Optically variable devices (OVDs) are in tremendous demand as optical indicators against the increasing threat of counterfeiting. Conventional OVDs are exposed to the danger of fraudulent replication with advances in printing technology and widespread copying methods of security features. Metasurfaces, two-dimensional arrays of subwavelength structures known as meta-atoms, have been nominated as a candidate for a new generation of OVDs as they exhibit exceptional behaviors that can provide a more robust solution for optical anti-counterfeiting. Unlike conventional OVDs, metasurfacedriven OVDs (mOVDs) can contain multiple optical responses in a single device, making them difficult to reverse engineered. Well-known examples of mOVDs include ultrahighresolution structural color printing, various types of holography, and polarization encoding. In this review, we discuss the new generation of mOVDs. The fundamentals of plasmonic and dielectric metasurfaces are presented to explain how the optical responses of metasurfaces can be manipulated. Then, examples of monofunctional, tunable, and multifunctional mOVDs are discussed. We follow up with a discussion of the fabrication methods needed to realize these mOVDs, classified into prototyping and manufacturing techniques. Finally, we provide an outlook and classification of mOVDs with respect to their capacity and security level. We believe this newly proposed concept of OVDs may bring about a new era of optical anticounterfeit technology leveraging the novel concepts of nano-optics and nanotechnology.

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We describe the general characteristics and the first result of a new synchrotron beamline at the Pohang Light Source in Korea. The beamline, operated by a Korean-Taiwanese-Swiss consortium, is dedicated to microimaging experiment in real time with coherent x rays. The performances of the first tests already reach excellent levels when compared to other similar facilities worldwide. The key feature is the use of unmonochromatized x rays to achieve very high lateral and time resolution.

Humidity‐responsive structural coloration is actively investigated to realize real‐time humidity sensors for applications in smart farming, food storage, and healthcare management. Here, humidity‐tunable nano pixels are investigated with a 700 nm resolution that demonstrates full standard RGB (sRGB) gamut coverage with a millisecond‐response time. The color pixels are designed as Fabry–Pérot (F–P) etalons which consist of an aluminum mirror substrate, humidity‐responsive polyvinyl alcohol (PVA) spacer, and a top layer of disordered silver nanoparticles (NPs). The measured volume change of the PVA reaches up to 62.5% when the relative humidity (RH) is manipulated from 20 to 90%. The disordered silver NP layer permits the penetration of water molecules into the PVA layer, enhancing the speed of absorption and swelling down to the millisecond level. Based on the real‐time response of the hydrogel‐based F–P etalons with a high‐throughput 3D nanoimprint technique, a high‐resolution multicolored color print that can have potential applications in display technologies and optical encryption, is demonstrated.

Figure 6. a) Schematic and optical image of a nanolaser that consists of Si PC and monolayer Molybdenum telluride. b) i) The illustration of the upconversion nanolaser that consists of UCNPs coated on the plasmonic lattice. ii) The diagram exhibits the energy transfer mechanism in UCNP. c) Perovskite-based lasing device. Left upper illustration is the near-field profile representing third-order Mie resonance. SEM image shows the CsPbBr 3cube with a size of 310 nm. In the emission spectrum, an extremely sharp peak that stands for lasing action is observed. Inset represents the interference pattern that appears in the optical image of the perovskite cube. d) Perovskite-based BIC lasing device. Schematic shows the vortex lasing system composed of hole patterned perovskite film and a blue laser for pumping. i) The dispersion relation is photonic bands of the perovskite hole pattern in the direction of ΓX and ΓM around 550 nm. ii) The donut-shaped far-field profile and self-interference pattern. The white arrows denote the fork shape which means the vortex beam nature. (a) Reproduced with permission. [198] Copyright 2017, Springer Nature. (b) Reproduced with permission. [156]