Optically-based methods and apparatus for performing document authentication

• US 5,903,340 A
• Filed: 04/10/1997
• Issued: 05/11/1999
• Est. Priority Date: 03/18/1994
• Status: Expired due to Term

• Current Assignee: Brown University
• Original Assignee: Brown University
• Inventors: Driscoll, Timothy J, Lawandy, Nabil M
• Primary Examiner(s): Kim, Robert H.
• Application Number:
  US08/835,655
• Time in Patent Office: 761 Days
• Field of Search: 356/71
• US Class Current: 356/71
• CPC Class Codes: G07D 7/005 Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations
• CPC Class Codes: G07D 7/1205 Testing spectral properties

Abstract

This invention teaches a method for authenticating a document. The method includes the steps of: (a) providing a document to be authenticated; (b) illuminating at least a portion of the document with laser light that exceeds a threshold fluence; (c) detecting a narrow band laser-like emission of at least one wavelength from the document in response to the step of illuminating; and (d) declaring the document to be authentic only if the laser-like emission is detected.

Claims

1. A method for authenticating a document, comprising the steps of:

providing a document to be authenticated;

illuminating at least a portion of the document with laser light that exceeds a threshold fluence;

detecting a narrow band substantially non-saturable amplified spontaneous emission of at least one wavelength from the document in response to the step of illuminating; and

declaring the document to be authentic only if the emission is detected.

2. A method as in claim 1, wherein step of providing a document provides a document having embedded threads, individual ones of which comprise a substrate material and an optical gain medium in combination with scatterers for providing the emission in response to the step of illuminating.

3. A method as in claim 1, wherein step of providing a document provides a document having an ink bearing surface, the ink including an optical gain medium in combination with scatterers for providing the emission in response to the step of illuminating.

4. A method as in claim 1, wherein step of providing a document provides a document having a fluorescent whitening agent (FWA), the FWA functioning as an optical gain medium in combination with scatterers for providing the emission in response to the step of illuminating.

5. A method as in claim 1, wherein step of providing a document provides a document having embedded threads, individual ones of said threads being coated with a polymer-based coating, the polymer-based coating functioning as an optical gain medium in combination with scatterers for providing the emission in response to the step of illuminating.

6. A method as in claim 1, wherein step of providing a document provides a document having embedded threads, each of the threads being comprised of N filaments individual ones of which comprise a substrate material and an optical gain medium in combination with scatterers for providing the emission in response to the step of illuminating, wherein each thread emits light at N distinguishable wavelengths.

7. A method as in claim 1, wherein step of providing a document provides a document having embedded threads, each of the threads being comprised of a multilayered structure having a least one layer comprised of the optical gain material, and an underlying metalization layer.

8. A method as in claim 7, wherein the at least one layer of optical gain material is differentiated into a plurality of regions, each of the regions emitting with a characteristic wavelength.

9. A method as in claim 7, wherein the underlying metalization layer is patterned.

10. A method as in claim 7, wherein the underlying metalization layer is patterned and modulates a thickness of an overlying layer comprised of the optical gain material.

11. A method as set forth in claim 1, wherein the step of detecting detects a presence of a secondary emission peak that results from a photoconversion of a primary emission peak.

12. A document, comprising:

a matrix formed as a planar substrate; and

at least one security structure embedded in said matrix, said at lest one security structure comprising an optical gain medium that is responsive to illumination with laser light that exceeds a threshold fluence for emitting a narrow band substantially non-saturable amplified spontaneous emission of at least one wavelength.

13. A document as in claim 12, wherein said security structure is comprised of a metalized substrate having a coating comprised of said gain medium on at least one surface.

14. A document as in claim 12, wherein said security structure is comprised of one or more filaments that include said gain medium.

15. A document as in claim 12, wherein said security structure is comprised of a planchette that includes said gain medium.

16. A document as in claim 12, wherein said security structure is comprised of a metalized substrate having a coating comprised of said optical gain medium on at least one surface, said metalized substrate being disposed such that a distance from said at least one surface to an illuminated surface of said planar substrate varies along a length of said metalized substrate.

