Nonlinear Propagation Research Articles

Nonlinear Optical Signal Generation Mediated by a Plasmonic Azimuthally Chirped Grating

Plasmonic gratings are simple and effective platforms for nonlinear signal generation since they provide a well-defined momentum for photon-plasmon coupling and local hot spots for frequency conversion. Here, a plasmonic azimuthally chirped grating (ACG), which provides spatially resolved broadband momentum for photon-plasmon coupling, was exploited to investigate the plasmonic enhancement effect in two nonlinear optical processes, namely two-photon photoluminescence (TPPL) and second harmonic generation (SHG). The spatial distributions of the nonlinear signals were determined experimentally by hyperspectral mapping with ultrashort pulsed excitation. The experimental spatial distributions of nonlinear signals agree very well with the analytical prediction based on photon-plasmon coupling with the momentum of the ACG, revealing the "antenna" function of the grating in plasmonic nonlinear signal generation. This work highlights the importance of the antenna effect of the gratings for nonlinear signal generation and provides insight into the enhancement mechanism of plasmonic gratings in addition to local hot spot engineering.

Nonlinear Rayleigh wave propagation in thermoelastic media in dual-phase-lag.

A model of generalized thermoelasticity within dual-phase-lag is used to investigate nonlinear Rayleigh wave propagation in a half-space of a transversely isotropic elastic material. It is assumed that the coefficient of heat conduction is temperature-dependent, a fact that plays an important role in the coupling behaviour analysis of thermoelastic and piezo-thermoelastic solids. Taking such a dependence into account becomes a necessity at higher temperatures and in nano-structures, when the material properties can no longer be considered as constants. Normal mode analysis is applied to find a particular solution to the problem under consideration. A concrete case is solved under prescribed boundary conditions and tentative values of the different material coefficients. The results are discussed to reveal the effect of temperature dependence of the heat conduction coefficient, as well as the thermal relaxation times, on nonlinear Rayleigh wave propagation. All quantities of practical interest are illustrated in two-and three-dimensional plots. The presented results may be useful in the detection of the second harmonic amplitudes through measurements related to the propagating heat wave.

Magnetoacoustic Waves in a Dissipative Quantum Plasma With Spin-1/2 and Exchange-Correlation Effects

Using quantum magneto-hydrodynamic theory, the nonlinear propagation of magnetoacoustic waves have been investigated in a quantum magneto-plasma having dissipative ions fluid as well as quantum electrons and positrons, including exchange-correlation and electrons/positrons spin effects. The Korteweg-devris-Burger equation is derived employing the reductive perturbation method. It has been found that the quantum magneto-plasma system under consideration supports buth magnetoacoustic solitary and shock waves depending on the values of the plasma parameters. The effects of quantum plasma parameters (such as exchange-correlation coefficients, magnetic field strength, kinematic viscosity and the concentrations of electrons and positrons) on the magnetoacoustic shock waves (both monotonic shock waves and oscillatory shock waves) are examined. The profiles of both monotonic and oscillatory shock waves are found to be significantly affected by these parameters.The results of the current study may be useful to understand the properties of magnetoacoustic waves propagating in dense space plasma environments where the quantum mechanical effects of electrons and positrons are included.

Low-Power Design of Digital LDO With Nonlinear Symmetric Frequency Generation

This brief proposes a digital LDO (Low DropOut regulator) with a built-in non-linear VCO (Voltage Controlled Oscillator) to achieve both the fast transient response and low power operation. This on-chip VCO generates a clock signal whose frequency is a non-linear symmetric function of the output voltage error. Here, we propose a design technique to realize the symmetric frequency generation with low power consumption. We demonstrate a design example of LDO using our proposed technique in a commercial 65 nm low-power CMOS process. We evaluate the LDO using transistor-level simulation using HSPICE. It achieves 0.03- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11 ~\mu \text{A}$ </tex-math></inline-formula> of quiescent current with an input voltage range of 0.6-1.2 V and an average current efficiency of 99.68% across <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50\times $ </tex-math></inline-formula> load range.

