查看更多>>摘要：? 2021 Elsevier B.V.Polarization conversion of electromagnetic wave plays an important role in practical application. In this paper, a terahertz band ultra-wideband tunable linear-to-circular polarization converter based on GST metasurface is proposed. It consists of two triangular metals, a phase change material (GST), a dielectric plate and a metal floor. The proposed polarization converter can convert linearly polarized waves into circularly polarized waves in different frequency bands by controlling the crystallization state of GST through temperature, without the need of re-optimization and remanufacturing structure. It has the characteristics of ultra-wideband and high efficiency. The proposed polarization converter has potential for miniaturization and integration of terahertz systems.
查看更多>>摘要：? 2021 Elsevier B.V.Plasmon-induced transparency (PIT) based sensors have attracted various attention for application in environmental monitoring, medical samples detection, food safety, and biochemical applications due to it is capable of detecting the minute changes in the refractive index. However, restricted by the limitation of the structure complexity and low sensing performance, the practical large-scale application of PIT-based sensors still remains a great challenge. Herein, we propose a simple dual-layer graphene metamaterial in which the continuity of the graphene layer is retained, providing a lot of convenience for the manufacturing of the device. Coupled mode theory (CMT) is used to demonstrate the physical mechanism of PIT. Particularly, The PIT windows delivered by this device can be modulated effectively by simply changing the Fermi energy and the parameter of the graphene strips. What is more, the relationship between the sensing performance and parameters of the device is described by charts. It is found that the device exhibits a high sensitivity of 15739 nm/RIU and a maximum figure of merit (FOM) of 469. The current work may pave the way for the further research on the applications and designs of nanosensors used in highly integrated optical circuits.
查看更多>>摘要：? 2021 Elsevier B.V.Laser rock-breaking will produce cracks on the rock, and the cracking of the cracks affects the efficiency of laser rock-breaking. In this paper, the laser rock-breaking experimental platform was set up, the morphological characteristics of granite damage and the distribution of temperature field under different laser irradiation times (2～10 s) were analyzed by SEM and infrared thermal imager. The results show that the temperature of the melting zone under the action of laser is maximum, and the damage manifests itself in the form of step-like pattern fracture. While the damage form of damage zone and thermal affected zone is mainly crack cracking. With the increase of laser irradiation time, the temperature gradient at the same location on the granite surface becomes larger. According to the temperature distribution of granite, innovatively proposed a laser rock breaking simulation model based on the discrete element method, which can reflect the cracking process of rock under the laser. The simulation results show that crack cracking is a dynamic failure process. During the laser irradiation process, the melting zone cracking manifests itself as a tensile failure, while the damage zone and thermal affected zone were dominated by tensile–shear composite damage. The laser rock-breaking efficiency can be improved by controlling the laser damage to the rock in the form of tensile damage. Finally, innovatively established a method for evaluating rock damage under laser action, which can be used to quantitatively evaluate the damage degree of laser rock-breaking and provide a new means for the preferential selection of laser parameters in future drilling processes.
查看更多>>摘要：? 2021 Elsevier B.V.A two-dimensional beam steering device is an essential optical element for many applications, such as free-space optical communications, light detection and ranging, and microscopy. The purpose of the paper is to develop a two-dimensional beam steering device with a simple structure and a large beam steering angle. The principle of beam steering is based on the decentred lens. The decentred lens is placed on the center of the dielectric elastomer and the movement of the decentred lens is actuated by the dielectric elastomer The dielectric elastomer is divided into four quadrants and the top and bottom surfaces of the four quadrants of dielectric elastomer are coated by compliant electrodes. Through applying different voltages on the four quadrants, the decentred lens can move and the beam is steered in a two-dimensional direction. We develop a prototype and carried out imaging experiments to verify the proposed beam steering method. The experimental results show that the maximum translation distance of the decentred lens is 1.496 mm at an actuation voltage of 5 kV. The function of two-dimensional beam steering is realized and the maximum beam steering angle of the device is 11.98°. Such a two-dimensional beam steering device promises a potential solution in various beam steering systems.
查看更多>>摘要：? 2021 Elsevier B.V.In this paper, we declare that the scattering system of coherence light passing through a thin-layer highly scattering medium can be treated as a 4f system of single random phase encoding (SRPE). Assuming no energy loss, the target image behind a thin-layer highly scattering medium can be recovered by using an attack method in a SRPE-4f encryption system. The idea originates from the analysis of speckle field and theoretical model of the system. On the one hand, the statistical distribution of the speckle in the scattering system is consistent with that of the cyphertext in the corresponding SRPE-4f encryption system, which provides the base for equivalent replacement. On the other hand, the point spread function of a thin-layer highly scattering medium is equivalent to the Fourier transform of random phase mask of the SRPE-4f system, which can be used for key estimation in scattering imaging. Both the theory analysis and results of the experiment verify the validity and feasibility of our proposed, and we believe this contribution will open up a novel way to deepen the research of imaging through scattering medium.
