Shifting bright spatial solitons in LiNbO₃

We observe spatial bright solitons in a transversely shifting LiNbO₃ crystal. In this scheme, the photovoltaic nonlinearity in LiNbO₃ can be switched from self-defocusing to self-focusing by continuous shifting of the beam. Moreover, the shifting velocity has a strong influence on the wave shape of the bright spatial solitons.     

一维光伏空间灰孤子及其稳定性研究

从考虑背景光的光伏作用后的光束在光伏媒质中传播的方程出发,证明了在折射率改变为正的光伏媒质中也可以形成灰孤子。光束以灰孤子状态在光伏晶体中传播时,其横向相位必须具有一个与光强分布有关的形式分布,表达式为φ（s）=v[η-∫y^-2（η）dη],其中v是灰孤子的横向运动速度,η是无量纲化坐标,y（η）是归一化的光场振幅。分别讨论了光束灰度、光强振幅、信号光与背景光的有效Glass系数之比R对一维的光伏空间灰孤子宽度、横向总相移和横向运动速度的影响,并分析了光伏灰孤子的稳定性。当光束的灰度m为0时,这一理论可直接退化为光伏暗孤子的理论。     

Break up of bound-N-spatial-soliton in a ramp waveguide

We present an analytical and numerical investigation of the propagation of spatial solitons in a nonlinear waveguide with ramp linear refractive index profile (ramp waveguide). For the propagation of a single soliton beam in a ramp waveguide, the particle theory shows that the soliton beam follows a parabolic curve in the region where the linear refractive index increases and a straight line outside the waveguide. The acceleration of the soliton depends on the beam intensity: higher amplitude solitons experience higher acceleration. Numerical calculations using an implicit Crank–Nicolson scheme confirm the result of the particle theory. Combining these propagation properties with the theory about bound-N-soliton, we study the break up of such a bound-N-soliton in a ramp waveguide. In a ramp waveguide, a bound-N-soliton will always be splitted into N independent solitons with the higher amplitude soliton emitted first. The amplitude of the separated solitons after break up are calculated using the soliton theory as if the solitons are independent. Numerical simulations show that the results agree quite well with this theoretical prediction, indicating that the interaction during break up has only little influence.     

Discrete light bullets in two-dimensional photonic lattices: Collision scenarios

We report systematic results of collisions between discrete spatiotemporal optical solitons in two-dimensional photonic lattices. We show that the outcomes of collisions strongly depend on the initial soliton parameters, such as their input amplitudes (energies) and their transverse velocities. Four generic outcomes are identified in the study of collisions between discrete light bullets located in the corner, at the edge, and in the center of the photonic lattice: (a) merger of both low and high amplitude solitons into a single one, at small values of the kick parameter (soliton transverse velocity), (b) spreading of low amplitude solitons at intermediate values of the kick parameter, (c) bouncing of high amplitude solitons at intermediate values of the kick parameter, which is accompanied by a sharp modification of input soliton transverse velocities, and (d) quasi-elastic (symmetric) interactions of both low and high amplitude solitons at large values of the kick parameter.     

STABILITY OF BRIGHT SCREENING-PHOTOVOLTAIC SPATIAL SOLITONS

We present a theoretical analysis of the stability of screening-photovoltaic (SP) spatial solitons in biased photovoltaic-photorefractive materials in the case of neglecting the loss of the material and the effect of diffusion. When an incident optical beam is a SP soliton, this beam propagates along a linear path with its shape kept unchanged. When the maximum amplitude, width and functional form of an incident optical beam are slightly different from those of a SP soliton, the beam reshapes itself and tries to evolve into a solitary wave after a short distance. That is, these SP solitons are stable against small perturbations. However, optical beams that significantly differ from SP soliton solutions tend to experience larger cycles of compression and expansion, and their maximum amplitudes oscillate with propagation distances. The larger the perturbations, the stronger the oscillation.     

Break up of bound-N-spatial-soliton in a ramp waveguide

We present an analytical and numerical investigation of the propagation of spatial solitons in a nonlinear waveguide with ramp linear refractive index profile (ramp waveguide). For the propagation of a single soliton beam in a ramp waveguide, the particle theory shows that the soliton beam follows a parabolic curve in the region where the linear refractive index increases and a straight line outside the waveguide. The acceleration of the soliton depends on the beam intensity: higher amplitude solitons experience higher acceleration. Numerical calculations using an implicit Crank-Nicolson scheme confirm the result of the particle theory. Combining these propagation properties with the theory about bound-N-soliton, we study the break up of such a bound-N-soliton in a ramp waveguide. In a ramp waveguide, a bound-N-soliton will always be splitted intoN independent solitons with the higher amplitude soliton emitted first. The amplitude of the separated solitons after break up are calculated using the soliton theory as if the solitons are independent. Numerical simulations show that the results agree quite well with this theoretical prediction, indicating that the interaction during break up has only little influence. On Leave from Jurusan Matematika, Universitas Brawijaya, Jl. MT Haryono 167 Malang Indonesia.     

