IMPROVED OPTICALLY VARIABLE DEVICES

摘要

A security device comprises a substrate (1) having an array of microlenses (3) on one side and one or more corresponding arrays of microimages (4) on the other side. The microimages (4) are located at a distance from the microlenses (3) substantially equal to the focal length of the microlenses. The substrate (1) is sufficiently transparent to enable light to pass through the microlenses (3) so as to reach the microimages (4). Each microimage (4) is defined by an anti-reflection structure on the substrate (1) formed by a periodic array of identical structural elements, light passing through the substrate and impinging on the microimages being reflected to a different extent than light which does not impinge on the microimages thereby rendering the microimages visible.