2021

• Record 169 of
  
  Title:Classification of Pneumonia Images Based on Improved VGG19 Convolutional Neural Network (Invited)
  
  Author(s):Xiong, Feng(1); He, Di(1); Liu, Yujie(1); Qi, Meijie(1); Gao, Peng(1); Zhang, Zhoufeng(2); Liu, Lixin(1,2)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 10  DOI: 10.3788/gzxb20215010.1010001  Published: October 25, 2021  
  Abstract:In this paper, two improved network models, SVM (Linear)-based VGG19 and XGBoost-based VGG19, are constructed by combining the VGG19 convolutional neural network with two machine learning algorithms. Moreover, the VGG19 model and the two improved models are employed to classify bacterial pneumonia and viral pneumonia images. Additionally, the performances of the three models are evaluated and compared, the results show that the average accuracies of the three models are all above 85.9%. The improved VGG19 models show superior stability in accuracy over conventional VGG19 model, and the comprehensive performance of XGBoost-based VGG19 model is best, which verifies the effectiveness of deep learning models combined with machine learning models. © 2021, Science Press. All right reserved.
  Accession Number: 20214811256426
• Record 170 of
  
  Title:WEIGHTED SPARSITY CONSTRAINT TENSOR FACTORIZATION FOR HYPERSPECTRAL UNMIXING
  
  Author(s):Yuan, Yuan(1); Dong, Le(2,3)
  Source: International Geoscience and Remote Sensing Symposium (IGARSS)  Volume: 2021-July  Issue:   DOI: 10.1109/IGARSS47720.2021.9553154  Published: 2021  
  Abstract:Recently, the unmixing methods based on non-negative tensor factorization (NTF) have received a lot of attention. Many NTF-based methods combine total variation (TV) regularization, aiming at maintaining the smoothness of the abundance maps to improve the performance of unmixing. However, the existing TV regularization ignores the sparsity sharing on the spatial difference images among different bands. To tackle this issue, a weighted total variation regularizer on the spatial difference maps of abundances is proposed in this paper, which uses the L2,1 norm to explore the sparse structure in abundances along the spectral dimension. In addition, the L1/2 norm is used to enhance the spatial sparsity of abundances. The proposed method can not only enhance the sparsity in abundances, but also keep the spatial similarity characteristics of data. Compared with the existing popular methods, the proposed method has superior performance on both synthetic data and real data. © 2021 IEEE.
  Accession Number: 20221111780067
• Record 171 of
  
  Title:Single-mode fiber to GRIN-rod lenses coupling efficiency and tolerance analysis
  
  Author(s):Song, Wei(1,2); Xie, Youjin(1); Li, Zhiguo(1); Hao, Wei(1); Yan, Peipie(1); Li, Xin(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 11780  Issue:   DOI: 10.1117/12.2590659  Published: 2021  
  Abstract:The single-mode fiber coupling efficiency with graded-index rod lenses can achieve higher coupling efficiency, compared with the direct alignment coupling of the single-mode fiber. The assembly error of direct alignment has a far greater impact on the coupling efficiency of the fiber than the GRIN lenses coupling to fiber. The analysis of the influence of the coupling error on the optical fiber coupling efficiency provides important theoretical support and guidance for processing and assembly. Axial error, radial error and angular tilt will all have different effects on fiber coupling efficiency. However, the fiber coupling system is not only limited to the coupling of the fiber and GRIN lenses, but also can be coupled with one or more lenses to analyze the advantages and disadvantages of multiple coupling methods. © 2021 SPIE
  Accession Number: 20211410174167
• Record 172 of
  
  Title:Beam shaping technology based on phase-only liquid-crystal spatial light modulator
  
  Author(s):Wang, Shan(1,2); Zhao, Hualong(1); Yang, Xiaojun(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12060  Issue:   DOI: 10.1117/12.2606722  Published: 2021  
  Abstract:The liquid crystal spatial light modulator is an effective method to change the quality of the laser beam light field distribution, and the phase hologram is the key to the function of the pure phase liquid crystal spatial light modulator. An improved iterative algorithm for beam shaping is proposed, which is improved on the basis of the traditional G-S algorithm. The improved algorithm is more universal, has better rapid convergence and design flexibility. By proposing an optimization factor ζ, the original uneven light intensity distribution in the light field is compensated, and the advantages of the G-S algorithm that the light field is reshaped by the clear boundary are retained and the uniformity of the light field distribution is improved. The experimental results show that the liquid crystal spatial light modulator can improve the nearfield beam quality very well, the energy utilization rate of the shaped output beam is 97%, and its top unevenness is 25.6%. © 2021 SPIE.
  Accession Number: 20220211446975
• Record 173 of
  
