Abstract:To increase the angular bandwidth of volume holographic grating, we fabricate holographic gratings based on grating multiplexing technique by using thin films of photopolymers and polymer dispersed liquid crystals. Experimental results confirm that the liquid crystal materials increase the refractive index modulation of the grating, enabling high diffraction efficiency with wide angular response compared to pure polymer materials. We observe that the fabricated holographic grating has near 80% of diffraction efficiency and about 18° of angular bandwidth, which can be further improved by modifying the liquid crystal/polymer mixtures and the grating multiplexing technique. The grating can be used to fabricate holographic waveguide structures for emerging applications in the near-eye display systems. This work has been supported by the National Natural Science Foundation of China (Nos.61575097, 21473093 and 11704201), and the Natural Science Foundation of Tianjin City (No.17JCQNJC01600). E-mail:drliuhl@nankai.edu.cn

Abstract: Magnetic absorber in optical frequency can be fulfilled through metamaterials designing. Therein, magnetic resonance in metal-dielectric-metal metasurfaces can be manipulated conveniently, and studying the parameters impacts is the primary for applications. In this work, through changing the grating width and the thickness of silica, the magnetic resonance modes have been studied, the conditions of the phase change zone from magnetic resonance (MR) to Fabry-Pérot (FP) are given out in Ag-SiO2-Ag grating magnetic metasurfaces. The results indicate that the MR mode in metal-dielectric-metal configuration is mainly decided on the dielectric duty factor other than the sole behaviors of the thickness of dielectric and size of nanostructures. The physical mechanism is elucidated through simulated electromagnetic field distributions using finite difference time domain (FDTD) solution, and numerical analysis of effective refraction index of Ag-SiO2-Ag magnetic metasurfaces. This study may prompt development of metamaterials in basic research in condensed physics and in optical devices applications. This work has been supported by the Natural Science Foundation of Shandong Province (No.2015ZRB019MD), the National Science Fund for Young Scholars (No.11704219), the Doctoral Research Started Funding of Qufu Normal University (No.BSQD20130152), the Open Subject of Key Laboratory of Magnetism and Magnetic Materials, Ministry of Education, Lanzhou University (No.LZUMMM2019013). E-mail:xzhangqf@mail.qfnu.edu.cn

Abstract:An in-line high efficient polarizer, composed of magnetic-ionic-liquid-adorned (MIL-adorned) hollow-core anti-resonant fiber (HARF), is theoretically proposed and experimentally demonstrated. The protocol is based on the selective conversion of polarization mode into leaky mode and attenuates quickly in MIL and the polarizer is featured by the magnetically tunable polarization extinction ratio (PER) and the thermally controllable operation bandwidth.

Abstract:We report the generation of harmonic noise-like mode-locked pulses in a thulium-doped fiber laser. In this laser, mode-locking can be realized through the nonlinear polarization rotation (NPR) technique. The ring cavity configuration uses 5 m of a Tm-doped dual-cladding fiber, as a gain medium, pumped by a 793 nm diode laser. The cavity uses a couple of polarization controllers (PCs) and polarization-dependent isolator to form a nonlinear polarization-rotating saturable absorber. By carefully adjusting of the PCs, the laser generates noise-like mode-locked pulses at the 2.04 μm band. With the increase of the pump power, the laser generates harmonics of the mode-locking fundamental repetition frequency of 6.88 MHz, from which we can obtain the second harmonic in a controlled mode. The obtained results may be useful for enhancing the understanding of the mechanism and characteristics of noise-like pulse at the 2 μm band. This work has been supported by the Scientific and Technological Research Program of Chongqing Municipal Education Commission (No.CSTC2017zdcy-zdzx0069), and the Natural Science Foundation of Chongqing (No.CSTC2018jcyjA0655). E-mail:wangxf@cqupt.edu.cn

Abstract:An intermediate-coupling variational method is presented to investigate the surface electron states in wurtzite AxB1-xN (A, B=Al, Ga and In) ternary mixed crystals (TMCs). Corresponding effective Hamiltonian are derived by considering the surface-optical-phonon (SO-phonon) influence and anisotropic structural effect. The surface-state energies of electron, the coupling constants and the average penetrating depths of the electronic surface-state wave functions have been numerical computed as a function of the composition x and the surface potential V0 for the wurtzite AlxGa1-xN, AlxIn1-xN and InxGa1-xN, respectively. The results show that the surface-state levels of electron are reduced with the increasing of the composition x in wurtzite AxB1-xN. It is also found that the electron-surface-optical-phonon (e-SO-p) coupling lowers the surface-state energies of electron and the shifts of the electronic surface-state energy level in the wurtzite AlxGa1-xN and AlxIn1-xN increase with the increasing of the composition x. However, in the wurtzite InxGa1-xN, the case is contrary. The influence of the e-SO-p interaction on the surface electron states can not be neglected in wurtzite AxB1-xN. This work has been supported by the Research Program of Science and Technology at Universities of Inner Mongolia Autonomous Region (No.NJZY16071), the Natural Science Foundation of Inner Mongolia (No.2020MS01008), and the National Natural Science Foundation Project of China (No.11664030). E-mail:zwyan@imau.edu.cn

Abstract:The nonlinear optical properties of P3HT in orthodichlorobenzene were investigated by Z-scan technique using second harmonic generation (532 nm) of mode-locked Nd:YAG laser in the picosecond domain. The experimental results show the magnitude of their nonlinear refraction indices was up to the order of 10-11 esu. The reverse saturable absorption of P3HT solution was observed and their nonlinear absorption coefficients reach up to 3.4 cm/GW. The strong optical nonlinearity of P3HT may find its new application in the photoclectric field. This work has been supported by the National Natural Science Foundation of China (No.11204214), and the Natural Science Foundation of Tianjin (No.14JCQNJC01900). E-mail:ourdaywufeng2000@163.com

