2019
2019
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Record 601 of
Title:Streaking of Argon L-Shell Auger Emissions with> 250 eV Attosecond X-Ray Pulses
Author(s):Han, Seunghwoi(1); Xu, Peng(1); Wang, Yishan(2); Zhao, Kun(3); Chang, Zenghu(1)Source: 2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings Volume: Issue: DOI: 10.23919/CLEO.2019.8749227 Published: May 2019Abstract:We investigate the Argon Auger decay using isolated attosecond X-ray pulses reach the Carbon K-edge. A home-built electron spectrometer resolves and measures lifetimes of L-shell vacancies of Argon in pump-probe experiment. ?2019 The Author(s) 2019 OSA.Accession Number: 20192907216273 -
Record 602 of
Title:High-performance microwave photonic true time delays based on an integrated optical micro-comb source
Author(s):Wu, Jiayang(1); Xu, Xingyuan(1); Tan, Mengxi(1); Nguyen, Thach G.(2); Chu, Sai T.(3); Little, Brent E.(4); Morandotti, Roberto(5,6,7); Mitchell, Arnan(2); Moss, David(1)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 10921 Issue: DOI: 10.1117/12.2508146 Published: 2019Abstract:Microwave photonic true time delay lines (TTDLs), which can introduce multiple progressive time delays, are one of the basic building blocks of microwave photonic systems. Offering intrinsically low loss, ultra-wide operation bandwidth, and strong immunity to electromagnetic interference, photonic TTDLs have wide applications for phased array antennas (PAAs), microwave photonic filters, analog-to digital or digital-to-analog conversion, and arbitrary waveform generation. Here, we demonstrate significantly improved performance of a microwave photonic TTDL based on optical micro-comb generated by an integrated microring resonator with a free spectral range (FSR) of ～49 GHz, which performs as a highquality multi-wavelength source for the TTDL. The broadband (>100 nm) optical micro-comb achieved with a record low FSR of 49 GHz results in an unprecedented record high channel number (81 over the C band) the highest number of channels for an integrated comb source used for microwave photonic processing. As compared with conventional TTDLs implemented by discrete laser arrays, the system cost, size, and complexity of our TTDL can be significantly reduced. We investigate the performance of a phased array antenna based on our TTDL and show that the large channel count leads to a high angular resolution and wide tuning range of the beam steering angle. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems. ? 2019 SPIE.Accession Number: 20192106949251 -
Record 603 of
Title:First field-trial of a high capacity micro-comb based optical communications system
Author(s):Corcoran, Bill(1); Tan, Mengxi(2); Xu, Xingyuan(2); Wu, Jiayang(2); Nguyen, Thach G.(3); Chu, Sai T.(4); Little, Brent E.(5); Morandotti, Roberto(6,7,8); Boes, Andreas(3); Mitchell, Arnan(3); Moss, David J.(2)Source: IET Conference Publications Volume: 2019 Issue: CP765 DOI: null Published: 2019Abstract:We present the first demonstration of micro-comb based communications system in installed optical fibre. Robust soliton-crystal states enable open-loop control, and achieve 32.5 Tb/s (8.2 b/s/Hz spectral efficiency) over 72.8 km, providing a path to compact, high capacity transceivers for legacy fibre, metro-area systems. ? 2019 Institution of Engineering and Technology. All rights reserved.Accession Number: 20202608878456 -
Record 604 of
Title:One-dimensional gap solitons in quintic and cubic–quintic fractional nonlinear Schr?dinger equations with a periodically modulated linear potential
Author(s):Zeng, Liangwei(1,2); Zeng, Jianhua(1,2)Source: Nonlinear Dynamics Volume: 98 Issue: 2 DOI: 10.1007/s11071-019-05240-x Published: October 1, 2019Abstract:Competing nonlinearities, such as the cubic (Kerr) and quintic nonlinear terms whose strengths are of opposite signs (the coefficients in front of the nonlinearities), exist in various physical media (in particular, in optical and matter-wave media). A benign competition between self-focusing cubic and self-defocusing quintic nonlinear nonlinearities (known as cubic–quintic model) plays an important role in creating and stabilizing the self-trapping of D-dimensional localized structures, in the contexts of standard nonlinear Schr?dinger equation. We incorporate an external periodic potential (linear lattice) into this model and extend it to the space-fractional scenario that begins to surface in very recent years—the nonlinear fractional Schr?dinger equation (NLFSE), therefore obtaining the cubic–quintic or the purely quintic NLFSE, and investigate the propagation and stability properties of self-trapped modes therein. Two types of one-dimensional localized gap modes are found, including the fundamental and dipole-mode gap solitons. Employing the techniques based on the linear-stability analysis and direct numerical simulations, we get the stability regions of all the localized modes; and particularly, the anti-Vakhitov–Kolokolov criterion applies for the stable portions of soliton families generated in the frameworks of quintic-only nonlinearity and competing cubic–quintic nonlinear terms. ? 2019, Springer Nature B.V.Accession Number: 20194307576392 -
