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Scientific Reports: unclonable patterns for secure authentication by photonic crystal assembly

High-fidelity spherical cholesteric liquid crystal Bragg reflectors generating unclonable patterns for secure authentication

Yong Geng, JungHyun Noh, Irena Drevenšek-Olenik, Romano Rupp, Gabriele Lenzini & Jan P. F. Lagerwall

Farbmuster der Reflexionen, die von einer Anordnung von Mikrokugeln ausgelöst wird, wenn diese mit weißem Licht beleuchtet werden. Ein solches farbliches Muster stellt jenes unverwechselbare Merkmal dar, welches zur Authentifizierung verwendet werden kann (Copyright: Yong Geng, Universität Luxembourg).

Abstract

Monodisperse cholesteric liquid crystal microspheres exhibit spherically symmetric Bragg reflection, generating, via photonic cross communication, dynamically tuneable multi-coloured patterns. These patterns, uniquely defined by the particular sphere arrangement, could render cholesteric microspheres very useful in countless security applications, as tags to identify and authenticate their carriers, mainly physical objects or persons. However, the optical quality of the cholesteric droplets studied so far is unsatisfactory, especially after polymerisation, a step required for obtaining durable samples that can be used for object identification. We show that a transition from droplets to shells solves all key problems, giving rise to sharp patterns and excellent optical quality even after polymerisation, the polymerised shells sustaining considerable mechanical deformation. Moreover, we demonstrate that, counter to prior expectation, cross communication takes place even between non-identical shells. This opens additional communication channels that add significantly to the complexity and unique character of the generated patterns.

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