Covert Optical Fingerprints Within Overt Structural Colors via Cascaded Cavity Resonances

Structural colors and stochastic optical fingerprints are difficult to integrate within a single nanophotonic platform because deterministic optical uniformity often conflicts with disorder-driven optical randomness. Here, we introduce cascaded cavity resonances to weakly correlate and control these two optical functionalities through vertically integrated layered and nanogap cavities. In this multiscale architecture, layered photonic cavities govern overt far-field structural coloration, whereas localized plasmonic nanogap cavities generate covert stochastic optical scattering with minimal dependence on the overt optical appearance. The proposed architecture, consisting of a Cu mirror, HfO₂ dielectric layers, and disordered Cu nanoparticles, is fabricated entirely through a monolithic all-vacuum deposition process. In particular, cooled glancing-angle deposition suppresses nanoparticle coalescence during growth, enabling dense yet short-range-correlated nanoparticle assemblies with short nanoscale correlation lengths (∼44 nm) and high nominal stochastic encoding density exceeding 6.94×10⁷ bit/mm². Leveraging these properties, we realize wafer-scale optical physical unclonable functions containing 22,500 independently encoded optical fingerprints together with rapid authentication and robust environmental stability. These results therefore demonstrate a scalable methodology to bridge deterministic nanophotonics and stochastic security media through precision multiscale resonance engineering.