2017

• Record 205 of
  
  Title:Statistical Hypothesis Detector for Abnormal Event Detection in Crowded Scenes
  
  Author(s):Yuan, Yuan(1); Feng, Yachuang(1,2); Lu, Xiaoqiang(1)
  Source: IEEE Transactions on Cybernetics  Volume: 47  Issue: 11  DOI: 10.1109/TCYB.2016.2572609  Published: November 2017  
  Abstract:Abnormal event detection is now a challenging task, especially for crowded scenes. Many existing methods learn a normal event model in the training phase, and events which cannot be well represented are treated as abnormalities. However, they fail to make use of abnormal event patterns, which are elements to comprise abnormal events. Moreover, normal patterns in testing videos may be divergent from training ones, due to the existence of abnormalities. To address these problems, in this paper, an abnormality detector is proposed to detect abnormal events based on a statistical hypothesis test. The proposed detector treats each sample as a combination of a set of event patterns. Due to the unavailability of labeled abnormalities for training, abnormal patterns are adaptively extracted from incoming unlabeled testing samples. Contributions of this paper are listed as follows: 1) we introduce the idea of a statistical hypothesis test into the framework of abnormality detection, and abnormal events are identified as ones containing abnormal event patterns while possessing high abnormality detector scores; 2) due to the complexity of video events, noise seldom follows a simple distribution. For this reason, we approximate the complex noise distribution by employing a mixture of Gaussian. This benefits the modeling of video events and improves abnormality detection accuracies; and 3) because of the existence of abnormalities, there are always some unusually occurring normal events in the testing videos, which differ from the training ones. To represent normal events precisely, an online updating strategy is proposed to cover these cases in the normal event patterns. As a result, false detections are eliminated mostly. Extensive experiments and comparisons with state-of-the-art methods verify the effectiveness of the proposed algorithm. © 2013 IEEE.
  Accession Number: 20162502526680
• Record 206 of
  
  Title:All-fiber dissipative soliton laser based on single-walled carbon nanotube absorber in normal dispersion regime
  
  Author(s):Duan, L.N.(1); Li, L.(2); Wang, Y.G.(2); Wang, X.(2)
  Source: Optik  Volume: 137  Issue:   DOI: 10.1016/j.ijleo.2017.03.028  Published: May 1, 2017  
  Abstract:We demonstrat a compact Yb-doped fiber (YDF) laser based on the single-walled carbon nanotube (SWCNT) wall-paper absorber. It can operate at dissipative solitons mode-locking state stably for more than 24 h at the room temperature, and there is no significant degradation of the laser spectra, pulse train, and output power. The spectral bandwidth of the mode-locked pulses varies from 0.35 to 0.64 nm depending on the level of the pump power. The amplified pulses possess single pulse energy of 3.87 nJ and pulse duration of 421.9 ps. The repetition rate is ∼23.83 MHz. The largest output power reaches 92.3 mW. © 2017 Elsevier GmbH
  Accession Number: 20171103448305
• Record 207 of
  
  Title:Weakly Supervised Multimodal Kernel for Categorizing Aerial Photographs
  
  Author(s):Xia, Yingjie(1); Zhang, Luming(1); Liu, Zhenguang(2); Nie, Liqiang(3); Li, Xuelong(4)
  Source: IEEE Transactions on Image Processing  Volume: 26  Issue: 8  DOI: 10.1109/TIP.2016.2639438  Published: August 2017  
  Abstract:Accurately distinguishing aerial photographs from different categories is a promising technique in computer vision. It can facilitate a series of applications, such as video surveillance and vehicle navigation. In this paper, a new image kernel is proposed for effectively recognizing aerial photographs. The key is to encode high-level semantic cues into local image patches in a weakly supervised way, and integrate multimodal visual features using a newly developed hashing algorithm. The flowchart can be elaborated as follows. Given an aerial photo, we first extract a number of graphlets to describe its topological structure. For each graphlet, we utilize color and texture to capture its appearance, and a weakly supervised algorithm to capture its semantics. Thereafter, aerial photo categorization can be naturally formulated as graphlet-to-graphlet matching. As the number of graphlets from each aerial photo is huge, to accelerate matching, we present a hashing algorithm to seamlessly fuze the multiple visual features into binary codes. Finally, an image kernel is calculated by fast matching the binary codes corresponding to each graphlet. And a multi-class SVM is learned for aerial photo categorization. We demonstrate the advantage of our proposed model by comparing it with state-of-the-art image descriptors. Moreover, an in-depth study of the descriptiveness of the hash-based graphlet is presented. © 2017 IEEE.
  Accession Number: 20172503791797
• Record 208 of
  
