Patent ID: 6560017
Filing Date: 2003-05-06
Classification: G06K

Abstract:
A method of providing secure identification for an article, comprising:(a) providing on said article a diffraction grating strip comprising a pattern of a series of diffraction grating elements, each said diffraction grating element to diffract light, from a light source, in one of at least first, second, third, and fourth selected different planes, each of said diffraction grating elements which diffract light in said first, second, or third planes being separated from another diffraction grating element which diffracts light in said first, second, or third planes by a diffraction grating element which diffracts light in said fourth plane; and (b) selectively obliterating selected ones of said diffraction grating element which diffract light in said fourth plane, such as to form a binary number consisting of obliterated and non-obliterated ones of said diffraction grating elements which diffract light in said fourth plane.