Abstract:In this work, we comprehensively study the electronic and photocatalytic properties of single-layer and multilayer bismuth oxyhalides BiOX (X=Cl, Br, and I) sheets by means of extensive density functional theory, which have been successfully synthesized in the previous experimental studies. Our computational simulations show that single-layer BiOX sheets possess indirect band gap, suitable band edge alignments, and pronounced optical properties, suggesting that they can be utilized as photocatalysts for splitting H2O into H2 and O2 from theoretical aspects. In the case of multilayer BiOX sheets, some primary physical properties determined the photocatalytic performance are rather robust, almost independent of the layer number. According to these calculated results, we are optimistic that BiOX sheets, especially for single-layer BiOI, have great chances to be used for photocatalytic water splitting.

Abstract:As virtual networks services emerge increasingly with higher requirement of flexibility and robust, great complex challenges caused by physical-layer impairments are presented to the elastic optical networks (EON). Aimed to solve this problem, this paper proposes a physical impairment awareness based virtual network mapping stragegy of EON. The physical impairments awareness model is established, including both of linear factors and nonlinear ones. On this basis, this paper proposes a virtual network mapping strategy with detailed procedures, combined with node importance factors during the virtual network mapping procedure. Test results show that the proposed approach is able to reduce blocking rate and enhance services supporting ability of EON.

Abstract:In order to solve the ringing effect caused by the incorrect estimation of the blur kernel, an improved blind image deblurring algorithm based on the dark channel prior is proposed. First, in the blur kernel estimation stage, high-pass filtering is introduced to enhance the image quality and enhance the edge information to make the blur kernel estimation more accurate. A combination of super Laplacian prior and dark channel prior is introduced to estimate the potential clear image. Then the accurate blur kernel is estimated through alternate iterations from coarse to fine. In the image restoration stage, a weighted least square filter is introduced to suppress the ringing effect of the original clear image to further improve the quality of image restoration. Finally, image deconvolution based on Laplace priors and L0 regularized priors is used to restore clear images. Experimental results show that our approach improves the peak signal-to-noise ratio (PSNR) by about 0.4 dB and structural similarity (SSIM) by about 0.01, respectively. Compared with the existing image deblurring algorithms, this method can estimate the blur information more accurately, so that the restored image can achieve the effect of keeping the edges and removing ringing.

Abstract:For the correlation filtering (CF) tracking algorithm is not robust enough and cannot adapt to scale changes, target occlusion (OCC) and other complex interferences. We introduce a CF tracking algorithm based on superpixel and multifeature fusion (CFSMF). First, superpixel segmentation and clustering are performed for the target and its surrounding environment in the initial frame. Then, a target appearance is reconstructed through block segmentation-based overlapping analysis to remove redundant information. On this basis, the histogram of gradient (HOG) and HSI color features of the target sub-block are extracted to interact with their respective position filters. Accordingly, the target position is determined by the weighted fusion of the response values. In the scale prediction stage, we independently train a scale filter with a multiscale pyramid constructed at the estimated target location. The object scale is estimated in terms of the filter response, thereby enabling the tracking algorithm to adapt to the object scale change. Lastly, we introduce an OCC criterion for determining whether to update the model or not. Compared with the classical tracking algorithm kernelized correlation filters (KCF), the proposed algorithm boosts the tracking success rate by 20% and tracking accuracy by 15.9%. Our algorithm in this paper could track the target stably even when the target is occluded and its scale changes. This work has been supported in part by the National Key Research and Development Project of China (No.2018YFB1601200), the Key Projects of the Civil Aviation Joint Fund of the National Natural Science Foundation of China (No.U1533203), and the Fundamental Research Funds for the Central Universities (No.3122018C004). E-mail:carole_zhang@vip.163.com

Abstract:The purpose of this study was to optimize the light delivery method in a prostate photoacoustic imaging system. A three dimensional (3D) optical model of the human prostate was developed, and the optical energy distribution in the prostate was estimated via three-dimensional Monte Carlo simulation. Then, the feasibility of prostate photoacoustic imaging (PAI) using two endoscopic light delivery methods was studied. Photoacoustic pressure generation and the corresponding photoacoustic images had been obtained and the comparisons were made between each other. Also, the results of cylinder diffusing light source with different lengths were compared. After that, phantom experiment was carried out to validate the simulation results. Our results would be significant in the optimizing photoacoustic imaging system for an accurate diagnosis of prostate cancer.

Abstract:By introducing the hyperbolic sine function to Airy beam, the dynamic behavior and propagation characteristics of partially coherent sinh-Airy beams in oceanic turbulence are studied using approximate analytical intensity expression. The influence of sinh modulation parameter, coherence length and ocean parameters on intensity evolution, beam width and kurtosis parameter is mainly discussed. The results show that a non-zero sinh modulation parameter presents not only the insensitivity to oceanic turbulence, but a smaller beam width. Furthermore, it also improves kurtosis parameter. These findings bring advantages in signal reception for long distance. In addition, a larger relative intensity of temperature or salinity fluctuations, mean square temperature dissipation rate, or a smaller dissipation rate of turbulence kinetic energy is more liable to increase beam width, or decrease intensity and kurtosis parameter of partially coherent sinh-Airy beams. The results provide an opportunity for improving signal reception of underwater communication or target detection by Airy beams or their groups.