查看更多>>摘要：? 2021 Elsevier B.V.In this paper, we established the relationship model between Rayleigh length of incident Gaussian beam and in-plane angular spin splitting (IPASS) under arbitrary linear polarization, and systematically investigated the effect of Rayleigh length on the IPASS. The results show that the IPASS shifts decrease with the increase of Rayleigh length, and the smaller the Rayleigh length, the greater its impact on IPASS. The maximum IPASS shift can almost reach half of the beam divergence angle by adjusting incident angle and polarization angle. In addition, several interesting characters of IPASS are discovered.
查看更多>>摘要：? 2021 Elsevier B.V.Aspheres and freeform surfaces are well measured with null optics but the transverse coordinates on the test surface are not linear with the pixels on the imaging plane. Such a mapping distortion must be corrected before the measured surface error map is used for corrective figuring process. Conventional mapping distortion correction involves tediously finding the coordinates of a sequence of fiducial marks on both the test surface and the imaging plane. This paper presents a pure ray tracing method without use of fiducial marks by introducing a dummy spherical surface between the point source and the null optics, acting like a virtual reference sphere (RS). It is linearly mapped to the imaging plane with the linear scale easily calibrated. On the other hand, the virtual RS is exactly mapped to the test surface by tracing a bundle of dense rays. This virtual surface thus bridges the gap between coordinates on the imaging plane and those on the test surface. Two experimental examples of null test of on-axis and off-axis aspheres demonstrate the effectiveness of mapping distortion correction.
查看更多>>摘要：? 2021 Elsevier B.V.We develop a fiber pH sensor using a spider dragline silk (SDS). SDS obtained from an Araneus Ventricosus is a pH-sensitive natural protein. We wrap the SDS on a tapered single-mode optical fiber (TSOF) to fabricate the sensing structure. The fiber taper is too thin to confine the laser propagating in the fiber, leading to the leakage of the strong evanescent field. Therefore, the higher-order modes will couple to the SDS, and we may obtain a multimode interference (MMI) spectrum. The pH of the solution will change the protein structure of the SDS. Thus, the effective refractive index (RI) of the SDS will vary with pH. Therefore, the change of pH causes the shift of the MMI spectrum. The pH detection range is 6.5 to 7.9. Compared with other PH sensors, the materials used in this sensor are biocompatible and the sensitivity of this sensor is competitive. The maximum pH sensitivity is as high as 7.7 nm of wavelength shift per pH level. In our experiment, the resolution of optical spectrum analyze is 0.2 nm. Therefore, the pH change that corresponds to the minimum detectable wavelength shift is 0.03. The sensor is low in cost, environmental-friendly, and has good repeatability.
查看更多>>摘要：? 2021 Elsevier B.V.Imaging through scattering layers has a wide range of applications. However, even a thin layer can scatter the light into a random speckle pattern thus difficult to image. Speckle correlation-based methods enable noninvasive imaging of objects hidden behind such layers whereas, still suffer from inaccurate solutions and losing the orientation information of the object. In this paper, we proposed a novel deterministic phase-retrieval algorithm to fully reconstruct the object from its speckle pattern and experimentally demonstrated that the new method can retrieve a high-quality image from a single-shot speckle pattern. Compared to other phase retrieval techniques, it maintains the orientation information correctly in a single reconstruction and is more robust in noisy conditions.
查看更多>>摘要：? 2021 Elsevier B.V.Single-molecule localization microscopy (SMLM) achieves super-resolution based on a series of images of sparsely distributed molecules, which makes it time-consuming. To improve the temporal resolution, several high-density localization algorithms have been developed, and the computational speed is considered one of the important factors for evaluating their performance. In this study, for the first time, a three-dimensional (3D) multiple measurement vector compressed sensing (3D-MMV-CS) model was constructed and then solved using a multiple sparse Bayesian learning algorithm to realize 3D single-molecule localization and obtain 3D super-resolved fluorescence images. The 3D-MMV-CS successfully recovered a 3D super-resolved image from a series of simulated high-density fluorescence images. The computation time for reconstruction only increases marginally with an increase in the number of raw images and approximately stays constant with an increase in the density of fluorescent molecules. Simulation results demonstrated that, when the number of raw images reaches 1900, compared with the other two algorithms L1-Homotopy and compressed sensing STORM (CSSTORM) with CVX, the 3D-MMV-CS method is 100 times faster than the former and five orders of magnitude faster than the latter. This outstanding performance in computation speed would allow the 3D-MMV-CS approach to be routinely applicable to SMLM. Validation test of the 3D-MMV-CS method was performed successfully with experimental data from an astigmatism-based 3D SMLM system.
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