<title>Guilloche in diffractive optically variable image devices</title>

Abstract

In diffractive optically variable image devices (DOVIDs) used as anticounterfeiting elements new features appear, which are directly adapted from traditional security paper techniques such as microprints or guilloche. Usually, they are used in combination with standard optically variable diffractive effects. Modern versatile DOVID printers and microlithographic UV and e-beam techniques allow to obtain a wide range of optically variable effects and hidden features. In this paper, we present various possibilities of employing guilloche in security DOVIDs. The first is an animated guilloche widely used in DOVIDs composed of diffraction gratings such as KinegramsTM and KineformsTM as well as in high resolution dot-matrix elements. The second possibility is the multicolor guilloche, used by means of 2D rainbow holograms. Such an optically variable guilloche is visible in wide range of observation angles, however, it is darker than grating structures. Increased visibility may be achieved using computer generated holograms (CGH) structures what results in widely visible and bright DOVIDs. With CGH structures it is also possible to combine kinematic guilloche with hidden features visible using a special reader and to introduce completely new kinds of effects resulting in a multicolor guilloche with colors changing in cyclic way and others special effects guilloches showing the kinematic effects and/or various color changing effects.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.