Modeling of nonequilibrium cross-diffusion systems

In this research, we investigate the modeling of cross-diffusion systems that are not in equilibrium. For a particular equation, it is shown that the parameter values exist and have a numerical solution. A source describes the system of equations considered in this study as being based on the majority of physical processes, such as the cross-diffusion process in this system, thermal conductivity, and polytrophic filtration of gas and liquid in nonlinear media. Numerous partial solutions exist for these equations. The development of an integral self-similar solution is one of the most important approaches to analyzing the problem at hand. Initial construction of a system of self-similar equations using a nonlinear subtraction technique. The front for the equation of nonlinear heat generation with doubled energy was estimated, the localization process was observed, new effects were observed, an algorithm was constructed based on the obtained self-similar solution, a program code was developed in the programming language, and the process modeling was visualized.

Effects of acoustic nonlinearity on communication performance in soft tissues.

Acoustic communication has been gaining traction as an alternative communication method in nontraditional media, such as underwater or through tissue. Acoustic propagation is known to be a nonlinear phenomenon; nonlinear propagation of acoustic waves in soft tissues at biomedical frequencies and intensities has been widely demonstrated. However, the effects of acoustic nonlinearity on communication performance in biological tissues have not yet been examined. In this work, nonlinear propagation of a communication signal in soft tissues is analyzed. The relationship between communication parameters (signal amplitude, bandwidth, and center frequency) and nonlinear distortion of the communication signal propagating in soft tissues with different acoustic properties is investigated. Simulated experiments revealed that, unlike linear channels, bit error rates increase as signal amplitude and bandwidth increase. Linear and decision feedback equalizers fail to address the increased error rates. When tissue properties and transmission parameters can be estimated, receivers based on maximum likelihood sequence estimation approach the performance of an ideal receiver in an ideal additive white Gaussian noise channel.

Smooth Nonlinearity Generation with lnCosh and Realization of Chaotic Oscillator

In this work, a new cubic-like smooth nonlinearity is generated by modifying Chua’s piecewise-linear segmental nonlinear function using logarithmic cos-hyperbolic function implementation. A logarithmic cos-hyperbolic function possessing smooth symmetric nonlinear characteristics is implemented through CMOS-based circuit design using the current mode approach. The nonlinear design is then incorporated in a new third-order chaotic oscillator configuration to produce chaotic oscillations. This chaotic circuit is tuned to develop different attractors through the bifurcation parameter. Moreover, the dynamics of chaos such as antimonotonicity and coexistence of attractors are also depicted in circuit simulation by tuning various controlling parameters. Additionally, some numerical analyses are performed on this dynamic system to justify the existence of chaoticity and attractors’ development. This design has been optimized for low-voltage and moderately high dominant frequency of oscillations. Simulations are done using 180-nm CMOS technology in Cadence Virtuoso. Experimental results are presented to verify the workability of the proposed chaotic system.

Scanning Induction Thermography for Bearing Ring Under AC-DC Composite Magnetization

Induction thermography is a promising nondestructive testing technique with the advantages of high efficiency, lift-off tolerance, and defect imaging. To fulfill scanning detection and quantify the defect in bearing rings, this paper proposes scanning eddy current thermography under AC-DC composite magnetization. With DC magnetization, the defect will cause permeability disturbance in the bearing ring surface. Under high-frequency AC magnetization, disturbed permeability will generate a non-uniform thermal response captured by the infrared camera. To investigate the detection principle, a multi-physics coupling simulation model for permeability and thermal distribution in the scanning process is built, involving DC-AC composite magnetization, nonlinear ferromagnetic material, heat generation, heat conduction, and scanning movement. Then, a thermal data post-processing method for scanning imaging and crack quantification is proposed. Finally, the scanning induction thermography system for bearing rings is designed and developed. The experimental results show that the proposed scanning method can quantify bearing ring cracks with depths up to 2.0 mm.

