Soliton Modes Research Articles

Supermode spatial solitons via competing nonlocal nonlinearities

We study spatial soliton formation in a system with competing nonlinearities. In doing so, we consider a specific nonlinear response that involves both focusing and defocusing nonlocal contributions. We demonstrate that at a sufficiently high input power level, the interplay between these nonlocal nonlinearities may lead to the formation of in-phase, two-hump, fundamental spatial solitons. The conditions required for the existence of these two-peak spatial solitons are also presented. Full Text: PDF ReferencesG. Stegeman and M. Segev, "Optical Spatial Solitons and Their Interactions: Universality and Diversity", Science 286, 1518 (1999). CrossRef Y. Kivshar and G. P. Agrawal, Optical Solitons: From Fibers to Photonic Crystals (Academic, San Diego, 2003).P. Varatharajah et al., "Stationary nonlinear surface waves and their stability in diffusive Kerr media", Opt. Lett. 13, 690 (1988). CrossRef G. Assanto and M. Peccianti, "Spatial solitons in nematic liquid crystals," IEEE J. Quantum Electron. 39, 13 (2003). CrossRef G. Assanto, ed. Nematicons: Spatial Optical Solitons in Nematic Liquid Crystals (Wiley, 2012). CrossRef O. Bang, W. Krolikowski, J. Wyller, J.J. Rasmussen, "Collapse arrest and soliton stabilization in nonlocal nonlinear media", Phys. Rev. E 66, 046619 (2002). CrossRef X. Hutsebaut, C. Cambournac, M. Haelterman, A. Adamski, K. Neyts, "Single-component higher-order mode solitons in liquid crystals," Opt. Commun. 333, 211 (2004). CrossRef C. Conti, M. Peccianti, and G. Assanto, "Route to nonlocality and observation of accessible solitons," Phys. Rev. Lett. 91, 073901 (2003). CrossRef U. A. Laudyn, P. S. Jung, M.A. Karpierz, and G. Assanto, "Quasi two-dimensional astigmatic solitons in soft chiral metastructures," Sci. Rep. 6, 22923 (2016). CrossRef U. A. Laudyn, P. S. Jung, M. A. Karpierz, G. Assanto, "Power-induced evolution and increased dimensionality of nonlinear modes in reorientational soft matter," Opt. Lett. 39(22), 6399–6402 (2014). CrossRef Y. V. Izdebskaya, V. G. Shvedov, P. S. Jung, and W. Krolikowski, "Stable vortex soliton in nonlocal media with orientational nonlinearity," Opt. Lett. 43, 66-69 (2018) CrossRef P.S. Jung, W. Krolikowski, U.A. Laudyn, M. Trippenbach and M.A. Karpierz, "Supermode spatial optical solitons in liquid crystals with competing nonlinearities", Phys. Rev. A 95, 023820 (2017) CrossRef P.S. Jung, W. Krolikowski, U.A. Laudyn, M.A. Karpierz and M. Trippenbach, "Semi-analytical approach to supermode spatial solitons formation in nematic liquid crystals", Opt. Express 25, 23893 (2017) CrossRef S. Jungling and J. C. Chen, "A study and optimization of eigenmode calculations using the imaginary-distance beam-propagation method", IEEE J. Quantum Electron. 30, 2098 (1994). CrossRef P.S. Jung, K. Rutkowska and M.A. Karpierz, "Evanescent field boundary conditions for modelling of light propagation", Journal of Computational Science 25, 115 (2018) CrossRef A.A. Hardy, W. Streifer, "Coupled mode theory of parallel waveguides," IEEE J. Lightwave Techn. LT-3, 1135 (1985) CrossRef M. Matuszewski, B.A. Malomed, and M. Trippenbach, "Spontaneous symmetry breaking of solitons trapped in a double channel potential," Phys. Rev. A 75, 063621 (2007) CrossRef

