Match filters for a real time fingerprint sensor and verification system

• US 6,111,671 A
• Filed: 11/18/1999
• Issued: 08/29/2000
• Est. Priority Date: 07/07/1995
• Status: Expired due to Fees

• Current Assignee: Advanced Precision Technology, Inc. (Exact Identification Corp.)
• Original Assignee: Advanced Precision Technology, Inc. (Exact Identification Corp.)
• Inventors: Bahuguna, Ramendra D., Corboline, Thomas M.
• Primary Examiner(s): Schuberg, Darren E.
• Application Number:
  US09/444,050
• Time in Patent Office: 285 Days
• Field of Search: 359/2, 359/15, 359/30, 359/561, 356/71
• US Class Current: 359/30
• CPC Class Codes: G06V 10/88 Image or video recognition using optical means, e.g. reference filters, holographic masks, frequency domain filters or spatial domain filters
• CPC Class Codes: G06V 40/12 Fingerprints or palmprints
• CPC Class Codes: G06V 40/13 Sensors therefor

Abstract

A real time fingerprint verification system includes a recording device and a verification device each having a fingerprint scanner for generating a flat, dimensionally undistorted, high contrast, fingerprint image, and an intensity sensitive, spatial light modulator (SLM) for receiving and transforming the flat fingerprint image into a planar, coherent light image. In the recording device, the planar coherent light image beam of the fingerprint from the SLM is Fourier transformed, and input into a microscope objective lens system which expands the Fourier transformed beam image sufficiently to allow mechanical blocking of its central portion or order, whereupon it is directed to interact as an object beam with a reference beam from the particular coherent light source to record a holographic matched filter. In the verification device, the planar coherent light image beam of the fingerprint is Fourier transformed and input into a microscope objective lens system to allow similar mechanical blocking of its central portion or order whereupon it is directed to interrogates a previously recorded holographic matched filter of a fingerprint image as an object beam for determining a match or not between the respective recorded and interrogating images. The spatial light modulator (SLM) in both the respective recording and verification devices enables phase correlation (optical path length determination) of one device to another device. X-Y alignment and rotational orinentation of the respective real time image and holographic matched filter image is accomplished by jittering (orbiting and angularly oscillating) either the interrogating object beam, real time, relative to the matched filter or visa versa.

Claims

1. An optical apparatus suited for recording fingerprint hologram matched filters comprising in combination:

a. a scanner for generating a flat, dimensionally undistorted, high contrast, fingerprint light image;

b. a recording, intensity sensitive, spatial light modulator (RSLM) having planar write and read faces receiving the flat, dimensionally undistorted, high contrast fingerprint light image from the scanner on its write face,

c. a common source of coherent light providing a collimated, coherent light, object beam and a collimated, coherent light, reference beam wherein;

(i) the object beam is directed to the planar read face of the recording spatial light modulator (RSLM) for transforming the received, flat, high contrast fingerprint image received by the planar `write` face of the spatial light modulator (RSLM) into a planar coherent light fingerprint image; and

(ii) the reference beam is directed to a hologram plane located an optical path length (MF) from the read face of the spatial light modulator (RSLM) determined for assuring phase correlation with an interrogating, coherent light object beam image of a fingerprint read from a read face of a verifying spatial light modulator (VSLM) of a verification optical fingerprint apparatus,

d. means for optically directing the planar, coherent light fingerprint image from the spatial light modulator to a Fourier transform focus creating a coherent light, phase distribution image of the fingerprint in a focal plane;

e. a lens optically expanding the coherent light, phase distribution image of the fingerprint in the focal plane;

f. an optical element blocking a central region of the expanded, coherent light, phase distribution image of the fingerprint eliminating a central region from the phase distribution image;

g. means for optically directing the expanded and blocked coherent light, phase distribution image of the fingerprint to the hologram plane; and

h. an optically sensitive material located in the hologram plane for recording a hologram of the reference beam and the expanded and blocked coherent light, phase distribution image of the fingerprint, whereby, the hologram once developed is suitable as a match filter for any verification optical fingerprint apparatus presenting an interrogating, coherent light object beam of a comparison fingerprint, optical path length (MF) from a read face of a verifying spatial light modulator (VSLM).

2. The optical apparatus of claim 1 further including means for adjusting optical path length respectively of the reference beam and the object beam to the hologram plane, whereby, matched filters may be recorded with optical path lengths correlated for specific optical systems contemplated for optically interrogating the particular recorded matched filters.

3. The optical apparatus of claim 1 wherein the expanded and blocked coherent light phase distribution image of the fingerprint is directed to the hologram plane along an optical axis which intersects with the reference beam at an angle θ

in a horizontal plane perpendicular to the hologram plane, and further including means for polarizing the coherent light of the reference beam and the coherent light of the expanded and blocked phase distribution image of the fingerprint vertically with respect to such horizontal plane.

