查看更多>>摘要：? 2021The extrinsic chirality of metasurfaces refers to the chirality produced by the oblique incidence of light, which is observed in achiral meta-structures. Here we propose a new scheme for tunable extrinsic chirality of terahertz metasurface controlled by near-infrared continuous wave. The metasurface is composed of silicon substrate and single-layer metal units, in which the silicon substrate is used as a photosensitive element. The simulated results show that the maximum circular dichroism (CD) in transmission reaches 0.58, when the terahertz wave is incident on the metasurface with an angle of 83 degree. Furthermore, the terahertz CD will decrease under an illumination of optical beam. Simultaneously changing the incidence angle and the power of the pump light, continuous and active control of CD from 0 to 0.58 can be observed. In experiment, the same trend can also be obtained. The metasurface is simple in structure, and it is the first report for the optical tunable extrinsic chirality in terahertz band as far as we know.
查看更多>>摘要：? 2021 Elsevier B.V.Fringe projection profilometry has wide applications in three-dimensional measurement. When the fringes are projected onto the shiny surfaces with a large reflectivity, however, the saturation regions and dark regions are often generated on the surface due to the inconsistent reflection characteristics of the measured object. The saturation and dark regions make the modulation of captured fringe patterns degraded, and the accuracy of the three-dimensional measurement is significantly affected. To solve this problem, an improved network for high dynamic range fringe pattern is designed In this network, we introduce a low modulation region detection module based on U-net to obtain the saturation and dark regions in the fringe patterns. Then, the detailed fringe information in the low modulation regions can be predicted through a fringe enhancement module which takes advantage of the global distribution and detail intensity of the fringe patterns. In the experiment, a mass of simulated and actual low modulation fringe patterns are processed through the proposed network. The experimental results show that the designed network can effectively remove the noise of the captured fringe patterns and repair the low modulation regions captured from the shiny surfaces. Combined with phase calculation, the improved high dynamic range fringe patterns are used for three-dimensional data calculation. A standard metal gauge block with a height of 5 mm is measured and the root mean square error of the height is improved from 0.55 mm to 0.06 mm. This proves the proposed method can effectively improve the quality of fringe patterns projected on complex reflective surfaces.
查看更多>>摘要：? 2022 Elsevier B.V.Fringe projection profilometry is an effective technique for handheld three-dimensional shape measurement because of its high resolution and accuracy. However, it is hard to precisely achieve rapid measurement for complex scenarios using traditional fringe analysis methods without additional patterns or camera(s). Recovering the absolute phase from single-frequency fringe patterns of complex scenarios is challenging and still not well-addressed. This paper proposed a learning-based approach to address the unwrapping of one single-frequency phase map. A fully convolutional neural network is introduced to learn the mapping from wrapped phase to fringe-order without additional images under the constraint of the boundary fringe-order. This network is designed as a lightweight one and can operate in real-time for high-resolution phase maps. Experiments on a real large-scale dataset demonstrated that the presented method could unwrap single-frequency phase maps of handheld 3D measurement with motion blur, phase discontinuity, and isolated regions.
查看更多>>摘要：? 2022 Elsevier B.V.Infrared (IR) camouflage is used to conceal objects in infrared vision for confrontation with infrared detection in civilian and military applications. Nowadays, it gets more and more concerns. Many IR camouflage emitters usually concentrate on one application scene, whereas it is the trend to develop tunable IR camouflage emitter applied in multiple scenes. Here, we propose a scene-adaptive IR camouflage emitter with two modes of “0” and “1”. It can switch modes to adapt different application scenes according to object temperature. The emitter can switch to mode “0” for low-temperature (below 341K) object, such as civilian and military architectures. It can achieve IR camouflage and radiative cooling in 5-8μm simultaneously. The emitter can switch to mode “1” for high-temperature (above 341K) object. The average emissivity in 3-14μm plunges to 0.2. It can achieve well performed infrared camouflage. We believe that the proposed emitter can facilitate development in adaptive thermal camouflage, thermal management and multi-purpose camouflage device.