Topological light-trapping on a dislocation

Topological insulators have unconventional gapless edge states where disorder-induced back-scattering is suppressed. In photonics, such edge states lead to unidirectional waveguides which are useful for integrated photonic circuitry. Cavity modes, another type of fundamental component in photonic chips, however, are not protected by band topology because of their lower dimensions. Here we demonstrate that concurrent wavevector space and real-space topology, dubbed as dual-topology, can lead to light-trapping in lower dimensions. The resultant photonic-bound state emerges as a Jackiw–Rebbi soliton mode localized on a dislocation in a two-dimensional photonic crystal, as proposed theoretically and discovered experimentally. Such a strongly confined cavity mode is found to be robust against perturbations. Our study unveils a mechanism for topological light-trapping in lower dimensions, which is invaluable for fundamental physics and various applications in photonics.

Generation of soliton bubbles in a sine-Gordon system with localised inhomogeneities

Nonlinear wave propagation plays a crucial role in the functioning of many physical and biophysical systems. In the propagation regime, disturbances due to the presence of local external perturbations, such as localised defects or boundary interphase walls have gained great attention. In this article, the complex phenomena that occur when sine-Gordon line solitons collide with localised inhomogeneities are investigated. By a one-dimensional theory, it is shown that internal modes of two-dimensional sine-Gordon solitons can be activated depending on the topological properties of the inhomogeneities. Shape mode instabilities cause the formation of bubble-like and drop-like structures for both stationary and travelling line solitons. It is shown that such structures are formed and stabilised by arrays of localised inhomogeneities distributed in space. Implications of the observed phenomena in physical and biological systems are discussed.

Hermite-Gaussian–like soliton in the nonlocal nonlinear fractional Schrödinger equation

The propagation of an optical beam in the nonlocal nonlinear fractional Schrödinger equation (NNFSE) was numerically investigated. The results reveal that the stability of beam propagation decreases as the Lévy index decreases in the local fractional case. However, the nonlocal response can effectively enhance the stability of beam propagation and leads to a completely stable solitons formation in the NNFSE. In addition, the shapes of fundamental mode solitons are determined by the Lévy indexes and nonlocalities. For the high-order solitons case, the shapes slightly vary with the change of nonlocality, but are strongly dependent on the Lévy index. Furthermore, the critical power of the stable soliton decreases as the Lévy index decreases since the decrease of the Lévy index will weaken the diffraction effect.

Коллективные возбуждения в альфа-спиральной молекуле белка

Continuous energy supply, a necessary condition for life, excites a state far from thermodynamic equilibrium, in particular coherent electric polar vibrations depending on water ordering in the cell. The collective, low-frequency vibrational excitations in protein macromolecules in the terahertz frequency region are suggested to orchestrate many protein processes such as enzymatic activity, electron/energy transport, conformation transitions and others. The most significant type of excitations is long-lived coherent vibronic modes and waves which are either spreading over large protein subdomains or being localised states. Two possible mechanisms of the formation of collective dynamic modes in the form of Frohlich collective mode and Davydov soliton were previously suggested. We developed a unified quantum-mechanics approach to describe conditions of the formation of Frohlich vibronic state and Davidov soliton in alphahelical protein molecules interacting with the environment. We distinguish three subsystems in the model, i.e., (i) oscillating peptide groups (PGs), interacting with (ii) the subsystem of side residuals of proteins, which in turn interacts with the environment (surrounding water), which is responsible for dissipation and fluctuation processes and modelled by a system of harmonic oscillators. It was shown that the equation of motion for dynamic variables of PG chain (phonon variables) can be transformed to the nonlinear Schrodinger equation for order parameters, which determines energy “pumping” due to protein interaction with a reservoir. Solution of the order parameter equation was shown to admit bifurcation into the solution corresponding to the formation of weak damped collective vibronic mode with growing amplitude. It was also shown that the solution corresponding to Davydov soliton can exist at certain boundary conditions in this bifurcation region. The suggested mechanism of emergent of macroscopic dissipative structures in the form of collective vibronic modes in proteins is discussed in connection with recent experimental data on long-lived collective protein excitation in the terahertz frequency region