  Title:Development of 808 nm Quasi-Continuous Wave Laser Diode Bar with 600 W Output Power
  
  Author(s):Wang, Zhenfu(1); Li, Te(1); Yang, Guowen(1,2); Song, Yunfei(1)
  Source: Zhongguo Jiguang/Chinese Journal of Lasers  Volume: 44  Issue: 6  DOI: 10.3788/CJL201744.0601004  Published: June 10, 2017  
  Abstract:Design of 808 nm epitaxial layer structure is demonstrated, and a very low internal loss less than 0.5 cm-1 is achieved. The quasi-continuous wave (QCW) high peak power 808 nm laser bar is fabricated with this high efficiency wafer. The bar with a filled factor of 85%, emitter number of 60, emitting width of 140 μm, and cavity length of 2 mm is measured at QCW mode. The peak power is 613 W with a slope efficiency of 1.34 W/A (drive current of 500 A, pulse width of 200 μs, repetition frequency of 400 Hz, duty ratio of 8%). The peak wavelength is about 807.46 nm with a spectral half-width full-maximum of 2.88 nm. The lifetime test is also demonstrated at QCW 300 W (8% duty ratio), the lifetime of five bars is all above 3.63×109 shot, the current fluctuation is lower than 10% at the constant power of 300 W, which satisfies commercial application requirement. © 2017, Chinese Lasers Press. All right reserved.
  Accession Number: 20173003979034
• Record 209 of
  
  Title:Adaptive Multimedia Data Forwarding for Privacy Preservation in Vehicular Ad-Hoc Networks
  
  Author(s):Xia, Yingjie(1); Chen, Wenzhi(1); Liu, Xuejiao(2); Zhang, Luming(3); Li, Xuelong(4); Xiang, Yang(5)
  Source: IEEE Transactions on Intelligent Transportation Systems  Volume: 18  Issue: 10  DOI: 10.1109/TITS.2017.2653103  Published: October 2017  
  Abstract:Vehicular ad-hoc networks (VANETs) have drawn much attention of researchers. The vehicles in VANETs frequently join and leave the networks, and therefore restructure the network dynamically and automatically. Forwarded messages in vehicular ad-hoc networks are primarily multimedia data, including structured data, plain text, sound, and video, which require access control with efficient privacy preservation. Ciphertext-policy attribute-based encryption (CP-ABE) is adopted to meet the requirements. However, solutions based on traditional CP-ABE suffer from challenges of the limited computational resources on-board units equipped in the vehicles, especially for the complex policies of encryption and decryption. In this paper, we propose a CP-ABE delegation scheme, which allows road side units (RSUs) to perform most of the computation, for the purpose of improving the decryption efficiency of the vehicles. By using decision tree to jointly optimize multiple factors, such as the distance from RSU, the communication and computational cost, the CP-ABE delegation scheme is adaptively activated based on the estimation of various vehicles decryption overhead. Experimental results thoroughly demonstrate that our scheme is effective and efficient for multimedia data forwarding in vehicular ad-hoc networks with privacy preservation. © 2017 IEEE.
  Accession Number: 20170603336429
• Record 210 of
  
  Title:Thermal characteristics of compact conduction-cooled high power diode laser array packages
  
  Author(s):Zhang, Pu(1); Liu, Xingsheng(1,2); Zhu, Qiwen(1); Wang, Jingwei(2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 10085  Issue:   DOI: 10.1117/12.2250258  Published: 2017  
  Abstract:Thermal management is one of the most important factors affecting the performance of high power diode lasers. In this paper, transient thermal behavior of conduction-cooled high power diode lasers has been studied using finite element method. The effects of heat sink geometry, ceramics size on the junction temperature of high power diode laser packages have been analyzed. Based on the simulations, heat dissipation capability of high power diode laser packages is improved and compact conduction-cooled diode laser array packages with 3 bars and 5 bars are fabricated. The power ∼ current and spectrum of the optimized high power diode laser array packages at different operation parameters are characterized at different pulse widths, repetition frequencies and TEC temperatures. The effects of temperature on the output power and spectrum are discussed. The lifetime test of high power diode laser array packages is also performed. It shows that the conduction-cooled high power diode laser array packages have good optical performance. © 2017 SPIE.
  Accession Number: 20172103685887
• Record 211 of
  