Directional State Transition Tensors for Capturing Dominant Nonlinear Effects in Orbital Dynamics

Higher-order methods such as state transition tensors (STTs) have shown promise for a variety of applications in astrodynamics, but can be limited in their use due to their potentially large computational and storage requirements. In this paper we present a method for approximating STTs by aligning the STTs with particularly unstable directions. This strategy allows us to isolate the most important terms in the higher-order STTs and ignore any less important terms. This method, which we call directional state transition tensors (DSTTs), is applied to several examples in two- and three-body dynamic systems, and it is shown to perform well for both nonlinear state and state uncertainty propagation. The method produces similar results to the full STTs, but requires significantly fewer elements to be stored, which can result in up to improvements in speed for nonlinear uncertainty propagation computations. DSTTs are promising for expanding the use of STTs to situations with highly nonlinear dynamics but limited computational resources, such as on-board a spacecraft.

Supercontinuum generation in highly birefringent fiber infiltrated with carbon disulfide

Supercontinuum generation in highly birefringent fiber infiltrated with carbon disulfide is numerically studied with a linearly polarized femtosecond laser (1560 nm wavelength, 90 fs pulse duration) as a pump source. The fiber has two polarized modes (x- and y-polarized LP01) with different dispersion characteristics, meaning all-normal dispersion for the y-polarized mode and anomalous dispersion for the x-polarized mode. We build a numerical modeling for nonlinear propagation including Kerr effects and Raman effects with positive and negative nonlinear refractive. Our results point out that spectral bandwidth, flatness, and coherence of supercontinuum generation depend on the input polarized angle (an angle with respect to the x-axis) of the laser pulses. In particular, the input pulses polarized near slow-axis (x-axis) provide 1.5 octave-spanning soliton-induced SC generation with bandwidth from 1000 nm to 3300 nm via 10 kW input peak power, while input pulses polarized near the fast-axis (y-axis) create octave-spanning all-normal dispersion supercontinuum generation (from 1200 nm to 2500 nm). Modification of the input angle enables controlling spectro-temporal properties of supercontinuum generation, such as polarization state, coherence, spectral bandwidth, and flatness. In addition, the use of highly birefringent fiber also enables suppression of polarization modulation instability; therefore coherence solely depends on effects of modulation instability and it is possible to tailor via changing the input angle.

Nonlinear approximation for buoyancy-driven mixed convection heat and mass transfer flow over an inclined porous plate with Joule heating, nonlinear thermal radiation, viscous dissipation and thermophoresis effects

This study considered a classical magnetohydrodynamics (MHD) mixed convection heat and mass transfer flow over an inclined porous plate with thermophoresis, Joule heating, viscous dissipation, and nonlinear thermal radiation. The impact of nonlinear density variation with temperature and concentration (NDTC) in the buoyancy term is also taken into consideration. The mathematical model is first transformed into ordinary differential equations (ODEs) by similarity variables. The reduced ODEs are solved through the classical Runge–Kutta algorithm after utilizing the shooting technique. Some major findings of the analysis include; the heat transfer rate increases with the fluid injection but it decreases the rate of particle deposition and skin friction. Regarding the fluid suction, the heat transfer rate is observed to decrease as the fluid suction intensifies whereas increases the particle deposition and shear stress at the plate surface. As (a classical horizontal flat plate), the rate of heat transfer enhances but decreases the particle deposition rate and plate shear stress. With blowing/suction and in the presence of the magnetic parameter, the plate shear stress and heat transfer increase with nonlinear thermal radiation propagation whereas decreases the particle deposition. The species concentration near the porous plate, velocity, and temperature curves is enhanced by escalating the dissipation parameter. The radiative heat flux boosts the fluid temperature that consequently enhanced the velocity and the species concentration near the porous plate. The fluid velocity past the porous plate is higher in the case of a vertical plate () compared to the classical flow over a horizontal porous plate ().

Light-Induced Self-Oscillations and Spoiling of the Bragg Resonance Due to Nonlinear Optical Propagation in Heliconical Cholesteric Liquid Crystals

In a recent paper, we have reported the results of a study of the nonlinear light propagation of a beam traveling along the helix direction of a heliconical cholesteric liquid crystal, showing that optical reorientation leads to instabilities in the optical transmission when the light wavelength is close to the Bragg resonance. Here we report a detailed study of this phenomenon, using Ambartsumian’s layer addition modified method to take into account the continuous modification of the wave field during propagation. We show that the whole transmission spectrum is modified by increasing the light intensity and point out that self-induced oscillations take place at lower intensities on the red side edge of the Bragg resonance while stable values of transmittivity are still observed on the blue side edge. A further increase in the intensity leads to oscillations of lower amplitude on the blue side while an irregular behavior of the transmission is achieved on the red side. At higher intensities, the Bragg resonance disappears and transmission becomes unstable for any light wavelength. A simple phenomenological model is proposed to account for the onset of the oscillations and the asymmetry of the behavior at the opposite side of the Bragg resonance. We also point out that the static electric field is a driving parameter to switch from stable to oscillatory to irregular behavior in the transmittivity at a given light wavelength.

