2019

• Record 181 of
  
  Title:Preparation and Photoluminescence Properties of Fluorophosphate Glasses with High Efficient White Light Emission
  
  Author(s):Zheng, Jia-Jin(1,2); Lu, Qiang(1); Zheng, Rui-Lin(1); Zou, Hui(1); Yu, Ke-Han(1); Wei, Wei(1)
  Source: Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis  Volume: 39  Issue: 1  DOI: 10.3964/j.issn.1000-0593(2019)01-0039-06  Published: January 1, 2019  
  Abstract:A series of Sn2+, Dy3+ and Sn2+-Dy3+ co-doped fluorophosphate glasses (FPGs) for white light emitting phosphor have been prepared by the melt quenching method. Under the UV light excitation, FPG: Sn2+ and FPG:Dy3+ can obtain blue and yellow light, respectively. The emission color of FPG:Sn2+-Dy3+ can be tuned from blue to white color by properly adjusting the concentration of Dy3+ ions under the excitation of 280 nm UV light, which can be attributed to the energy transfer from Sn2+ to Dy3+ ions. The energy transfer mechanism was investigated and analyzed according to the photoluminescence, lifetime decay and CIE chromaticity coordinate. In addition, the FPG:Sn2+fluorophosphate glass shows the highest color rendering index of 94 and the quantum efficiency of 81.3%, and the Sn2+-Dy3+ co-doped fluorophosphate glasses show better white color coordinates. By controlling the concentration of Dy3+, the FPGs can present a white light with a CIE chromaticity coordinate of (0.311, 0.330), which is very close to the equal energy point. The corresponding quantum efficiency and the luminance are 56.3% and 6 706 cd•m-2, respectively. The results of this study demonstrate that the FPGs are promising candidate for commercial white light emitting applications. © 2019, Peking University Press. All right reserved.
  Accession Number: 20191506772810
• Record 182 of
  
  Title:Single-shot spatiotemporal intensity measurement of picosecond laser pulses with compressed ultrafast photography
  
  Author(s):Cao, Fengyan(1); Yang, Chengshuai(1); Qi, Dalong(1); Yao, Jiali(1); He, Yilin(1); Wang, Xing(2); Wen, Wenlong(2); Tian, Jinshou(2); Jia, Tianqing(1); Sun, Zhenrong(1); Zhang, Shian(1,3)
  Source: Optics and Lasers in Engineering  Volume: 116  Issue:   DOI: 10.1016/j.optlaseng.2019.01.002  Published: May 2019  
  Abstract:The spatiotemporal measurement of the ultrashort laser pulses is of great significance in the diagnosis of the instrument performance and the exploration of the laser and matter interaction. In this work, we report an advanced compressed ultrafast photography (CUP) technique to measure the spatiotemporal intensity distribution of the picosecond laser pulses with a single shot. This CUP technique is based on a three-dimensional image reconstruction strategy by employing the random codes to encode the space-time-evolving laser pulse and decode it based on a compressed sensing (CS) algorithm. In our CUP system, the measurable laser wavelength depends on the spectral response of the streak camera, which can cover a wide range from ultraviolet (200 nm) to near infrared (850 nm). Based on the CUP system we develop, we successfully measure the spatiotemporal intensity evolutions of some typical laser pulses, such as the 800 nm picosecond laser pulse, the 800 and 400 nm two-color picosecond laser pulses and the supercontinuum picosecond laser pulse. These experimental results show that the CUP technique can well characterize the spatiotemporal intensity information of the picosecond laser pulses. Moreover, this technique has the remarkable advantages with the single shot measurement and without the reference laser pulse. © 2019 Elsevier Ltd
  Accession Number: 20190306372514
• Record 183 of
  
  Title:Skeleton-Based Action Recognition with Key-Segment Descriptor and Temporal Step Matrix Model
  
