Stable droplets and dark-ring cavity solitons in nonlinear optical devices

Two kinds of cavity solitons, stable circular domain walls (droplets) and dark-ring cavity solitons, are presented in models of vectorial Kerr resonators and degenerate optical parametric oscillators. These structures are universal in systems with two equivalent homogeneous states and are found for parameter values close to those of a modulational instability of a flat front. Stable droplets owe their existence to curvature effects and, therefore, they are not present in one-dimensional systems. We show that stable droplets nucleate out of dark-ring cavity solitons and that in some systems there are regimes in which they coexist.     

局域单PT对称势中基态孤子的传输特性研究

具有Parity-Time (PT)对称性的光学系统是近年提出的一种新型光学结构,在光开关、光子信息处理器件等方面具有潜在的应用.文章数值研究了局域单PT对称光学系统中基态孤子的存在范围与稳定特性.研究结果表明:基态孤子存在一临界传播常数,该传播常数对应线性模下的本征值.孤子的能量随着传播常数的增加而增加,但随着PT对称势的调制深度的增加而减少.基态孤子在较深和较浅的PT对称势中都能稳定地传输.     

Quadratic cavity solitons-the up-conversion case

We derive mean-field equations for intra-cavity second-harmonic generation. Based on this model, we show that a variety of quadratic cavity solitons can exist. Highly symmetric and resting cavity solitons originate from primary bifurcations of the underlying stationary plane wave solutions. For certain control parameters, these solutions may undergo a secondary bifurcation leading to symmetry-reduced and/or moving/breathing quadratic cavity solitons. In particular, we predict for the first time the existence of triangular cavity solitons and derive a criterion for an nonequilibrium Ising-Bloch transition.     

克尔双周期PT对称光晶格中的空间光孤子

数值研究了克尔双周期Parity-time对称光晶格中能存在的空间光孤子。通过平面波展开法详细研究了此光晶格的带隙结构并获得其相变点。数值研究了此光晶格中能存在的空间光孤子及其传播稳定性。数值结果显示位于不同周期波导上的空间光孤子其稳定性区间不同。     

Topologically multicharged and multihumped rotating solitons in wide-aperture lasers with a saturable absorber

We present results of a semianalytical and numerical study of transverse two-dimensional stationary and oscillating solitons in a wide-aperture laser with a saturable absorber and fast nonlinearity of both gain and absorption. We determine the stability conditions and bifurcations of axially symmetric solitons with screw wavefront dislocations of different order. We demonstrate the existence of asymmetric rotating laser solitons with different numbers of intensity maxima.     

分布放大传输系统中暗孤子链的传输特性研究

研究了由低掺杂浓度的分布式掺铒光纤级联传输系统中,多个暗孤子组成的暗孤子链的传输特性,结果表明：在分布放大传输中,奇或偶数个暗孤子组成的暗孤子链的传输特性存在较大的差异,其中奇数个暗孤子组成的暗孤子链的传输稳定性较好,而偶数个暗孤子组成的暗孤子链在传输过程中存在明显的由暗孤子相互作用引起的孤子自频率漂移和孤子变形。     

Characterization of stationary patterns and their link with cavity solitons in semiconductor microresonators

We study the periodic structures that emerge beyond the instability threshold point in a semiconductor microcavity driven by a coherent stationary holding beam; the active layer of the microresonator is bulk GaAs or multiple quantum-well GaAs-AlGaAs. We apply a numerical technique to directly establish stationary solutions of the dynamical equations governing the electric field inside the cavity and the carrier density of the active material. To overcome the heavy computational requirements in the case of two-dimensional patterns, we consider small nonorthogonal integration grids, whose geometrical properties are those of the pattern elementary cell. We investigate the mechanism of pattern formation in connection with the modulational instability threshold, and we study, both in one and two dimensions, the bifurcation structure of various branches of patterns. We show how cavity solitons are related to periodic structures and we study the behavior that cavity soliton branches may exhibit in two dimensions.     

光折变晶体中的光生伏打灰空间孤子

在自散焦介质中，平面波的传播对小的调制扰动是绝对稳定的，暗空间孤子正是作为平面波背景上的一种局域暗迹而存在的。基于这种调制稳定性，给出了由光生伏打自散焦非线性支持的一维灰空间孤子的演化方程，并在光生伏打光折变LiNbO3：Fe晶体中给出了它的静态解。数值研究了这种灰空间孤子的诸多性质：例如在不同的孤子灰度下的孤子轮廓和它的相位分布；光生伏打灰孤子的归一化横向传播速度和归一化半峰全宽随归一化的背景光强和孤子灰度的变化等。所有这些性质都可以通过调节孤子波两侧的相位差加以控制，并详细地比较了光生伏打灰孤子和屏蔽灰孤子之间的异同。     

Stable propagation of dark solitons in dispersion maps of eithersign of path-average dispersion

In fibres with alternating dispersion, dark solitons are shown to propagate stably as far as can be told from numerical simulation. This holds even in the case of a dispersion map with average anomalous dispersion, i.e. in the regime which for homogeneous fibres is the `forbidden' regime for dark solitons. We have shown that the pulse shape is characteristically modified in the dispersion-managed fibre, and we see indications of a modified soliton power. These results demonstrate an appealing symmetry with earlier corresponding finding that bright solitons are modified in shape and power, and can extend their existence into their `forbidden' regime     

Optical patterns and cavity solitons in quantum-dot microresonators

We study optical transverse instabilities in quantum-dot (QD) microresonators. We develop a model for the QD susceptibility taking into account the inhomogeneous broadening of the dot emission. A linear stability analysis and numerical integration of the resulting equations are performed. Special attention is paid to the formation of such structures as optical patterns and cavity solitons, which could play an important role in the field of optical information processing. Implications for actual QD materials are discussed in view of applications.     