4. The optical apparatus of claim 1 wherein the means for generating a flat, dimensionally undistorted, high contrast, fingerprint image comprises in combination

(i) a prism having a base surface, at least one slanted side input surface and a top transmission surface parallel its base surface,

(ii)) a flat holographic phase grating having an one flat surface optically coupled with the base surface of the prism and an exterior surface;

(iii)) 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 (⊥

) 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 the transparent coverslip,

the total internally reflected light from the finger-surface interface propagating 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.

5. The optical apparatus of claim 1 wherein the means for generating a flat, dimensionally undistorted, high contrast, fingerprint image comprises in combination,

(i) a right angled prism having a hypotenuse surface and a first and a second right angle surface,

(ii) 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;

(iii) 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,

the totally internally reflected light containing a true image of the finger-surface interface being reflected out of 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 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.

6. The optical apparatus of claim 1 wherein a two dimensional pattern may be written by digital image format data onto the planar read face of the recording spatial light modulator (RSLM), the collimated coherent light object beam directed to the read face of the spatial light modulator transforming that two dimensional pattern into a planar coherent light image of that pattern, and wherein the flat, dimensionally undistorted, high contrast, fingerprint light image is replicated as a two dimensional pattern in digital image format data which is input into a digital data processing system coupled to the recording spatial light modulator (RSLM) for writing the two dimensional pattern from the digital image format data derived from the flat, dimensionally undistorted, high contrast, fingerprint light image, to the planar write face of the spatial light modulator.

7. The optical apparatus of claim 1 wherein means for generating a flat, dimensionally undistorted, high contrast, fingerprint image comprises, in combination:

i. a means for providing a bright field having dark pattern presenting a planar image of a fingerprint;

j. a camera for receiving and converting the bright field and dark pattern of the planar image of the fingerprint into digital image format data;

k. a central processing unit (CPU) coupled for;

(i) receiving and processing the digital image format data from the camera; and

(ii) writing a representation of the bright field and dark pattern based upon the digital image format data to the planar `read` face of the spatial light modulator.

8. The optical apparatus of claim 7 wherein the means for providing a bright field having dark pattern presenting a planar image of a fingerprint comprises a flat, ink-based, manually recorded, fingerprint image.

9. The optical apparatus of claim 7 wherein the means for providing a bright field having dark pattern presenting a planar image of a fingerprint is a photographic reproduction of a flat, ink-base fingerprint image, manually recorded on paper.

10. The optical apparatus of claim 7 and further including a digital database information storage system coupled to the central processing unit for storing digital image format data for a plurality of fingerprint images, and for providing the central processing unit with digital image format data for particular fingerprint images upon request.

11. The optical apparatus of claim 7 wherein the representation of the bright field and dark pattern based upon the digital image format data written by the CPU to the planar read face of the spatial light modulator has a dark field and a bright pattern.

12. A method for recording fingerprint hologram matched filters comprising the steps of:

a. generating a flat, dimensionally undistorted, high contrast, fingerprint light image;

b. optically projecting the flat dimensionally undistorted, high contrast, fingerprint image onto a planar write face of a recording intensity sensitive spatial light modulator (RSLM);

c. providing a collimated, coherent light, object beam and a collimated, coherent light, reference beam from a common source of coherent light wherein;

(i) the object beam is directed for reflection from a planar `read` face of the recording, intensity sensitive spatial light modulator (RSLM) to create a planar, coherent light fingerprint image; and

(ii) the reference beam is directed to a hologram plane;

d. selecting an optical path length (MF) measured from the read face of the recording spatial light modulator (RSLM) to the hologram plane for assuring phase correlation with a interrogating, coherent light object beam image of a fingerprint read from a read face of a verifying spatial light modulator (VSLM) of a chosen verification optical fingerprint apparatus,

e. optically directing the planar, coherent light fingerprint image from the spatial light modulator to a Fourier transform focus creating a coherent light, phase distribution image of the fingerprint in a focal plane;

f. optically expanding the coherent light, phase distribution image of the fingerprint in the focal plane;

g. optically blocking a central region of the expanded, coherent light, phase distribution image of the fingerprint eliminating a central region from the phase distribution image;

h. optically directing the expanded and blocked coherent light, phase distribution image of the fingerprint to the hologram plane; and

i. recording a hologram of the reference beam and the expanded and blocked, coherent light, phase distribution image of the fingerprint using an optically sensitive material located in the hologram plane; and

j. developing the hologram recorded in the optically sensitive material creating a match filter suitable for the chosen verification optical fingerprint apparatus.