2020
2020
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Record 133 of
Title:Ultrafast formation of transient 2D diamond-like structure in twisted bilayer graphene
Author(s):Luo, Duan(1,2,3); Hui, Dandan(2,3); Wen, Bin(4); Li, Renkai(5); Yang, Jie(5); Shen, Xiaozhe(5); Reid, Alexander Hume(5); Weathersby, Stephen(5); Kozina, Michael E.(5); Park, Suji(5); Ren, Yang(6); Loeffler, Troy D.(1); Sankaranarayanan, S.K.R.S.(1); Chan, Maria K.Y.(1); Wang, Xing(2); Tian, Jinshou(2,7); Arslan, Ilke(1); Wang, Xijie(5); Rajh, Tijana(1); Wen, Jianguo(1)Source: arXiv Volume: Issue: DOI: null Published: March 18, 2020Abstract:Due to the absence of matching carbon atoms at honeycomb centers with carbon atoms in adjacent graphene sheets, theorists predicted that a sliding process is needed to form AA, AB', or ABC stacking when directly converting graphite into sp3 bonded diamond. Here, using twisted bilayer graphene (TBG), which naturally provides AA and AB' stacking configurations, we report the ultrafast formation of a transient 2D diamond-like structure (which is not observed in aligned graphene) under femtosecond laser irradiation. This photoinduced phase transition (PIPT) is evidenced by the appearance of new bond lengths of 1.94 ? and 3.14 ? in the time-dependent differential pair distribution function (ΔPDF) using MeV ultrafast electron diffraction (UED). Molecular dynamics and first principles calculation indicate that sp3 bonds nucleate at AA and AB' stacked areas in moiré pattern. This work sheds light on the direct graphite-to-diamond transformation mechanism, which has not been fully understood for more than 60 years. Copyright ? 2020, The Authors. All rights reserved.Accession Number: 20200395061 -
Record 134 of
Title:Enhanced four-wave-mixing with 2D layered graphene oxide films integrated with CMOS compatible micro-ring resonators
Author(s):Wu, Jiayang(1); Yang, Yunyi(1,2); Qu, Yang(1); Jia, Linnan(1); Zhang, Yuning(1); Xu, Xingyuan(1); Chu, Sai T.(3); Little, Brent E.(4); Morandotti, Roberto(5,6); Jia, Baohua(1,2); Moss, David J.(1)Source: arXiv Volume: Issue: DOI: null Published: February 10, 2020Abstract:Layered two-dimensional (2D) graphene oxide (GO) films are integrated with micro-ring resonators (MRRs) to experimentally demonstrate enhanced nonlinear optics in the form of four-wave mixing (FWM). Both uniformly coated and patterned GO films are integrated on CMOS-compatible doped silica MRRs using a large-area, transfer-free, layer-by-layer GO coating method together with photolithography and lift-off processes, yielding precise control of the film thickness, placement, and coating length. The high Kerr nonlinearity and low loss of the GO films combined with the strong light-matter interaction within the MRRs results in a significant improvement in the FWM efficiency in the hybrid MRRs. Detailed FWM measurements are performed at different pump powers and resonant wavelengths for the uniformly coated MRRs with 1-5 layers of GO as well as the patterned devices with 10-50 layers of GO. The experimental results show good agreement with theory, achieving up to ～7.6-dB enhancement in the FWM conversion efficiency (CE) for an MRR uniformly coated with 1 layer of GO and ～10.3-dB for a patterned device with 50 layers of GO. By fitting the measured CE as a function of pump power for devices with different numbers of GO layers, we also extract the dependence of GO's third-order nonlinearity on layer number and pump power, revealing interesting physical insights about the evolution of the layered GO films from 2D monolayers to quasi bulk-like behavior. These results confirm the high nonlinear optical performance of integrated photonic resonators incorporated with 2D layered GO films. Copyright ? 2020, The Authors. All rights reserved.Accession Number: 20200450315 -
Record 135 of
Title:Ultrafast formation of a transient two-dimensional diamondlike structure in twisted bilayer graphene
Author(s):Luo, Duan(1,2,3); Hui, Dandan(2,3); Wen, Bin(4); Li, Renkai(5); Yang, Jie(5); Shen, Xiaozhe(5); Reid, Alexander Hume(5); Weathersby, Stephen(5); Kozina, Michael E.(5); Park, Suji(5); Ren, Yang(6); Loeffler, Troy D.(1); Sankaranarayanan, S.K.R.S.(1); Chan, Maria K. Y.(1); Wang, Xing(2); Tian, Jinshou(2,7); Arslan, Ilke(1); Wang, Xijie(5); Rajh, Tijana(1); Wen, Jianguo(1)Source: Physical Review B Volume: 102 Issue: 15 DOI: 10.1103/PhysRevB.102.155431 Published: October 29, 2020Abstract:Due to the absence of matching carbon atoms at honeycomb centers with carbon atoms in adjacent graphene sheets, theorists predicted that a sliding process is needed to form AA, AB′, or ABC stacking when directly converting graphite into sp3 bonded diamond. Here, using twisted bilayer graphene, which naturally provides AA and AB′ stacking configurations, we report the ultrafast formation of a transient two-dimensional diamondlike structure (which is not observed in aligned graphene) under femtosecond laser irradiation. This photoinduced phase transition is evidenced by the appearance of bond lengths of 1.94 and 3.14 ? in the time-dependent differential pair distribution function using MeV ultrafast electron diffraction. Molecular dynamics and first-principles calculation indicate that sp3 bonds nucleate at AA and AB′ stacked areas in a moiré pattern. This work sheds light on the direct graphite-to-diamond transformation mechanism, which has not been fully understood for more than 60 years. ? 2020 American Physical Society.Accession Number: 20204509469344 -
