Amplification characteristics in active tapered segmented cladding fiber with large mode area
Caijian Xie, Tigang Ning, Jingjing Zheng, Li Pei, Jianshuai Wang, Jing Li, Haidong You, Chuangye Wang, and Xuekai Gao
A kind of tapered segmented cladding fiber (T-SCF) with large mode area (LMA) is proposed, and the mode and amplification characteristics of T-SCFs with concave, linear, and convex tapered structures are investigated based on finite-element method (FEM) and few-mode steady-state rate equation. Simulation results indicate that the concave tapered structure can introduce high loss for high-order modes (HOMs) that is advantageous to achieve single-mode operation, whereas the convex tapered structure provides large effective mode area that can help to mitigate nonlinear effects. Meanwhile, the small-to-large amplification scheme shows further advantages on stripping off HOMs, and the large-to-small amplification scheme decreases the heat load density induced by the high-power pump. Moreover, single-mode propagation performance, effective mode area, and heat load density of the T-SCF are superior to those of tapered step index fiber (T-SIF). These theoretical model and numerical results can provide instructive suggestions for designing high-power fiber lasers and amplifiers.
  • Jun. 22, 2021
  • High Power Laser Science and Engineering
  • Vol.9 Issue, 2 02000e32 (2021)
  • DOI:10.1017/hpl.2021.20
Application of Object-Oriented Median Absolute Deviation Method to Building Extraction
Gong Xunqiang, Liu Xinglei, Lu Tieding, and Chen Zhigao
Buildings are extremely important artificial feature objects. Extracting buildings can provide technical support for urban planning, population estimation, and landscape analysis. Object-oriented classification is an effective method for extracting ground objects and has been widely used in the extraction of building information. The object-oriented morphological building index method has good practicability, but the effect of extracting sparse buildings still needs to be improved. To solve this problem, the median absolute deviation is applied to the object-oriented building extraction, and the two situations of dense and sparse buildings are analyzed. Precision, recall, and F1 score are used to evaluate the extraction results. Experimental results show that the object-oriented median absolute deviation method extracts sparse buildings significantly better than the object-oriented classification and object-oriented morphological building index methods.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1212005 (2021)
  • DOI:10.3788/LOP202158.1212005
Strain Field Calculation by 3D Digital Image Correlation Method Based on Subset Projection and Savitzky-Golay Filter
Gu Jun
The digital image correlation (DIC) method is a non-contact, full-field deformation measurement method. The three-dimensional DIC breaks through the requirement that the surface of the test piece is planar in the two-dimensional DIC system, and obtains the three-dimensional surface displacement field data of the test piece through a stereo or multi-view camera system. First, a local subset is used to fit the least square plane, and the discrete points on the three-dimensional spatial curved surface are projected into the two-dimensional plane. Then, the Savitzky-Golay filter is used to solve the local strain tensor. Finally, the characterization of the strain field of a free-form test piece is realized, especially the errors of the small-plane projection method are investigated. The results show that the calculation error of the strain field caused by the projection process is much smaller than the transmission of the systematic error component contained in the displacement field data. When the strain subset size M=5, the strain field error is about 30 με. When M=10, the strain field error is about 10 με.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1212004 (2021)
  • DOI:10.3788/LOP202158.1212004
Single Pixel Detection Theory of Flat Surface Reflectivity Anomaly
Ouyang Haoyi, Chen Wanjun, Li Hai, and Yang Chuping
To detect the abnormal quality of smooth surfaces under standardized quality control, a single-pixel detection theory about the abnormal reflectivity of a flat surface is proposed. The proposed method uses a single-pixel detector and only needs to project a single frame of structured light (illumination design). First, the radiation flux distribution of a single-pixel detection about the abnormal reflectivity of a flat surface is derived. It is shown that under uniform illumination conditions, the spatial distribution of the radiation flux to the detector is nonuniform. Thus, a special illumination design can achieve the uniform radiation flux distribution and convert the abnormal reflectivity distribution of a flat surface