  Title:Fiber-coupled Chromatic Confocal 3D Measurement System and Comparative Study of Spectral Data Processing Algorithms
  
  Author(s):Wang, Jiayi(1); Liu, Tao(1); Tang, Xiaofeng(1); Hu, Jiaqi(1); Wang, Xing(2); Li, Guoqing(1); He, Tao(1); Yang, Shuming(1)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 11  DOI: 10.3788/gzxb20215011.1112001  Published: November 25, 2021  
  Abstract:A simple aspheric chromatic dispersion lens group of low cost is designed using Zemax, and an integrated fiber-coupled chromatic confocal 3D measurement system is developed. Performances of four peak wavelength extraction methods, i.e. the maximum method, centroid method, Gaussian fitting method and spline interpolation method, have been compared and analyzed quantitatively. In addition, calibration accuracy of Gaussian fitting method and spline interpolation method is tested and compared through the axial resolution and displacement measurement experiments. The experimental results show that the axial measurement range of the built system is 1 mm. The Gaussian fitting method has higher accuracy and better stability among the four peak extraction algorithms. The axial resolution of the system using Gaussian fitting based and spline interpolation based calibration methods can both reach 0.2 μm and the displacement measurement accuracy is better than 1% within the whole measurement range; a quartz glass with a thickness of 0.219 mm is measured, and the relative measurement error of the average value is 0.5%. Finally, the developed system is applied to the 3D surface measurement of a step structure, a flexible electrode and a MEMS unit, and the experimental results indicate that the proposed system can perform high-precision 3D measurements of complex microstructures and transparent material thicknesses. © 2021, Science Press. All right reserved.
  Accession Number: 20215011321430
• Record 174 of
  
  Title:Optical design of volume phase holographic grating Raman spectrometer for lunar mineral detection
  
  Author(s):Linghu, Birong(1,2); Xue, Bin(1); Zhao, Yiyi(1); Wang, Hui(3)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 12064  Issue:   DOI: 10.1117/12.2606573  Published: 2021  
  Abstract:In order to overcome the problems of low diffraction efficiency, large aberrations and stray light of traditional ruled gratings in reflective Raman spectrometers, combined with the characteristics of the Raman signals of lunar surface minerals, a volume phase holographic (VPH) grating Raman spectrometer system for lunar surface detection was designed. The spectral range of the spectrometer is 140∼3073cm-1, and the field of view is 3°. According to the Kogelnik coupled wave theory, the diffractive efficiency of the designed VPH grating is more than 95% at the central wavelength, and the average efficiency is more than 80% in the whole spectral range. After optimizing with zemax, the MTF of the entire spectrometer system at the Nyquist frequency is greater than 0.45, and a spectral resolution of 10 cm-1 can be achieved. Copyright © 2021 SPIE.
  Accession Number: 20220211450478
• Record 175 of
  
  Title:Research on High Precision Locating of Laser Spot Center in Free-Space Laser Communication System
  
  Author(s):Meng, Xiangsheng(1,2,3); Ma, Caiwen(1,3); Tian, Yan(1,3); Han, Junfeng(1,3); Liang, Dongsheng(1,3)
  Source: IEEE Information Technology, Networking, Electronic and Automation Control Conference, ITNEC 2021  Volume:   Issue:   DOI: 10.1109/ITNEC52019.2021.9587297  Published: October 15, 2021  
  Abstract:The gray centroid algorithm is usually used as the centroid locating algorithm in the free-space laser communication system. However, the limited spatial resolution of the image detector will produce homogenization effect, which results in gray quantization error. Moreover, the spot information will lost when we detecting the object with threshold. The two problems mentioned above will make the locating accuracy worse when using the conventional algorithm. In this paper, we use the squared weighting centroid with threshold algorithm combined with the hardware optimized interpolation subdivision algorithm to improve the locating accuracy. As the weight of bright pixels increased, and the spot information loss decreased due to subdivision, the locating accuracy improved significantly. The simulation results show that the locating accuracy has improved by at least 50%, and the experiment results confirmed that the tracking error (2.57μrad) using the improved algorithm is less than that (4.11μrad) of the conventional algorithm. © 2021 IEEE.
  Accession Number: 20214711192499
• Record 176 of
  