Record 136 of
Title:Photonic radio frequency arbitrary waveform generator based on an integrated 49GHz FSR kerr micro-comb source
Author(s):Moss, David J.(1); Tan, Mengxi(1); Xu, Xingyuan(1,2); Boes, Andreas(3); Corcoran, Bill(4); Wu, Jiayang(1); Nguyen, Thach G.(3); Chu, Sai T.(5); Little, Brent E.(6); Morandotti, Roberto(7,8); Mitchell, Arnan(3)Source: TechRxiv Volume: Issue: DOI: 10.36227/techrxiv.12276623 Published: May 9, 2020Abstract:We report a photonic-based radio frequency (RF) arbitrary waveform generator (AWG) using a soliton crystal micro-comb source with a free spectral range (FSR) of 48.9 GHz. We successfully achieve arbitrary shapes including square waveforms with a tunable duty ratio ranging from 10% to 90%, sawtooth waveforms with a tunable slope ratio of 0.2 to 1, and a symmetric concave quadratic chirp waveform with an instantaneous frequency of sub GHz. We achieve good agreement between theory and experiment, validating the effectiveness of this approach towards realizing high-performance, broad bandwidth, nearly user-defined RF waveform generation. ? 2020, CC BY.Accession Number: 20220138550 -
Record 137 of
Title:Visual Tracking Via Temporally-Regularized Context-Aware Correlation Filters
Author(s):Liao, Jiawen(1); Qi, Chun(2); Cao, Jianzhong(1); Bian, He(1)Source: Proceedings - International Conference on Image Processing, ICIP Volume: 2020-October Issue: DOI: 10.1109/ICIP40778.2020.9191027 Published: October 2020Abstract:Classical discriminative correlation filter (DCF) model suffers from boundary effects, several modified discriminative correlation filter models have been proposed to mitigate this drawback using enlarged search region, and remarkable performance improvement has been reported by related papers. However, model deterioration is still not well addressed when facing occlusion and other challenging scenarios. In this work, we propose a novel Temporally-regularized Context-aware Correlation Filters (TCCF) model to model the target appearance more robustly. We take advantage of the enlarged search region to obtain more negative samples to make the filter sufficiently trained, and a temporal regularizer, which restricting variation in filter models between frames, is seamlessly integrated into the original formulation. Our model is derived from the new discriminative learning loss formulation, a closed form solution for multidimensional features is provided, which is solved efficiently using Alternating Direction Method of Multipliers (ADMM). Extensive experiments on standard OTB-2015, TempleColor-128 and VOT-2016 benchmarks show that the proposed approach performs favorably against many state-of-the-art methods with real-time performance of 28fps on single CPU. ? 2020 IEEE.Accession Number: 20210109724500 -
Record 138 of
Title:Long-distance underwater optical wireless communication with PPLN wavelength conversion
Author(s):Yang, Yi(1); Fan, Lirong(1); He, Fengtao(1); Song, Yuqin(1); Duan, Zuoliang(1); Zhu, Yunzhou(2); Li, Bili(2)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11717 Issue: DOI: 10.1117/12.2587316 Published: 2020Abstract:In this thesis, we designed and experimentally demonstrated a high-power high-speed underwater optical wireless communication (UOWC) system with wavelength conversion construction. External modulation based on 1064nm laser is used for high-speed information communication, as well as the optical amplifier is used to obtain enough optical power of 1064nm laser. After that, according to the quasi-phase-matching (QPM) conditions, the PPLN optical structure is designed to improve the wavelength conversion efficiency for achieving higher 532nm laser output power in 24.5a., ~40°C. Compared to the 532nm LD modulation system, this system can output 1.4W 532nm laser power in 100Mbps. This system experiments in single link 100m water tap of the attenuation coefficient 0.73dB/m equivalent to the clear ocean, and the measured bit error rate (BER) is 6.2×10-6 in 100Mbps pseudo-random binary sequence (PRBS) data without the forward error correction (FEC). Based on receiver sensitivity and the seawater channel optical transmission model, the transmission performance was predicted to be 340m@100Mbps and 100m@2Gbps in the attenuation coefficient equivalent to pure seawater. ? 2020 SPIE.Accession Number: 20210109714362 -
