Synergy of moire principles and diffraction by periodic structures in optical devices for document security

Recording of periodic structures is employed, instead of printing techniques, for moire pattern to be generated. Diffraction gratings are utilized not only as substitutes of printing inks here but also to employ variation of visual appearance for revealing information encoded in a data-carrier structure. Two designs are analysed - one relying on very precise alignment of a decoding overlay grid and the other one allowing the use of the decoding grid to be avoided. The latter design is found more suitable to serve as an authentication element at first-line inspection.