A secure an optical identification method and the means required for this purpose

摘要

Card (30) includes a substrate (32) which has disposed thereon for secure identification a diffraction grating strip (34) comprising a pattern of a series of diffraction grating elements (40A-D), each said diffraction grating element (40A-D) to diffract light, from a light source, in one of at least three selected different planes; serially illuminating said diffraction grating elements (40A-D), detecting changes in plane of diffracted light as said diffraction grating elements (40A-D) are serially illuminated, and generating first information representative of said changes in plane; storing said first information representative of said changes in plane; subsequently, serially illuminating said diffraction grating elements (40A-D), detecting changes in plane of diffracted light as said diffraction grating elements (40A-D) are serially illuminated, and generating second information representative of said changes in plane; and then, comparing the first and second information to determine the authenticity or not of said article.;In a further aspect of the application, a coded pattern is placed on said diffraction grating strip, with one of said coded pattern and said pattern of diffraction grating elements precessing with respect to the other and the coded pattern is read, stored, and compared as part of said first and second information, as above.