Bright-dark Soliton Pairs Research Articles

Dark-bright photovoltaic soliton pair with two-wavelength components

We present a scheme to realize coupled dark-bright photovoltaic spatial-soliton pairs with two-wavelength components. With the propagating beam method we numeri cally study the spatial dynamic properties of these coupled solitons, finding th e possibility to use such coupled solitons in all-optical beam switching.

Self-deflection of a bright soliton in a separate bright-dark spatial soliton pair based on a higher-order space charge field

The self-deflection of a bright solitary beam can be controlled by a dark solitary beam via a parametric coupling effect between the bright and dark solitary beams in a separate bright-dark spatial soliton pair supported by an unbiased series photorefractive crystal circuit. The spatial shift of the bright solitary beam centre as a function of the input intensity of the dark solitary beam () is investigated by taking into account the higher-order space charge field in the dynamics of the bright solitary beam via both numerical and perturbation methods under steady-state conditions. The deflection amount (Δs0), defined as the value of the spatial shift at the output surface of the crystal, is a monotonic and nonlinear function of . When is weak or strong enough, Δs0 is, in fact, unchanged with , whereas Δs0 increases or decreases monotonically with in a middle range of . The corresponding variation range (δs) depends strongly on the value of the input intensity of the bright solitary beam (r). There are some peak and valley values in the curve of δs versus r under some conditions. When increases, the bright solitary beam can scan toward both the direction same as and opposite to the crystal's c-axis. Whether the direction is the same as or opposite to the c-axis depends on the parameter values and configuration of the crystal circuit, as well as the value of r. Some potential applications are discussed.

Effects of dark soliton on self-deflection of bright soliton in a separate bright-dark soliton pair

Based on the theory of one-dimensional separate soliton pairs formed in a serial photorefractive crystal circuit, the effects of the dark soliton on the self-deflection of the bright one in one separate bright-dark soliton pair are investigated by taking the diffusion term into account. The numerical results obtained by solving the nonlinear propagation equation show that the bright soliton moves on a parabolic trajectory in the crystal and its spatial shift changes with the input intensity of the dark soliton. These effects are further studied using perturbation analysis and the characteristics of the spatial shift of the bright soliton varying with the input maximum intensity of the dark soltion are analysed. The position of the bright soliton at the output surface of the crystal can be determined accurately according to the formula obtained from perturbation method.

Soliton parametric coupling in a series photorefractive crystal circuit

We provide a comprehensive numerical investigation on the dynamical evolutions, stabilities, and self-deflections of both solitons in a separate dark–dark, bright–dark or bright–bright soliton pair supported by a series photorefractive crystal circuit. The effects of parametric coupling between the two solitons on the evolutions, stabilities and self-deflections of the two soliton are investigated. Results show that whether an optical beam can evolve into a stable solitary state in a crystal depends not only on the initial conditions of that optical beam, but also on the initial conditions of the other optical beam in the other crystal. Changing the input intensity of a dark soliton can affect the self-deflection of other solitons. Some potential applications of the controlled behavior through the dark soliton in the bright–dark soliton pair are discussed.

Effects of dark soliton on self-deflection of bright soliton in a separate bright-dark soliton pair

Abstract Based on the theory of one-dimensional separate soliton pairs formed in a serial photorefractive crystal circuit, the effects of the dark soliton on the self-deflection of the bright one in one separate bright-dark soliton pair are investigated by taking the diffusion term into account. The numerical results obtained by solving the nonlinear propagation equation show that the bright soliton moves on a parabolic trajectory in the crystal and its spatial shift changes with the input intensity of the dark soliton. These effects are further studied using perturbation analysis and the characteristics of the spatial shift of the bright soliton varying with the input maximum intensity of the dark soltion are analysed. The position of the bright soliton at the output surface of the crystal can be determined accurately according to the formula obtained from perturbation method.

Evolution of separate screening soliton pairs in a biased series photorefractive crystal circuit.

This paper presents calculations for an idea in photorefractive spatial soliton, namely, screening solitons form in a biased series photorefractive crystal circuit consisting of two photorefractive crystals connected electronically by electrode leads in a chain with a voltage source. A system of two coupled equations is derived under appropriate conditions for two-beam propagation in the crystal circuit. The possibility of obtaining steady-state bright and dark screening soliton solutions is investigated in one dimension and, the existence of dark-dark, bright-dark, and bright-bright separate screening soliton pairs in such a circuit is proved. The numerical results show that the two solitons in a soliton pair can affect each other by the light-induced current and their coupling can affect their spatial profiles, dynamical evolutions, stabilities, and self-deflection. Under the limit in which the optical wave has a spatial extent much less than the width of the crystal, only the dark soliton can affect the other soliton by the light-induced current, but the bright soliton cannot. For a bright-dark or dark-dark soliton pair, the dark soliton in a weak input intensity can be obtained for a larger nonlinearity than for a stronger input intensity. For a bright-dark soliton pair, increasing the input intensity of the dark soliton can increase the bending angle of the bright soliton. Some potential applications are discussed.

