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 ( 1 ),
an optical waveguide ( 7 ) arranged on and/or in said substrate ( 1 ), and
at least a coupler ( 10 a , 10 b ) for coupling light into said waveguide ( 7 ) or out from said waveguide ( 7 ).
2 . The security document of claim 1 , comprising a first and a second coupler ( 10 a , 10 b ), wherein light coupled into said waveguide ( 7 ) by means of said first coupler ( 10 a ) is at least partially transmitted to and coupled out by said second coupler ( 10 b ).
3 . The security document of claim 1 , wherein said coupler ( 10 b ) comprises at least one perforation ( 14 ) extending through said waveguide ( 7 ).
4 . The security document of claim 3 , wherein said coupler ( 10 b ) comprises a plurality of perforations ( 14 ) extending through said waveguide ( 7 ) and said substrate ( 1 ).
5 . The security document of claim 1 , wherein said substrate ( 1 ) is non-transparent and comprises at least one transparent window or half-window ( 8 a , 8 b ), wherein at least one coupler ( 10 a , 10 b ) is arranged in said window or half-window ( 8 a , 8 b ).
6 . The security document of claim 5 , wherein said substrate ( 1 ) comprises at least a first and a second transparent window or half-window ( 8 a , 8 b ), wherein a first coupler ( 10 b ) is arranged in said first window or half-window ( 8 a ) and a second coupler ( 10 b ) is arranged in said second window or half-window ( 8 b ), and wherein said waveguide ( 7 ) extends between said first and said second window or half-window ( 8 a , 8 b ).
7 . The security document of claim 1 , wherein said coupler ( 10 a , 10 b ) comprises a grating ( 11 ).
8 . The security document of claim 1 , wherein said coupler ( 10 a , 10 b ) comprises light scattering objects embedded in or arranged on said waveguide ( 7 ).
9 . The security document of claim 1 , comprising a fluorescent or luminescent dye arranged in or on said waveguide ( 7 ) for coupling light into our out from said waveguide ( 7 ).
10 . The security document of claim 9 , comprising luminescent dyes of at least two different luminescent colors.
11 . The security document of claim 1 , comprising a periodic microlens-array ( 15 ), and wherein said coupler ( 10 a , 10 b ) has a periodic structure, with the microlens-array having a period substantially equal to said periodic structure.
12 . The security document of claim 1 , wherein said waveguide ( 7 ) is embedded at least partially in the substrate ( 1 ).
13 . The security document of claim 1 , wherein said waveguide ( 7 ) comprises at least a first layer ( 7 a ) and a second layer ( 7 b ), with said first layer ( 7 a ) having a refractive index higher than said second layer ( 7 b ), wherein said second layer ( 7 b ) is arranged between said first layer ( 7 a ) and an absorbing part of said substrate ( 1 ).
14 . The security document of claim 13 , wherein said waveguide ( 7 ) further comprises a third layer ( 7 c ), with said first layer ( 7 a ) having a refractive index higher than said third layer ( 7 c ), and wherein said first layer ( 7 a ) is arranged between said second and third layers ( 7 b , 7 c ).
15 . The security document of claim 1 , further comprising a light source coupled to said waveguide ( 7 ).
16 . The security document of claim 1 , wherein said waveguide ( 7 ) is a security thread embedded at least partially in said substrate ( 1 ).
17 . The security document of claim 1 , wherein said waveguide ( 7 ) is a plastic foil having substantially the same size as said substrate ( 1 ).