查看更多>>摘要：? 2022 Elsevier B.V.This study aims to design an optoelectronic integrated chip to read absolute code information. A detector array matching the code disk was designed to better realize high-speed low-light detection. For the pseudo-random code channel, the readout circuit adopted a linear array CMOS image sensor architecture, where each pixel corresponded to an independent readout unit, making the readout signal more advantageous in terms of both reading speed and noise. For the incremental code channel, the readout circuit followed a distributed arrangement design, and a two-stage pipelined amplifier architecture was adopted to eliminate the influence of even harmonics and ensure the quality of the read signal. Finally, a high-precision angular displacement sensor test platform based on an optical continuous closed-loop was built to test the encoder prototype equipped with the chip. The results show that an angular resolution of 22 bits and a subdivision accuracy of 5.64″ have been achieved.
查看更多>>摘要：? 2022 Elsevier B.V.Hybrid Free-Space Optical (FSO) and millimeter Wave (mmWave) systems have emerged as a promising candidate for backhaul networks of 5G and beyond radio access technologies due to the unique complementary properties against different channel and environment conditions. Therefore, in this study, we investigate the transmitter link selection problem for multiple-input multiple-output (MIMO) hybrid FSO-mmWave systems from a physical layer security point of view in the presence of different types of eavesdroppers. In particular, we propose convolutional neural network (CNN)-based link selection schemes to maximize the secrecy performance by activating the antennas and lasers at the transmitter side based on predefined configurations. The impact of fundamental physical layer parameters on the secrecy performance of a hybrid system is examined by taking the availability of channel state information (CSI), channel estimation errors, weather conditions, pointing error in FSO system, link distances, signal-to-noise ratios, path losses into account. In the light of the results, we show that the proposed CNN-based link selection scheme achieves the same performance as the conventional link selection mechanism.
查看更多>>摘要：? 2022 Elsevier B.V.An optical color ghost cryptography and steganography based on multi-discriminator generative adversarial network (MDGAN) is proposed. The system comprises a digital light projector configured to project color patterns onto a secret image and a bucket detector for collecting the light intensity in the output plane, rather than using three basic independent color channels. By applying a non-obvious data integration process, the detected bucket signals are hidden into those of a non-secret image. It can be shown that the decrypted images with conventional decryption methods always have serious noise and distortion. In this method, the periphery and detail of the secret images are reconstructed by using a pretrained MDGAN, where a multi-discriminator is employed to achieve a better image understanding. By continuously optimizing the parameters of the generator network, a high quality of image reconstruction can be achieved even if the sampling rate is extremely low. The feasibility of the proposed method is demonstrated by numerical simulations.
查看更多>>摘要：? 2022 Elsevier B.V.Oscillators based on levitated particles in high vacuum are a promising technique for realization of ultrasensitive detectors for precision force sensing. Direct particle loading under high vacuum is made difficult by decreased damping, which causes particle to escape during vacuum pumping. Theoretical investigations of the capture regions of optical traps in vacuum are necessary for developing new loading methods and improving loading efficiencies. We define an effective capture region (ECR) as a criterion for capture of particles, whose initial condition can be considered as the equivalent to a later-in-time situation of the actual trajectories. Quantitative analyses of the effective capture region (ECR) based on particle dynamics show that the ECR shrinks drastically at specific pressure interval. This shrinking interval is consistent with the experimental escaping pressure, indicating the nanoparticle escape mechanism.
查看更多>>摘要：? 2022 Elsevier B.V.In this article, a model is built to analyze the degradation of PER in linearly polarized fiber laser caused by incoherent polarization coupling during the amplification process. The model, for the first time could study the effect of heat on birefringence and the incoherent coupling process during the double-cladding linearly polarized fiber lasers’ amplification process. The model could well explain the PER degradation in our 340 W tandem pumped fiber laser and direct pumped fiber lasers in other groups’ reports. Also, the PER maintenance capability of tandem pumping and direct pumping is first analyzed.
查看更多>>摘要：? 2022 Elsevier B.V.The topological edge state (TES) and the topological corner state (TCS) have provided new method of manipulating the behavior of light. In this paper, we propose topological photonic crystals (PCs) with C4 symmetry, and the electric field distribution and polarization of eigenmodes are investigated via the finite element method. Through the lattice transformation, different Zak phases and polarizations of eigenmodes in the PCs can be obtained. Further, one-dimensional TES and zero-dimensional TCS with strong robustness are realized by the combination of PCs with different Zak phases. This work paves a new way for manipulating the behavior of light based on the properties of TES and TCS, which will promote the development of the integrated optical field.
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