Generation of two-soliton and three-soliton molecules in a circular fiber array laser

In this work, the generation of two-soliton and three-soliton molecules in a circular fiber array laser with an active optical central fiber is studied. Certain fibers of the array are excited by Gaussian and super-Gaussian pulses. The central fiber of the circular fiber laser is a rare-earth doped fiber. A circular fiber array is employed as a saturable absorber in a soliton mode locked fiber laser. Generation of two-soliton and three-soliton molecules are observed in our simulation. Numerical calculation of binding energy shows that the super-Gaussian pulse tends to be more stable, and therefore it would be a proper choice for the generation of soliton molecules in the circular fiber array laser.

Controlling the stability of nonlinear optical modes via electromagnetically induced transparency

We propose a scheme to generate and stabilize the high-dimensional spatial solitons via electromagnetically induced transparency (EIT). The system we consider is a resonant atomic ensemble having $\mathrm{\ensuremath{\Lambda}}$ configuration. We illustrate that under EIT conditions the equation satisfied by the probe field envelope is reduced to a saturable nonlinear Schr\odinger equation with the trapping potential, provided by a far-detuned laser field and a random magnetic field. We present high-dimensional soliton solutions exhibiting many interesting characteristics, including diversity (i.e., many different types of soliton solutions can be found, including bright, ring multipole bright, ring multipole defect mode, multiring bright, multiring defect mode, and vortices solitons), the phase transition between bright soliton and higher-order defect modes (i.e., the phase transition can be realized by controlling the nonlinear coefficient or the intensity of the trapping potential), and stability (i.e., various solitons can be stabilized by the Gaussian potential provided by the far detuned laser field, or the random potential provided by the magnetic field). We also find that some solitons are the extension of the linear eigenmode, whereas others entirely derive from the role of nonlinearity. Compared with previous studies, we not only show the diverse soliton solutions in the same system but also find the boundary of the phase transition for the type of solitons. In addition, we present the possibility of using the random potential to stabilize various solitons and vortices.

Dynamics of coupled mode solitons in bursting neural networks.

Using an electrically coupled chain of Hindmarsh-Rose neural models, we analytically derived the nonlinearly coupled complex Ginzburg-Landau equations. This is realized by superimposing the lower and upper cutoff modes of wave propagation and by employing the multiple scale expansions in the semidiscrete approximation. We explore the modified Hirota method to analytically obtain the bright-bright pulse soliton solutions of our nonlinearly coupled equations. With these bright solitons as initial conditions of our numerical scheme, and knowing that electrical signals are the basis of information transfer in the nervous system, it is found that prior to collisions at the boundaries of the network, neural information is purely conveyed by bisolitons at lower cutoff mode. After collision, the bisolitons are completely annihilated and neural information is now relayed by the upper cutoff mode via the propagation of plane waves. It is also shown that the linear gain of the system is inextricably linked to the complex physiological mechanisms of ion mobility, since the speeds and spatial profiles of the coupled nerve impulses vary with the gain. A linear stability analysis performed on the coupled system mainly confirms the instability of plane waves in the neural network, with a glaring example of the transition of weak plane waves into a dark soliton and then static kinks. Numerical simulations have confirmed the annihilation phenomenon subsequent to collision in neural systems. They equally showed that the symmetry breaking of the pulse solution of the system leaves in the network static internal modes, sometime referred to as Goldstone modes.

Towards visible soliton microcomb generation

Frequency combs have applications that extend from the ultra-violet into the mid-infrared bands. Microcombs, a miniature and often semiconductor-chip-based device, can potentially access most of these applications, but are currently more limited in spectral reach. Here, we demonstrate mode-locked silica microcombs with emission near the edge of the visible spectrum. By using both geometrical and mode-hybridization dispersion control, devices are engineered for soliton generation while also maintaining optical Q factors as high as 80 million. Electronics-bandwidth-compatible (20 GHz) soliton mode locking is achieved with low pumping powers (parametric oscillation threshold powers as low as 5.4 mW). These are the shortest wavelength soliton microcombs demonstrated to date and could be used in miniature optical clocks. The results should also extend to visible and potentially ultra-violet bands.

