Optical authentication component and method of fabricating said component
An optical authentication component visible in reflection having a structure imprinted on a substrate of index n 0 , a thin layer, made of a dielectric material having a refractive index n 1 , deposited on the structure, and a layer made of a material having an index n 2 similar to n 0 , encapsulating the structure coated with the thin layer, is disclosed. The structure has a first pattern modulated by a second pattern, the first pattern is a bas-relief with an array of facets, having shapes which are defined to simulate an image in relief of an object in relief, and the second pattern is a periodic grating that modulates the first pattern which produces, after the thin layer has been deposited and the structure has been encapsulated, a first color at a first viewing angle and a different second color at a second viewing angle, obtained by azimuthal rotation of the component.
1. An optical authentication component visible in reflection, comprising:
at least one structure imprinted on a substrate of refractive index n 0 ;
a thin layer having a thickness between 50 and 150 nanometers, made of a dielectric material having a refractive index n 1 different from n 0 , deposited on said at least one structure; and
a layer, made of a material having a refractive index n 2 , encapsulating the at least one structure coated with the thin layer, wherein n 2 is approximately the same as n 0 ,
wherein the at least one structure comprises a first pattern and a second pattern that modulates the first pattern:
the first pattern being a bas-relief comprising an array of facets the shapes of which are defined in order to simulate an image in relief of an object in relief;
the second pattern being a periodic grating that modulates the first pattern in order to produce, after the thin layer has been deposited and said at least one structure has been encapsulated, a first color at a first viewing angle and a different second color at a second viewing angle obtained by azimuthal rotation of the optical authentication component.
2. The optical component as claimed in claim 1 , wherein said first pattern forms a recognizable graphic when the component is observed in order to check authenticity.
3. The optical component as claimed in claim 1 , wherein the refractive index difference Δn between the refractive indices n 1 and n 0 is greater than about 0.5.
4. The optical component as claimed claim 1 , wherein the dielectric material of refractive index n 1 comprises at least one material from the group consisting of: zinc sulfide and titanium dioxide.
5. The optical component as claimed in claim 1 , wherein a depth of the first pattern is between 0.5 and 7 microns and a depth of the second pattern is between 50 and 300 nanometers.
6. The optical component as claimed in claim 1 , wherein the second pattern has a pitch of between 200 and 500 nanometers.
7. The optical component as claimed in claim 6 , wherein the facets of the first pattern have crests forming an alternation of ridges, a separation between more than 90% of the pairs of adjacent ridges of the first pattern being at least two times larger than the pitch of the second pattern.
8. The optical component as claimed in claim 1 , wherein the second pattern is a one-dimensional periodic grating.
9. The optical component as claimed in claim 1 , wherein the second pattern is a two-dimensional periodic grating.
10. The optical component as claimed in claim 1 , wherein the substrate and the dielectric material forming the thin layer are transparent.
11. The optical component as claimed in claim 1 , further comprising:
a polymer layer deposited on the substrate;
an opaque layer deposited on the layer encapsulating the at least one structure; and
an adhesive layer deposited on the opaque layer, for adhesive bonding to the surface of a document.
12. The optical component as claimed in claim 1 , wherein facets of the first pattern have a shape which is approximated by areas comprising two or more levels.