Generation of terahertz waves based on nonlinear frequency conversion with stimulated Raman adiabatic passage.

In recent years, high-power, tunable terahertz (THZ) radiation sources have become the key areas of research in the world. The method of THZ waves by nonlinear optical difference frequency generation (DFG) has the advantages of wide tuning, high power, room temperature operation, and compact structure. However, the conversion efficiency of the current difference frequency method is low, which needs a trade-off between conversion efficiency and tuning range. We apply the nonlinear optical cascade difference frequency conversion theory based on stimulated Raman adiabatic passage (STIRAP) and propose a theoretical scheme to generate THZ waves. Numerical simulation investigates the cascaded difference frequency process of generating THZ waves with the help of the nonlinear medium lithium niobate (LN) crystal. The theoretical analysis shows that the maximum quantum conversion efficiency from signal laser to THZ waves is 43.2 % when the wavelength of the tuned signal laser varies between 1.044 - 1.065 µm with the fixed two pump laser wavelengths constant. The tunable THZ waves of 0.48 - 5.0 THz can be obtained and the maximum output intensity of THZ waves is 2.17 MW/cm2, and the method is robust to temperature variations. It also provides a novel idea for the cascaded difference frequency generation of THZ waves.

Transmission and reflection of three-dimensional Boussinesq internal gravity wave packets in nonuniform retrograde shear flow

Simulated fully localized internal gravity wave packets with moderately large initial amplitude exhibit finite transmission across a reflection level, due to the combined effects of the wave-induced shear locally cancelling the retrograde background shear, modulational instability, and the nonlinear generation and evolution of secondary wave packets.

Designing a single-mode anomalous dispersion silicon core fiber for temporal multiplet formation.

A highly nonlinear single-mode anomalous dispersion silicon core fiber (SCF) is suitably designed and optimized to generate a high repetition rate pulse train in the temporal domain from a single input pulse at a sufficiently shorter optimum length in comparison to silica-based standard fibers used for the same purpose. The large amount of Kerr-induced nonlinearity of a SCF is effectively utilized here such that input Gaussian pulses or pulse trains transform into a highly repetitive temporal multiplet. The effects of free-carrier generation-induced change in absorption and dispersion are included while studying the nonlinear pulse propagation through the SCF. To declare the generated pulse as a superior-graded triplet, a Q parameter, as a function of relative pulse parameters of the individual pulses of a triplet, is defined for the first time, to the best of our knowledge. Different pulse parameters are thoroughly optimized as well as the effect of external gain is examined from the perspective of requirement of shorter fiber length and development of quality triplets. Finally, the work is further extended for the formation of quadruplet pulses by the same type of SCF. It is to be mentioned here that such a methodical study for the generation of a temporal multiplet using a semiconductor core fiber has not been reported earlier.

Dynamic Interactions between Local Energy Systems Coupled by Power and Gas Distribution Networks

Supplied with electricity and natural gas, local energy systems (LESs) with gas-fired generations increase the operational flexibility of urban energy supply. However, the increasing usage of these LESs may lead to adverse impacts on the urban energy system supply via power and/or gas distribution networks. Dynamic interactions between the LESs, electricity, and gas networks subject to different disturbances need to be investigated due to the complexity of the problem. To address this issue, this paper first presents the topology and operating mode of the LESs as well as the relationship with power and gas networks. Second, an extended microturbine model is developed to reflect the nonlinear dynamic propagation of disturbances between the two networks. A general model of the interconnected LESs is developed to analyze the mutual impacts between gas and electricity networks under different modes. Finally, an iterative method is proposed to simulate the mechanism of disturbance propagation between the electricity network, gas network, and LESs, incorporating the impacts of loads and renewables. Case studies reveal that simultaneous regulation of multiple gas-fired generators would reduce the minimum pressure to 50% of the steady-state value. The resulted pressure drop is even lower than the case with higher total gas demand but only one gas-fired generator regulated. Moreover, it is shown that state fluctuations of the gas system last 20 times longer than the electricity system within the LESs. The electrical link between LESs, such as soft opening point with shorter response time, could smooth the fluctuations.