  Title:Fabrication and experimental characterization of precise high-efficiency 2D multi-mode fiber array coupler
  
  Author(s):Zhou, Xiaojun(1); Song, Aiguo(1); Kong, Depeng(2); Yu, Weixing(2)
  Source: Optical Fiber Technology  Volume: 63  Issue:   DOI: 10.1016/j.yofte.2021.102488  Published: May 2021  
  Abstract:In this paper a method for fabricating precise high-efficiency 2D multi-mode fiber array coupler is proposed, and the coupler's performance is experimentally characterized. By improving the design of 2D fiber array coupler, the average concentricity error of the fiber array is down to 0.9 μm. After coupling with microlens array, the average coupling efficiency of the coupler is up to 57.51%. It is demonstrated that the precise microhole position and fiber cladding diameter, supported by microlens array, can provide an excellent coupling performance. This 2D fiber array coupler can be widely applied in LIDAR, optical communication systems and microwave photonics systems, provide the functions of high-speed image capture, interconnection and optical signals time-space transformation. © 2021 Elsevier Inc.
  Accession Number: 20211010037996
• Record 177 of
  
  Title:Design of Spatial Resolution PDV Probe Based on Double Telecentric Lens
  
  Author(s):Yang, Jun(1,2,3); Yan, Yadong(1); Li, Qi(1); Shi, Guokai(3); Wang, Zhao(3); Zhang, Yang(3); Zhang, Suoqi(3); He, Junhua(1)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 50  Issue: 7  DOI: 10.3788/gzxb20215007.0712002  Published: July 25, 2021  
  Abstract:In order to simultaneously measure the multi-point velocity of a plane target in the range of 5 mm in material dynamics experiments or structural response research, a laser transmitting and receiving probe with spatial resolution for photonic Doppler velocimetry is developed based on the dense fiber array and double telecentric lens. The optical design and structural design are described, and the installation and testing of the probe are performed. The test results of output spot characteristics show that the vertical axis magnification of the probe is consistent with the design value. The minimum diameter of the spot at the focusing position is 109 μm and the maximum is 202 μm. The test results of the receiving efficiency of the probe to the diffuse reflection target show that each fiber in the probe is not crosstalk, and the receiving efficiency of the fiber near the center is large, while that of the two sides is small. © 2021, Science Press. All right reserved.
  Accession Number: 20213110707126
• Record 178 of
  
  Title:Development and prospect on driving laser for attosecond pulse
  
  Author(s):Yuan, Hao(1,2); Cao, Huabao(1); Wang, Hushan(1); Liu, Xin(1,2); Sun, Xianwei(1); Wang, Yishan(1); Zhao, Wei(1); Fu, Yuxi(1)
  Source: Kexue Tongbao/Chinese Science Bulletin  Volume: 66  Issue: 8  DOI: 10.1360/TB-2020-0594  Published: March 15, 2021  
  Abstract:Attosecond light source is a new type of light source that was born at the beginning of the 21st century, which has a short pulse, broad spectrum, high temporal and spatial coherence and wide tunability, thus being widely employed in various research fieds. From ultrafast motion of electrons in atoms to charge transfer in biological macromolecules, attosecond pulses is currently the only tool that can track and capture these ultrafast dynamics. Attosecond pulse enables us to investigate ultrafast dynamics of micro-world both in nanometer and attosecond scales. However, the mechanism of attosecond pulse generation is completely different from general ultrafast lasers. Instead, attosecond pulse is generated by a highly nonlinear interaction between strong ultrafast femtosecond laser and matter, which is called high-order harmonic generation (HHG). The mechanism of HHG can be understood by a classical three step model. First, an electron is ionized from an atom by a strong laser electric field through tunnel ionization. Then the free electron is accelerated by the laser field and gains energy. Finally, the electron recombines with the parent ion when the laser field changes its sign with emission of a photon, whose energy equals its kinetic energy gained in the laser field plus ionization potential of the atom. Apparently, HHG is strongly affected by the laser waveform. Several key parameters of driving laser, such as wavelength, intensity, and carrier envelope phase strongly affect the process of HHG. Thus, the characteristics of attosecond pulses are determined by the driving laser. The rapid development of attosecond pulse technology strongly depends on the development of driving laser technology. In the beginning, chirped pulse amplification (CPA) technology greatly promoted the development of attosecond light sources. The femtosecond CPA systems based on Ti: sapphire crystal has been the main driving laser to generate attosecond light pulses. The driving laser wavelength is in the near infrared region near 800 nm, which generally has a pulse duration of multiple optical cycles. By employing post-compression technology to shorten pulse durations of CPA systems to few-cycle, isolated attosecond pulses in the extreme ultraviolet (XUV) can be generated, which is called the first generation of attosecond light source. Recently, optical parametric amplification (OPA) systems have been widely used as driving laser due to its flexible wavelength tunability. Using OPA, longer driving laser wavelength up to the midinfrared (MIR) can be obtained, which pushes the attosecond pulses to the soft X-ray region, and has been called the second generation of attosecond light sources. Due to broad spectrum and higher photon energy, attosecond pulses have a shorter duration in the soft X-ray region compared with XUV region, given that the temporal chirp is properly compensated. In 2017, reseachers generated soft X-ray isolated attosecond pulses, which was driven by mid-infrared pulses centered at 1.8 µm. These attosecond pulses, whose duration reaches 53 as and spectrum surpasses carbon K-edge, provide a tool for studying the ultrafast dynamics of diamond, graphene and other carbon materials. In this paper, we start with the principle of attosecond pulses generation based on HHG. Then, we introduce different technologies and their development for obtaining driving laser pulses for HHG. Finally, we introduce prospect on development of driving laser pulses for attosecond pulses generation. © 2021, Science Press. All right reserved.
  Accession Number: 20211310141835
• Record 179 of
  