  Title:Wavelength-switchable passively mode-locked fiber laser with mechanically exfoliated molybdenum ditelluride on side-polished fiber
  
  Author(s):Wang, Guomei(1)
  Source: Optics and Laser Technology  Volume: 96  Issue:   DOI: 10.1016/j.optlastec.2017.05.030  Published: November 1, 2017  
  Abstract:We experimentally investigated the nonlinear saturable absorption characteristics of molybdenum ditelluride (MoTe2) and demonstrated a wavelength-switchable mode-locked erbium-doped fiber laser (EDFL) by using MoTe2 thin film on side-polished fiber (SPF) as saturable absorber. Here, the MoTe2 thin film was efficiently fabricated via mechanical exfoliation method and transferred onto the SPF with the assistance of polydimethylsiloxane (PDMS). MoTe2-covered SPF (MSPF) exhibits the nonlinear saturable absorption for pulses with different polarization states. Optical solitons with spectral bandwidth of 1.06 (1.31) nm centered at ∼1559 (∼1528) nm and pulse duration of 2.46 (2.04) ps can be obtained from the EDFL by adjusting the polarization controller (PC) properly. The time-bandwidth product (TBP) of the pulses was calculated as 0.322 (0.344). © 2017 Elsevier Ltd
  Accession Number: 20172303738779
• Record 212 of
  
  Title:A Single-Longitudinal-Mode Passively Q-Switched Nd:YVO4 Laser Using Black Phosphorus Saturable Absorber
  
  Author(s):Sun, Zhe(1); Cheng, Guang-Hua(1); Liu, Huan(1); Wang, Xi(1); Wang, Yong-Gang(1)
  Source: Chinese Physics Letters  Volume: 34  Issue: 1  DOI: 10.1088/0256-307X/34/1/014204  Published: January 2017  
  Abstract:A black phosphorus (BP) saturable absorber (SA) solution with different concentrations (1.0 and 0.5 mg/ml) is fabricated with the liquid-phase exfoliation method. By using the BP-SA, a compact diode-pumped passively Q-switched Nd:YVO4 laser is demonstrated. One reflecting Bragg gratings is used as the output coupler for mode selection. By inserting those BP-SA solutions in the laser cavity, the maximum single longitude mode, Q-switched output powers of 126mW at 692.5 kHz and 149mW at 630.3 kHz are achieved at the pump power of 8.0 W, corresponding to the pulse durations of 144 ns and 196 ns, respectively. Moreover, longitudinal-mode characteristics of Q-switched output laser in different optical cavity lengths based on two-kind BP-SA solution concentrations are investigated. Our results show that BP-SA could also be developed as an effective SA for the -switched, single longitudinal mode pulse laser. © 2017 Chinese Physical Society and IOP Publishing Ltd.
  Accession Number: 20220711660778
• Record 213 of
  
  Title:High power, high efficiency continuous-wave 808 nm laser diode arrays
  
  Author(s):Wang, Zhenfu(1); Li, Te(1); Yang, Guowen(1); Song, Yunfei(1)
  Source: Optics and Laser Technology  Volume: 97  Issue:   DOI: 10.1016/j.optlastec.2017.07.015  Published: December 1, 2017  
  Abstract:The continuous-wave 100 W-class 808 nm laser diode arrays with extremely high power conversion efficiency of 68% were reported at the heatsink temperature of 25 °C. To the best of our knowledge, this was the highest power conversion efficiency at continuous-wave 106 W 808 nm laser diode array with 50% fill factor so far. An asymmetric broad waveguide epitaxial structure with very low internal optical loss of 0.5 cm−1 was presented. In order to improve the efficiency, various fill factor devices were studied. The 50 W laser diode array with 30% fill factoir and 1.0 mm cavity length demonstrated power conversion efficiency of 71% at heatsink temperature of 15 °C. © 2017
  Accession Number: 20173003984796
• Record 214 of
  
