Optical device with ordered scatterer arrays for secure identity and a method of producing the same

12134,280

17/232154

April 16, 2021

An optical device with ordered scatterer arrays for secure identity and a method of producing the same This invention discloses a method for configurable spatial control and modification of optically active resonantly coupled scatterer arrays to produce identifiable security features and a corresponding photonic secure identity device. The invention comprises at least the steps of (i) producing a deposition template from said master stamp, (ii) synthesis of a plasmonic particle colloid, (iii) producing an optically active, two-dimensional security tag template using self-assembly of said particles on said deposition template, (iv) producing a customized secure identity device from said security tag template by selective removal or modification of optical properties using ultrashort laser pulses. The produced customized plasmonic-photonic device can then be used as secure identity and anti-counterfeiting means. The device exploits customized spatial control and modification of optically active plasmonic particle arrays demonstrating surface lattice resonance optical signature to produce easily identifiable security features.

Kaunas University of Technology (Kaunas, LT)

Kaunas University of Technology (Kaunas, LT)

1. A secure identity optical device for anti-counterfeiting measures which is configured to produce visually (801 , 902 , 1004 , 1103), spectroscopically (701), or microscopically (102 , 103 , 801 , 902) verifiable security features wherein the optical device comprises at least: a substrate (201); and a plurality of optical scatterers (101 , 202) being plasmonic nanoparticles affixed onto the substrate (201) and separated from adjacent scatterers (202) by a distance to form a two-dimensional pattern of said optical scatterers; characterized in that said optical scatterer pattern comprises at least one of: a) a specifically designed binary pattern (102 , 105 , 104 , 801 , 1003 , 1101), wherein some scatterers either are (202) or are not (204) in a selected location on the substrate; b) a specifically designed colour-based pattern (103 , 902), wherein some scatterers (902) scatter a measurably different colour of light compared to adjacent scatterers (901); c) a specifically designed photonic interaction between said scatterers (202), wherein said interaction results in features in an optical spectrum (701); or d) a combination of any of a), b) and c).

2. The device of claim 1 , wherein said scatterer pattern comprises at least one of: a) a varying distance between adjacent scatterers (202 , 601); b) a plurality of optical scatterer arrangements, comprising more than one optical scatterers within each scatterer arrangements selected from scatterer dimers (205), trimers, and tetramers.

3. The device of claim 1 , wherein said pattern of optical scatterers is arranged so that, upon illuminating with electromagnetic radiation, it provides an optical Rayleigh spectral anomaly condition, producing a surface lattice resonance SLR spectral feature in the spectrum of the electromagnetic radiation due to the combination of said Rayleigh anomaly and localized surface plasmon resonance LSPR of said optical scatterers.

4. The device of claim 1 , wherein said binary pattern constitutes a computer-generated hologram (1003) of an image (1002), which can be reconstructed in a far-field by monochromatic illumination (1004).

5. The device of claim 1 , wherein said binary pattern constitutes an array of finite-sized areas, wherein each area comprising lines of scatterers arranged as halo-pixels (1101) whereby said halo-pixel array produces a visual holographic image (1103).

6. The device of claim 1 , further comprising a transparent superstrate material (1201) secured on top of the substrate (1203) and enclosing said scatterers (1202) underneath.

7. A method of producing the device of claim 1 , comprising steps of: providing a substrate (201) with an array of obstacles (203) for allocating scatterers onto the substrate; synthesizing a colloid solution (402) comprising monodisperse scatterers (403); depositing the colloid solution (402) onto the substrate (404) with an array of obstacles (407) wherein self-assembly of said scatterers (403) occurs on said substrate.

8. The method of claim 7 , further comprising a step of depositing one or more transparent protective layers (1201) on top of the substrate (1203).

9. A method of creating a customized binary pattern on the device of claim 1 , comprising steps of: providing a substrate (1303) with an array of scatterers (1302); providing one or more laser beams (1301) of monochromatic light radiation; providing optomechanical means to focus at least one laser beam (1301) onto said substrate (1303) with the array of scatterers (1302); translating the substrate (1303) or/and positioning the laser spot (1301) over said substrate (1303); providing means of controlling the laser patterning process; focusing the laser beam energy selectively to the array of scatterers (1302) causing any one of: selective reshaping, fracturing, coalescence, removal of said scatterers (1302), or any combination thereof; and repeating the penultimate step a plurality of times for a plurality of spots in different locations of the substrate (1303) to define a custom pattern in the array of scatterers (102 , 103 , 104 , 801 , 902 , 1003).

10. A method of verifying the device of claim 1 , comprising any steps of: verifying signatures in the optical spectra (701) scattered by the device under illumination, verifying a binary or colour image or a text present on the device seen through an optical microscope under dark-field illumination (102 , 103 , 105 , 501 , 801 , 901), verifying a dot-matrix hologram under white-light illumination (1103), verifying on a screen when a computer-generated hologram present on the device is illuminated using monochromatic visible light (1004), or verifying by any combination of above steps, depending on customizations on the device by the method of claim 9 .

11. The method of claim 9 , wherein the light radiation is provided in the form of two or more laser beams (1402) that are spatially and temporally overlapped and concentrated into a single spot on the surface (1403) by means of directing and focusing optics and form an interference pattern (1401) with a laterally varying intensity with some periodicity, said interference pattern (1401) applied onto the array of scatterers (1403).

12. The method of claim 11 , wherein the overlapping laser beams interference and periodicity pattern are controlled by using any of the following: varying a number of of the overlapping laser beams (1402); varying a light phase and/or polarization of each laser beam (1402); varying the angle between overlapping beams (1402); varying a spatial orientation of the overlapping laser beams interference pattern (1401) with respect to the substrate (1404) and the array of scatterers (1403).

13. The method of claim 9 , wherein said scatterers (1302) are selectively affected by the focused laser beam (1301), to form a binary pattern (102 , 105 , 104), a colour-based pattern (103), or a combination of the binary pattern and the colour-based pattern, by one or more steps: removal of the scatterer from the array of scatterers (1302 ; a group thereof; reshaping a scatterer so that the array of scatterers (1302) locally changes the central wavelength of scattered electromagnetic radiation; fracturing a scatterer into smaller scatterers so that said array (1302) gains new scatterers having shifted central wavelength of scattered electromagnetic radiation; and coalescing into bigger scatterers so that the array of scatterers (1302) locally changes its central wavelength of scattered electromagnetic radiation.

14. The method of claim 9 , wherein the multiple laser beams (1402) are applied on the scatterers' array to impose diffraction gratings comprising a decorative pattern where each separate spot contains a predefined pattern imposed in the two-dimensional scatterer array (1101), thereby the overall system forms a dot-matrix hologram (1102).

15. The method of claim 9 , wherein the at least one laser beam (1301) is used to spatially alter the array of scatterers (1302) to form binary patterns comprising any combination of: a microtext, a nanotext, or any combination thereof (102); a two-dimensional binary image (801); a computer-generated-hologram (104 , 1003) of an image (1002); and an array of larger pixels comprising lines of scatterers (105 , 1101) forming a dot matrix hologram (1102).

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