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- 2019
- Distributed optical fiber sensing
- Optical frequency domain reflection
- Polynomial regression algorithm
- Nonlinear tuning compensation
- Optoelectronic Information Science and Engineering
- Hebei University of Technology
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Terahertz Differential Computed Tomography: a Relevant Nondestructive Inspection Application
摘要： In recent years, tremendous advances have been made in the choice of materials used in the industry. With weight reduction as the goal, composite and polymer materials are more and more popular but they are almost transparent to X-ray. Because of this, interest has grown in other wavelengths like terahertz (THz). Due to a difference in how X-ray and THz propagate, X-ray CT algorithms cannot be directly used. For example, THz induces refraction making the reconstruction problem nonlinear. In this paper, we present a new algorithm which complies with beam profile intensities, refraction, and reflection. It is based on linearizing the reconstruction process around a computer-aided design (CAD) model of the object to be reconstructed. The method we propose computes the deviation between the object and this model.
关键词： Terahertz computed tomography,Inverse problem,Nondestructive testing,Modeling,Monte Carlo,Refraction,Nonlinear problem,Projection simulation
更新于2025-09-23 15:22:29
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On-chip Optical Vector Quadrature De-multiplexer Proposal for QAM De-aggregation by Single Bi-directional SOA-based Phase-sensitive Amplifier
摘要： In this paper, a simple optical vector quadrature de-multiplexer (QD) scheme is proposed for de-aggregating input 10 Gbaud 16/32/64 quadrature amplitude modulation (QAM) signals into two pulse amplitude modulation (PAM) streams. The proposed QD is based on a single bi-directional degenerate phase-sensitive amplifier (PSA), where the wavelength and the polarization status of the extracted in-phase and quadrature components stay the same as the input signal. Since the proposed QD is realized using PSA based on semiconductor optical amplifier (SOA), it is also possible to realize an on-chip QD system, providing an integrated platform for optical signal processing. Through numerical simulation, the transfer characteristics of the proposed QD system show that the SOA-based PSA has a high phase-sensitive gain extinction ratio of 44.1 dB. The constellations, error vector magnitudes (EVMs), and bit-error rates (BERs) of the data streams after the de-aggregation are numerically investigated to verify the proposed QD scheme. For the 10 Gbaud 16/32/64 QAM signals with an input optical signal-to-noise ratio (OSNR) of 25 dB, the de-aggregated PAM4/PAM6/PAM8 signals show 6.1, 5.6, and 8.2 dB receiver OSNR improvements at the BER of 10?3, respectively. Also, to optimize the performance of the subsystem, the BER performance dependence on the phase difference between two arms in the subsystem is also examined. The simulation results reveal that the proposed QD can accomplish the function of optical vector de-aggregation well for the high-level QAM signals. The proposed QD can be applied to information de-aggregation, format conversion, and direct detection for optical vector signals, which may have great potential values for the flexible optical networks.
关键词： Optical fiber communication,semiconductor optical amplifiers,nonlinear optical devices,optical signal processing
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE Research and Applications of Photonics In Defense Conference (RAPID) - Miramar Beach, FL (2018.8.22-2018.8.24)] 2018 IEEE Research and Applications of Photonics In Defense Conference (RAPID) - Optical Parametric Oscillation in Random Polycrystalline χ <sup>(2)</sup> Medium
摘要： We demonstrate the first OPO based on random phase matching. The OPO was based on ZnSe ceramic pumped by 62-fs, λ=2.35-μm Cr:ZnS laser pulses, had 90-mW pump threshold and produced an ultra-broad spectrum spanning 3–7.5 μm.
关键词： parametric processes,Parametric processes,Nonlinear optics
更新于2025-09-23 15:22:29
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Nonlinear Analytic Solution of Eulerian Beam-Wave Interaction Theory Considering Harmonic Interaction of Traveling-Wave Tube Amplifiers
摘要： In this paper, a novel Eulerian nonlinear beam-wave interaction (BWI) theory considering harmonic interaction of a helix traveling-wave tube (TWT) is developed. Derived from this Eulerian model, the novel Eulerian nonlinear analytic solutions (the fourth-order analytic solution of fundamental and the second-order analytic solution of harmonic) are first obtained by the method of successive approximation. The analytic relationships between electric fields of fundamental/harmonic frequencies and electron phases are also found. Then, the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory are compared to a Lagrangian theory. C-band and Ku-band helix TWTs based on a single pitch section are included in the simulation. It is found that the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory agree well with the Lagrangian theory at 1-dB gain compression point. Interestingly, the saturation effects caused by electron overtaking cannot be found by the traditional Eulerian analysis but can be described by the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory. Moreover, Eulerian nonlinear analytic solutions are simpler and more accurately than existing approaches and, thus, allow analytical progress. This paper confirms that the Eulerian nonlinear analytic solutions can outperform the previous proposals.
