Azimuthally modulated scattering device

Abstract

Optical elements with anisotropic, patterned surface relief microstructures in which information is encoded in the distribution of the orientation of different zones. From the analysis of the distribution of the light scattered from the element, the orientation distribution in the element and therefore the encoded information can be evaluated. The elements are particularly useful for securing documents and articles against counterfeiting and falsification.

1 . An optical element comprising:
 a region with a patterned anisotropic surface relief microstructure, which has zones with different anisotropy directions θ i ,   wherein information is encoded in the distribution of zones with the different anisotropy directions.   
     
     
         2 . The optical element according to  claim 1 , wherein the information is encoded by the fraction of the areas of zones with the anisotropy direction along θ i  with regard to the total area with anisotropic surface relief microstructure in that region. 
     
     
         3 . The optical element according to  claim 1 , wherein the pattern is combined with an OVD feature. 
     
     
         4 . A method of using an element according to  claim 1  comprising:
 applying the element to banknotes or other value documents and using the element as a security feature in the banknotes or other value documents. 
 
     
     
         5 . A method for evaluating the information encoded in the orientation distribution of an element according to  claim 1 , comprising
 detection of the spatial light distribution scattered from an element comprising a region with a patterned anisotropic surface relief microstructure, which has zones with different anisotropy directions θ i ,   wherein information is encoded in the distribution of zones with the different anisotropy directions, and   evaluation of the fractions f i (θ i ) from the measured spatial light distribution,   wherein f i (θ i ) is the fraction of the areas of zones with the anisotropy direction along θ i  with regard to the total area with anisotropic surface relief microstructure in that region.   
     
     
         6 . The method according to  claim 5 , wherein the evaluation of the information encoded in the orientation distribution comprises making a measurement of the spatial light distribution using a conoscopy imaging system. 
     
     
         7 . The method for manufacturing of an optical element according to  claim 1 , comprising
 use of an encoding algorithm to generate a pattern of an orientation distribution, which represents the information to be encoded, and   manufacturing of a patterned anisotropic surface relief microstructure, which has zones with different anisotropy directions θ i , according to the pattern that has been calculated.