  Title:Experimental investigation of high power pulsed 2.8 μm Er3+-doped ZBLAN fiber lasers
  
  Author(s):Shen, Yanlong(1,2,3,4); Wang, Yishan(1,5); Huang, Ke(3); Luan, Kunpeng(3); Chen, Hongwei(3); Tao, Mengmeng(3); Yu, Li(3); Yi, Aiping(3); Si, Jinhai(2)
  Source: Proceedings of SPIE - The International Society for Optical Engineering  Volume: 10173  Issue:   DOI: 10.1117/12.2267824  Published: 2017  
  Abstract:We report on the recent progress on high power pulsed 2.8 μm Er3+-doped ZBLAN fiber laser through techniques of passively and actively Q-switching in our research group. In passively Q-switched operation, a diode-cladding-pumped mid-infrared passively Q-switched Er3+-doped ZBLAN fiber laser with an average output power of watt-level based on a semiconductor saturable absorber mirror (SESAM) was demonstrated. Stable pulse train was produced at a slope efficient of 17.8% with respect to launched pump power. The maximum average power of 1.01 W at a repetition rate of 146.3 kHz was achieved with a corresponding pulse energy of 6.9 μJ. The maximum peak power was calculated to be 21.9 W. In actively Q-switched operation, a diode-pumped actively Q-switched Er3+-doped ZBLAN fiber laser at 2.8 μm with an optical chopper was reported. The maximum laser pulse energy of up to 130 μJ and a pulse width of 127.3 ns at a repetition rate of 10 kHz with an operating wavelength of 2.78 μm was obtained, yielding the maximum peak power of exceeding 1.1 kW. © 2017 SPIE.
  Accession Number: 20174904498553
• Record 215 of
  
  Title:Spatiotemporal evolution of continuous-wave field and dark soliton formation in a microcavity with normal dispersion
  
  Author(s):Hu, Xiaohong(1,2,3); Zhang, Wei(1); Liu, Yuanshan(1); Feng, Ye(1); Zhang, Wenfu(1); Wang, Leiran(1); Wang, Yishan(1,3); Zhao, Wei(1,3)
  Source: Chinese Physics B  Volume: 26  Issue: 7  DOI: 10.1088/1674-1056/26/7/074216  Published: June 2017  
  Abstract:Stable dark soliton and dark pulse formation in normally dispersive and red-detuned microcavities are investigated by numerically solving the normalized Lugiato-Lefever equation. The soliton essence is proved by fitting the calculated field intensity profile with the analytical formula of a dark soliton. Meanwhile, we find that a dark soliton can be generated either from the nonlinear evolution of an optical shock wave or narrowing of a locally broad dark pulse with smoother fronts. Explicit analytical expression is obtained to describe the oscillatory fronts of the optical shock wave. Furthermore, from the calculation results, we show that for smaller frequency detunings, e.g., a © 2017 Chinese Physical Society and IOP Publishing Ltd.
  Accession Number: 20172803927144
• Record 216 of
  
  Title:Hundred micro-joules level high power chirped pulse amplification of femtosecond laser based on single crystal fiber
  
  Author(s):Li, Feng(1,2,3); Yang, Zhi(1); Lv, Zhiguo(1); Hu, Xiaohong(1); Wei, Yufeng(1); Li, Qianglong(1); Tang, Shukuai(1,2); Wang, Yishan(1,3); Yang, Xiaojun(1); Zhao, Wei(1,3)
  Source: IEEE Photonics Journal  Volume: 9  Issue: 6  DOI: 10.1109/JPHOT.2017.2780197  Published: December 2017  
  Abstract:We demonstrate a hundred micro-Joules level femtosecond laser system based on a compact and simple two-stage Yb:YAG single crystal fiber chirped pulse amplification system which delivers compressed power of 15.57 W, pulse width of 715 fs. The different amplification performance with different input seed power is experimentally studied. A maximum direct amplified power output of 44 W at 100 kHz is obtained for an input seed power of 12 W. To the best of our knowledge, this is the highest average power of femtosecond laser based on single crystal fiber at hundred micro-Joules energy level. © 2017 IEEE.
  Accession Number: 20175004537183