- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Tilted-pulse-front space-time wave packets
摘要： Tilted-pulse-front pulses, which are produced via dispersive devices that introduce angular dispersion, are useful in many areas of nonlinear optics. Such pulses typically have large transverse cross sections and propagate for limited distances to offset the impact of diffractive space-time coupling that leads to spectral walk-off. Here we show that sculpting the spatio-temporal spectral profile of a pulsed plane wave enables the synthesis of propagation-invariant wave packets endowed with a tilted intensity pulse front with respect to the propagation axis. These wave packets are based on new elementary propagation-invariant wave-packet solutions to the wave equation obtained by a complexification of the space and time degrees of freedom.
关键词： Propagation-invariant pulses,Tilted-front-pulses,Diffraction-free,Space-time wave packets
更新于2025-09-19 17:15:36
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[IEEE 2019 International Electronics Symposium (IES) - Surabaya, Indonesia (2019.9.27-2019.9.28)] 2019 International Electronics Symposium (IES) - Identification and Protection of Series DC Arc Fault for Photovoltaic Systems Based on Fast Fourier Transform
摘要： This letter develops a distributed algorithm for relay pairing in bandwidth exchange (BE) based cooperative forwarding scenarios, where each node can delegate a fraction of its allocated resources to a neighboring node as an incentive for relaying. Determining the relay pairs that maximize the overall network utility yields a non-bipartite matching problem, which incurs a considerable computational load when implemented in a centralized way. To resolve this challenge, we use a message-passing framework to develop an efficient distributed solution. Simulation results verify that the proposed algorithm outperforms existing approaches.
关键词： bandwidth exchange,message passing algorithm,Affinity propagation,cooperative forwarding
更新于2025-09-19 17:13:59
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Spin excitations in laser-molecular-beam epitaxy grown nanosized YIG films: towards low relaxation and desirable magnetization profile
摘要： We describe synthesis of nanosized Y3Fe5O12 (YIG) films grown by laser-molecular-beam epitaxy on Gd3Ga5O12 (GGG) and Nd3Ga5O12 (NdGG) substrates with (111) orientation and present results of ferromagnetic resonance (FMR) and spin wave propagation studies in these heterostructures. It is found that magnetic parameters of YIG films grown on NdGG and GGG substrates are considerably different. FMR spectra of YIG/NdGG structures are characterized by a large number of narrow peaks, while FMR spectra of YIG/GGG structures consist of a small number of peaks or one peak. The effective magnetization of YIG films grown on NdGG substrates is less than that of YIG films grown on GGG and is more sensitive to the growth conditions. A lateral inhomogeneity of YIG/NdGG structures is observed in spin wave propagation experiments. For YIG/NdGG and YIG/GGG structures the FMR linewidth ?H of a single peak sharply increases with temperature decrease from 298 to 67 K. The observed increase of ?H is explained by typical relaxation processes caused by the presence of Fe2+ ions. From the spin-wave propagation study it is also found that relaxation of spin-waves explains only a minor part of the FMR single peak linewidth in YIG/NdGG structures. On the basis of obtained results, YIG/GGG/semiconductor- and YIG/NdGG/semiconductor-heterostructures with expected low spin-wave relaxation and desirable effective magnetization profile are proposed.
关键词： magnetization profile,ferromagnetic resonance,spin wave propagation,laser-molecular-beam epitaxy,YIG films
更新于2025-09-19 17:13:59
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Nose-Cone Conformal Substrate-Integrated Waveguide Slot Array Antenna for X-Band Radar Applications
摘要： This paper presents the design of nose-cone conformal substrate-integrated waveguide (SIW) slot array antenna for modern radar applications. Firstly, the wave propagation characteristics have been investigated in doubly curved SIW, and it has been observed that they are non-uniform along the longitudinal direction of nose-cone conformal SIW. To ensure the constant wave propagation along the length of conformal SIW, the conventional design of SIW is reformulated for nose-cone conformal SIW and circuit model modification has been demonstrated. Secondly, the procedure for designing a SIW-based array on curved surfaces has been developed. In the proposed design, rectangular waveguide (RWG) to SIW feeding structure has been used to avoid spurious radiations. Finally, 1 × 6 element-based nose-cone conformal slotted array has been designed and compared with planar and cylindrical conformal arrays. It has been observed from the results that the nose-cone conformal slot array offers low sidelobe levels (SLLs) and high gain. For the validation of the proposed design, the conformal slotted array has been fabricated and measured, which exhibited a reasonable agreement between the measured and the simulated data.
关键词： substrate-integrated waveguide,high gain,X-band radar,nose-cone conformal,wave propagation,sidelobe levels,slot array antenna
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Ultrafast Light Source at 1.8 ??m Based on Thulium-Doped Fibers for Three-Photon Microscopy
摘要： Optical tomographic imaging requires an accurate forward model as well as regularization to mitigate missing-data artifacts and to suppress noise. Nonlinear forward models can provide more accurate interpretation of the measured data than their linear counterparts, but they generally result in computationally prohibitive reconstruction algorithms. Although sparsity-driven regularizers significantly improve the quality of reconstructed image, they further increase the computational burden of imaging. In this paper, we present a novel iterative imaging method for optical tomography that combines a nonlinear forward model based on the beam propagation method (BPM) with an edge-preserving three-dimensional (3-D) total variation (TV) regularizer. The central element of our approach is a time-reversal scheme, which allows for an efficient computation of the derivative of the transmitted wave-field with respect to the distribution of the refractive index. This time-reversal scheme together with our stochastic proximal-gradient algorithm makes it possible to optimize under a nonlinear forward model in a computationally tractable way, thus enabling a high-quality imaging of the refractive index throughout the object. We demonstrate the effectiveness of our method through several experiments on simulated and experimentally measured data.
