Speckle analysis of reconfigurable disordered photonic materials made of polymer dispersed liquid crystals

Photonic devices greatly benefit from the ability to reconfigure their optical properties. To achieve this with disordered optical materials, it is possible to make use of polymer dispersed liquid crystals (PDLCs) in which the scattering originates from randomly distributed liquid crystal droplets that respond to external stimuli, such as light, temperature, and magnetic or electric fields. In this work, we present a speckle-based analysis to investigate the reconfigurability of the dynamic and static scattering properties of dye-doped PDLCs, as a function of dye concentration and light intensity. Our findings allow us to distinguish between reversible and non-reversible molecular rearrangements after a light-induced phase transition, occurring on millisecond timescale. The degree of reversibility is quantified using cross-correlation analysis based on the Pearson correlation coefficient. As a proof-of-concept application, we exploit their non-reversible reconfiguration properties to create a cryptographic optical physical unclonable function whose behavior can progressively be erased in case of malicious attacks. We demonstrate a non-reversibility, assessed through the uniqueness metric, that ranges from 30% to 40% depending on dye content. Leveraging their intensity-dependent scattering properties, these disordered materials emerge as ideal candidates for advanced nonlinear information processing and secret-free security applications.