  Author(s):Li, Ruimin(1,2,3); Fu, Hong(3); Lo, Wai-Lun(3); Chi, Zheru(4); Song, Zongxi(1); Wen, Desheng(1)
  Source: IEEE Access  Volume: 7  Issue:   DOI: 10.1109/ACCESS.2019.2954744  Published: 2019  
  Abstract:Human action recognition based on skeleton has played a key role in various computer vision-related applications, such as smart surveillance, human-computer interaction, and medical rehabilitation. However, due to various viewing angles, diverse body sizes, and occasional noisy data, etc., this remains a challenging task. The existing deep learning-based methods require long time to train the models and may fail to provide an interpretable descriptor to code the temporal-spatial feature of the skeleton sequence. In this paper, a key-segment descriptor and a temporal step matrix model are proposed to semantically present the temporal-spatial skeleton data. First, a skeleton normalization is developed to make the skeleton sequence robust to the absolute body size and initial body orientation. Second, the normalized skeleton data is divided into skeleton segments, which are treated as the action units, combining 3D skeleton pose and the motion. Each skeleton sequence is coded as a meaningful and characteristic key segment sequence based on the key segment dictionary formed by the segments from all the training samples. Third, the temporal structure of the key segment sequence is coded into a step matrix by the proposed temporal step matrix model, and the multiscale temporal information is stored in step matrices with various steps. Experimental results on three challenging datasets demonstrate that the proposed method outperforms all the hand-crafted methods and it is comparable to recent deep learning-based methods. © 2013 IEEE.
  Accession Number: 20200308028810
• Record 184 of
  
  Title:Instance-Level Embedding Adaptation for Few-Shot Learning
  
  Author(s):Hao, Fusheng(1,2,3); Cheng, Jun(3,4); Wang, Lei(3,4); Cao, Jianzhong(1)
  Source: IEEE Access  Volume: 7  Issue:   DOI: 10.1109/ACCESS.2019.2906665  Published: 2019  
  Abstract:Few-shot learning aims to recognize novel categories from just a few labeled instances. Existing metric learning-based approaches perform classifications by nearest neighbor search in the embedding space. The embedding function is a deep neural network and usually shared by all novel categories. However, these brute approaches lack a fast adaptation mechanism like meta-learning when dealing with novel categories. To tackle this, we present a novel instance-level embedding adaptation mechanism, aiming at rapidly adapting embedding deep features to improve their generalization ability in recognizing novel categories. To this end, we design an Attention Adaptation Module to pull a query instance and its corresponding class center as close as possible. Note that, each query instance is pulled closer to its corresponding class center before performing nearest neighbor classifications. This instance-level reduction of intra-class distance increases the probability of correct classifications, and thus improves the generalization ability to embed deep features and promoting the performance. The extensive experiments are conducted on two benchmark datasets: miniImageNet and CUB. Our approach yields very promising results on both datasets. In addition, in a realistic cross-domain evaluation setting, our method also achieves the-state-of-the-art performance. © 2013 IEEE.
  Accession Number: 20205009606010
• Record 185 of
  
  Title:Forward Simulation of Limb-Viewing Michelson Wind Imaging Interferometer Based on O3 Radiation Source
  
  Author(s):He, Weiwei(1); Wu, Kuijun(2); Feng, Yutao(3); Wang, Houmao(4); Fu, Di(3); Liu, Qiuxin(1); Yan, Xiaohu(1)
  Source: Guangxue Xuebao/Acta Optica Sinica  Volume: 39  Issue: 5  DOI: 10.3788/AOS201939.0512005  Published: May 10, 2019  
  Abstract:An important method to observe stratospheric winds is to invert the Doppler frequency shift of fine spectra with a Michelson interferometer using an O3 radiation probe source in the 8.823-μm waveband. Therefore, the spectral characteristics of O3 limb radiation were analyzed to determine the best target spectral line. The target spectral line was extracted via the combined filtering of a three-level infrared Fabry-Perot etalon. The four-step interferometric images were obtained during daytime and nighttime limb-viewing with the established numerical model of the Michelson interferometer. Via an error analysis, the result was validated to ensure that, in the range of 15-45 km, the measurement errors of the wind in the line of sight are within a range of 1-2 m/s for both daytime and nighttime observations. Consequently, the stratospheric winds can be detected globally and round the clock using a Michelson interferometer with O3 radiation as the probe source. © 2019, Chinese Lasers Press. All right reserved.
  Accession Number: 20193107246206
• Record 186 of
  
  Title:High sensitivity curvature sensor based on seven core fiber
  
  Author(s):Dong, Shandong(1,2); Tan, Fengze(3); Dong, Bo(4); Yu, Changyuan(3); Guo, Yongxin(1,2)
  Source: OECC/PSC 2019 - 24th OptoElectronics and Communications Conference/International Conference Photonics in Switching and Computing 2019  Volume:   Issue:   DOI: 10.23919/PS.2019.8817707  Published: July 2019  
  Abstract:This paper presents a structure of single-mode fiber (SMF)-seven-core-fiber (SCF)-SMF, with a core-offset in one splicing point. Its maximum curvature sensitivity reaches 33.4363 nm/m-1, within the measurement range of 0.86 m-1 -1.21 m-1. © 2019 The Institute of Electronics, Information and Communication Engineers (IEICE).
  Accession Number: 20193807460811
• Record 187 of
  