关键词： analysis,nonlinear,traveling-wave tubes (TWTs),Eulerian,Analytic solution,beam-wave interaction (BWI),harmonic
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe) - Palermo (2018.6.12-2018.6.15)] 2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe) - Nonlinear Multi-Scale Dynamics Modeling of a Piezoelectric Energy Harvester
摘要： Hysteretic effects play a crucial role in the behavior of devices based on piezoelectric materials. Most of the research focuses on modeling these effects for controlling the dynamic response of piezoelectric actuators. Few studies discuss how hysteresis influences power generation and performances of energy harvesters based on such active materials. In this paper, a recently developed physics-based model of a PZT crystal is employed to assess the effects of material mesoscopic variables on the macroscopic response of a piezoelectric energy harvester modeled as a SDOF system. A multi-scale approach is adopted where, at the mesoscale, crystal domain switching - the source of hysteretic behavior - is taken into account through a probabilistic thermodynamic approach. Effects of hysteretic nonlinearities on harvesting performances of the considered device are investigated by means of simulations. A comparison between predictions of two models - with and without hysteresis - is also reported.
关键词： Piezoelectric,Hysteresis,Energy harvesting,Nonlinear Multi-scale Dynamics
更新于2025-09-23 15:22:29
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Propagation of Lorentz beam in strongly nonlocal nonlinear media
摘要： Based on the Collins formula in strongly nonlocal nonlinear media (SNNM), the analytical expression for Lorentz beam passing through SNNM has been derived. It is found that the propagation behavior of Lorentz beam is variable and closely related to the parameters of initial ellipticity p and input power. The beam has its own critical power in x and y directions, respectively. If the Lorentz beam with critical power in a certain direction enters in SNNM, its beam width will remain constant in that direction during propagation, otherwise its beam width varies periodically, as either broad or compressed. Moreover, when p ? 1, the beam spot is always symmetrical in x and y directions; when p 6? 1, the beam spot is no longer symmetrical in x and y directions. Numerical simulations are carried out to illustrate these quintessential propagation properties.
关键词： propagation,Nonlocal nonlinear media,Lorentz beam
更新于2025-09-23 15:22:29
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Relay-Zone Technique for Numerical Boundary Treatments in Simulating Dark Solitons
摘要： To simulate dark solitons in the defocusing nonlinear Schr?dinger equation, we introduce a relay-zone technique, by alternately using a Robin boundary condition to treat the nonzero far field, and a derivative boundary condition to match the dark soliton. Numerical tests and comparisons demonstrate the effectiveness of the proposed boundary treatment. Stability and interaction of dark solitons are also studied.
关键词： Nonlinear Schr?dinger equation,Artificial boundary condition,Dark soliton
更新于2025-09-23 15:22:29
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Geometrically nonlinear analysis of Timoshenko piezoelectric nanobeams with flexoelectricity effect based on Eringen's differential model
摘要： This study analyzes the nonlinear free vibration and post-buckling of nanobeams with flexoelectric effect based on Eringen’s differential model. The nanobeam is modeled based on Timoshenko beam's theory. The von-Kármán strain-displacement relation together with the electrical Gibbs free energy and Hamilton's principle are employed to derive equations of motion. The nonlinear free vibration frequencies are obtained for pinned-pinned (P-P) and clamped-clamped(C-C) boundary conditions. Multiple scales method is employed to obtain the closed-form solution for the nonlinear governing equations. By employing this methodology, the natural frequencies of nanobeams are obtained and their post-buckling behavior is examined. The influence of nonlocal parameter, amplitude ratio, and input voltage on the top surface and flexoelectricity constant on nonlinear free vibration and post-buckling characteristics of nanobeamis investigated. In this paper, it is concluded that the flexoelectricity has a significant effect on free vibration of the beams in nano scale and its effect has to be considered in designing nano-electro-mechanical systems (NEMS) such as nano- generators and nano-sensors.
关键词： Nonlinear vibration,Flexoelectricity,Nonlocal elasticity,Postbuckling
更新于2025-09-23 15:22:29
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Modulational instability and homoclinic orbit solutions in vector nonlinear Schr?dinger equation
摘要： Modulational instability has been used to explain the formation of breathers and rogue waves qualitatively. In this paper, we show modulational instability can be used to explain the structure of them in a quantitative way. In the first place, we develop a method to derive general forms for Akhmediev breathers, rogue waves and their multiple or high order ones in a N-component nonlinear Schr?dinger equations. The existence condition for each pattern is clarified clearly with a compact algebraic equation. Moreover, we show that the existence condition of ABs and RWs is consistent with the dispersion relation of the linear stability analysis on the background solution. The results further deepen our understanding on the quantitative relations between modulational instability and homoclinic orbits solutions.
关键词： general multi-high-order rogue wave,vector nonlinear Schr?dinger equation,modulational instability analysis,Akhmediev breathers
更新于2025-09-23 15:22:29
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BaV2O6·H2O: A nonlinear optical crystal with a large bandgap
摘要： The first Ba-containing hydrated vanadate as nonlinear optical (NLO) material, BaV2O6·H2O, was synthesized by facile hydrothermal method. The single-crystal X-ray diffraction result shows that this compound crystallizes in the acentric orthorhombic space group of P212121 with cell parameters a = 7.3993(6) ?, b = 8.9934(7) ?, and c = 9.7206(8) ?. UV–vis-IR diffuse reflectance spectrum shows that the compound has a large bandgap of 4.60 eV and moderate transparency range. The title compound shows second-harmonic generation (SHG) efficiency about 0.5 times of KH2PO4 (KDP). The structure-property relationship of BaV2O6·H2O was clarified by the first-principles studies.
关键词： Vanadate,Nonlinear optical material,Large bandgap,Hydrothermal method
更新于2025-09-23 15:22:29