Abstract:A theoretical analysis was conducted on the intrinsic bond between multi-point responses caused by the same single vibration in phase sensitive optical time-domain reflectometer (OTDR). Temporal similarity of signals collected from adjacent sample locations were investigated. Referring to correlation coefficient as well as the relative energy level, a method of extracting disturbed position in φ-OTDR based on signal relevance evaluation is proposed to perform fast screening of massive φ-OTDR raw data to pinpoint those signals with significance. As proof of concept, a manual excavation experiment was conducted along an oil pipeline, where on-site data was analyzed. The results showed that the proposed method can accurately screen out real vibration signals and filter out pure noise so that computation resources could be allocated with better rationality.

Abstract:This paper investigates the properties of silicon cells (SI) and perovskite solar cells (PSC) under bias condition by using impedance spectroscopy. The parallel resistances Rpof SI and PSC are found to decrease with increasing bias, but the capacitance Cpshows the opposite trend. Comparing Rpwith Cp, bias has a greater impact on the Cp of both cells. However, the bias has little effect on the series resistance Rs of both cells. Compared with SI cell, the bias is seen to be a greater impact on the Rp and a smaller impact on Cp of PSC. The carrier lifetime τn in SI and PSC first increases and then decreases with bias, and the carrier diffusion length Ld increases almost linearly with bias. Compared to SI cell, the bias has a greater impact on PSC’s Ld.

Abstract:In order to explore the effect of unstable resonator stability on laser beam quality, the numerical simulation of mid-infrared laser and visible laser was carried out in GLAD software. The simulation results showed that the existence of defocus aberration, tilt aberration and astigmatic aberration in the unstable resonator can cause the center of the far-field spot of the output annular beam to drift, the number of peripheral diffraction rings to increase, the beam quality to deteriorate, and the degree of effect is different. It is also found that on the basis of the effect of tilt aberration and astigmatism aberration, the introduction of defocus aberration can improve the output laser beam quality to a certain extent. In addition, under the condition of the same aberrations, the effects of different wavelength lasers are roughly the same. However, in terms of the degree of effects, the short-wave laser is much higher than the medium-long-wave laser, which verifies that the resonator debugging of the short-wave laser is more difficult than that of the medium-long-wave laser in the experimental process. The simulation results can provide an important reference for the optimization design of the laser system, the processing of cavity mirror and the formulation of the correction range index of the adaptive optical system.

Abstract:Optical fiber Bragg grating (FBG) sensors have advanced significantly in the last several years. The use of innovative FBG in temperature and pressure measurement is examined in this study. The benefits of FBGs, such as their compact size, low weight, resilience to corrosion, immunity to electromagnetic interference, distributed sensing, and remote monitoring, have brought attention to the growing research in this field of structural health monitoring of civil infrastructures. In this investigation, a novel model is proposed and implemented using ANSYS workbench and GratingMOD tool. It is shown that the central wavelength of FBG sensors increased from 1 550 nm to 1 556 nm when the temperature rose from 10 °C to 40 °C. In a similar vein, the central wavelength grew from 1 551.166 7 nm to 1 560.056 nm over a pressure range from 100 MPa to 600 MPa. The claimed work will make it possible to calibrate sensors more precisely, guaranteeing accurate data and being useful in monitoring numerous parameters at once, making them beneficial in a variety of applications.

Abstract:This paper designs an all-dielectric metasurface with tunable chiral properties in the near-infrared range, whose working wavelength is 1 250—2 200 nm. The metasurface exhibits circular dichroism (CD) and asymmetric transmission (AT) characteristics for circularly polarized light. The metasurface is a double-layer structure composed of Ge2Sb2Se4Te1 (GSST). The CD values of amorphous GSST reach 0.83 and 0.82 at 1 570 nm and 1 640 nm, respectively. The AT values reach 0.65 and 0.77 at 1 570 nm and 1 640 nm, respectively, with a value of −0.62 at 1 680 nm. The CD value of crystalline GSST reaches 0.81 at 2 070 nm, with smaller AT. In addition, whether it is incident by linearly polarized waves or circularly polarized waves, this metasurface has low absorption in the working band, which gives it the potential to make adjustable integrated photonic devices.