into the cumulative reflectivity anomaly (or total radiation flux anomaly). In the experiment, the corresponding detection device is designed. The radiation flux distribution on the flat surface to the detector under uniform illumination and the illumination design for achieving uniform radiation flux distribution are numerically calculated. They are consistent with the actual results. Under the illumination condition of uniform radiation flux distribution, the total radiation flux of seven types of qualified ceramic tiles and the abnormal total radiation flux caused by two kinds of surface defect—cracks and scratches were investigated. The results showed that the two surface defects lead to significant changes in the total radiation flux. The effectiveness of the theory and feasibility of the technology are preliminarily verified.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1212003 (2021)
  • DOI:10.3788/LOP202158.1212003
Laser Dazzler with Automatic Focal Length Adjustment for Pedestrians
Cui Hongsheng, and Jiang Tao
Police laser blinding devices are primarily used in the field of security. A human target will lose vision temporarily when exposed to the green laser emitted by the device because the human eye is sensitive to the 532-nm green laser. The laser light must cover the target human body as much as possible to improve utilization of the laser. This subject obtains video from the camera and detects pedestrian targets through a video processing system based on digital signal processing (DSP) using the Gentle Adaboost algorithm. The detection results include the size and location of the pedestrian targets. According to the size of the pedestrian, a single chip microcomputer control circuit controls the laser lens to focus on pedestrian targets automatically to accommodate pedestrian targets.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1212002 (2021)
  • DOI:10.3788/LOP202158.1212002
Three-Dimensional Shape Measurement Based on Hybrid Dual-Frequency Fringe Projection
Liu Lu, Xi Dongdong, Chen Zhijian, Cheng Lei, and Wang Yuwei
The dual-frequency fringe projection is an important method for three-dimensional (3D) shape measurement. In the actual measurement process, how to balance the speed and accuracy has a remarkable impact on practical applications. This paper introduces a hybrid dual frequency algorithm, which needs to project four fringe images, including three high frequency fringe images and one low frequency fringe image. First, the background intensity and truncation phase of high frequency fringes are calculated based on three-step phase shift. Second, the background intensity is subtracted from the low-frequency fringes, and the low-frequency truncated phase is extracted by Hilbert transform. The low frequency truncation phase is unwrapped by the geometric constraint method, and the low frequency truncated phase is used to unwrap the high-frequency truncated phase. In order to verify the effectiveness of the proposed method, simulation and experimental studies are carried out respectively. Experimental results show that the proposed method can effectively restore the three-dimensional shape of the measured object.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1212001 (2021)
  • DOI:10.3788/LOP202158.1212001
Research on Image Mosaic Method Based on Binocular Vision Feature Point Matching
Wang Caidong, Liu Fengyang, Li Zhihang, Chen Zhihong, Cheng Yan, and Zheng Huadong
Aiming at the technical difficulties of the visual online inspection of large workpieces, an image mosaic method based on binocular vision feature point matching is proposed. Feature points are detected and matched based on an improved scale-invariant feature transform algorithm. A random sampling consensus algorithm is used to estimate the parameters of the transformation model to eliminate mismatched points, and a weighted smooth fusion method is used to fuse the spliced traces to complete the image splicing and fusion. The flexible visual detection system platform is built and the detection experiment of the workpiece feature area is carried out. The experimental datas are compared with the actual value of the workpiece feature area to verify the correctness and effectiveness of the mosaic method. Experimental results show that the proposed method meets the requirements of fast image stitching using a binocular-vision system in actual industrial production.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1211002 (2021)
  • DOI:10.3788/LOP202158.1211002
Alignment Method of a Large Aperture Telescope Based on the Eigen Coefficient
Liang Qiongxin, Huang Jinlong, Pan Nian, and Chen Kewei