Anisotropic field-induced gap in the quasi-one-dimensional antiferromagnet KCuMoO4(OH)

We investigated magnetic and thermodynamic properties of $S$ = 1/2 quasi-one-dimensional antiferromagnet KCuMoO$_4$(OH) through single crystalline magnetization and heat capacity measurements. At zero field, it behaves as a uniform $S$ = 1/2 Heisenberg antiferromagnet with $J$ = 238 K, and exhibits a canted antiferromagnetism below $T_\mathrm{N}$ = 1.52 K. In addition, a magnetic field $H$ induces the anisotropy in magnetization and opens a gap in the spin excitation spectrum. These properties are understood in terms of an effective staggered field induced by staggered g-tensors and Dzyaloshinsky-Moriya (DM) interactions. Temperature-dependencies of the heat capacity and their field variations are consistent with those expected for quantum sine-Gordon model, indicating that spin excitations consist of soliton, anti-soliton and breather modes. From field-dependencies of the soliton mass, the staggered field normalized by the uniform field $c_\mathrm{s}$ is estimated as 0.041, 0.174, and 0.030, for $H \parallel a$, $b$, and $c$, respectively. Such a large variation of $c_\mathrm{s}$ is understood as the combination of staggered g-tensors and DM interactions which induce the staggered field in the opposite direction for $H \parallel a$ and $c$ but almost the same direction for $H \parallel b$ at each Cu site.

Chiral Edge Mode in the Coupled Dynamics of Magnetic Solitons in a Honeycomb Lattice.

Motivated by a recent experimental demonstration of a chiral edge mode in an array of spinning gyroscopes, we theoretically study the coupled gyration modes of topological magnetic solitons, vortices and magnetic bubbles, arranged as a honeycomb lattice. The soliton lattice under suitable conditions is shown to support a chiral edge mode like its mechanical analogue, the existence of which can be understood by mapping the system to the Haldane model for an electronic system. The direction of the chiral edge mode is associated with the topological charge of the constituent solitons, which can be manipulated by an external field or by an electric-current pulse. The direction can also be controlled by distorting the honeycomb lattice. Our results indicate that the lattices of magnetic solitons can serve as reprogrammable topological metamaterials.

Raman self-induced-transparency soliton trains in hollow-core photonic crystals

Periodic trains of non-topological dark and bright optical solitons are proposed as one of the possible nonlinear optical structures that could be generated during Raman transitions in nonlinear hollow-core photonic crystal fibers filled with gas. It is shown that Stokes-like probe fields, generated by stimulated Raman transitions upon propagation of the master pump in the hollow-core fiber, form a broadband spectrum, whose discrete branch is populated by several distinct localized periodic soliton modes with well-defined “quantum numbers”. Such soliton trains, which are intended to complement recently proposed single-pulse and single-dark solitons for multi-channel communication applications, can be formed by temporal quantum entanglements of the single-soliton fields. Attention is laid on a possibility to generate such soliton trains in the absence of Kerr nonlinearity, and total controllability of their shape profiles including their temporal periods and average widths is demonstrated through variations of characteristic parameters of the hollow-core photonic crystal fiber.

Bubblelike structures generated by activation of internal shape modes in two-dimensional sine-Gordon line solitons.

Nonlinear waves that collide with localized defects exhibit complex behavior. Apart from reflection, transmission, and annihilation of an incident wave, a local inhomogeneity can activate internal modes of solitons, producing many impressive phenomena. In this work we investigate a two-dimensional sine-Gordon model perturbed by a family of localized forces. We observed the formation of bubblelike and droplike structures due to local internal shape mode instabilities. We describe the formation of such structures on the basis of a one-dimensional theory of activation of internal modes of sine-Gordon solitons. An interpretation of the observed phenomena, in the context of phase transition theory, is given. Implications in Josephson junctions with a current dipole device are discussed.

