초록 ▼

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 t

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.

대표청구항 ▼

[ We claim:] [1.] A fingerprint sensor for generating a light waveform image of finger surface ridges, comprising, in combination,a) a trapezoid prism having a base surface, at least one slanted side input surface and a top transmission surface parallel its base surface,b) a flat holographic phase g

[ We claim:] [1.] A fingerprint sensor for generating a light waveform image of finger surface ridges, comprising, in combination,a) a trapezoid prism having a base surface, at least one slanted side input surface and a top transmission surface parallel its base surface,b) a flat holographic phase grating having an one flat surface optically coupled with the base surface of the prism and an exterior surface;c) a thin transparent coverslip optically coupled with, covering and protecting the exterior surface of the holographic phase grating presenting a surface upon which a finger may be pressed to provide a finger-surface interface which both reflects and transmits light, the holographic phase grating diffracting illuminating light totally internally reflecting from the finger-surface interface to propagate as a converging light beam having an axis normally oriented (.perp.) with respect to the base and top transmission surfaces of the prism;d) a source of light for illuminating the finger-surface interface through the slanted side input surface of the prism, the illuminating light being refracted and absorbed in areas where finger surface ridges are in contact with the transparent coverslip, and being totally internally reflected in areas corresponding to valleys between and pores in the finger surface ridges not in contact with transparent coverslip, reby the total internally reflected light from the finger-surface interface propagates as a converging beam to, through and out the top transmission surface of the trapezoidal prism, the converging beam of light containing a true image of the finger-surface interface wherein the areas corresponding to finger surface ridges in contact with the coverslip are dark, the areas corresponding to valleys between and pores in the finger surface ridges not in contact with the coverslip are bright.