Wavefront detection is the main technical means of enhancing telescope alignment. Due to the limited internal space for the large aperture optical system, we propose a computer-aided alignment method based on eigenmode coefficients to solve misalignments in telescopes. Compared with the traditional sensitivity matrix method, in the proposed method, the amount of calculation is small, the detector does not need to be partitioned, and the structure of the wavefront reconstruction matrix is simplified. We analyze the relationship between the eigenmode coefficient and the misalignment of the secondary mirror, and establish a sensitivity matrix model between the two. The alignment of the 1-m aperture on-axis three-mirror telescope was simulated. In the misalignment range of decenter ±0.3 mm and the tilt ±0.2° for the secondary mirror, an aberration correction was achieved in two-step iteration, and the root-mean-square of the central field wavefront aberration was less than λ/14, which has a good practical value for the alignment of large aperture optical systems in the future.
  • Jun. 22, 2021
  • Laser & Optoelectronics Progress
  • Vol.58 Issue, 12 1211001 (2021)
  • DOI:10.3788/LOP202158.1211001
Reconfigurable Optical Chaotic Logic Operations with Fast Rate of Picoseconds Scale
XU Geliang, XU Jian, KONG Lingli, HUANG Qifeng, QIU Xianting, GUO Yangyang, and CHENG Feng
In order to realize dynamic and reconfigurable optical chaotic logic operations, a specific technical scheme based on Vertical Cavity Surface Emitting Laser (VCSEL) feedback by its own light and linear electro-optic modulation effect has been proposed. The normalized injection current is modulated as logic input, the transverse electric field is modulated as control signal, and the logic output is demodulated by the difference between the average value and the threshold value of the x-polarized light intensity from the output of VCSEL. By transforming the logic operation relationship between control signal and logic input, the system can switch freely among basic logic operations such as NOT, AND, NAND, OR, NOR, XOR and XNOR. When the code width is 600 ps and the noise intensity is as high as 2.75×109, the success probability of the logic operation still equals 1, indicating that the system has good anti-noise performance. And when the noise intensity equals 2.5×109, the success probability always equals 1 if the code width is at least 579 ps. The above results have great reference value for the development of fast and stable combinational logic operation devices.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 174 (2021)
  • DOI:10.3788/gzxb20215005.0506008
Connotation and System of Computational Imaging(Invited)
SHAO Xiaopeng, SU Yun, LIU Jinpeng, LIU Fei, LI Wei, and XI Teli
Limited by industrial design thoughts, the traditional optoelectronic imaging technique has already reached its performance limitation. So that it is difficult to meet the increasing application demands in the information era. The Computational Imaging Technology (CIT) is the inevitable development of the information era. By deeply coupled with mathematical calculations and signal processing in the process of information acquisition, transmission and interpretation, the bottlenecks in physical information obtaining, modeling and solving are effectively broken by CIT. And the qualitative improvement in dimensions, scale and resolution of information are achieved. Although CIT is rapidly developing, its research layout is fragmented and decentralized, and there is no systematic system to lead the technology development. Therefore, in this paper, the concept and connotation of CIT are condensed, and the CIT system is established. Furthermore the basic commonality problems and key technologies to be solved are analyzed, especially the problem of nonlinear imaging model. The four typical imaging requirements of distance, resolution, field of view and system size are analyzed. And the corresponding key issues of super-large aperture imaging system, imaging beyond diffraction limit, bionic optics, interpretation of light field information, computational optical system design and computational detector are expounded. A global perspective is provided in this paper for related researchers to better promote the technology development and application.
  • Jun. 22, 2021
  • Acta Photonica Sinica
  • Vol.50 Issue, 5 1 (2021)
  • DOI:10.3788/gzxb20215005.0511001
Optics Physics Geography All Subjects

Special lssue

Special Issue on High Power Laser Science and Engineering 2021 (2021)

Submission Open:25 February 2021; Submission Deadline: 31 July 2021

Editor (s): Colin Danson, Jianqiang Zhu

Special Issue on XFELs (2021)

Submission Open:1 January 2021; Submission Deadline: 1 July 2021

Editor (s): Max Lederer, Haixiao Deng, Sergio Carbajo

Special Issue on 60th Celebration of First Laser (2020)

Submission Open:1 January 2020; Submission Deadline: 31 December 2020

Editor (s):