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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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Generation of solitons in media with arbitrary degree of nonlocality using an optimization procedure
摘要： Using a recently developed technique based on the Rayleigh-Ritz optimization principle, we generate solitons for media with an arbitrary degree of nonlocality. We demonstrate that it is possible to obtain a plethora of complex self-trapped beams using known solutions to the harmonic oscillator for one-dimensional (1D), 2D, and 3D systems, but working directly with a generalized nonlinear nonlocal Schr?dinger equation. We compare the parameters obtained variationally between the phenomenological Gaussian response and other more realistic nonlocal responses. We report that, for both kinds of nonlocal models, our approach obtains variational solutions that can remain self-trapped for certain conditions. We corroborate that, in general, the soliton dynamics can be different between the Gaussian response and the more realistic media for an arbitrary degree of nonlocality.
关键词： nonlinear Schr?dinger equation,variational approximation,nonlocality,solitons,optical beams
更新于2025-09-23 15:22:29
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Nonlinear optical response of a two-dimensional semi-Dirac system in terahertz regime
摘要： We demonstrate a strong nonlinear optical response in a two-dimensional semi-Dirac system in the terahertz regime. By applying the Boltzmann transport theory for the intra-band process and a quantum mechanics method for the inter-band process, we obtained the three-photon current response. It is found that both the intra- and inter-band excitations make significant contributions to the nonlinear response. The third order conductivities (TOCs) σyy(3) are about two magnitudes higher than that of σxx(3). Interestingly, for the inter-band TOCs, there is a sign change when the chemical potential varies across the saddle point in the conduction band in kx direction (that is parabolic), due to the competition between the two opposite nonlinear current contributed by the electrons at states k > kD and k < kD, respectively. Finally, we show that the nonlinear response in terahertz regime is significant at experimentally accessible field strengths. Our results suggest that this system could be of potential applications in photonic device for frequency up-conversion.
关键词： black phosphorous,semi-Dirac system,nonlinear optical response,Boltzmann transport theory
更新于2025-09-23 15:22:29
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[IEEE 2018 Dynamics of Systems, Mechanisms and Machines (Dynamics) - Omsk, Russia (2018.11.13-2018.11.15)] 2018 Dynamics of Systems, Mechanisms and Machines (Dynamics) - Automatic Nonlinear Modeling Technique for Gaas HEMT
摘要： A new technique for nonlinear transistor modeling is suggested. The technique includes an analytical extraction and a multistage optimization, providing fully automated modeling. An extraction algorithm for the parameters of an internal voltage-controlled current source Ids is shown. A fully automated workflow of small-signal model extraction is presented. An approach for obtaining parameters of nonlinear capacitances is described. A 0.15um GaAs pHEMT nonlinear model was built and verified with measured IV-curve, multi-bias S-parameters and power characteristics.
关键词： compact nonlinear model,microwave transistor,large-signal model,GaAs HEMT
更新于2025-09-23 15:22:29
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Optical matching of a multimode gradient fibre and single-mode stepped-index fibre in a photopolymerizable composition
摘要： The opportunity to optically match waveguides characterized by an essentially different field structure in a photopolymerizable medium is investigated. The example of a multimode gradient fibre (core diameter 50 μm) and a single-mode stepped-index fibre SMF-28 (core diameter 8.2 μm) shows that the efficiency of radiation transmission from the wide fibre into the narrow one can reach 60% at a distance between their end faces of about 900 μm.
关键词： nonlinear optics,photopolymer,optical matching of fibres,fibre optics,laser radiation
更新于2025-09-23 15:22:29
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Development of highly nonlinear polarization-maintaining fibers with normal dispersion across entire transmission window
摘要： A determined polarization state of light is required in nonlinear optics applications related to ultrashort and single-cycle light pulse generation. Such short timescales require up to one full octave of the spectral width of light. A fiber-based, pulse-preserving and linearly polarized supercontinuum can meet these requirements. We report on the development—from linear simulations of the fiber structure, through fabrication of physical fibers to their versatile characterization—of polarization-maintaining, highly nonlinear photonic crystal fibers, intended for femtosecond pumping at a wavelength of 1560 nm. A full octave of linearly polarized light around this wavelength would enable the covering of amplification bandwidths of the three major fiber amplifiers, from ytterbium-doped systems up to thulium- and holmium-doped fiber amplifiers, with a coherent, linearly polarized seed signal. At the same time, an all-normal chromatic dispersion profile over an entire transmission window, and a small dispersion of nonlinearity in the developed fibers, would facilitate use of commercially available femtosecond fiber lasers as pump sources for the developed fibers.
