emerging from the top surface of the trapezoidal prism contains high contrast, detailed images of ridges, valleys and pores of a finger-surface interface oriented in a plane normal to the optical axis. The holographic phase grating diffracting reflected light from the finger-surface interface into a converging light beam not only eliminates image distortion due dimensional compression, and aberrations, but also eliminates `hot spots` in the reduced image before capture. The converging beam from the holographic phase grating also allows shorter optical lengths and significant dimensional miniaturization of such sensors. 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