Metalens is one kind of two-dimensional ultrathin lenses with subwavelength artificial structures that can focus light in a compact, flexible way. However, most strategies for designing metalenses only work on one specific spin state of light (i.e., either right-or left-circularly polarized light), hindering simultaneous control of both spins. Utilizing both the Pancharatnam-Berry phase and the propagation phase, we can rationally control the phase for each spin state of light. As proof-of-concept demonstrations, here we numerically and experimentally realize the independent focusing and manipulation of both spins of light by V-antenna metasurfaces, which can be regarded as the demonstration of the photonic spin Hall effect. Our multidimensional metalens is able to focus light of different spins at designated positions along both transverse and longitudinal directions. It can be used as a polarization analyzer to distinguish the polarization state of incident light. In addition, our multifunctional metalens can act either as a convex lens or an axicon, depending on the spin of light. The demonstrated multidimensional and multifunctional metalens has versatile potentials in spin-dependent nanophotonics, ranging from optical imaging and micro/nano-object manipulation to optical sensing.

In this study, an integrated gray-level gradient method is applied to extract the three-dimensional (3D) velocity fields of sprays. This method consists of a conventional edge-sharpness method and a new method, namely, the overall-sharpness method, which is an efficient supplement of the former. And then the synchronization system is designed and assembled to record double-exposure spray holograms in a short time interval. Finally, using the integrated gray-level gradient method and some image processing techniques, the 3D coordinates of droplets are easily obtained, which can be used to evaluate the 3D velocity fields and the size features of spray droplets in different spray injection pressures. It proves that the integrated gray-level gradient method is well applied to measure the characteristics of sprays in in-line digital holography.

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Multichannel metasurfaces become one of the most significant development trends, as they exhibit versatile manipulation abilities on electromagnetic fields and provide a promising approach to constitute compact devices with various complex functions, especially in optical encryption due to its capabilities of multichannel, high complexity, and high concealment. However, the existent multichannel metasurfaces based optical encryption technology can only realize two channels in the near-field, or perform three channels in near- and far-field. In this paper, a four-channel display metasurface used to encrypt information by three optical parameters as security keys is firstly proposed and experimentally demonstrated, which is different from the previous three-channel metasurface combined nanoprinting and hologram in near- and far-field. The novel design strategy of the four-channel metasurface can effectively enhance the information capacity and increase the difficulty of leaks without causing manufacturing challenges and additional costs. In addition, the simulation and experimental results demonstrate that the designed metasurface with four independent channels can separately display distinguishable nanoprinting images under decoding keys of special optical parameters. The proposed four-channel display metasurface with advantages of high capacity and ultracompactness will pave a way for multichannel applications in nano display, information storage, optical anticounterfeiting, and other relevant fields.

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Image steganography based on intelligent devices is one of the effective routes for safely and quickly transferring secret information. However, optical image steganography has attracted far less attention than digital one due to the state‐of‐the‐art technology limitations of high‐resolution optical imaging in integrated devices. Optical metasurfaces, composed of ultrathin subwavelength meta‐atoms, are extensively considered for flat optical‐imaging nano‐components with high‐resolutions as competitive candidates for next‐generation miniaturized devices. Here, multiplex imaging metasurfaces composed of single nanorods are proposed under a detailed strategy to realize optical image steganography. The simulation and experimental results demonstrate that an optical steganographic metasurface can simultaneously transfer independent secret image information to two receivers with special keys, without raising suspicions for the general public under the cloak of a cover image. The proposed optical steganographic strategy by metasurfaces can arbitrarily distribute a continuous grayscale image together with a black‐and‐white image in separate channels, implying the distinguishing feature of high‐density information capacity for integration and miniaturization in optical meta‐devices.

To cover the whole range of operating conditions of aero-engine, a double-layer LPV model is built so as to take into account of the variability due to the flight altitude, Mach number and the rotational speed. With this framework, the problem of designing LPV state-feedback robust controller that guarantees desired bounds on both