METHOD FOR OPTICAL CHARACTERIZATION AND EVALUATION OF OPTICALLY VARIABLE DEVICES AND MEDIA

Abstract

Methods for evaluating an optically variable device (“OVD”) or optically variable media (“OVM”) are disclosed. The methods include the steps of applying light of a single wavelength from a calibrated light source to the OVD or OVM; measuring the light diffracted by the OVD or OVM with an integrating sphere; measuring the total incident light on the OVD or OVM; and calculating a diffraction efficiency for the OVD or OVM at the single wavelength based on the measurement of light diffracted and the measurement of total incident light.

Description

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary system for measuring optically variable devices and optically variable media.

FIG. 2 is a graph of measured diffraction spectra of two holographic films.

FIG. 3 is a graph of reflection spectra for a Spectralon reference.

FIG. 4 is a corrected graph of measured diffraction spectra of two holographic films.

FIG. 5 is graph of predicted hologram efficiency versus grating depth.

FIG. 6 is a graph of measured and predicted hologram efficiency versus grating depth.

FIG. 7 is a graph of a measured diffraction spectra and theoretical fits versus grating depth.

Claims

1. A method of evaluating an Optically Variable Device (OVD) or Optically Variable Media (OVM), comprising the steps of: a. applying light of a single wavelength from a calibrated light source to the OVD or OVM;b. measuring light diffracted by the OVD or OVM with an integrating sphere;c. measuring total incident light on the OVD or OVM; andd. calculating a diffraction efficiency for the OVD or OVM at said single wavelength based on said measurement of light diffracted and said measurement of total incident light.

2. The method of claim 1, further comprising the steps of: a. repeating the steps of claim 1 for a plurality of wavelengths;b. calculating an efficiency result for said plurality of wavelengths

3. The method of claim 2, wherein said efficiency result is selected from the group consisting of a. an average diffraction efficiency;b. a weighted average diffraction efficiency;c. an integral diffraction efficiency; andd. a weighted integral diffraction efficiency

4. The method of claim 2, further comprising correcting said efficiency result and said predicted efficiency result to account for a wavelength dependent response of a human eye.

5. The method of claim 4, wherein said wavelength dependent response of a human eye comprises red, green and blue components.

6. The method of claim 1, wherein applying said calibrated light is done with a spectrometer.

7. A method of evaluating optical characteristics of an Optical Variable Device (OVD) or Optically Variable Media (OVM), comprising the steps of: a. measuring a diffraction efficiency the OVD or OVM for a plurality of wavelengths;b. establishing a desired optical characteristic for a particular OVD or OVM design; andc. evaluating a plurality of OVDs or OVMs having said particular design by performing step “a” for each one of said plurality and comparing the result of step “a” with said desired optical characteristic.

8. The method of claim 7, wherein said desired optical characteristic is selected from the group consisting of: a. diffraction efficiency;b. reflectivity;c. scatter;d. weighted average diffraction efficiency;e. weighted average reflectivity;f. weighted average scatter; andg. color spectra.

9. The method of claim 7, wherein said optical characteristic is established though manually selecting a particular OVD or OVM target through human perception.

10. The method of claim 7, wherein said target is established through a theoretical model, wherein said theoretical model predicts efficiency over a plurality of wavelengths.

11. The method of claim 7, wherein said measured diffraction efficiency is selected from the group consisting of: a an average diffraction efficiency;b. a weighted average diffraction efficiency;c. an integral of the diffraction efficiency; andd. weighted integral of the diffraction efficiency.

12. The method of claim 7, wherein said predicted diffraction efficiency is calculated by a method selected from the group comprising: a. standard diffraction theory;b. electrodynamics calculations;c. a Fourier transform;d. a 2D Fourier transform;e. a power spectrum distribution model;f. standard diffraction theory calculated using numerical methods on a computer;g. electrodynamics calculations calculated using numerical methods on a computer;h. a Fourier transform calculated using numerical methods on a computer;i. a 2D Fourier transform calculated using numerical methods on a computer; andj. a power spectrum distribution model calculated using numerical methods on a computer.

13. The method of claim 7, wherein the OVD or OVM is selected from the group consisting of: a. a surface relief hologram;b. a reflection hologram;c. an absorption hologram;d. a transmission hologram;e. a polarization hologram;f. a phase gratings;g. a multi-layer diffractive device;h. a multi-layer refractive device;i. a random scattered surface;j. a random scattered inclusions;k. a random scattered layer.

