CODIERUNG VON OPTISCHER PLATTEN FUR ABNEHMER KENNZEICHNUNG

Techniques for marking of optical data discs with a unique characteristic marking for purposes of identification and verification of authenticity. The marking, referred to as a 'watermark', can be a name, logo, design, picture or other pattern which is applied within the structure of the data disc. The watermark is applied to the master disc, and will therefore be reproduced in all production replica discs through the use of standard stamper and replica processes. In a preferred embodiment the watermark is a modification to the periodic diffraction grating effect created by the encoded data by alteration of the thickness or depth of the data feature with respect to the reference plane of the data structure in areas defining the watermark. The watermark can then be seen in the final disc as a discontinuity or difference in the rainbow-like diffraction pattern on the surface. In other embodiments, a hologram of the watermark is formed in zones on the disc, in the form of hologram interference patterns formed interspersed with the data features. These holograms can be viewed in the final disc, with white light in one embodiment, or with an illuminating laser in another embodiment, as virtual images of the watermark object.