CaeSaR Tags – Unclonable Patterns for Secure Authentication

University of Luxembourg Technology Overview
Cholesteric Spherical Reflector (CSR; CaeSaR) are omnidirectional chiral Bragg reflectors, which means that they strongly reflect a narrow wavelength range (color) of light with specific (circular) polarization in every direction when illuminated. Bringing several CSRs of slightly different types into a locked-in random arrangement leads to dynamic optical pattern formation by optical cross communication between the CSRs. Because the location, color and polarization of each spot in this pattern is uniquely defined by the arrangement of CSRs and how the tag is illuminated and viewed, the tag comprises a unique fingerprint for the protected object, which cannot be cloned or simulated.
The CaeSaR tag, functioning as a Physical Unclonable Function (PUF), can be integrated in the item during production or printed or coated afterwards, as most suitable. Manual coating can be done as simple as applying a drop of nail polish whereas rapid automized coating would be realized by depositing a liquid droplet onto the target surface, cured into a solid by brief UV illumination. Read-out can be done with a mobile device together with low-cost optical components.

Tags can be made visible or invisible, as desired, for overt or covert labels. They can be applied to any shape of surface, added as a coating or integrated near the surface during production of the item to be protected/tracked.
Each tag generates an extremely rich set of unique optical patterns, with large variations depending on viewing angle, illumination direction, illuminated/viewed area and wavelength and polarization of light
Circular polarization of reflected light makes a tag easy to detect for the right device, although it is invisible to humans

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