Optical security device comprising a layer having a microstructured surface and a dielectric layer filling in or complementary to the microstructured surface
A color shifting security device has a Fabry-Perot type structure wherein a dielectric layer is disposed between a reflector and an absorbing layer. The absorber and reflector layers may be conforming and the dielectric layer therebetween is non-conforming, filling the regions in the micro structured adjacent absorbing or reflecting layer, at least one of which has a microstructure therein or thereon. By having the dielectric layer not conform to the microstructure it is next to, its thickness varies in cross section, which allows for different colors to be seen where the thickness varies.
1. An optical device comprising:
a first absorbing or reflecting layer having a microstructured surface;
a second absorbing or reflecting layer having a lower surface; and
a first dielectric layer disposed between the first absorbing or reflecting layer and the second absorbing or reflecting layer,
wherein the first dielectric layer has a first surface complementary with the microstructured surface and a second surface complementary with the lower surface,
wherein the first dielectric layer at least partially fills in valleys within the microstructured surface,
wherein a first region of the first dielectric layer has a first thickness, and
wherein a second region of the first dielectric layer has a second thickness different than the first thickness.
2. The optical device of claim 1 , wherein the second surface of the first dielectric layer is substantially planar.
3. The optical device of claim 1 , further comprising:
a second dielectric layer.
4. The optical device of claim 3 , wherein the second dielectric layer conforms to the microstructured surface.
5. The optical device of claim 3 , wherein the second dielectric layer is disposed between the first absorbing or reflecting layer and the first dielectric layer.
6. The optical device of claim 3 , wherein the second dielectric layer is contacting and complementary with the microstructured surface.
7. The optical device of claim 1 , wherein the first dielectric layer includes a first material that conforms to the microstructured surface and a second non-confirming material that fills in grooves within the first material.
8. The optical device of claim 1 , wherein a visible color difference is present when viewing the optical device through the first region of the first dielectric layer and the second region of the first dielectric layer from a same location, simultaneously, when light is incident upon the optical device.
9. The optical device as defined in claim 1 , wherein the first absorbing or reflecting layer, the second absorbing or reflecting layer, and the first dielectric layer together form a Fabry-Perot cavity.
10. The optical device of claim 1 , wherein the first absorbing or reflecting layer or the second absorbing or reflecting layer has a substantially uniform thickness that varies by no more than 20%.
11. The optical device of claim 1 , wherein a difference in thickness of a cross-section of the first dielectric layer is more than ⅛ wavelengths of visible light and less than 8 quarter wavelengths of visible light.
12. The optical device of claim 1 , wherein a valley, of the valleys of the microstructured surface, in cross-section is a flat-bottomed valley.
13. The optical device of claim 1 , wherein a peak, of the microstructured surface, in cross-section is a flat-topped peak.
14. The optical device of claim 1 , wherein the second absorbing or reflecting layer is a reflector layer.
15. The optical device of claim 1 , wherein the first absorbing or reflecting layer is an absorbing layer.
16. The optical device of claim 1 , wherein the second absorbing or reflecting layer is an absorbing layer.
17. An optical device comprising:
a Fabry-Perot cavity comprising:
a first layer having a microstructured upper surface, wherein the first layer is one of an absorbing layer or a reflecting layer;
a second layer, wherein the second layer is one of an absorbing layer or a reflecting layer; and
a dielectric layer having an upper surface and a lower surface disposed between the microstructured upper surface of the first layer and the second layer,
wherein the lower surface of the dielectric layer conforms to the microstructured upper surface of the first layer,
wherein the dielectric layer at least partially fills in valleys within the microstructured upper surface, and
wherein a first region of the dielectric layer has a first thickness that is different from a second thickness of a second region of the dielectric layer.
18. The optical device of claim 17 , wherein the first layer is the absorbing layer.
19. An optical device comprising:
one or more deposited layers forming a microstructure, wherein at least one of the deposited layers is a reflecting or absorbing layer;
a dielectric material filling in grooves within the microstructure to form a planar surface over a continuous region of the microstructure; and
an absorbing or reflective cover layer covering at least a part of the continuous region.
20. The optical device of claim 19 , wherein the dielectric material is an infill non-conforming material.