Optical vortex solitons in parametric wave mixing

We analyze two-component spatial optical vortex solitons supported by parametric wave mixing processes in a nonlinear bulk medium. We study two distinct cases of such localized waves, namely, parametric vortex solitons due to phase-matched second-harmonic generation in an optical medium with competing quadratic and cubic nonlinear response, and vortex solitons in the presence of third-harmonic generation in a cubic medium. We find, analytically and numerically, the structure of two-component vortex solitons, and also investigate modulational instability of their plane-wave background. In particular, we predict and analyze in detail novel types of vortex solitons, a "halo-vortex," consisting of a two-component vortex core surrounded by a bright ring of its harmonic field, and a "ring-vortex" soliton which is a vortex in a harmonic field that guides a ring-like localized mode of the fundamental-frequency field.     

Dipole-mode vector solitons

We find a new type of optical vector soliton that originates from trapping of a dipole mode by the soliton-induced waveguides. These solitons, which appear as a consequence of the vector nature of the two-component system, are more stable than the previously found optical vortex solitons and represent a new type of extremely robust nonlinear vector structure.     

Incoherently coupled screening photovoltaic spatial solitons in biased photovoltaic photorefractive crystals

Propagation characteristics and stability properties of two-component composite screening photovoltaic spatial solitons have been analyzed in this paper. Employing paraxial ray approximation, we have identified a very large family of new two-component composite screening photovoltaic solitons in photovoltaic-photorefractive crystals. These composite solitons can exist only when the carrier beams have the same polarization, wavelength and are mutually incoherent. We have identified a wide parameter space involving spatial width and power where these composite solitons can exist as a stationary entity. The identified regions of existence of solitons give a deeper understanding of these solitons and reveal some interesting properties. We have shown that composite solitons with different widths cannot propagate as a stationary entity. A relevant example has been provided where the crystal is LiNbO₃ or BaTiO₃. In addition, we have shown that in the new family of solitons, a degenerate pair with equal peak power possesses bistable property. Both paraxial theory and numerical simulation show that the identified family of composite solitons is stable.     

Bright and dark spatial solitons in non-Kerr media

An overview of the theory of self-guided optical beams, spatial optical solitons supported by non-Kerr non-linearities, is presented. This includes bright and dark solitons in optical media with intensity-dependent non-linear response as well as two-component solitary waves supported by parametric wave mixing in quadratic or cubic media. The properties of non-linear spatially localized waves are discussed for qualitatively different types of soliton bearing non-integrable non-linear models, including the scalar model described by a generalized non-linear Schrödinger equation and the models of the second- and third-harmonic generation. Special attention is paid to the recent advances of the theory of soliton stability and soliton internal modes.     

Dynamic and static position control of optical feedback solitons

We report on the experimental implementation of an external control for optical feedback solitons using incoherent spatial intensity distributions in a liquid crystal light valve (LCLV) optical single feedback system. The external control provides excellent experimental possibilities for static and dynamic control of the lateral positions of the optical feedback solitons which will be demonstrated. Particularly, the influence of different gradients onto the drift motion of spatial solitons is experimentally investigated in detail. In agreement with theoretical predictions, the drift velocity of the soliton increases according to the steepness of the gradient. Additionally, a completely incoherent addressing scheme including creation and erasure of feedback solitons is demonstrated for the LCLV setup.     

Circularly polarized optical spatial solitons

We present, experimentally and theoretically, a polymer material system that supports optical spatial solitons of circular polarization. We demonstrate one-dimensional circularly polarized dark solitons supported by photoisomerization nonlinearity in a bulk polymer.     

Soliton stability against polarization-mode-dispersion in dispersion-managed systems

We study the dynamics of two-component solitons in a dispersion-managed (DM) system, built as a periodic concatenation of segments of optical fibers with anomalous and normal group-velocity dispersion (GVD). The model includes, in addition to the usual GVD and nonlinear terms, birefringence and polarization-mode-dispersion (PMD), in the form of the polarization scrambling (random rotation of the polarization) taking place at randomly distributed defects. We propose a numerical algorithm for finding optimized DM solitons in such a system, which secure stable transmission over a large distance. The analysis includes effects of the PMD-induced noise, together with the noise due to the spontaneous amplifier emission, and the input-source noise. It is concluded that, if the group-velocity birefringence is not excessively large, the use of the optimized solitons makes it possible to tolerate the PMD effects in the long-haul DM link.     