Abstract:Traditional orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) system is susceptible to high peak-to-average power ratio (PAPR), thus leading to low power efficiency. To address this issue, a sparse code multiple access (SCMA) codebook design method has been proposed to lower the PAPR of the clipping based OFDM-VLC system. Then, the codebooks of the high-dimension mother constellation (MC) and low-dimension MC are optimized, respectively. Specifically, for high-dimension MCs like T16-quadrature amplitude modulation (T16-QAM), the constellation points (CLPs) with higher transmit power are mapped to the CLPs with lower power. For low-dimension MCs like 4-pulse amplitude modulation (4-PAM), a contracted mapping method is proposed to reduce the power of the CLPs located on the real axis of the MC. Simulations show that the proposed method could achieve better PAPR performance for any value of the clipping ratio with only a slight bit error rate (BER) performance loss compared to the original codebook design. Besides, the smaller clipping ratio would induce better PAPR performance but worse BER performance. Moreover, the increasing number of iterations in the logarithm domain message passing algorithm (log-MPA) could improve the BER performance. This work will benefit the research and development of SCMA-OFDM-VLC systems.

Abstract:Performance of non-line-of-sight (NLOS) ultraviolet (UV) communication is closely related with the communication range, system geometry and the atmosphere aerosol properties. In this paper, we investigate the path loss of the NLOS UV communication systems in both monodisperse and polydisperse aerosol systems based on the Monte-Carlo method. The mixed aerosols composed of black carbon and sulfate are considered as the transmission media. The core-shell, homogeneous, and external mixing model are assumed. Simulation results show that the performance of the NLOS UV communication in the monodisperse aerosol is similar to that in polydisperse aerosol. The mixed state of the aerosols has significant influence on the performance of the communication system. The path loss of the communication system in externally mixed aerosol is smaller than that in internally mixed aerosol. Our simulation results are useful for the design of the NLOS UV communication systems.

Abstract:Light guide plate (LGP) is a kind of material used in the backlight module. How to improve the quality control of LGP has become the focus of research in the industry. To address issues such as low gray contrast and a high proportion of small target defects in LGP images, an improved you only look once version 5 (YOLOv5) neural network based on multi-scale dilation convolution and a novel loss function is proposed. First, the LGP image is preprocessed, and then the context amplification module (CAM) is integrated into the feature fusion part of the detection algorithm to fuse multi-scale expansion convolution features to obtain rich context information. The extended intersection over union (XIoU) is selected as the location regression loss function. The results show that this method can effectively improve the detection accuracy and positioning accuracy. Compared with YOLOv5, the proposed method achieves an average accuracy increase of 4.7% and a recall rate increase of 2.7%. It can achieve accurate detection of defects, such as white/bright spots, black spots, line scratches, and surface foreign objects in LGP.

Abstract:Aiming at the existing semantic segmentation process due to the loss of pixel features and the complexity of calculating too many parameters, which leads to unsatisfactory segmentation results and too long time, this paper proposes a lightweight semantic segmentation algorithm based on the fusion of multiple modules. The algorithm is based on the pyramid scene parsing network (PSPNet). Firstly, MobileNetV2 network is chosen as the feature extraction network to construct the lightweight network structure. In the training of the network, a freeze and thaw method is used, and the Focal Loss function is added to balance the proportion of positive and negative samples. After that, spatial and channel reconstruction convolution (SCConv) is introduced in the pyramid pooling module to reduce the segmentation task. The computational cost due to redundant feature extraction is reduced. Finally, the coordinate attention (CA) and the efficient channel attention network (ECA-Net) are incorporated to make the multi-modules integrate with each other to enhance the salient features and improve the segmentation accuracy. Through the ablation and comparison experiments, the average pixel accuracy on PASCAL VOC 2012 dataset reaches 85.23%, the computation amount is reduced by 45.79%, and the training speed is improved by 68.69%. The average pixel accuracy on Cityscapes dataset reaches 86.75%, the average intersection and merger ratio reaches 73.86%, and the interaction of multiple modules with correlation performance makes the algorithm improved and optimized, effectively solving the problems of low segmentation accuracy and slow training speed in the algorithm, which has a significant accuracy advantage in the lightweight model, and can generally improve the efficiency of image semantic segmentation.