Vector dark spatial solitons

The dark spatial solution of TM type is shown to exist in a uniform selfdefocusing nonlinear medium in the range of the beam effective index n/sub eff/ from 0.82n/sub 0/ to n/sub 0/ of the linear refractive index of the medium. This contrasts with the dark spatial soliton of TE type which exists over all the possible values of n/sub eff/ ranging from 0 to n/sub 0/. The field profile of this TM dark wave is also found to depend on the beam effective index, deviating from the hyperbolic tanh function of TE type with decreasing n/sub eff/.<>     

Dark spatial solitons sequence in the biased centrosymmetric photorefractive crystal

We theoretically investigate the evolution of dark screening spatial solitons originating from the quadratic electro-optic effect in biased centrosymmetric photorefractive (CP) crystal by using beam propagation method (BPM). The results indicate that the multiple dark solitons sequence can be obtained in the CP crystal with the odd or even initial conditions. If the initial width of the dark notch is smaller, only a fundamental soliton or a Y-junction soliton pair is generated. When the initial width of the dark notch and the bias electric field are increased, the multiple dark spatial solitons sequence is formed, which realized a progressive transition from a low-order soliton to a higher-order solitons sequence in both odd and even conditions. The solitons characteristic is similar to that of screening solitons in the non-centrosymmetric photorefractive (NCP) crystals.     

视紫红酯中热致暗空间光孤子实验

设计了热致暗空间光孤子的实验光路和偶边界条件的实施方案,在视紫红酯中实现了热致暗空间光孤子实验,研究了孤子随传输距离和光强的演化,并采用分步傅里叶变换法进行了数值模拟,发现两者的结果一致。     

外加电场双光子光伏光折变晶体中的空间孤子

证明在外加电场的双光子光伏光折变晶体中存在明、暗稳态空间孤子波,它源于双光子光折变效应。结果表明：当光伏效应可以忽略时,这种孤子类似于双光子屏蔽孤子;当没有外加电场时,它退化成闭路条件下的双光子光伏孤子。在不同条件下屏蔽孤子和光伏孤子理论都可以从这一统一理论中得到。     

中心对称和非中心对称单光子光折变空间屏蔽灰孤子的时间特性

为了得到中心对称和非中心对称外加电场单光子光折变晶体中空间屏蔽灰孤子时间特性的结果,基于中心对称和非中心对称单光子光折变效应的基本理论,推导出了含时间参量的空间电荷场和光波的动态演化方程,采用数值方法,分别研究了基于中心对称和非中心对称单光子光折变晶体中灰孤子强度包络和强度半峰全宽的时间特性。结果表明:当孤子的峰值强度与暗辐射的比值较大时,孤子的半峰全宽先是随时间递减到一个最小值,然后逐渐增加到一个稳定的常数值。当孤子的峰值强度与暗辐射的比值较小时,孤子的半峰全宽随时间的增加而单调减小,最终达到一稳定状态。对不同时刻灰孤子的动态演化特性进行了研究,中心对称和非中心对称空间灰孤子有类似的时间演化特性。     

PT对称光晶格中的缺陷暗孤子

数值研究了实部具有缺陷的parity-time对称光晶格中的缺陷暗孤子。当衍射与自散焦非线性效应平衡时,暗孤子能够被获得;当自散焦介质中的parity-time对称光晶格实部被附加一个缺陷后,缺陷暗孤子也能够被获得。数值结果显示：缺陷暗孤子可以在很大参数范围内存在并且能稳定传播;parity-time对称光晶格实部附加的缺陷强度有一最大值,超过此值缺陷暗孤子不存在;parity-time对称光晶格的虚部振幅对缺陷暗孤子的稳定性有影响。     

Spatial solitons in nematic liquid crystals

Nematic liquid crystals exhibit a saturable nonlinearity, nonlocal in time and in space, owing to light-induced reorientation of the molecular director. In such media, (2 + 1)-dimensional spatial solitons can be obtained at milliwatt-power levels and confine weaker co-polarized signals of different wavelengths, employing either coherent or partially incoherent excitations. Our experimental observations of solitons and related phenomena, ranging from angular steering to mutual interactions, are reviewed. Models are briefly discussed and used to predict and interpret the results.     

光纤暗孤子相互作用

用变分原理导出了非线性Schrodinger方程两个暗孤子间的相互作用,它作为孤子间距Δ和初位相差θ的函数,随Δ的增大而指数地衰减。当两个孤子间初位相差θπ/2时相互排斥,θπ/2时相互吸引,θ=π/2时几乎不存在相互作用。解析与数值计算结果相符。验证了与已有理论的一致有效性。     

在损耗光纤中的暗孤子传输特性

本文采用数值分析和扰动法研究了光纤损耗的存在对正常色散区暗孤子的影响，结果表明：暗孤子的脉宽在相同损耗光纤中总比亮孤子扩展得更慢；对于零色散波长大于１．５５μｍ的色散移位光纤，暗孤子的放大周期比亮孤子的放大周期大一倍。这对于未来的海底光纤通信将具有很大的吸引力。关于暗孤子的二阶理论，现有的文章很少，仅文献［１］也只做了Ｈ１的理论推导工作，且误差还很大。本文首次推导出Ｈ１的精确解、并得出了关于暗孤子准确、完善的二阶理论结果。     

Observation of spatial solitons in AlGaAs waveguides

The first observation of spatial optical solitons in the semiconductor AlGaAs is reported. Operating in the spectral region close to half the bandgap allows the positive nonlinearity of the semiconductor to be fully used, while minimising the effects of two-photon absorption.<>     

Bright and dark Bragg solitons in a fiber Bragg grating

We investigate the nonlinear pulse propagation through the fiber Bragg grating structure where the pulse dynamics are governed by the nonlinear-coupled mode (NLCM) equations. Using multiple scale analysis, we reduce the NLCM equations into the perturbed nonlinear Schrodinger (PNLS) type equation. To construct the bright and dark Bragg solitons in the upper and lower branches of the dispersion curve, we solve the PNLS equation using the coupled amplitude-phase method.     

