Fabry‐Perot‐based Layer Stacks for Ellipsometric Encoding

Public, hidden, and forensic features either encoded or directly legible are used for authentication. Fabry‐Perot layer stacks as information carriers in combination with imaging ellipsometry as optical read‐out system provide all‐in‐one anti‐counterfeiting capability that may establish the new security level “encoded forensic”. Different layer designs are described with regard to all three security levels: public features (e.g. color and tilt effect) perceptible by the human eye, hidden features (e.g. spectroscopic response in the UV or IR), and forensic features (ellipsometric quantities Ψ and Δ as a function of wavelength λ and angle of incidence AOI). Physically uncloneable functions (PUF) could be realized as a result of a multi‐material and a multi‐parameter deposition approach as well as by means of specific design features of the Fabry‐Perot layer stack. Hence, they are not subject to any reverse engineering strategies. Examples of stratified, micro‐structured, and laser‐modified Fabry‐Perot layer systems are considered that may be used at all perception levels (e.g. human eye, bar code reader, and imaging ellipsometry) for authentication against product counterfeiting and related areas.