关键词： Optical phase tomography,beam propagation method,compressive sensing,total variation regularization,stochastic proximal-gradient,sparse reconstruction
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Solar Forecasting for Low Voltage Network Operations: Selected Case Studies in Australia
摘要： We introduce a distributed cooperative framework and method for Bayesian estimation and control in decentralized agent networks. Our framework combines joint estimation of time-varying global and local states with information-seeking control optimizing the behavior of the agents. It is suited to nonlinear and non-Gaussian problems and, in particular, to location-aware networks. For cooperative estimation, a combination of belief propagation message passing and consensus is used. For cooperative control, the negative posterior joint entropy of all states is maximized via a gradient ascent. The estimation layer provides the control layer with probabilistic information in the form of sample representations of probability distributions. Simulation results demonstrate intelligent behavior of the agents and excellent estimation performance for a simultaneous self-localization and target tracking problem. In a cooperative localization scenario with only one anchor, mobile agents can localize themselves after a short time with an accuracy that is higher than the accuracy of the performed distance measurements.
关键词： consensus,Agent networks,distributed estimation,belief propagation,information-seeking control,sensor networks,distributed target tracking,sequential estimation,cooperative localization,distributed control,message passing
更新于2025-09-19 17:13:59
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Nonlinear Optics - Novel Results in Theory and Applications || Polarization Properties of the Solitons Generated in the Process of Pulse Breakup in Twisted Fiber Pumped by ns Pulses
摘要： Common optical fibers are randomly birefringent, and solitons formatting and traveling in them are randomly polarized. However, it is desirable to have solitons with a well-defined polarization. With pump relatively long pulses, the nonlinear effects of modulation instability (MI) and stimulated Raman scattering (SRS) are dominant at the initial stage of the process of supercontinuum (SC) generation; modulation instability results in pulse breakup and formation of short pulses that evolve finally to a bunch of solitons and dispersive waves. We do the research of the polarization of solitons formed by the pulse breakup process by the effect of modulation instability with pump pulses of nanoseconds in standard fiber (SMF-28) with circular birefringence introduced by fiber twist, and the twisted fiber mitigates the random linear birefringence. In this work, we found that polarization ellipticity of solitons is distributed randomly; nevertheless, the average polarization ellipticity is closer to the circular than the polarization ellipticity of the input pulse. In the experimental setup. 200 m of SMF-28 fiber twisted by 6 turns/m was used. We used 1 ns pulse to pump the fiber. The results showed that at circular polarization of the input pulse solitons at the fiber output have polarizations close to the circular, while in the fiber without twist, the soliton polarization was random.
关键词： pulse propagation and temporal solitons,birefringence and polarization,fiber optic,stimulated Raman scattering,nonlinear optics
更新于2025-09-19 17:13:59
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Unidirectional and robust propagating surface magnetoplasmon in magneto-optical coaxial waveguides
摘要： In this paper, a novel coaxial waveguide constituted by a hollow cylinder made of a magneto-optical material and a metal wire at the axis is proposed. The surface magnetoplasmon and guided modes of the waveguide are studied. The results show that the dispersion relation and electromagnetic field distribution are highly sensitive to the operating frequency and physical dimensions of the structure. It is demonstrated that there exist three different types of modes, that is bulk-mode, surface mode, and regular mode. By adjusting the operating frequency and reducing the inner diameter of the hollow cylinder, the regular mode is suppressed and only the surface mode remains, which shows one-way propagating property. Moreover, the one-way surface mode is robust against backscattering at defect and surface roughness, which has a good potential in practice. The unique properties of this waveguide are demonstrated through mode analyses as well as numerical simulations.
关键词： electromagnetic field distribution,dispersion relation,surface magnetoplasmon,one-way propagation,magneto-optical coaxial waveguides
更新于2025-09-19 17:13:59
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Electron holography for vortex beams
摘要： A combined technology of vortex beam technique and electron holography has been developed. A range of about 10 times the diameter of the grating opening was irradiated and electron holography, electron vortex beam, orbital angular momentum, helical wavefront, wave propagation two-wave interference between a Bragg diffraction wave as a vortex beam and transmitted wave from and around a fork-shaped grating was recorded as a hologram. Reconstruction by using the Fourier transform method has been simultaneously performed for amplitude and phase distributions. Furthermore, by using a wave aberration function, amplitude and phase distributions at various propagation positions were reconstructed numerically, resulting in confirmation of vortex beam twists.
关键词： helical wavefront,electron holography,electron vortex beam,orbital angular momentum,wave propagation
更新于2025-09-19 17:13:59
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Numerical approaches for solving the nonlinear Schr??dinger equation in the nonlinear fiber optics formalism
摘要： This work presents a novel numerical stability analysis of a collection of pseudo-spectral methods, also known as split-step methods, for solving pulse propagation modelled by the nonlinear Schr¨odinger equation in the nonlinear ?ber optics formalism. In order to guarantee the convergence of di?erent pulse propagation dynamics, the numerical solutions of the pseudo-spectral methods (split-step Fourier method, symmetric split-step Fourier method, fourth order Runge-Kutta in the interaction picture method, and an optimization of split-step Fourier schemes for pulse propagation over long distances) are tested by the validation of the conservation laws that govern this system. The presented numerical results are an illustrative guide to consider in the selection of an appropriate numerical method in future investigations of a wide variety of propagation problems that involve the interplay of the linear and nonlinear contribution in the nonlinear Schr¨odinger equation, in order to reproduce accurately a speci?c phenomenology using this formalism.
关键词： nonlinear ?ber optics,Nonlinear Schr¨odinger equation,split-step methods,optical ?ber,optical pulse propagation
更新于2025-09-19 17:13:59