Slow Solitons Research Articles

饱和参数对高阶双稳态慢光孤子的影响

饱和参数对高阶双稳态慢光孤子的影响

Influence of Non-Maxwellian Particles on Dust Acoustic Waves in a Dusty Magnetized Plasma

In this paper an investigation into dust acoustic solitary waves (DASWs) in the presence of superthermal electrons and ions in a magnetized plasma with cold dust grains and trapped electrons is discussed. The dynamic of both electrons and ions is simulated by the generalized Lorentzian (κ) distribution function (DF). The dust grains are cold and their dynamics are studied by hydrodynamic equations. The basic set of fluid equations is reduced to modified Korteweg-de Vries (mKdV) equation using Reductive Perturbation Theory (RPT). Two types of solitary waves, fast and slow dust acoustic soliton (DAS) exist in this plasma. Calculations reveal that compressive solitary structures are possibly propagated in the plasma where dust grains are negatively (or positively) charged. The properties of DASs are also investigated numerically.

Compressive and Rarefactive Solitons for Fast and Slow Ion Acoustic Waves in Multi-Ion Plasmas

The Kadomtsev–Petviashvili (KP) equation is derived for an electrostatic wave in unmagnetized multi-ion plasmas using the reductive perturbation method. It is found that two ion sound waves with fast and slow speeds can propagate in such a multi-ion plasma provided both ions are considered to be inertial and one of the ion component in two ion species plasma is taken to be warm as well. The potential hump (compressive) and dip (rarefactive) structures of the slow and fast ion acoustic waves are obtained for different combinations of multi-ion plasmas i.e., H+(warm)–O+(cold)–e, H+(warm)–H+(cold)–e, O+(cold)–H-(warm)–e, and H+(cold)–H-(warm)–e. It is found that, in the case of multi-ion H+(warm)–O+(cold)–e and H+(warm)–H+(cold)–e plasmas, the slow ion acoustic wave solitons form both potential hump (compressive) and dip (rarefactive) profiles depending on the temperature and concentration of the warm ion species, while the fast ion acoustic wave solitons only form the potential hump structures. However, in ...

Coupling Between Whistler Waves and Ion-Scale Solitary Waves: Cluster Measurements in the Magnetotail During a Substorm

We present a new model of self-consistent coupling between low frequency, ion-scale coherent structures with high frequency whistler waves in order to interpret Cluster data. The idea relies on the possibility of trapping whistler waves by inhomogeneous external fields where they can be spatially confined and propagate for times much longer than their characteristic electronic time scale. Here we take the example of a slow magnetosonic soliton acting as a wave guide in analogy with the ducting properties of an inhomogeneous plasma. The soliton is characterized by a magnetic dip and density hump that traps and advects high frequency waves over many ion times. The model represents a new possible way of explaining space measurements often detecting the presence of whistler waves in correspondence to magnetic depressions and density humps. This approach, here given by means of slow solitons, but more general than that, is alternative to the standard approach of considering whistler wave packets as associated with nonpropagating magnetic holes resulting from a mirror-type instability.

Bragg solitons in nonlinearPT-symmetric periodic potentials

It is shown that slow Bragg soliton solutions are possible in nonlinear complex parity-time (PT) symmetric periodic structures. Analysis indicates that the PT-symmetric component of the periodic optical refractive index can modify the grating band structure and hence the effective coupling between the forward and backward waves. Starting from a classical modified massive Thirring model, solitary wave solutions are obtained in closed form. The basic properties of these slow solitary waves and their dependence on their respective PT-symmetric gain/loss profile are then explored via numerical simulations.

Blue Self-Frequency Shift of Slow Solitons and Radiation Locking in a Line-Defect Waveguide

We investigate experimentally resonant radiation processes driven by slow solitons in a dispersion-engineered photonic crystal waveguide in a regime virtually free of dissipative nonlinear processes (two-photon absorption and Raman scattering). Strong (30% energy conversion) Cherenkov-like radiation accompanied by the blue self-frequency shift of the soliton is observed close to the zero dispersion point, and is explained in terms of the soliton-radiation locking of the velocity.

Evolution of Slow Dual Steady-State Optical Solitons in a Cold Three-State Medium

The generalized nonlinear Schrödinger equation, which describes the evolution of dual steady-state optical solitons in a cold three-state medium, is written as the Hamiltonian symplectic structure. The symplectic method is applied to investigate evolution of dual steady-state optical solitons. By adjusting the initial pulses, the saturation parameter variables and the distances of optical solitons, the different behaviors of dual steady-state optical solitons are analyzed.