17. Apparatus for authenticating a document, comprising:

a laser for illuminating all or a portion of a document, said laser outputting light having wavelengths that are predetermined to generate a narrow band substantially non-saturable amplified spontaneous emission, having at least one predetermined emission wavelength, from the document or a structure contained within the document;

at least one photodetector responsive to said predetermined emission wavelength for detecting the presence of the at least one predetermined emission wavelength; and

decision means, having an input coupled to an output of said at least one photodetector, for indicating the authenticity of the document based at least in part on a detection of the at least one predetermined emission wavelength.

18. Apparatus as in claim 17, wherein said structure is comprised of an embedded security thread comprised of a substrate material and an optical gain medium in combination with scatterers for providing the emission.

19. Apparatus as in claim 17, wherein the document has an ink bearing surface, the ink including an optical gain medium in combination with scatterers for providing the emission.

20. Apparatus as in claim 17, wherein the document has a fluorescent whitening agent (FWA), the FWA functioning as an optical gain medium in combination with scatterers for providing the emission.

21. Apparatus as in claim 17, wherein said structure is comprised of an embedded security thread coated with a polymer-based coating, the polymer-based coating functioning as an optical gain medium in combination with scatterers for providing the emission.

22. Apparatus as in claim 17, wherein said structure is comprised of an embedded security thread comprised of N filaments individual ones of which comprise a substrate material and an optical gain medium in combination with scatterers for providing the emission, wherein each thread emits light at N distinguishable wavelengths.

23. Apparatus as in claim 17, wherein said structure is comprised of an embedded multilayered security thread having at least one layer comprised of an optical gain medium, and an underlying metalization layer.

24. Apparatus as in claim 23, wherein the at least one layer of optical gain material is differentiated into a plurality of regions, each of the regions emitting with a characteristic wavelength.

25. Apparatus as in claim 23, wherein the underlying metalization layer is patterned.

26. Apparatus as in claim 23, wherein the underlying metalization layer is patterned and modulates a thickness of an overlying layer comprised of the optical gain medium.

27. Apparatus as in claim 17, wherein said structure is comprised of a metalized substrate having a coating comprised of an optical gain medium on at least one surface.

28. Apparatus as in claim 17, wherein said structure is comprised of one or more filaments that include an optical gain medium integrally formed therewith or coated thereon.

29. Apparatus as in claim 17, wherein said structure is comprised of a planchette that includes an optical gain medium.

30. Apparatus as in claim 17, wherein said structure is comprised of a metalized substrate having a coating comprised of an optical gain medium on at least one surface, said metalized substrate being disposed such that a distance from said at least one surface to an illuminated surface of said document varies along a length of said metalized substrate.

31. Apparatus for distinguishing a first type of currency having a first monetary value from other types of currency having different monetary values, comprising:

a laser for illuminating all or a portion of a currency of interest, said laser outputting light having wavelengths that are predetermined to generate a narrow band substantially non-saturable amplified spontaneous emission, having at least one predetermined emission wavelength, from the first type of currency or a structure contained within the first type of currency;

at least one photodetector responsive to said predetermined emission wavelength for detecting the presence of the at least one predetermined emission wavelength; and

decision means, having an input coupled to an output of said at least one photodetector, for distinguishing the currency has being one of the first type or another type based at least in part on the output of said photodetector.

32. A fiber, said fiber being responsive to incident light having wavelengths selected to generate a narrow band substantially non-saturable amplified spontaneous emission from said fiber, said emission comprising at least one narrow band of emission wavelengths defined at least in part by scattering at boundaries of said fiber.

33. A fiber as in claim 32, wherein said fiber comprises a portion of a document.

34. A fiber as in claim 32, wherein said fiber comprises a portion of a negotiable instrument.

35. A fiber as in claim 32, wherein said fiber comprises a portion of a currency.

36. A fiber as in claim 32, wherein said fiber comprises a portion of an object that represents a unit of monetary value.

37. An object that is responsive to incident light having wavelengths selected to generate a narrow band substantially non-saturable amplified spontaneous emission from said object, said emission comprising at least one narrow band of emission wavelengths defined at least in part by scattering at boundaries of said object.

38. An object as in claim 37, wherein said object comprises a portion of a document.

39. An object as in claim 37, wherein said object comprises a portion of a negotiable instrument.

40. An object as in claim 37, wherein said object comprises a portion of a currency.

41. An object as in claim 37, wherein said object comprises a portion of an object that represents a unit of monetary value.