×

Prism fingerprint sensor using a holographic optical element

  • US 5,629,764 A
  • Filed: 07/07/1995
  • Issued: 05/13/1997
  • Est. Priority Date: 07/07/1995
  • Status: Expired due to Fees
First Claim
Patent Images

1. 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 (⊥

  • ) 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.

View all claims
  • 2 Assignments
Timeline View
Assignment View
    ×
    ×