Security Device with a zero-order diffractive microstructure
A security Device comprises a zero order diffractive microstructure ( 5 ) buried within a substrate ( 3 ). One or more further optical structures, such as microlenses ( 1 ), may be formed on a surface ( 2 ) of the substrate ( 3 ). The further optical structures modify the optical characteristics of the zero order diffractive microstructure ( 5 ). Various alternatives or additional optical structures and methods of producing them are described in additional embodiments.
1. A security device comprising:
a zero-order diffractive microstructure buried within a substrate, the zero-order diffractive microstructure including a high refractive index material; and
a further structure embedded in the substrate, the further structure comprising a colour filter, wherein the further structure modifies optical characteristics produced by the zero-order diffractive microstructure, and wherein the colour filter comprises a fluorophor coated onto or placed at a short distance from the high index material so as to interact with an evanescent field near the zero-order diffractive microstructure.
2. The security device of claim 1 , wherein the colour filter is formed by adding a material with colour filter function between a surface of the substrate to be viewed by a user and the zero-order diffractive microstructure.
3. The security device of claim 1 , wherein the colour filter is provided between a surface of the substrate to be viewed by a user and the zero-order diffractive microstructure.
4. The security device of claim 1 , wherein the colour filter comprises an optically modifiable material having an optical property that is modifiable by irradiation.
5. The security device of claim 4 , wherein the optical property is modified by irradiation with a laser.
6. The security device of claim 1 , wherein the colour filter is locally optically modifiable to add information to the security device.
7. The security device of claim 6 , wherein the information comprises at least one of a serial number, a barcode, or an image.
8. The security device of claim 7 , wherein the barcode is (i) one dimensional or (ii) two dimensional.
9. The security device of claim 1 , wherein the colour filter modifies a spectrum of incident light and a spectrum of light reflected from the zero-order diffractive microstructure.
10. The security device of claim 1 , wherein the colour filter comprises an optically modifiable material, the optically modifiable material being locally optically modified by irradiating a surface of the substrate.
11. The security device of claim 1 , wherein the colour filter has been locally optically modified by irradiation of a surface of the substrate.
12. A method for manufacturing a security device comprising:
forming a zero-order diffractive microstructure comprising a high refractive index material; and
coating a further structure, the further structure including a colour filter comprising a fluorophor, onto the high refractive index material, wherein the further structure modifies optical characteristics produced by the zero-order microstructure by interacting with an evanescent field near the zero-order diffractive microstructure.
13. The method of claim 12 , wherein the colour filter comprises an optically modifiable material, and the method further comprises locally modifying the optically modifiable material by irradiating a surface of a substrate containing the zero-order diffractive microstructure, such that an optical property of the optically modifiable material is changed.
14. The method of claim 13 , wherein the irradiating the surface of the substrate comprises irradiating the surface of the substrate with a laser.
15. A method comprising:
adding information to a security device, the security device comprising a zero-order diffractive microstructure buried within a substrate, and a further structure including a colour filter embedded in the substrate, wherein the colour filter comprises fluorophors coated onto or placed at a short distance from a high refractive index material of the zero-order diffractive microstructure, wherein the further structure modifies optical characteristics produced by the zero-order microstructure, and wherein the colour filter comprises an optically modifiable material; and
locally modifying the optically modifiable material by irradiating a surface of the substrate, such that an optical property of the optically modifiable material is changed.
16. The method of claim 15 , wherein irradiating the surface of the substrate further comprises adding at least one of a serial number, a barcode, or an image.
17. The method of claim 16 , wherein the barcode is (i) one dimensional or (ii) two dimensional.
18. The method of claim 15 , wherein the irradiating the surface of the substrate comprises irradiating the surface of the substrate with a laser.