Coupling between whistler waves and slow-mode solitary waves

The interplay between electron- and ion-scale phenomena is of general interest for both laboratory and space plasma physics. In this paper, we investigate the linear coupling between whistler waves and slow magnetosonic solitons through two-fluid numerical simulations. Whistler waves can be trapped in the presence of inhomogeneous external fields such as a density hump or hole where they can propagate for times much longer than their characteristic time scale, as shown by laboratory experiments and space measurements. Space measurements have detected whistler waves also in correspondence to magnetic holes, i.e., to density humps with magnetic field minima extending on ion-scales. This raises the interesting question of how ion-scale structures can couple to whistler waves. Slow magnetosonic solitons share some of the main features of a magnetic hole. Using the ducting properties of an inhomogeneous plasma as a guide, we present a numerical study of whistler waves that are trapped and transported inside propagating slow magnetosonic solitons.

Trapping of slow solitons by longitudinal inhomogeneity in high-index photonic crystal fibers

Soliton propagation in slow-light states of nonuniform high-index photonic crystal fibers (PCFs) is studied numerically by a recently developed time-propagating 1+1D equation. It is demonstrated that very slow solitons can be highly stable against even short-period roughness. Soliton trapping by longitudinal inhomogeneities is also found as the soliton velocity decreases due to Raman scattering. Practical limitations and opportunities based on the simulation results are briefly discussed.

Matched slow optical soliton pairs via biexciton coherence in quantum dots

We theoretically investigate the simultaneous formation and stable propagation of slow optical soliton pairs in semiconductor quantum dots with a four-level biexciton-exciton cascade configuration. Owing to the destructive interference set up by two continuous wave control fields that couple to a biexciton state, the linear as well as nonlinear dispersion can be dramatically enhanced simultaneously with the absorptions of two weak probe fields being almost suppressed. These results reveal that the detrimental distortions of the two weak-pulsed probe fields due to dispersion effects can be well balanced by the self-phase modulation effect under very low input light intensity, which leads to the slow temporal optical soliton pairs with matched group velocity and amplitude. We also show that the propagation of slow optical solitons can be strongly modified by the biexciton coherence.

Creating very slow optical gap solitons with a grating-assisted coupler

We show that optical gap solitons can be produced with velocities down to 4% of the group velocity of light using a grating-assisted coupler, i.e., a fiber Bragg grating that is linearly coupled to a non-Bragg fiber over a finite domain. Forward- and backward-moving light pulses in the non-Bragg fiber(s) that reach the coupling region simultaneously couple into the Bragg fiber and form a moving soliton, which then propagates beyond the coupling region. Two of these solitons can collide to create an even slower or stopped soliton.

Interaction properties of complex modified Korteweg–de Vries (mKdV) solitons

Interaction properties of complex solitons are studied for the two U ( 1 ) -invariant integrable generalizations of the modified Korteweg–de Vries (mKdV) equation, given by the Hirota equation and the Sasa–Satsuma equation, which share the same traveling wave (single-soliton) solution having a sech profile characterized by a constant speed and a constant phase angle. For both equations, nonlinear interactions in which a fast soliton collides with a slow soliton are shown to be described by 2 -soliton solutions that can have three different types of interaction profile, depending on the speed ratio and the relative phase angle of the individual solitons. In all cases, the shapes and speeds of the solitons are found to be preserved apart from a shift in position such that their center of momentum moves at a constant speed. Moreover, for the Hirota equation, the phase angles of the fast and slow solitons are found to remain unchanged, while, for the Sasa–Satsuma equation, the phase angles are shown to undergo a shift such that the relative phase between the fast and slow solitons changes sign.

Numerical investigation of slow solitons in Bragg gratings with a hyperbolic tangent apodization**

This paper numerically and analytically investigates the formation and propagation motion of optical soliton in the Bragg grating. We choose the fibre Bragg grating with hyperbolic tangent apodization in the middle section in order to obtain slower solitons. Optical fibre soliton but not Bragg grating soliton is used as input pulse in the discussion, which is much more approximate to the light source for the practical purpose. We discuss in detail the effects of the soliton's velocity with some parameters in the process of transmission. The results show that by choosing special parameters, one can make the soliton slow-down with a little distortion and energy decay and obtain tunable time-delay on a small scale.

Raman gap soliton in one-dimensional photonic crystal: A FDTD analysis

In this paper, Finite-Difference Time-Domain (FDTD) calculation of Maxwell's equations for simulation of Raman gap soliton is used. We investigated the generation of stationary gap solitons as well as slow gap solitons due to Raman shift in the one-dimensional photonic crystal. It is shown that by different intensities of the pump pulse, the generation position of slow Raman gap soliton can be altered. In addition, the dependence between generation position of Raman gap soliton and its velocity is verified.

