Optical encryption strategy inspired by the Chinese tiger-shaped tally with dynamic tunable circular dichroism

During the Warring States period in ancient China, the tiger-shaped tally (TST) was used to securely transmit military commands. It served as the ultimate symbol of the emperor for troop mobilization, and its loss could even mean the total collapse of centralized military control. Inspired by this ancient authentication mechanism, an optical encryption strategy is proposed based on dynamically tunable circular dichroism (CD). The TST are metastructure-photonic crystal composed of periodically alternating layers of tilted potassium bromide and silver. Specifically, the configuration consists of an upper fixed Z-shaped configuration (TST1), a SiO₂ spacer layer, and a lower rotated Z-shaped configuration (TST2). By varying the tilt angle (φ), the azimuthal rotation angle (δ) of TST2, and the incident angle (θ) of the circularly polarized wave, different CD states can be achieved in perfect coordination with TST1. The strategy integrates computational encryption algorithms with physical encryption mechanisms derived from the verification principle of the TST to achieve multi-level information security protection, offering a technical pathway for the development of optical information security technologies.