  Title:Modeling of high-speed laser photography system for field projectile testing
  
  Author(s):Sun, Ce(1); Jia, Yangyu(2); Wang, Danni(3)
  Source: Optik  Volume: 241  Issue:   DOI: 10.1016/j.ijleo.2021.166980  Published: September 2021  
  Abstract:Field projectile testing plays a crucial role in national defense. Laser high-speed photography records transient processes with high temporal and spatial resolution and is an effective diagnostic method for range testing. In this study, a laser high-speed photography model is established from detailed aspects, including laser pulse energy for reflective imaging, accurate synchronization of pulse train and shutter signal, minimum exposure time and shooting frequency for targets with different velocities, and magnification correction used in the image measurement. Shooting experiments conducted in Nanshan Test center verify the correctness of the theoretical analysis and parameter selection. The models and methods described in this article can be a guidance for field testing. © 2021 Elsevier GmbH
  Accession Number: 20211910318384
• Record 180 of
  
  Title:Spectroscopic properties of ErF3 doped tellurite-gallium oxyfluoride glass for ∼3 μm laser materials
  
  Author(s):Wan, Rui(1,2); Wang, Pengfei(1,2); Li, Shengwu(1,2); Ma, Yuan(1,2); Zhang, Guangwei(3)
  Source: Journal of Applied Physics  Volume: 129  Issue: 15  DOI: 10.1063/5.0047010  Published: April 21, 2021  
  Abstract:ErF3-doped TeO2-Ga2O3-BaF2-AlF3-Y2O3 (TGBAY) glasses with high fluorescence efficiency and a high thermal damage threshold were developed for potential mid-infrared fiber laser applications. A model 2.7-μm fiber laser based on this material was analyzed using rate and propagation equations. Under 808 and 980 nm laser pumping, fluorescence emissions with central wavelength at 1.55 and 2.73 μm were detected. Based on the Judd-Ofelt (J-O) theory, the intensity parameters (Ωλ, λ = 2, 4, and 6) and radiative transition property were calculated and characterized through absorption and emission spectra. The results indicated that tellurite-gallium oxyfluoride glass had a high glass transition temperature (Tg, ∼391 °C), large emission cross sections at 1.55 μm (6.32 × 10−21 cm2) and 2.73 μm (9.68 × 10−21 cm2) as well as a longer fluorescence lifetime (6.84 ms at 1.55 μm and 262 μs at 2.73 μm) relative to the conventional Er3+-doped tellurite glass. The temperature dependence of the emission spectra indicated that TGBAY-2Er glass was more favorable to achieve infrared emission at low temperatures. Numerical simulation revealed the feasibility of achieving a ∼2.7 μm fiber laser operation based on the developed Er3+-doped tellurite-gallium oxyfluoride glass fiber. © 2021 Author(s).
  Accession Number: 20211710250118