DNA adsorption on graphene

We study analytically the properties of the optical absorption and the spatial weak-light solitons in a quantum dot molecule system with the interdot tunneling coupling (ITC). It is shown that, for the linear case, there exists tunneling induced transparency (TIT) in the context of a weak ITC, while the TIT can be replaced by Autler-Townes splitting in the presence of a strong ITC. For the nonlinear case, it is probable to realize the spatial optical solitons even under weak light intensity. Interestingly, we find that there appears transformation behavior between the bright and dark solitons by properly turning both the ITC strength and the detuning of the probe field. Meanwhile, the transformation condition of the bright and dark solitons is obtained. Additionally it is also found that the amplitude of the solitons first descends and then rises with the increasing of ITC strength. Our results may have potential applications for nonlinear optical experiments and optical telecommunication engineering in solid systems.     

Embedded solitons in a three-wave system

We report a rich spectrum of isolated solitons residing inside (embedded into) the continuous radiation spectrum in a simple model of three-wave spatial interaction in a second-harmonic-generating planar optical waveguide equipped with a quasi-one-dimensional Bragg grating. An infinite sequence of fundamental embedded solitons is found, each one differing by the number of internal oscillations. Branches of these zero-walkoff spatial solitons give rise, through bifurcations, to several secondary branches of walking solitons. The structure of the bifurcating branches suggests a multistable configuration of spatial optical solitons, which may find straightforward applications for all-optical switching.     

Observation of a discrete family of dissipative solitons in a nonlinear optical system

We report on the observation of a discrete family of spatial dissipative solitons in a simple optical pattern forming system, which is based on a modified single-mirror feedback arrangement. After a pitchfork bifurcation the system possesses two (nearly) equivalent coexisting states of different polarizations. The spatial solitons correspond to excursions from one of the two states serving as a background state towards the other one. The members of the soliton family differ in the number of high-amplitude radial oscillations. The observations are in good agreement with numerical simulations and general expectations for dissipative solitons.     

Bessel型光晶格中自旋-轨道耦合极化激元凝聚的稳态结构

Bessel型光晶格是一种非空间周期性的柱对称的光晶格势场,其兼具无限深势阱和环状势阱的特征,在0阶Bessel光晶格势场中央形成深势阱,而在非0阶Beseel光晶格势场中能形成具有中央势垒的环状浅势阱.极化激元是一种半光半物质的准粒子,该准粒子甚至可以在室温条件下发生玻色-爱因斯坦凝聚相变,形成极化激元凝聚.另外,通过极化激元能级的腔诱导TE-TM分裂能在极化激元凝聚中实现足够强的自旋-轨道耦合作用.极化激元凝聚能在室温条件下实现,在其中又存在自旋-轨道耦合作用,其为量子物理的研究提供了全新的平台.本文把Bessel光晶格势场引入到极化激元凝聚系统,研究了存在自旋-轨道耦合作用下的旋量双组分极化激元凝聚系统的稳态结构.通过求解Gross-Pitaevskii方程给出了极化激元凝聚系统在实验室坐标系和旋转坐标系中极化激元凝聚系统的稳态结构,由于Bessel势场的引入,使得稳态结构更具有多样性.给出了实验室坐标系中在中央深势阱中存在的基础型高斯孤立子、多极孤立子和在环状浅势阱中存在环状孤立子和多极孤立子的稳态结构;给出了旋转坐标系中存在的涡旋环状孤立子,及其由于自旋-轨道相互作用引起的组...     

空间调制作用下Bessel型光晶格中物质波孤立子的稳定性

利用变分法和数值计算方法研究了空间调制作用下Bessel型光晶格中玻色-爱因斯坦凝聚体系中孤立子的稳定性, 给出了存在随空间非周期变化的线性Bessel型光晶格和非线性光晶格(原子之间非线性相互作用的空间调制)时, 各种参数组合下涡旋和非涡旋孤立子的稳定性条件. 首先, 利用圆对称的高斯型试探波函数得出描述体系稳定性参数满足的Euler-Lagrange方程和变分法分析体系稳定性所需要的有效作用势能的表达式. 然后, 根据有效作用势能是否具有局域最小值判断体系是否具有稳定状态, 得出体系具有稳定状态时参数所满足的条件. 最后, 利用有限差分法求解Gross-Pitaevskii方程验证变分法结果的正确性, 所得结果和变分法结果一致. 关键词： Bessel型光晶格 非线性光晶格 孤立子 稳定性     

