Optical Physically Unclonable Function Based on Electrospun Fluorescent Random Fibrous Media

Physical Unclonable Functions (PUFs) are unique cryptographic mechanisms derived from non-deterministic random variables introduced during their fabrication process. PUFs have garnered significant interest in recent years, especially in combating counterfeit activities and ensuring privacy and confidentiality of sensitive information. Among the different categories of PUFs, those exploiting optical principles have gained prominence due to inherent benefits like high entropy, complex output patterns, and strong resistance against modeling and replication-based attacks. The use of random lasers provides an especially attractive aspect of optical-based PUFs that distinguishes it from conventional laser-based PUFs systems. This emission is a phenomenon of Anderson light localization, which occurs when light undergoes intense scattering within a disordered medium. However, the fabrication of large-scale random media that can induce random lasing remains a formidable challenge due to economic viability. In this study, we propose an innovative solution by capitalizing on electrospinning. We demonstrate the feasibility of fabricating an optical PUF device that incorporates random lasing properties using this method and investigate its potential use in security applications.<br/>For implementing the optical PUFs, we employed the electrospinning technique to generate nano/microfibers. We created a solution by dissolving 2 g of polymethyl methacrylic acid (PMMA) in 9 g of dimethylformamide (DMF) and acetone, stirring it at 60 °C for eight hours. To acquire emission properties within the 560 nm to 640 nm, we used 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostryl)-4H-pyran (DCM) dissolved in a 2 mM solution at 60 °C for two hours. This solution then underwent the electrospinning process through a 23 gauge nozzle, applying a high voltage of 14 kV and maintaining a dispensing rate of 1 mL/hr. The process resulted in the fabrication of random microfibers, with homogeneous diameter distribution and thickness. Despite uniform diameters, the fabricated samples showed different optical properties due to variations in fiber structures at separate locations within the sample.<br/>To verify the occurrence of random lasing, we initiated an optical stimulation procedure using a UV laser with a wavelength of 355 nm with 10 Hz repetition rate. The laser was concentrated on the fabricated sample using a convex lens. The wavelength information of the resulting random laser was collected using an objective lens and a spectrometer. We gathered wavelength data, which showed random peaks within the 580 nm to 620 nm range, indicating the occurrence of random lasing. We further processed the data to leverage the peaks acquired from optical PUF devices, removing the spontaneous emission with post-processing.<br/>Utilizing a De-biasing method, we extract random bits from the PUFs, thereby significantly enhancing the uniformity of the digitized data. To validate the uniqueness and reproducibility of the bits generated from the PUFs, we calculated the Hamming distance and applied the NIST Randomness Test Suite (NIST SP 800-22). The random laser-based PUFs show excellent performance in terms of randomness, uniqueness, and reproducibility. With an inter-Hamming distance near 0.5, there was a high level of differentiation between bits produced from different samples. Notably, the intra-Hamming distance approached zero, indicating the high reproducibility of the random laser-based PUF. This research brings to light the potential of creating large-scale optical PUFs with random lasing properties, offering a promising direction for future cryptographic applications.<br/><br/>This work was supported by the National Research Foundation of Korea funded by the Korean Government (grant RS-2023-00210438, NRF-2022M3C1A3081312)