Record 139 of
Title:Designing time and frequency entanglement for generation of high-dimensional photon cluster states
Author(s):Roztocki, Piotr(1); Chemnitz, Mario(1); Maclellan, Benjamin(1); Sciara, Stefania(1,2); Reimer, Christian(1,3); Islam, Mehedi(1); Cortes, Luis Romero(1); Zhang, Yanbing(1); Fisher, Bennet(1); Loranger, Sebastien(5); Kashyap, Raman(5,6); Cino, Alfonso(2); Chu, Sai T.(7); Little, Brent E.(8); Moss, David J.(9); Caspani, Lucia(10); Munro, William J.(11,12); Azana, Jose(1); Kues, Michael(1,4); Morandotti, Roberto(1,13)Source: International Conference on Transparent Optical Networks Volume: 2020-July Issue: DOI: 10.1109/ICTON51198.2020.9203265 Published: July 2020Abstract:The development of quantum technologies for quantum information science demands the realization and precise control of complex (multipartite and high dimensional) entangled systems on practical and scalable platforms. Quantum frequency combs (QFCs) generated via spontaneous four-wave mixing in integrated microring resonators represent a powerful tool towards this goal. They enable the generation of complex photon states within a single spatial mode as well as their manipulation using standard fiber-based telecommunication components. Here, we review recent progress in the development of QFCs, with a focus on our results that highlight their importance for the realization of complex quantum states. In particular, we outline our work on the use of integrated QFCs for the generation of high-dimensional multipartite optical cluster states and their unidirectional processing, being at the core of measurement-based quantum computation. These results confirm that engineering the time-frequency entanglement properties of QFC may provide a stable, practical, low-cost, and established platform for the development of near-future quantum devices for out-of-the-lab applications, ranging from practical quantum computing to more secure communications. ? 2020 IEEE.Accession Number: 20204209357447 -
Record 140 of
Title:Remote Sensing Image Color Correction Method Based on Automatic Piecewise Polynomial Method
Author(s):Chu, Nan-Qing(1); Li, Xu-Yang(1); Yi, Hong-Wei(1); Ren, Zhi-Guang(1); Ma, Zi-Xuan(1)Source: 2020 5th Optoelectronics Global Conference, OGC 2020 Volume: Issue: DOI: 10.1109/OGC50007.2020.9260437 Published: September 7, 2020Abstract:In the process of remote sensing image restoration, color correction is very important. The polynomial algorithmcolor correction method based on standard color card is the most commonly used method. However, the traditional polynomial fitting method needs to determine the most appropriate combination of polynomials, and only one polynomial function fitting method is used. So it is difficult to guarantee high accuracy and good generalization performance at the same time. In order to solve the above problems effectively, this paper proposes an automatic piecewise polynomial fitting method. This study established the mapping between collected RGB value and standard RGB value through the calibration of the X-rite Color Checker, and represented the color difference by computing ?E in CIELab color space. This improved algorithm adopts the idea of segmentation to select the most suitable function in different intervals, and the interval of segmentation is automatically determined by the chromatic aberration standard. The experimental results show that this algorithm has high correction accuracy and this algorithm is more adaptable to photos under different lighting conditions. ? 2020 IEEE.Accession Number: 20210109723777 -
Record 141 of
Title:Design of near Infrared Continuous Zoom Optical System
Author(s):Ma, Zi-Xuan(1); Li, Xu-Yang(1); Ren, Zhi-Guang(1); Chu, Nan-Qing(1)Source: 2020 5th Optoelectronics Global Conference, OGC 2020 Volume: Issue: DOI: 10.1109/OGC50007.2020.9260417 Published: September 7, 2020Abstract:In order to achieve continuous fine recognition of targets with limited distance, a large zoom ratio near infrared continuous zoom optical system has been designed. Based on the zoom system and its automatic design principle of aberrations, reasonable technical indicators were formulated, the initial structure of the system was determined, and the optical design software CodeV was used to optimize it to achieve a continuous zoom optical system with good imaging quality. The system uses a detector of 4.5-micron × 4.5-micron pixels, and the field of view is 2.7-degree × 2.7-degree ~ 12.7-degree × 12.7-degree, F number is 4.8, using mechanical positive group compensation method, composed of front group, zoom group, compensation group and rear group, including 14 spherical lenses. The design results were evaluated for image quality and the cam curve was solved. The design and analysis results show that the system achieves a continuous zoom of 70-mm350-mm in the 750-nano ~ 900-nano band. The optical modulation transfer function of the system is better than 0.3 at Ill-lp/mm, the maximum distortion is less than 2%, the image quality is good, and the processing cost is low. The system has the characteristics of large zoom ratio, high resolution, compact structure and smooth zoom curve, and can be used for fine recognition of limited distance targets. ? 2020 IEEE.Accession Number: 20210109723758 -
