Optical spectrum fingerprint: a novel application of optics as an encryption-decryption technique

摘要

Various optical phenomena and techniques have been used to encrypt sensitive data and detect counterfeit objects. When two multilayer dielectric films of different indices are deposited in an alternating pattern on a glass substrate to form an optical filter, the transmission of this filter presents an optical spectrum. Because of the two materials' different indices, layer sequences, and number of layers, the spectrum of any one of these filters is unique and exclusive. The spectrum and corresponding multilayer structure, therefore, can be considered a spectrum "fingerprint" and can be used to encrypt confidential information. One can design a multilayer sequenced layer structure as an encryption code. Knowing the spectrum of this code, they can also design a decryption filter to analyze the code spectrum and access the information embedded in the encrypted filter. High and low index materials Ta2O5 and SiO2 were used to fabricate multilayer film stacks with around 5 to 10 high-low pairs. The spectrum has multiple peaks in the visible wavelength range and is designed such that the spectrum appears colorless. A decryption multilayer film would block all but one of the peaks, the transmission of which would reveal the color. In this study, we present how we can design an encryption and decryption spectrum, how one can use these spectrum "fingerprints" to store confidential information and, when necessary, access said information by placing a decryption filter above the encryption filter.