Abstract
There has been considerable work on developing optical interference coatings that exhibit a change in color when viewed at different angles, since Dobrowolski (1) successfully demonstrated this technique for anticounterfitting. His group developed a multilayer, all-dielectric coating with a HL3HL3H design for Canadian currency. Today, many countries' currencies, valuable documents, or other important items, e.g., credit or identification cards, use optically variable devices (OVD) for security. OVD based on Fabry-Perot filters with metal reflectors and dielectric spacer layers have been demonstrated and successfully commercialized. OVD can be made as color shift films on a substrate ("foil") or deposited on a release layer or directly on a coating drum, then removed as flakes, ground into small particles and used as pigments in printing inks (2).
© 1998 Optical Society of America
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