film and an Ag layer. The structure of Ag layers can be easily controlled by adjusting the annealing temperature, allowing for systematic tuning of the optical efficiencies in the visible and long-wave infrared regions. Consequently, thermal management devices can selectively function as either a photothermal heater or a radiative cooler, depending on the morphology of Ag layers. In particular, the photothermal device can function as an anti-fogging solution for structural designs without requiring external energy. Furthermore, the stacked metal-insulator-metal structure induces plasmonic resonance phenomena, producing visible colors that range from vivid to dull hues. The tunable color variations enhance the suitability of the thermal management device for a wide range of architectural applications.

Optical physical unclonable functions (PUFs) have emerged as a promising cryptographic primitive for next-generation security. However, to harmonize with various modern networks, conventional optical PUF is inadequate due to a rigid key space with a fixed specification. This study implements hierarchically controllable randomness sources for multi-level key generation, exploiting speckle characteristics. By adjusting illumination diameter, the speckle size can be modulated, allowing the extraction of three-level keys with various lengths: 64, 256, and 1,024 bits. Performance evaluation reveals that all levels are superb in uniformity, uniqueness, reproducibility, and randomness. Moreover, it is proposed two feasible applications. The first is a hierarchical authentication architecture that spans from Internet of Things (IoT) devices to sensitive information, balancing security and resources. The second is a multi-stage image encryption algorithm, exhibiting holocryptic performance superior to conventional XOR-based encryption. This versatile platform sets a new paradigm for optical PUF, establishing a foundation for robust and expandable next-generation security.