DIFFRACTION GRATING

摘要

A diffraction grating of reflective or transmissive lines formed by a regular matrix of pixels each containing a respective curvilinear portion of one or more of said lines, which pixels when illuminated each generate a two-dimensional optical catastrophe image diffraction pattern whereby the total image diffraction pattern of the grating is optically variable but structurally stable. The invention further provides a diffraction grating of reflective or transmissive lines, comprising a multiplicity of diffraction grating regions (G), which are at least partly separated by multiplicity of grating free regions (N), each grating free region (N) having a dimension which is at least large enough to be resolved by the human eye, the total grating free areas not exceeding about 20 to 50 % of the total area of the grating.