  Title:Robust Subspace Clustering by Cauchy Loss Function
  
  Author(s):Li, Xuelong(1); Lu, Quanmao(2); Dong, Yongsheng(2,4); Tao, Dacheng(3)
  Source: IEEE Transactions on Neural Networks and Learning Systems  Volume: 30  Issue: 7  DOI: 10.1109/TNNLS.2018.2876327  Published: July 2019  
  Abstract:Subspace clustering is a problem of exploring the low-dimensional subspaces of high-dimensional data. State-of-the-art approaches are designed by following the model of spectral clustering-based method. These methods pay much attention to learn the representation matrix to construct a suitable similarity matrix and overlook the influence of the noise term on subspace clustering. However, the real data are always contaminated by the noise and the noise usually has a complicated statistical distribution. To alleviate this problem, in this paper, we propose a subspace clustering method based on Cauchy loss function (CLF). Particularly, it uses CLF to penalize the noise term for suppressing the large noise mixed in the real data. This is due to that the CLF's influence function has an upper bound that can alleviate the influence of a single sample, especially the sample with a large noise, on estimating the residuals. Furthermore, we theoretically prove the grouping effect of our proposed method, which means that highly correlated data can be grouped together. Finally, experimental results on five real data sets reveal that our proposed method outperforms several representative clustering methods. © 2012 IEEE.
  Accession Number: 20184606073297
• Record 188 of
  
  Title:Design and test of a flexure mount for lightweight mirror
  
  Author(s):Ren, Guo-Rui(1,2); Li, Chuang(1); Pang, Zhi-Hai(1); Chu, Chang-Bo(1); Zhang, Hao-Su(1); He, Tian-Bing(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 10837  Issue:   DOI: 10.1117/12.2504940  Published: 2019  
  Abstract:The 470mm lightweight primary mirror of a space telescope is made of ULE, and supported on a titanium hexapod. The hexapod consists of six bond pads, six titanium struts with flexures and three support parts. The hexapod provides a quasi-kinematic mount for the lightweight mirror, and the flexures are used to isolate optical elements from the mechanical and thermal deformations of the support structure, then the surface figure distortion of the mirror is minimized. In this paper, the finite element method is used to analyze the static and dynamic characteristics of the mirror assembly. Then, six pads are bonded to the mirror and the support hexapod is assembly. The vertical optical test of the primary mirror assembly is implemented. Vibration test of the mirror assembly is performed, and the test results are consistent with the results of the finite element analysis. © 2019 SPIE.
  Accession Number: 20190506432451
• Record 189 of
  
  Title:Manufacturing and testing of surface modified silicon carbide aspheric mirror
  
  Author(s):Ding, Jiao Teng(1,2); Fan, Xue Wu(1); Pang, Zhi Hai(1); Feng, Liang Jie(1); Chen, Qin Fang(1); Ma, Zhen(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 10837  Issue:   DOI: 10.1117/12.2504853  Published: 2019  
  Abstract:The manufacturing and testing of a surface modified silicon carbide mirror with a bowl-shaped structure was introduced. The entire process flow includes pre-modification silicon carbide substrate processing, silicon carbide substrate surface modification, and silicon modified layer processing. Firstly, before the modification, the conventional processing method of silicon carbide was used, and the effect of the support form on the figure was eliminated by multiple direction rotation testing.At the same time, the self-aligned compensation cross-test was completed and the accuracy of the aspherical surface coefficient was verified. In addition, the polishing process of the silicon modified layer material was studied, and the optimum process parameters suitable for polishing the silicon modified layer material were found out. Based on the above experiments, the modified optical processing adopts a combination of two kinds of polishing technology: flexible chemical mechanical polishing (FCMP)and ion beam figuring (IBF).The surface roughness and surface finish of silicon modified layer are improved by flexible chemical mechanical polishing technology. The high figure accuracy of silicon modified layer is achieved finally by ion beam figuring technology. Finally, the final result of the mirror after IBF is:the RMS values of the figure and roughness in the Φ450 mm aperture is 0.01λ (λ=632.8 nm) and 0.52 nm. The mirror's processing results fully meet the design specifications. © 2019 SPIE.
  Accession Number: 20190506432471
• Record 190 of
  
