Optical security device having a high refractive index layer between adjacent diffraction elements which have upper portions uncovered by the high refractive index layer

摘要

An optical security device is disclosed which includes a diffraction layer having a plurality of diffraction elements and a high refractive index layer, wherein the high refractive index layer is applied on the diffraction layer such that selected regions of the diffraction layer have the corresponding diffraction elements partially uncovered by the high refractive index layer and other regions are substantially covered by the high refractive index layer. Accordingly, the optical security device has a first security feature associated with the diffraction layer and a second security feature associated with the high refractive index layer. An image is viewable from the regions of the high refractive index layer, either, covertly by placed an index matched item over the device or, overtly, through selection of the thickness of the high refractive index layer.