Record 605 of
Title:Improved vector-extrapolation-based Richardson–Lucy algorithm used for wavefront coded imaging
Author(s):Zhao, Hui(1); Xia, Jingjing(1,2); Zhang, Ling(1,3); Fan, Xuewu(1)Source: Applied Optics Volume: 58 Issue: 13 DOI: 10.1364/AO.58.003630 Published: May 1, 2019Abstract:The Richardson–Lucy (RL) algorithm is a well-known nonlinear restoration method and has been widely applied in the fields of astronomical image restoration, microscopic image restoration, and so on because of its capability of generating high-quality restoration results and potential in realizing super-resolution. However, when being applied to restore the wavefront coded blurry images, the classical RL algorithm converges very slowly and has to be iterated many times before obtaining a satisfactory result, which severely prohibits its real-time application. Vector-extrapolation-based RL algorithm was invented to solve this problem, but the noise amplification increases fast, and additional post-processing is needed to further improve the signal-to-noise ratio. Therefore, in this paper, an improved RL algorithm is proposed by introducing an exponential modified correction term into the framework of the original vector-extrapolation-based RL algorithm. It not only results in a bigger iteration step, which ensures a faster convergence can be obtained, but also the noise amplification is effectively prohibited. Besides that, we design a structure-similarity-index-metric-based stopping criterion, based on which the optimum number of iterations for each color channel is obtained. Experimental results reveal that the total iterations decreases approximately 78.9%, and the restored images demonstrate a superior visual quality without denoising additionally. ? 2019 Optical Society of AmericaAccession Number: 20192006930706 -
Record 606 of
Title:Spatiotemporal interest point detector exploiting appearance and motion-variation information
Author(s):Li, Yanshan(1); Li, Qingteng(1); Huang, Qinghua(2,3,4); Xia, Rongjie(1); Li, Xuelong(4)Source: Journal of Electronic Imaging Volume: 28 Issue: 3 DOI: 10.1117/1.JEI.28.3.033002 Published: May 1, 2019Abstract:As a local invariant feature of videos, the spatiotemporal interest point (STIP) has been widely used in computer vision and pattern recognition. However, existing STIP detectors are generally extended from detection algorithms constructed for local invariant features of two-dimensional images, which does not explicitly exploit the motion information inherent in the temporal domain of videos, thus weakening the performance of existing STIP detectors in a video context. To remedy this, we aim to develop an STIP detector that uniformly captures appearance and motion information for video, thus yielding substantial performance improvement. Specifically, under the framework of geometric algebra, we first develop a spatiotemporal unified model of appearance and motion-variation information (UMAMV), and then a UMAMV-based scale space of the spatiotemporal domain is proposed to synthetically analyze appearance information and motion information in a video. Based on this model, we propose an STIP feature of UMAMV-SIFT that embraces both appearance and motion variation information of the videos. Three datasets with different sizes are utilized to evaluate the proposed model and the STIP detector. We present experimental results to show that the UMAMV-SIFT achieves state-of-the-art performance and is particularly effective when dataset is small. ? 2019 SPIE and IS&T.Accession Number: 20193007218513 -
Record 607 of
Title:A novel semi-soft decision scheme for cooperative spectrum sensing in cognitive radio networks