  Title:Influences of group velocity dispersion on ultrafast pulse shaping in time lens
  
  Author(s):Xie, Peng(1,2,3,4); Wen, Yu(5); Wan, Zishen(2,3); Wang, Yishan(1,4)
  Source: Physica Scripta  Volume: 94  Issue: 12  DOI: 10.1088/1402-4896/ab33d0  Published: September 5, 2019  
  Abstract:Time-lens technology is of significant interest in signal processing and optical communication. The impacts of group velocity dispersion (GVD) on ultrafast pulse shaping in a time-lens system based on four-wave mixing are explored in this paper. The output signals of temporal magnification and time-to-frequency conversion under different GVDs are theoretically investigated in detail. The simulation results imply that the femtosecond pulse is sensitive to GVD in propagation. GVD has an important effect on nonlinear parametric processes, which results in output signals presenting different pulse shapes and different frequency profiles. Furthermore, a model of silicon nitride waveguide with flat dispersion is proposed by finite element method and signal processing with negligible pulse distortion is realized in near-infrared region. © 2019 IOP Publishing Ltd.
  Accession Number: 20194507644919
• Record 191 of
  
  Title:KCCA-based radiation normalization method for hyperspectral remote sensing Images
  
  Author(s):Li, Haiwei(1); Song, Liyao(2); Yan, Qiangqiang(1); Chen, Tieqiao(1)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 11338  Issue:   DOI: 10.1117/12.2548069  Published: 2019  
  Abstract:Affected by the sensor itself, illumination, atmosphere, terrain and other factors, even if imaging the same region at the same time, the spectral characteristics of ground objects in different remote sensing images are also very different, and the surface parameters, ground object classification and target recognition results of the inversion are also different, which brings great uncertainty to quantitative analysis. The relative radiation correction effect of PIF, method is obvious and the operation is simple, and the accuracy of the effect depends greatly on the selection of the PIF point. The general relative radiometric correction methods are linearization correction without considering the nonlinear difference of multi-temporal images. At present, most radiation normalization methods assume that the transformation relation between images is linear, extract PIF points and establish radiation transformation model. In this paper, Kernel Canonical Correlation Analysis (KCCA) is used for the first time to normalize the radiation between multi-temporal hyperspectral images, which can greatly reduce the nonlinear difference in relative radiation correction. Based on the theory of nuclear canonical correlation analysis, the radiation normalization method of multi-temporal aerial hyperspectral images is proposed. The feature points of PIF are extracted in the nuclear projection space, and the nonlinear model is used for the radiation normalization of hyperspectral images, to improve the radiation normalization accuracy of multi-temporal hyperspectral images. Compared with Canonical Correlation Analysis (CCA), the number and precision of PIF point extraction can be significantly improved. This method can satisfy the radiation normalization between aerial hyperspectral multi-temporal images. © 2019 copyright SPIE. Downloading of the abstract is permitted for personal use only.
  Accession Number: 20200308056853
• Record 192 of
  
  Title:Optical design of off-axis three-mirror system with long focal length and wide field of view
  
  Author(s):Wang, Lei(1,2); Fan, Xuewu(1); Ni, Dongwei(1,2); Wang, Yuming(1,2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 10837  Issue:   DOI: 10.1117/12.2504962  Published: 2019  
  Abstract:High resolution, wild field of view (FOV) and high image quality are required in space and airborne remote sensing and space photography. However, the refraction system must use special materials or complex structures to eliminate the secondary spectrum, the two-mirror system possesses limited degrees of freedom in correcting aberrations, and the coaxial system has serious central shielding problem in the case of wild FOV. According to geometry optical theory and primary aberration theory, an off-axis three-mirror (TMA)system with long focal length and wide FOV was designed based on the coaxial three-mirror systems. The spectral range is visible light range, the focal length is 5000mm, the FOV is 10°, and the relative aperture is 1:12. The primary mirror and the third mirror are aspheric surfaces while the second mirror is quadratic surface. In this system, the central shielding problem is solved and the modulation transform function (MTF) is more than 0.6 at Nyquist spatial frequency 50lp/mm which is close to the diffraction limitation. Moreover, the full field diffusion plaque is controlled into 5μm. In all, the analysis results show that the image quality and each specification of the off-axis three-mirror system satisfy the application requirements. © 2019 SPIE.
  Accession Number: 20190506432487