Self-bending of photorefractive solitons

Self-bending of photorefractive solitons is caused by diffusion in photorefractive crystals and becomes an important effect when the beam size is in the range of the charge carriers diffusion length. In this paper we present an experimental and numerical examination of the beam bending dependence on relevant parameters such as the applied electric field and the beam intensity. We demonstrate that the bending dependence on the electric field in the low saturation regime has the form of a square function at low values of the field and becomes linear for higher values. For stronger saturation the curve gets the form of a square root function. The bending dependence on the beam intensity has a maximum at defined intensity. The experimental data are compared with numerical simulations, giving a good qualitative agreement.     

Optical ratchets with discrete cavity solitons

We propose a setup to observe soliton ratchet effects using discrete cavity solitons in a 1D array of coupled waveguide optical resonators. The net motion of solitons can be generated by an adiabatic shaking of the holding beam with zero average inclination angle. The resulting soliton velocity can be controlled by different parameters of the holding beam.     

Surface lattice solitons in diffusive nonlinear media

We address the properties of surface solitons supported by optical lattices imprinted in photorefractive media with asymmetrical diffusion nonlinearity. Such solitons exist only in finite gaps of the lattice spectrum. In contrast to latticeless geometries, where surface waves exist only when nonlinearity deflects light toward the material surface, the surface lattice solitons exist in settings where diffusion would cause beam bending against the surface.     

主客体式光折变聚合物中空间明孤子的动态演化特性

研究了主客体式光折变聚合物中空间明孤子的动态演化特性,讨论了振幅微扰和宽度微扰对其传播特性的影响.结果表明,入射波为明孤子波时,能够在聚合物中稳定直线传播 在较小微扰情况下,孤子波经短距离传播后能够演化为明孤子波 当微扰比较大时,光波不能在聚合物中稳定传播,而是呈现周期性震荡现象 关键词： 光折变效应 光折变聚合物 空间孤子     

Holographic solitons in photorefractive dissipative systems

A new kind of holographic soliton is proposed for a photorefractive dissipative system consisting of a biased photorefractive crystal and a strong pump beam with a uniform spatial distribution in both transverse dimensions. The self-trapping beam in the system can evolve into a spatial soliton when it couples coherently with the pump beam by two-wave mixing. Unlike the holographic solitons recently proposed by Cohen et al. [Opt. Lett. 27, 2031 (2002)], the most unique features of the present solitons are that they have a fixed amplitude and width that are determined completely by the system parameters and that their existence conditions are independent of the polarity of the bias field. Numerical simulations show that these solitons are stable relative to small perturbations.     

Moving Matter-Wave Solitons in Spin-Orbit Coupled Bose-Einstein Condensates

We investigate the moving matter-wave solitons in spin-orbit coupled Bose-Einstein condensates(BECs) by a perturbation method.Starting with the one-dimensional Gross-Pitaevskii equations,we derive a new KdV-like equation to which an approximate solution is obtained by assuming weak Raman coupling and strong spinorbit coupling.The derivation of the KdV-like equation may be useful to understand the properties of solitons excitation in spin-orbit coupled BECs.We find different types of moving solitons:dark-bright,bright-bright and dark-dark solitons.Interestingly,moving dark-dark soliton for attractive intra- and inter-species interactions is found,which depends on the Raman coupling.The amplitude and velocity of the moving solitons strongly depend on the Raman coupling and spin-orbit coupling.     

Interaction between multiple spatial solitons in the diffraction catastrophe region upon focusing a high-power laser beam in a nonlinear medium

When a high-power laser beam is focused in a nonlinear Kerr medium, beam self-diffraction by induced inhomogeneities of the refractive index is observed. A method for calculating the field amplitude and phase in the focal region with regard for self-diffraction by self-induced inhomogeneities is developed. Computer analysis of saturable Kerr media showed that the optical-field region with the least cross section of the focal pattern is followed by that of chaotically radiating “splashes” and long filaments. The latter radiate outward from the region of the caustic waist over long distances. They represent bright spatial solitons, which channel a significant portion of the primary beam energy. No less than 8–12 clear-cut solitons traveling in the positive z direction and moving apart in the transverse (x, y) plane are observed in the cross section. The field amplitude oscillates along each of the solitons. Various parameters of the saturable Kerr medium are taken into account.     