Author(s):Mi, Yin(1,2); Lu, Guangyue(2); Li, Yuxin(2); Bao, Zhiqiang(2)Source: Sensors (Switzerland) Volume: 19 Issue: 11 DOI: 10.3390/s19112522 Published: June 1, 2019Abstract:Spectrum sensing (SS) is an essential part of cognitive radio (CR) technology, and cooperative spectrum sensing (CSS) could efficiently improve the detection performance in environments with fading and shadowing effects, solving hidden terminal problems. Hard and Soft decision detection are usually employed at the fusion center (FC) to detect the presence or absence of the primary user (PU). However, soft decision detection achieves better sensing performance than hard decision detection at the expense of the local transmission band. In this paper, we propose a tradeoff scheme between the sensing performance and band cost. The sensing strategy is designed based on three modules. Firstly, a local detection module is used to detect the PU signal by energy detection (ED) and send decision results in terms of 1-bit or 2-bit information. Secondly, and most importantly, the FC estimates the received decision data through a data reconstruction module based on the statistical distribution such that the extra thresholds are not needed. Finally, a global decision module is in charge of fusing the estimated data and making a final decision. The results from a simulation show that the detection performance of the proposed scheme outperforms that of other algorithms. Moreover, savings on the transmission band cost can be made compared with soft decision detection. ? 2019 by the authors. Licensee MDPI, Basel, Switzerland.Accession Number: 20192807180457 -
Record 608 of
Title:Generation of coexisting high-energy pulses in a mode-locked all-fiber laser with a nonlinear multimodal interference technique
Author(s):Chen, Guangwei(1,2); Li, Wenlei(1,2); Wang, Guomei(1,2); Zhang, Wenfu(1,2); Zeng, Chao(1,2); Zhao, Wei(1,2)Source: Photonics Research Volume: 7 Issue: 2 DOI: 10.1364/PRJ.7.000187 Published: February 1, 2019Abstract:We demonstrate a passively mode-locked all-fiber laser incorporating a piece of graded-index multimode fiber as a mode-locking modulator based on a nonlinear multimodal interference technique, which generates two types of coexisting high-energy ultrashort pulses [i.e., the conventional soliton (CS) and the stretched pulse (SP)]. The CS with pulse energy as high as 0.38 nJ is obtained at the pump level of 130 mW. When the pump increases to 175 mW, the high-energy SP occurs at a suitable nonlinear phase bias and its pulse energy can reach 4 nJ at a 610 mW pump. The pulse durations of the generated CS and SP are 2.3 ps and 387 fs, respectively. The theory of nonlinear fiber optics, single-shot spectral measurement by the dispersive Fourier-transform technique, and simulation methods based on the Ginzburg–Landau equation are provided to characterize the laser physics and reveal the underlying principles of the generated CS and SP. A rogue wave, observed between the CS and SP regions, mirrors the laser physics behind the dynamics of generating a high-energy SP from a CS. The proposed all-fiber laser is versatile, cost-effective and easy to integrate, which provides a promising solution for high-energy pulse generation. ? 2019 Chinese Laser Press.Accession Number: 20191506749136 -
Record 609 of
Title:Self-healing dynamically controllable micro-comb
Author(s):Bao, Hualong(1); Gongora, Juan Sebastian Totero(1); Rowley, Maxwell(1); Chu, Sai T.(2); Little, Brent E.(3); Morandotti, Roberto(4,5,6); Moss, David J.(7); Peccianti, Marco(1); Pasquazi, Alessia(1)Source: Optics InfoBase Conference Papers Volume: Part F140-CLEO_Europe 2019 Issue: DOI: null Published: 2019Abstract:Micro-resonator-based frequency combs, or micro-combs, have gained considerable interest in recent years due to their many potential applications such as high-speed communication systems, spectroscopy and ultrafast optical clocks [1]. Most micro-combs systems are based on laser pumped optical parametric oscillation and are typically non-self-starting, requiring a well-defined warm-up strategy involving smart control [2]. An alternative approach to micro-combs is represented by the Filter-Driven Four-Wave Mixing (FD-FWM) laser [3-5], based on a nonlinear micro-resonator nested in a main amplifying fibre cavity. Although this system has demonstrated self-starting regimes, stable operation typically imposes a strict relation between the minimum free-spectral range (FSR) of the main-cavity and the Q-factor of the micro-resonator. The use of longer main-cavity fibre lengths (highly desirable for several positive features, such as a larger gain) results in unrecoverable unstable regimes, i.e. in super-mode instability, which arises from the existence of many oscillating main-cavity modes within each micro-resonator resonance. ? 2019 IEEEAccession Number: 20202008660547 -
Record 610 of
Title:Unsupervised learning of human action categories in still images with deep representations
