Metasurfaces provide a compact and powerful platform for manipulating the fundamental properties of light, and have shown unprecedented capabilities in both optical holographic display and information encryption. For increasing information display/storage capacity, metasurfaces with more polarization manipulation channel and full‐color holographic functionality are now an urgent requirement. Here, a minimalist dielectric metasurface with the capability of full‐color holography encoded with arbitrary polarization is proposed and experimentally demonstrated. Without the daunting exploratory and computational problem in nanostructure searching, full‐color holographic images can be multiplexed into arbitrary polarization channels through vectorial ptychography and k‐space ptychography based on tetratomic macropixel geometric phase metasurfaces. Thanks to the full degree of freedom tuning in polarization and color spaces, the application scenarios such as holographic 3D imaging and information encryption are realized. The strategy exhibits promising potential in applications of 3Dl display, augmented/virtual reality, high‐density data storage, and encryption.
In this work, a quasi-nondispersive and spin-decoupled phase modulation strategy was proposed based on the chiral structure. Owing to the spindependent response of the chiral structure, the evolution of the Aharonov− Anandan (AA) geometric phase can be controlled by tuning different structural parameters independently. Additionally, the chiral structure was designed nonresonant or weak-resonant to minimize the influence of strong resonant absorption and large dispersive propagation phase shift, leading to an efficiently quasi-nondispersive phase modulation. To prove the validity of the strategy, a series of umbrella-shaped reflection-type metal−insulator−metal structures were designed as the unit cells and simulated with the finite element method. Moreover, the metasurfaces were designed based on such unit cells to generate broadband orbital angular momentums with different topological charges and spin-switchable holograms, respectively. Simulated and experimental results are in good agreement with the theoretical results. To the best of our knowledge, broadband spindependent phase modulation has been achieved without intentionally merging other types of phases for the first time in this work. We believe that this strategy provides a flexible approach for complex spin-or polarization-related applications in optical communication, integrated optics, optical sensing, and other related fields.
Optical cryptography manifests itself a powerful platform for information security, which involves encrypting secret images into visual patterns. Recently, encryption schemes demonstrated on metasurface platform have revolutionized optical cryptography, as the versatile design concept allows for unrestrained creativity. Despite rapid progresses, most efforts focus on the functionalities of cryptography rather than addressing performance issues, such as deep security, information capacity, and reconstruction quality. Here, we develop an optical encryption scheme by integrating visual cryptography with metasurface-assisted pattern masking, referred to as Stokes meta-hologram. Based on spatially structured polarization pattern masking, Stokes meta-hologram allows multichannel vectorial encryption to mask multiple secret images into unrecognizable visual patterns, and retrieve them following Stokes vector analysis. Further, an asymmetric encryption scheme based on Stokes vector rotation transformation is proposed to settle the inherent problem of the need to share the key in symmetric encryption. Our results show that Stokes meta-hologram can achieve optical cryptography with effectively improved security, and thereby paves a promising pathway toward optical and quantum security, optical communications, and anticounterfeiting.
We propose a common criterion for the effect of Gouy phase on the distinct polarization transition of focused vector vortex beams (VVBs). Such polarization transition is strongly dependent on the parity of the smaller modulus between VVB's polarization order and topological charge. Significantly, the cross polarization transitions are observed at areas where the two spin components with equi-intensity are exactly overlapping and the Gouy phase difference (GPD) between them equals to (2k + 1)π, k is an integer. As a whole, the focal field shows radially variant polarization distributions resulting from the unequal intensity proportion of the two spin components. This polarization transition holds potential in modifying the patterns of periodic surface structure induced by femtosecond vector beams.
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