A Malware Propagation Model Considering Conformity Psychology in Social Networks

At present, malware is still a major security threat to computer networks. However, only a fraction of users with some security consciousness take security measures to protect computers on their own initiative, and others who know the current situation through social networks usually follow suit. This phenomenon is referred to as conformity psychology. It is obvious that more users will take countermeasures to prevent computers from being infected if the malware spreads to a certain extent. This paper proposes a deterministic nonlinear SEIQR propagation model to investigate the impact of conformity psychology on malware propagation. Both the local and global stabilities of malware-free equilibrium are proven while the existence and local stability of endemic equilibrium is proven by using the central manifold theory. Additionally, some numerical examples and simulation experiments based on two network datasets are performed to verify the theoretical analysis results. Finally, the sensitivity analysis of system parameters is carried out.

Phase space analysis of nonlinear wave propagation in a bistable mechanical metamaterial with a defect.

We study the dynamics of solitary waves traveling in a one-dimensional chain of bistable elements in the presence of a local inhomogeneity ("defect"). Numerical simulations reveal that depending upon its initial speed, an incoming solitary wave can get transmitted, captured, or reflected upon interaction with the defect. The dynamics are dominated by energy exchange between the wave and a breather mode localized at the defect. We derive a reduced-order two degree of freedom Hamiltonian model for wave-breather interaction and analyze it using dynamical systems techniques. Lobe dynamics analysis reveals the fine structure of phase space that leads to the complicated dynamics in this system. This work is a step toward developing a rational approach to defect engineering for manipulating nonlinear waves in mechanical metamaterials.

Long-wave infrared to short-wave infrared upconversion through sum-frequency generation in a silicon symmetric metasurface integrated with two-dimensional material

Optical resonances supported by subwavelength nanostructures have significant local-field enhancement effects and are important in the field of nanophotonics such as photoemission and nonlinear optics. In this paper, silicon metasurface with toroidal dipole resonance in the short-wave infrared band is investigated. The formation and properties of the high-quality toroidal dipole resonance are analyzed in detail by the near- and far-field analysis, and the electromagnetic multipole decomposition methods in the metasurface with different structural parameters. In addition, a layer of two-dimensional nonlinear material GaSe is combined with the silicon metasurface, to enhance the long-wave infrared to short-wave infrared upconversion by the nonlinear sum-frequency generation (SFG) process through toroidal dipole resonance. The upconversion efficiency in the GaSe/ silicon metasurface bilayer system is nearly a thousand times more than that in the GaSe/planar silicon bilayer system, indicating the effectiveness of the toroidal dipole resonance generated by the metasurface. This method provides a feasible and viable strategy for upconverting mid-wave infrared or long-wave infrared to near- or short-wave infrared by the nonlinear process induced by the metasurface, which is potentially very attractive for the sensing and imaging of long-wavelength photons that beyond the capability of mature silicon/germinium detectors.

Effects of external fields on the nonlinear optical rectification and second harmonic generation of GaAs/GaAlAs zigzag quantum well

For the first time, the impact of externally applied static electric and magnetic field on the nonlinear optical rectification (NOR) and second harmonic generation (SHG) coefficients of GaAs/GaAlAs zigzag quantum well is theoretically investigated in this study. Additionally, we examined the effect of physical parameters such as width and depth of the structure on these coefficients. We have numerically solved the time-independent Schrödinger equation by using the diagonalization method under the effective mass approximation for obtaining subband energy levels and wave functions of the structure, and then we have used the compact density matrix method to obtain the analytical expressions of NOR and SHG coefficients. The obtained numerical results showed that when the magnitude of the externally applied electric and magnetic fields is increased, the peak position of NOR and SHG shifts to blue, and by increasing the width and potential depth of the quantum well, it shifts to red.