关键词： normal dispersion,birefringence,fibers,nonlinear optics
更新于2025-09-23 15:22:29
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Sources of heading errors in optically pumped magnetometers operated in the Earth's magnetic field
摘要： When optically pumped magnetometers are aimed for use in the Earth’s magnetic field, the orientation of the sensor to the field direction is of special importance to achieve accurate measurement results. Measurement errors and inaccuracies related to the heading of the sensor can be an even more severe problem in the case of special operational configurations, such as the use of strong off-resonant pumping. We systematically study the main contributions to the heading error in systems that promise high magnetic field resolutions at the Earth’s magnetic field strengths, namely the nonlinear Zeeman splitting and the orientation-dependent light shift. The good correspondence of our theoretical analysis to experimental data demonstrates that both of these effects are related to a heading-dependent modification of the interaction between the laser light and the dipole moment of the atoms. Also, our results promise a compensation of both effects using a combination of clockwise and counterclockwise circular polarization.
关键词： optically pumped magnetometers,circular polarization,Earth's magnetic field,light shift,nonlinear Zeeman splitting,heading error
更新于2025-09-23 15:22:29
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A Switching Sequence for Unary Digital-to-Analog Converters Based on a Knight's Tour
摘要： This paper proposes a new switching sequence with the asymmetric placement of weighting elements for a unary digital-to-analog converter (DAC). The proposed sequence is based on a so-called knight’s tour according to the modified Warnsdorf’s rule. To estimate the efficiency of the proposed switching sequence, a 10-bit resistive DAC has been designed and fabricated in the UMC 180-nm technology. Experimental results show that in comparison with an array of weighting elements without compensation of the systematic error, the proposed switching sequence reduces the maximal integral (INL) and the mean INL by 20% on the average in the temperature range from ?40 °C to 85 °C. Besides that, the maximal INL does not depend on the temperature, while the mean INL decreases with temperature increase.
关键词： CMOS integrated circuits,digital–analog conversion,nonlinear circuits,dynamic range
更新于2025-09-23 15:22:29
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Precompensation and System Parameters Estimation for Low-Cost Nonlinear Tera-Hertz Transmitters in the Presence of I/Q Imbalance
摘要： Tera-Hertz (THz) transmission can offer several attractive applications, yet developing low-cost energy-efficient THz devices is at an early stage. The most promising low-cost THz transmitter architecture in the literature is the so-called frequency-multiplier-last architecture. However, it is incapable of transmitting quadrature amplitude modulation (QAM) due to the architecture's inherent nonlinear distortions. We study such nonlinear THz communication systems by incorporating the nonlinearity aspects of the low-cost THz devices and the inphase and quadrature (I/Q) imbalance effect into the signal model. Then, we propose a precompensation scheme to compensate the nonlinearity and I/Q imbalance effects, thus enabling the QAM-capable frequency-multiplier-last architecture for THz systems. The proposed precompensation scheme requires the knowledge of the system parameters. To estimate the system parameters, we propose a maximum-likelihood estimator and its practical implementation via an alternating estimation algorithm. We also derive closed-form expressions for the Cramér–Rao lower bounds (CRLBs) of the system parameters estimation, and design the pilot sequence used in estimating the system parameters. Numerical results show that the proposed precompensation schemes overcome the prominent problems experienced in the existing THz systems, namely severe nonlinear distortions of the modulation symbols as well as spectral spreading and/or large spectrum sidelobes, and mitigate the I/Q imbalance effect.
关键词： precompensation,estimation,QAM,I/Q imbalance,nonlinear distortion,Low-cost,Tera-Hertz
更新于2025-09-23 15:22:29
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Towards Applications of Stimulated Raman Scattering in Nanophotonics
摘要： Nanophotonics is a rapidly evolving field, exploring behaviour of light on the micro/nano scale and the interaction of micro/nano objects with light. The driving force for its development is the promise to go far beyond the conventional boundaries of photonics. Because of the diffraction limit, high-density regular optical components do not have the ability to confine light down to the microscale dimension. The footprint of devices becomes more critical for applications with limited physical space, such as on-chip silicon-based photonic devices. In this paper, a review of some of the most significant accomplishments in the field of stimulated Raman scattering in microstructures is reported. These findings indicate promising perspectives for integrated Raman lasers.
关键词： Raman laser,stimulated Raman scattering,nanophotonics,nonlinear optics
更新于2025-09-23 15:22:29
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Multiple Access With Polarity Division Sparse Code for Visible Light Communication
摘要： The increasing demand of mobile internet and Internet of Things poses challenging requirements for indoor wireless communication. Visible light communication (VLC) is a promising technology to alleviate the growing traffic problem. In addition, nonlinear distortion of light emitting diodes (LEDs) results in a poor link quality. In this paper, we propose multiple access with polarity division sparse code (PDSC) for VLC, which is based on nonorthogonal multiple access and spatial characteristic of LEDs. The experimental results indicate that the PDSC significantly enhances capacity and spectral efficiency of VLC network compared with orthogonal frequency division multiple access. We also demonstrate that the PDSC can optimize the problem of nonlinear distortion with polarity division. The experimental results reveal that PDSC is a promising multiple access scheme for the indoor VLC networks.
关键词： Nonorthogonal multiple access,visible light communication,PDSC,nonlinear distortion optimization
更新于2025-09-23 15:22:29