光折变明孤子的自偏转演化特性

利用一维稳态光折变空间光孤子的统一理论，研究了负载电阻对屏蔽、光伏和屏蔽光伏明孤子自偏转特性的影响。结果表明，无论加载电阻与否，这三种类型的光折变明孤子具有类似的自偏转特性，即孤子波沿一个抛物线轨迹运动。调节负载电阻可以改变孤子的偏转幅度，其中屏蔽光伏明孤子的可调范围最大。     

Self-induced transparency and electromagnetic pulse compression in a plasma or an electron beam under cyclotron resonance conditions

Based on analogy to the well-known process of the self-induced transparency of an optical pulse propagating through a passive two-level medium we describe similar effects for a microwave pulse interacting with a cold plasma or rectilinear electron beam under cyclotron resonance condition. It is shown that with increasing amplitude and duration of an incident pulse the linear cyclotron absorption is replaced by the self-induced transparency when the pulse propagates without damping. In fact, the initial pulse decomposes to one or several solitons with amplitude and duration defined by its velocity. In a certain parameter range, the single soliton formation is accompanied by significant compression of the initial electromagnetic pulse. We suggest using the effect of self-compression for producing multigigawatt picosecond microwave pulses.     

Effect of Thermionic Emission on Dust-Acoustic Solitons in a Dust-Electron Plasma

The effects of thermionic emission on dust-acoustic solitons with a very small but finite amplitude in a dustelectron plasma are studied using the reductive perturbation technique. The self-consistent variation of dust charge is taken into account. It is shown that the thermionic emission could significantly increase the dust positive charge. The dependences of the phase velocity, amplitude, and width of such solitons on the dust temperature and the dust work function of dust material are plotted and discussed.     

PARTICULAR SOLITONS IN NONLINEAR LATTICE

One soliton of particle velocity and its amplitude (maximum particle velocity of one soliton) in Toda lattice is given analytically. It has also been known numerically that the maximum particle velocity (when the collision of two solitons reaches their maximum, we define V_n at this time as its maximum particle velocity) during the collision of two solitons moving in the same direction is equal to the difference between the amplitudes of two solitons if the difference is large enough; however, the maximum particle velocity is equal to the adding up of the amplitudes of two solitons moving in the opposite directions. The relationship between the maximum value of e^-(r_n)-1 and their initial amplitude of e^-(r_n)-1 is also given analytically in Toda lattice if the amplitudes of the two solitons are the same and their moving directions are opposite. Compared with the Boussinesq equation, there are differences between the Toda lattice equation and the Boussinesq equation for solitons during the collision.     

Gradient induced motion control of drifting solitary structures in a nonlinear optical single feedback experiment

We realize an absolute position control of drifting dissipative optical solitons by injecting an incoherent amplitude parameter gradient onto the nonlinear optical system. This allows for two-dimensional, arbitrary control patterns. The control of the soliton drift velocity is studied applying a periodic, hexagonally shaped modulation. The guiding of dissipative solitons by one- and two-dimensional parameter modulations is demonstrated. Furthermore, one-dimensional, line-shaped parameter modulations are designed to act as barriers for dissipative solitons, allowing implementations of position selectors for solitons. The interaction of dissipative optical solitons with barriers is studied for different barrier parameters.     

Few-cycle relativistic solitons in plasmas

A set of exact one-dimensional solutions to coupled nonlinear equations describing the propagation of a relativistic ultrashort circularly polarized laser pulse in a cold collisionless and bounded plasma where electrons have an initial velocity in the laser propagating direction is presented. The solutions investigated here are in the form of quickly moving envelop solitons at a propagation velocity comparable to the light speed. The features of solitons in both underdense and overdense plasmas with electrons having different given initial velocities in the laser propagating direction are described. It is found that the amplitude of solitons is larger and soliton width shorter in plasmas where electrons have a larger initial velocity. In overdense plasmas, soliton duration is shorter, the amplitude higher than that in underdense plasmas where electrons have the same initial velocity.     

Switching spatial dissipative solitons in a VCSEL with frequency selective feedback

The process of switching on bistable spatial dissipative solitons in a VCSEL with frequency selective feedback is analyzed experimentally and theoretically. Two regimes of successful writing of spatial solitons with an external pulse are identified: for short durations of the writing beam pulse, the input amplitude has to increase, while for longer durations, the input amplitude can remain constant. Switch on spectrograms of the frequency spectrum show a transient dynamics over many modes of the external cavity with a drift of the central frequency from higher to lower frequency. Such a multi-mode regime is almost independent of the frequency of the writing beam. It is interpreted to be due to the existence of multiple unstable solitons with different frequencies which channel the transient dynamics. Good agreement between experimental results and numerical simulations in both the time and frequency domains is found.