Record 142 of
Title:A Denoising Method of Remote Sensing Images Based on Improved BM3D
Author(s):Chen, Junyu(1); Li, Haiwei(2); Chen, Tieqiao(2); Hu, Bingliang(2); Zhang, Geng(2); Wang, Shuang(2); Liu, Song(2)Source: ACM International Conference Proceeding Series Volume: Issue: DOI: 10.1145/3424978.3425125 Published: October 20, 2020Abstract:Denoising of remote sensing images is always one of the hotspots in the field of digital image processing. The quality of denoising determines the precision of subsequent processing directly. The BM3D algorithm takes the high similarity of image neighborhoods into consideration, which shows good stability and accuracy in the field of image denoising. However, in the case of strong noise, BM3D can't match the image-block precisely, which reduces the denoising effect for the remote sensing image. Therefore, in order to solve the problem of BM3D algorithm during the remote sensing image processing, we propose a local block-matching algorithm based on edge search strategy and residual filtering, according to the high similarity at the edge of the remote sensing image. We compare the proposed algorithm with the classic denoising method, and the experimental results show that the proposed algorithm not only protects the information of edge and detail, but also improves the value of PSNR. A better denoising effect was obtained on remote sensing images. ? 2020 ACM.Accession Number: 20204509451722 -
Record 143 of
Title:Detection method and evaluation of zoom CAM curve based on linear displacement
Author(s):Zhao, Yue(1); Kang, Shifa(1); Qin, Xing(1)Source: Proceedings of SPIE - The International Society for Optical Engineering Volume: 11617 Issue: DOI: 10.1117/12.2585040 Published: 2020Abstract:Zoom CAM curve is an important part of the optical system imaging. The processing accuracy of the curve directly affects the image clarity and consistency of the optical system. In this paper, a high precision measuring device for zoom CAM curve is designed, and an optimization method of testing results is adopted. According to the curve of the CAM rotation Angle and the number of teeth on the surface of the cylindrical, with mesh number as the sample size, relative to the CAM follower parts through the grating ruler curve of linear displacement measurement and corresponding data fitting. The regression analysis method is adopted to analyze the measurement results of the grating ruler based on the detection of the altimeter, and the regression equation is obtained and modified to optimize the measurement fitting data, so as to finally improve the detection accuracy of the zoom CAM curve. The confidence interval of machining accuracy based on grating ruler CAM curve is analyzed and evaluated by an example. The results show that the zoom CAM curve detection device and result optimization method proposed in this paper have the characteristics of high accuracy, high stability and easy realization. ? 2020 COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.Accession Number: 20210109718870 -
Record 144 of
Title:Optical design and fabrication of an all-aluminum unobscured two-mirror freeform imaging telescope
Author(s):Xie, Yongjun(1); Mao, Xianglong(1); Li, Jinpeng(1); Wang, Fengbiao(1); Wang, Peng(1); Gao, Rong(1); Li, Xing(1); Ren, Shangjie(1); Xu, Zhichen(1); Dong, Rongguang(1)Source: Applied Optics Volume: 59 Issue: 3 DOI: 10.1364/AO.379324 Published: January 20, 2020Abstract:Freeform optics offers more degrees of freedom to optical design that can benefit from a compact package size and a large field of view for imaging systems. Motivated by the advances in modern optical fabrication and metrology, freeform optics has been found in many applications. In this paper, we will describe the challenging optical design, fabrication, metrology, and assembly of an all-aluminum unobscured two-mirror freeform imaging telescope. The telescope has a large field of view of 20? × 15?. The freeform aluminum mirrors are manufactured by diamond turning based on a feedback modification strategy. The freeform mirrors are measured by a computer-generated hologram-based interferometric null test method. All-aluminum configuration has the advantages of being athermal and cost-effective. ? 2020 Optical Society of AmericaAccession Number: 20200408065611