DIFFRACTION GRATING AND METHOD OF MANUFACTURE

摘要

A diffraction grating providing an optically var- fable image includes a pixellated diffraction grating in which each pixel is an individual optical diffraction grat- ing so that the pixellated diffraction grating when illumi- nated generates an optically variable image. In another aspect the grating in some or all of the pixels of a dif- fracting grating formed by a regular matrix of pixels is arranged such that a reproduction of the grating by ref- lection contact printing generates a zero-order pattern which is grossly flawed by Moire or Talbot fringe ef- fects. A method of forming the diffraction, grating in- cludes producing a counterpart pixellated diffraction grating of a substantially optically invariable image wherein each pixel of the optically invariable image is maped to a respective pixel of the pixellated diffraction grating: Each grating pixel is an individual optical dif- fraction grating of the associated pixel in the optically invariable image, so that the pixellated diffraction grit- ing when illuminated generates an optically variable rep- roduction of the optically invariable image.