Interference properties of two-component matter wave solitons

Wave properties of solitons in a two-component Bose-Einstein condensate are investigated in detail.We demonstrate that dark solitons in one of components admit interference and tunneling behavior,in sharp contrast to the scalar dark solitons and vector dark solitons.Analytic analyses of interference properties show that spatial interference patterns are determined by the relative velocity of solitons,while temporal interference patterns depend on the velocities and widths of two solitons,differing from the interference properties of scalar bright solitons.Especially,for an attractive interactions system,we show that interference effects between the two dark solitons can induce some short-time density humps(whose densities are higher than background density).Moreover,the maximum hump value is remarkably sensitive to the variation of the solitons' parameters.For a repulsive interactions system,the temporal-spatial interference periods of dark-bright solitons have lower limits.Numerical simulation results suggest that interference patterns for the dark-bright solitons are more robust against noises than bright-dark solitons.These explicit interference properties can be used to measure the velocities and widths of solitons.It is expected that these interference behaviors can be observed experimentally and can be used to design matter wave soliton interferometer in vector systems.     

Watching dark solitons decay into vortex rings in a Bose-Einstein condensate

We have created spatial dark solitons in two-component Bose-Einstein condensates in which the soliton exists in one of the condensate components and the soliton nodal plane is filled with the second component. The filled solitons are stable for hundreds of milliseconds. The filling can be selectively removed, making the soliton more susceptible to dynamical instabilities. For a condensate in a spherically symmetric potential, these instabilities cause the dark soliton to decay into stable vortex rings. We have imaged the resulting vortex rings.     

Propagation of vector solitons in a quasi-resonant medium with stark deformation of quantum states

The nonlinear dynamics of a vector two-component optical pulse propagating in quasi-resonance conditions in a medium of nonsymmetric quantum objects is investigated for Stark splitting of quantum energy levels by an external electric field. We consider the case when the ordinary component of the optical pulse induces ?? transitions, while the extraordinary component induces the ?? transition and shifts the frequencies of the allowed transitions due to the dynamic Stark effect. It is found that under Zakharov-Benney resonance conditions, the propagation of the optical pulse is accompanied by generation of an electromagnetic pulse in the terahertz band and is described by the vector generalization of the nonlinear Yajima-Oikawa system. It is shown that this system (as well as its formal generalization with an arbitrary number of optical components) is integrable by the inverse scattering transformation method. The corresponding Darboux transformations are found for obtaining multisoliton solutions. The influence of transverse effects on the propagation of vector solitons is investigated. The conditions under which transverse dynamics leads to self-focusing (defocusing) of solitons are determined.     

A semi-classical approach to two-frequency solitons in a three-level cascade atomic system

A semi-classical theory of two intense optical fields interacting with a third-order non-linear medium composed of a three-level cascade atomic system is presented. It is predicted that non-linear atom-field interactions allow the formation of two-frequency bright, dark and grey spatial solitons. We demonstrate through numerical simulations and analytic stability analysis that the bright and grey solitons are stable.     

Soliton coupling in birefringent optical fiber with third-order dispersion

Nonlinear coupling of polarized solitons in birefringent optical fiber in the presence of third-order dispersion is considered in the framework of the coupled nonlinear Schrödinger equations. The influence of third-order dispersion on the interaction between solitons is investigated. For sufficiently strong third-order dispersion the interaction may even become repulsive. The stable conditions for solitons of partial pulses are analyzed and amplitude threshold, which decreases with third-order dispersion coefficient decreasing, for the capture of solitons of partial pulses into a coupled two-component pulse is obtained.     

Spatial solitons in Kerr and Kerr-like media

This is a review paper of basic knowledge and recent advances in the area of spatial solitons in Kerr and Kerr-like media. We consider spatial bright and dark solitons, solitons in waveguide geometries, optical bullets, vortex solitons and, briefly, dissipative cases. In our treatment, we use a Hamiltonian approach when considering stability issues.     

Attraction of nonlocal dark optical solitons

We study the formation and interaction of spatial dark optical solitons in materials with a nonlocal nonlinear response. We show that unlike in local materials, where dark solitons typically repel, the nonlocal nonlinearity leads to a long-range attraction and formation of stable bound states of dark solitons.     

Polarization vortex spatial optical solitons in Bessel optical lattices

We investigate the formation of polarization vortex spatial optical solitons in optical lattice induced by a non-diffracting Bessel beam. The properties of these solitons in zeroth-order and first-order Bessel lattices with focusing and defocusing Kerr nonlinearity are discussed. It is found that these solitons have some analogies with phase vortex solitons carrying single positive or negative topological charge in these lattices. Besides, these polarization vortex solitons have complicated dynamical characteristic and can be stabilized in some parameter region.