Manakov Soliton Pairs in Biased Photovoltaic PhotorefractiveCrystals

We study, theoretically, incoherently coupled screening-photovoltaic soliton pairs inbiased photovoltaic photorefractive crystals. Itis shown that when the total intensity of two coupled solitons is much lowerthan the effective dark irradiance, the coupled soliton equations reduce tothe Manakov equations. The dark-dark, bright-bright and dark-bright solitonpair solutions of these Manakov equations are obtained under an appropriateexternal bias field and a photovoltaic field, and the characteristics ofthese Manakov soliton pairs are also discussed in detail.

Incoherently Coupled Bright-Dark Soliton Pairs in Biased CentrosymmetricPhotorefractive Media

It is shown theoretically that incoherently coupledbright-dark soliton pairs can exist in biased centrosymmetricphotorefractive media under steady-state conditions. These soliton pairs canbe established provided that the two optical beams have the samepolarization, wavelength, and are mutually incoherent.

INCOHERENTLY COUPLED BRIGHT-DARK SCREENING-PHOTOVOLTAIC SOLITON PAIRS IN BIASED PHOTOVOLTAIC PHOTOREFRACTIVE CRYSTALS

We investigate the incoherent coupling of two mutually incoherent optical beams with the same polarization and wavelength in biased photovoltaic photorefractive crystals, and predict that incoherently coupled bright-dark screening-photovoltaic soliton pairs can be established in biased photovoltaic photorefractive crystals.

Suppression of transverse instabilities for vector solitons.

We analyze the transverse instability of two-component spatial solitons in a saturable nonlinear medium, in relation to recent experimental observations of spatial vector solitons in photorefractive media. We present the stability analysis for all three realizations: dark-bright, bright-bright, and dark-dark soliton pairs, and demonstrate that both the nonlinearity saturation and incoherent mode interaction can lead to a strong suppression of the soliton transverse instabilities.

Dark optical solitons: physics and applications

We present a detailed overview of the physics and applications of optical dark solitons: localized nonlinear waves (or `holes') existing on a stable continuous wave (or extended finite-width) background. Together with the traditional problems involving properties of dark solitons of the defocusing cubic nonlinear Schrödinger equation, we also describe recent theoretical results on optical vortex solitons; ring dark solitons; polarization domain walls; parametric dark solitons in a dispersive χ (2) medium; vector dark solitons; coupled dark–bright soliton pairs, and we discuss the instability-induced dynamics of dark solitons in the models of generalized (i.e., non-Kerr) optical nonlinearities. Special attention is paid to the experimental demonstrations of temporal dark solitons in optical fibres and spatial dark solitons, especially dark-soliton stripes and vortex solitons, in a defocusing bulk medium.

Incoherently coupled dark–bright photorefractive solitons

We report the observation of incoherently coupled dark-bright spatial soliton pairs in a biased bulk photorefractive crystal. When such a pair is decoupled, the dark component evolves into a triplet structure, whereas the bright one decays into a self-defocusing beam.

Subfemtosecond pulses in the multicascade stimulated Raman scattering

We explore recently predicted multifrequency 2π solitons in multicascade stimulated Raman scattering (SRS) that was mode locked by the dynamics of population at a Raman quantum transition; we show that these solitons are eigensolitons of a general solitary-wave solution. Soliton components at each frequency are bright pulses of the same (Lorentzian) shape, in contrast to the familiar bright–dark soliton pair in regular SRS and to 1/cosh regular 2π solitons. Coherent interference of these components gives rise to a train of well-resolved subfemtosecond pulses. From an observation viewpoint the simplest SRS 2π solitons are so-called bright–bright solitons in noncascade SRS with either two (laser + Stokes) or three (e.g., laser + Stokes + anti-Stokes) components.

Dark and bright vector spatial solitons in biased photorefractive media.

We show that the vector beam evolution equations in properly oriented biased photorefractive media can exhibit bright-dark soliton pair solutions under steady-state conditions. These wave pairs are obtained perturbatively provided that the intensities of the two optical beams are approximately equal. Our analysis indicates that these bright-dark vector solitons exist irrespective of the polarity of the external bias field. The stability of these vector pairs has been investigated numerically and it has been found that they are stable only in the regime of positive bias polarity. \textcopyright{} 1996 The American Physical Society.