Vector analysis of the space-charge field in nonconventionally biased photorefractive crystals

A theoretical model to numerically study the local space-charge field induced by light in a photorefractive crystal biased with two independent, perpendicularly oriented external static fields is introduced. This model appears attractive because it allows varying, in the crystal transverse plane, of the orientation of the external biasing static field with respect to that of the optical-field vector, then enhancing the tensorial properties of the crystal. The numerical analysis has revealed that, in a nonconventional biasing configuration, the spatial distributions of the space-charge-field vector transversal components exhibit a further anisotropy that has not been shown up to now. Nevertheless, from a practical point of view, such a boundary configuration could allow better management of the focusing characteristics of the material.     

Chirosolitons: unique spatial solitons in chiral media

We show analytically that unique spatial solitons (chirosolitons) can propagate in chiral media that exhibit Kerr-type nonlinearities. In contrast to the solitons in achiral media, unique features of the chirosolitons can be seen in their elliptically polarized nature, the bisoliton state, and the possibility of superluminous phase propagation. Conditions for supporting the bright- and dark-type chirosolitons are discussed     

双光子光折变材料中低振幅屏蔽光伏空间孤子

为了得到低振幅双光子屏蔽光伏空间孤子的结果,对外加电场的双光子光伏光折变介质中低振幅空间孤子进行了研究。给出了低振幅双光子屏蔽光伏亮和暗孤子的解析表达式,并推导出了孤子宽度的显式表达式。结果表明,低振幅双光子屏蔽光伏孤子可以看成是双光子低振幅屏蔽孤子和双光子低振幅光伏孤子的统一形式。当外加电场很强可忽略光伏效应时,它转化成低振幅屏蔽孤子;当外偏压为0时,它相当于开路或闭路的低振幅光伏孤子。该研究结果为空间光孤子理论的发展提供了理论依据。     

双光子光折变材料中的刚性光伏孤子

为了研究不同参量对双光子光折变材料中的刚性光伏空间孤子的影响,推导出了刚性光伏空间孤子的演化方程,根据实际的物理条件,采取一定的数学近似,对演化方程进行化简,从而得出演化方程的亮暗孤子的解析解,并讨论了不同参量,如光伏电场强度、背景暗辐射光强度、启动光强度、吸收系数和光波长对孤子的影响。结果表明,除了光伏电场强度,亮孤子的宽度随其增加而减小之外,亮孤子的宽度都随其它参量的增加而变大,只是变大趋势的速度不同。研究结果可为空间光孤子理论发展提供理论依据。     

The propagation of bright and dark solitons in lossy optical fibers

An analytic perturbation solution to the nonlinear Schrodinger equation with loss Γ for both normal and anomalous dispersion is developed. Explicit results are obtained through second order in the perturbation Γ. The results show that the dark pulse spreads less rapidly than the bright one and that total spreading as well as the difference in spreading rate for the two types of pulses decreases with loss. Comparisons are made with a zeroth-order perturbation theory and with numerical simulations, which are found to bracket the second-order results     

双光子光折变介质中Manakov屏蔽孤子的温度特性

为了研究双光子光折变介质中Manakov屏蔽孤子的温度特性,采用数值模拟的方法,得到了Manakov屏蔽孤子的强度包络,并分析了亮-暗Manakov屏蔽孤子对动态演化的温度特性。结果表明,亮-亮Manakov屏蔽孤子对的强度包络随着晶体温度的升高,其两孤子成分的峰值光强都逐渐减小,而其半峰全宽逐渐增加;暗-暗和亮-暗Manakov屏蔽孤子对具有类似的温度特性。说明通过改变晶体温度可以调控孤子的空间形态。     

利用多重尺度理论对暗孤子在变迹光栅中演化特性的研究

从光纤光栅中的耦合波理论出发,利用多重尺度理论推导出光栅中的有效薛定谔方程。并在正常色散区运用快速傅立叶方法数值模拟了暗孤子在升余弦变迹光纤光栅中的演化以及暗孤子之间的相互作用。结果表明,在一定条件下光纤光栅的正常色散区可以维持暗孤子的稳定传输,并且孤子的稳定性与f的取值（孤子离光子带隙的位置）和非线性系数有关。随着f的增大单孤子背景处出现震荡现象;而随着f的增大两个暗孤子中心和背景处都将出现震荡、演化产生灰孤子等现象,但暗孤子之间的相互作用始终很弱;而且f越大,两个孤子的稳定性对非线性效应越敏感。     

Generation of dark solitons by interaction between similaritons in Raman fiber amplifiers

We present a new method to generate dark soliton trains by exploiting the interaction between two time-delayed optical similaritons with the same wavelength. The temporal overlap of two similariton pulses creates a sinusoidal beating which subsequently evolves into an ultrahigh repetition-rate train of dark solitons through the combined effects of normal dispersion, nonlinearity, and adiabatic Raman gain. The experimental results are in good agreement with numerical predictions. We also investigate how the the repetition rate of the dark soliton train depends on the time separation between the initial pulses, the initial pulse energy, and the Raman gain. Finally, we numerically study the interaction between three similaritons of the same wavelength.