Security system with optical waveguide
A security document comprises a substrate ( 1 ) and an optical waveguide ( 7 ). Couplers ( 10 a, 10 b ) are provided in the waveguide ( 7 ) for coupling light into and out of the waveguide. The couplers ( 10 a, 10 b ) can e.g. by gratings, scattering objects, holograms, luminescent dyes or perforations. The authenticity of the document can be verified using methods based on the properties of the waveguide.
1. A security document comprising:
a substrate,
an optical waveguide arranged on and/or in said substrate, and
at least one coupler for coupling light into said waveguide or out from said waveguide,
wherein said security document comprises a periodic microlens-array, and
wherein said at least one coupler has a periodic structure, with the microlens-array having a period substantially equal to said periodic structure.
2. The security document of claim 1 , comprising a second coupler, wherein light coupled into said waveguide by means of said at least one coupler is at least partially transmitted to and coupled out by said second coupler.
3. The security document of claim 1 , wherein said substrate is non-transparent and comprises at least one transparent window or half-window, wherein the at least one coupler is arranged in said window or half-window.
4. The security document of claim 3 , wherein said substrate comprises, in addition to the at least one transparent window or half-window, a second transparent window or half-window, wherein the at least one coupler is arranged in said at least one window or half window and a second coupler is arranged in said second window or half-window, and wherein said waveguide extends between said at least one window or half-window and said second window or half-window.
5. The security document of claim 1 , wherein said at least one coupler comprises a grating.
6. The security document of claim 1 , wherein said at least one coupler comprises light scattering objects embedded in or arranged on said waveguide.
7. The security document of claim 1 , wherein said at least one coupler comprises a fluorescent or luminescent dye arranged in or on said waveguide for coupling light into our out from said waveguide.
8. The security document of claim 7 , wherein said at least one coupler comprises a plurality of luminescent dyes of at least two different luminescent colors.
9. The security document of claim 1 , wherein said waveguide is embedded at least partially in the substrate.
10. The security document of claim 1 , wherein said waveguide comprises at least a first layer and a second layer, with said first layer having a refractive index higher than said second layer, wherein said second layer is arranged between said first layer and an absorbing pan of said substrate.
11. The security document of claim 10 , wherein said waveguide further comprises a third layer with said first layer having a refractive index higher than said third layer, and wherein said first layer is arranged between said second and third layers.
12. The security document of claim 1 , further comprising a light source coupled to said waveguide.
13. The security document of claim 1 , wherein said waveguide is a security thread embedded at least partially in said substrate.
14. The security document of claim 1 , wherein said waveguide is a plastic foil having substantially the same size as said substrate.
15. The security document of claim 1 , wherein the period of the microlens-array deviates by 10% or less from a period of the periodic structure of the coupler.
16. A security document comprising:
a substrate,
an optical waveguide arranged on and/or in said substrate, and
at least one coupler for coupling light into said waveguide or out from said waveguide,
wherein said security document comprises a periodic microlens-array, and
wherein said at least one coupler has a periodic structure, and
wherein a period of the microlens-array deviates by 10% or less from a period of the periodic structure of the at least one coupler.