非局域非线性中奇异空间光孤子传输特性研究

基于非局域非线性介质中空间光孤子的理论模型,采用分部傅里叶算法,我们研究了空间孤子在二维非局域非线性介质中的传输特性及其稳定性。结果表明,在该介质中存在Laguerre-Gauss（拉盖尔-高斯）型的空间孤子;孤子的传输特性受非局域介质的调制系数、调制深度,以及光束的初始条件等调控,并且传输距离的越大,影响越显著。本文的结果对完善和充实空间孤子理论体系有重要意义。     

Inter-resonance soliton generation and trapping

We show a new type of actively mode-locked fiber laser that, despite the 2.5-km-long cavity and the average group-velocity dispersion of -20 ps²/km, generates solitons with duration of 2÷4 ps, 1-GHz repetition rate and timing jitter of 0.7 ps. Such short solitons are generated in an inter-resonance condition that favors a highly stable propagation regime. Soliton duration and timing jitter are both controlled by the self-frequency-modulation due to the background radiation emitted by the solitons themselves     

中心对称双光子低振幅亮屏蔽孤子的时间特性

为了得到中心对称双光子光折变晶体中低振幅亮屏蔽孤子的时间特性的结果,推导出了晶体中空间电荷场的时间特性,得到了亮孤子的归一化空间包络随时间变化的方程。采用数值分析的方法对亮孤子的归一化空间包络及其在晶体中的时间演化特性进行了理论分析。结果表明：孤子的空间包络宽度随时间的演化单调递减一个最小值直至稳态孤子的形成;在相同的演化时间下,孤子的半峰全宽随着孤子峰值强度和暗辐射比值的增大而变小。在不同的时刻,入射光束都可在中心对称双光子光折变晶体中演化成空间孤子。所得结果对完善光折变空间孤子的理论有十分重要的意义。     

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。     

具有强耦合外腔的半导体激光器稳定性极限条件

从理论上分析了强耦合外腔半导体激光器的稳定性。在外腔半导体激光器速率方程分析中引人了强反偏因子近似，通过增益速率－频率平面中的特性分析得到如下结论：对于给定参数的外腔半导体激光器，存在有一个技术不能超越的稳定性的理论极限条件。强反馈和短外腔长度有利于提高外腔半导体激器的稳定性．     

Theoretical and experimental studies of lattice solitons in nonlinear lumped networks

We have observed, by using a nonlinear lumped LC network, the fundamental properties of solitons indicated by Zabusky and Kruskal, where 1) an initial pulselike disturbance breaks into many solitons, 2) a soliton of high amplitude travels faster than one of low amplitude, and 3) solitons preserve their identities after interacting with each other nonlinearly. Some of the fundamental properties of solitons are explained physically in terms of properties of the nonlinear LC network, and are demonstrated mathematically by establishing analytical expressions for solitons in a particular network.     

耗散孤子和束缚态脉冲可切换的超连续谱产生

当超短脉冲进入高非线性光纤时,在色散和非线性效应的共同作用下,脉冲频谱中会产生一些新的频率分量,使得输出频谱比输入频谱宽得多。这种光谱被称为超连续谱。超连续谱光源具有光谱范围宽、方向性好、亮度高、空间相干性好等优点。在锁模激光器中,传统孤子、耗散孤子和类噪声脉冲可以作为种子源产生超连续谱。文中,笔者建立了一个NPR被动锁模光纤激光器来产生脉冲激光。然后,添加一段DCF以补偿腔中的色散,从而产生耗散孤子。同时,通过调节腔内PC,可以实现束缚态和耗散孤子的状态切换。输出脉冲经10 m单模光纤压缩后注入部分拉锥后的高非线性光纤以产生超连续谱。实验中,我们得到了脉宽为5.6 ps、重复频率为32 MHz、信噪比为52 dB的耗散孤子锁模脉冲,压缩后的脉冲宽度为868 fs,用作超连续谱产生。超连续谱的覆盖范围约为1200~2200 nm,其20 dB谱宽为357 nm。通过调节偏振控制器,实现耗散孤子脉冲与束缚态脉冲之间的切换,束缚态脉冲持续时间为1.4 ps,脉冲间隔为14 ps,信噪比为51 dB,产生1600~1870 nm的超连续光谱,20 dB的光谱宽度为135 nm。     

Molding light into solitons

The nature of soliton waves and the potential of optical solitons for long-distance repeaterless transmission are discussed, and the pioneering experiments are recounted. Techniques for generating and transmitting solitons are described. The discovery of the existence of a limit on transmission distance, due to timing jitter, and ways to extend that limit are discussed     

横向非周期性调制Kerr介质中的空间光孤子

数值方法研究了横向非周期调制Kerr介质中所支持的空间光孤子。数值模拟结果显示研究模型存在三种类型空间光孤子：低功率下的双峰孤子、高功率下的基本孤子和稳定传输的双极孤子。应用线性稳定性分析方法研究了三种类型空间光孤子的稳定传输的稳定谱,总结出三种类型光孤子稳定传输的条件。