14. The method of claim 7 where said evaluation is a part of a statistical process control method for the production of OVD or OVM.

15. The method of claim 7 where said evaluation is performed as a part of a real time process control method for the production of OVD or OVM.

16. The method of claim 7 where the evaluation is done on an OVD or OVM substantially made from a polymer.

17. The method of claim 7 where the OVD or OVM is made of a polymer selected from the group consisting of: a. polypropyleneb. ethylene propylene copolymers;c. ethylene propylene butene terpolymers;d. propylene butene copolymers;e. blends of polypropylene and propylene copolymersf. polyetheretherketone;e. polyimide;g. polyamide;h. polysulfone;i. polyphenylene sulphide;j. polyamideimide;k. polyethersulphone;l. polyetherimide;m. polyphenylsulphone;n. polycarbonate;o. polyacrylate, including polymethacrylate homopolymers and copolymers;p. polyester;q. epoxy-based polymers; andr. polysiloxane.

18. The method of claim 7 where the evaluation is performed on a film selected from the group consisting of a. an embossed film;b. a transferred holographic image;c. an unmetallized film; andd. a metallized film.

19. The method of claim 7 wherein said measuring is performed with an integrating sphere.

20. A method for evaluating an Optically Variable Device or Optically Variable Media under test having a grating depth and period, comprising the steps of: a. applying light of a single wavelength to the OVD or OVM under test with a calibrated light source;b. collecting and measuring light diffracted by said OVD or OVM under test with an integrating sphere;c. calculating a wavelength dependent diffraction efficiency of the OVD or OVM under test using said measured diffracted light;d. applying light of a single wavelength to the OVD or OVM under test with a calibrated light source;e. collecting and measuring light reflected by said OVD or OVM under test with an integrating sphere;f. calculating a wavelength dependent reflectivity for the OVD or OVM under test;g. Normalizing said diffraction efficiency relative to said reflectivity;h. Repeating steps “a”-“g” for a plurality of wavelengths;i. selecting an exemplary OVD or OVM having a known normalized diffraction efficiency; andj. Evaluating the OVD or OVM under test by comparing said normalized diffraction efficiency with said known normalized diffraction efficiency of said exemplary OVD or OVM.

21. The method of claim 20, wherein applying said calibrated light is done with a spectrometer.

22. The method of claim 20, wherein said target is established though manually selecting a particular OVD or OVM target through human perception.

23. The method of claim 20, wherein said target is established through a theoretical model, wherein said theoretical model predicts efficiency over a plurality of wavelengths.

24. The method of claim 23 wherein said theoretical model predicts a curve based on one of the group consisting of: a. standard diffraction theory;b. electrodynamics calculations;c. a Fourier transform;d. a 2D Fourier transform;e. a power spectrum distribution model;f. standard diffraction theory calculated using numerical methods on a computer;g. electrodynamics calculations calculated using numerical methods on a computer;h. a Fourier transform calculated using numerical methods on a computer;i. a 2D Fourier transform calculated using numerical methods on a computer; andj. a power spectrum distribution model calculated using numerical methods on a computer.

25. The method of claim 20 further comprising the step of:

26. The method of claim 20, wherein the OVD or OVM is selected from the group consisting of: a. a surface relief hologram;b. a reflection hologram;c. an absorption hologram;d. a transmission hologram;e. a polarization hologram;f. a phase gratings;g. a multi-layer diffractive device;h. a multi-layer refractive device;i. a random scattered surface;j. a random scattered inclusions;k. a random scattered layer.

27. The method of claim 20 wherein the OVD or OVM is substantially made from a polymer.

28. The method of claim 20 wherein the OVD or OVM is made of a polymer selected from the group consisting of a. polypropyleneb. ethylene propylene copolymers;c. ethylene propylene butene terpolymers;d. propylene butene copolymers;e. blends of polypropylene and propylene copolymersf. polyetheretherketone;e. polyimide;g. polyamide;h. polysulfone;i. polyphenylene sulphide;j. polyamideimide;k. polyethersulphone;l. polyetherimide;m. polyphenylsulphone;n. polycarbonate;o. polyacrylate, including polymethacrylate homopolymers and copolymers;p. polyester;q. epoxy-based polymers; andr. polysiloxane.

29. The method of claim 20 where the OVD or OVM comprises a film selected from the group consisting of a. an embossed film;b. a transferred holographic imagec. an unmetalized film; andd. a metalized film.