Author(s):Zheng, Yunpeng(1); Li, Xuelong(2); Lu, Xiaoqiang(3)Source: ACM Transactions on Multimedia Computing, Communications and Applications Volume: 15 Issue: 4 DOI: 10.1145/3362161 Published: December 2019Abstract:In this article, we propose a novel method for unsupervised learning of human action categories in still images. In contrast to previous methods, the proposed method explores distinctive information of actions directly from unlabeled image databases, attempting to learn discriminative deep representations in an unsupervised manner to distinguish different actions. In the proposed method, action image collections can be used without manual annotations. Specifically, (i) to deal with the problem that unsupervised discriminative deep representations are difficult to learn, the proposed method builds a training dataset with surrogate labels from the unlabeled dataset, then learns discriminative representations by alternately updating convolutional neural network (CNN) parameters and the surrogate training dataset in an iterative manner; (ii) to explore the discriminatory information among different action categories, training batches for updating the CNN parameters are built with triplet groups and the triplet loss function is introduced to update the CNN parameters; and (iii) to learn more discriminative deep representations, a Random Forest classifier is adopted to update the surrogate training dataset, and more beneficial triplet groups then can be built with the updated surrogate training dataset. Extensive experiments on four benchmark datasets demonstrate the effectiveness of the proposed method. ? 2019 Association for Computing Machinery.Accession Number: 20195207939683 -
Record 611 of
Title:Reconfigurable photonic rf filters based on integrated kerr frequency comb sources
Author(s):Xu, Xingyuan(1); Tan, Mengxi(1); Wu, Jiayang(1); Nguyen, Thach G.(2); Chu, Sai T.(3); Little, Brent E.(4); Morandotti, Roberto(5,6,7); Mitchell, Arnan(2); Moss, David J.(1)Source: 2019 IEEE International Topical Meeting on Microwave Photonics, MWP 2019 Volume: Issue: DOI: 10.1109/MWP.2019.8892063 Published: October 2019Abstract:We demonstrate two categories of photonic radio frequency (RF) filters based on integrated optical micro-combs. The first one is based on the transversal filtering structure and the second one is based on the channelization technique. The large number of wavelengths brought about by the microcomb results in a significantly increased RF spectral resolution and a large instantaneous bandwidth for the RF filters. For the RF transversal filter, we demonstrated Q factor enhancement, improved out-of-band rejection, tunable centre frequency, and reconfigurable filtering shapes. While a high resolution of 117 MHz, a large RF instantaneous bandwidth of 4.64 GHz, and programmable RF transfer functions including binary-coded notch filters and RF equalizing filters with reconfigurable slopes are demonstrated for the RF channelized filter. The microcomb-based approaches feature a potentially much smaller cost and footprint, and is promising for integrated photonic RF filters. ? 2019 IEEE.Accession Number: 20194807734934 -
Record 612 of
Title:Optimization of temporal gate by two-color chirped lasers for the generation of isolated attosecond pulse in soft X rays
Author(s):He, Liwei(1); Yuan, Guanglu(1); Wang, Kan(1); Hua, Weijie(1); Yu, Chao(1); Jin, Cheng(1,2)Source: Photonics Research Volume: 7 Issue: 12 DOI: 10.1364/PRJ.7.001407 Published: December 1, 2019Abstract:We propose a simple and efficient method to optimize two-color chirped laser pulses by forming a "temporal gate" for the generation of isolated attosecond pulses (IAPs) in soft X rays. We show that the generation process for higher and cutoff harmonics can be effectively limited within the temporal gate, and the harmonic emission interval can be further reduced with the help of phase-matching by only selecting the contribution from short-trajectory electrons. This two-color gating mechanism is verified by increasing the pulse duration, raising the gas pressure, and extending the target cutoff. Compared to the five-color waveform in Phys. Rev. Lett. 102, 063003 (2009), our waveform can be used to generate the IAP in the long-duration laser pulse while the cutoff energy is higher without the reduction of harmonic yields. Our work provides an alternative temporal gating scheme for the generation of IAPs by simultaneously improving the harmonic conversion efficiency, thus making the attosecond soft X rays an intense and highly time-resolved tabletop light source for future applications. ? 2019 Chinese Laser Press.Accession Number: 20195207903327