Ion- and electron-acoustic solitons and double layers in multi-component space plasmas

A general model for the ion- and electron-acoustic solitons and double layers in a multi-component unmagnetized plasma consisting of background electrons, counter-streaming electron beams and ions is discussed. The model is based on the multi-fluid equations and the Poisson equation, and uses the Sagdeev pseudo-potential techniques. For identical counter-streaming electron beams and depending upon the plasma parameters, three types of solutions, namely, ion-acoustic, slow and fast electron-acoustic soliton/double layer, are possible. Generally, the ion acoustic solitons have positive potentials, slow-electron acoustic solitons have negative potentials and fast electron-acoustic solitons and double layers can have either positive or negative potentials depending on the core electron density. As beam speed is increased, first ion-acoustic and then slow electron-acoustic solitons disappear. At large beam speed, only fast electron-acoustic solitons/double layers survive. The results may be relevant to the observations of the electrostatic solitary waves (ESWs) observed in the Earth’s magnetosphere.

Fast and slow magnetosonic waves in two-dimensional spin-1/2 quantum plasma

Using the spin-1/2 resistive quantum magnetohydrodynamics model, linear and nonlinear relations for slow and fast magnetosonic modes are derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The plasma resistivity is shown to play a role of dissipation in the system. With the aid of tanh method the traveling wave solution of Kadomstev–Petviashvili–Burgers is obtained. The solution shows a general shock wave profile superposed by a perturbative solitary-wave contribution. The dynamics of fast and slow magnetosonic shock and soliton, respectively, in the presence and absence of dissipation is investigated with respect to electron spin magnetization, quantum diffraction, and plasma statistic. It is found that results obtained from the spin quantum plasmas differ significantly from the nonspin quantum plasmas. The relevance of the present work to dense astrophysical plasmas such as pulsar magnetosphere is pointed out.

Slow-light dark solitons in insulator–insulator–metal plasmonic waveguides

The potential of slow-light propagation in an insulator–insulator–metal plasmonic waveguide is studied. Due to the high dispersion of the device in the frequency region where the signal group velocity is low, slow-light optical pulses broaden in time and intersymbol interference occurs, limiting the achievable data rates and transmission distance. In order to overcome this problem, we analytically and numerically investigate slow dark solitons in the normal dispersion regime of the waveguide. The storing capability of the waveguide is analyzed from an application point of view.

GIANT THIRD-ORDER KERR NONLINEARITIES AND SLOW OPTICAL SOLITONS IN DOUBLE QUANTUM-WELL

We show the formation of slow optical solitons in the asymmetric coupled double quantum wells (CQW) via a two-photon Raman resonance. With the consideration of real parameters in AlGaAs -based CQW, we indicate the possibility to have cancelation of the linear absorption, giant Kerr nonlinearities, and slow group velocity propagation of the weak probe pulse at the same one-photon detuning frequency around several THz .

Propagation of a sausage soliton in the solar lower atmosphere observed by Hinode/SOT

Abstract Acoustic waves and pulses propagating from the solar photosphere upwards may quickly develop into shocks due to the rapid decrease of atmospheric density. However, if they propagate along a magnetic flux tube, then the non-linear steepening may be balanced by tube dispersion effects. This may result in the formation of a sausage soliton. The aim of this Letter is to report observational evidence of a sausage soliton in the solar chromosphere. A time series of the Caii H line obtained at the solar limb with the Solar Optical Telescope (SOT) on board Hinode is analysed. Observations show an intensity blob, which propagates from 500 to 1700 km above the solar surface with a mean apparent speed of 35 km s−1. The speed is much higher than the expected local sound speed, therefore the blob cannot be a simple pressure pulse. The blob speed, length-to-width ratio and relative intensity correspond to a slow sausage soliton propagating along a magnetic tube. The blob width increases with height corresponding to the magnetic tube expansion in the stratified atmosphere. Propagation of the intensity blob may be the first observational evidence of a slow sausage soliton in the solar atmosphere.

Effect of Ion Temperature on Soliton Reflection in a Magnetized Positive-Ion–Negative-Ion Plasma With Two Types of Electrons

Analytical investigations are carried out for the soliton propagation and reflection in a magnetized positive-ion-negative-ion plasma having two types of electrons based on the reductive perturbation technique. It is found that this type of plasma does not support rarefactive solitons, which are otherwise found to propagate in negative-ion-containing plasmas with isothermal electrons. This is the consequence of the low-temperature electron component present in the plasma. Two types of compressive solitons, namely, the fast wave soliton and the slow wave soliton, are found to exist, but only the fast compressive solitons will reflect. The effect of ion temperature is to enhance the soliton reflection; the same is the case for an increased number of negative ions. However, the effect of low-temperature electrons is to weaken the soliton reflection. Interestingly, the solitons are found to downshift after their reflection, and this shift is less under the effects of stronger magnetic field, smaller wave propagation angle, and a higher concentration of low-temperature electrons. However, larger amplitude solitons are more downshifted, and the shift is more for higher ion temperature and when the wave propagates with larger phase velocity.