Arbitrarily large numbers of kink internal modes in inhomogeneous sine-Gordon equations

We prove analytically the existence of an infinite number of internal (shape) modes of sine-Gordon solitons in the presence of some inhomogeneous long-range forces, provided some conditions are satisfied.

Stretched and soliton femtosecond pulse generation with graphene saturable absorber by manipulating cavity dispersion

Graphene is at the center of a significant research effort for ultrafast photonics due to its unique optical properties. Here, we demonstrated the generation of stretched and soliton femtosecond mode-locking pulses in an erbium doped fiber laser (EDFLs) by using graphene saturable absorber and managing the net cavity dispersion. The novelty of this work arises due to the simple fabrication of the graphene SA and the realization of two types of mode-locking pulse by manipulating the cavity dispersion. At total cavity dispersion of −0.028ps2, stretched pulses train was successfully obtained. The laser has a pulse width of 750fs at repetition rate of 35.1MHz and pulse energy of 0.054nJ at maximum output power of 1.9mW. By varying the net cavity dispersion so that the anomalous dispersion has been achieved with total dispersion of −0.3ps2, soliton mode locked pulse train was successfully obtained. The laser has a pulse width of 820fs at repetition rate of 11.5MHz and pulse energy of 0.42nJ at output power of 4.85mW. These results make the proposed EDFLs suitable for applications in optical communications, metrology, environmental sensing, and biomedical diagnostics.

Oscillating electromagnetic soliton in an anisotropic ferromagnetic medium

We investigate theoretically the propagation of electromagnetic oscillating soliton in the form of breather in an anisotropic ferromagnetic medium. The interaction of magnetization with the magnetic field component of the electromagnetic (EM) wave has been studied by solving Maxwell's equations coupled with a Landau–Lifshitz equation for the magnetization of the medium. We made a small perturbation on the magnetization and magnetic field along the direction of propagation of EM wave in the framework of reductive perturbation method and the associated nonlinear magnetization dynamics is governed by a generalized derivative nonlinear Schrödinger (DNLS) equation. In order to understand the dynamics of the concerned system, we employ the Jacobi elliptic function method to solve the DNLS equation and deduce breatherlike soliton modes for the EM wave in the medium.

Modulational instability and localized modes in Heisenberg ferromagnetic chains with single-ion easy-axis anisotropy

A semiclassical theoretical study on the property of the modulational instability of corresponding linear spin-waves and the presence of nonlinear localized excitations in a discrete quantum ferromagnetic spin chain with single-ion easy-axis anisotropy is reported. We consider the Glauber coherent-state representation combined with the Dyson-Maleev transformation for local spin operators as the basic representation of the system, and derive the equation of motion by means of the Ehrenfest theorem. Using a modulational instability analysis of plane waves, we predict the existence regions of bright envelope solitons and intrinsic localized spin-wave modes. Besides, with the help of a semidiscrete multi-scale method, we obtain analytical solutions for the bright envelope soliton and intrinsic localized spin-wave mode. Moreover, we analyze their existence conditions, which agree with the results of modulational instability analysis.

Stability of gap solitons in the presence of a weak nonlocality in periodic potentials

In this work, we study the stability and internal modes of one-dimensional gap solitons employing the modified nonlinear Schrodinger equation with a sinusoidal potential together with the presence of a weak nonlocality. Using an analytical theory, it is proved that two soliton families bifurcate out from every Bloch-band edge under self-focusing or self-defocusing nonlinearity, and one of these is always unstable. Also we study the oscillatory instabilities and internal modes of the modified nonlinear Schrodinger equation.

Few-cycle solitons in the medium with permanent dipole moment under conditions of the induced birefringence

Propagation of electromagnetic pulse in the birefringent medium consisting of symmetric and asymmetrical molecules is investigated. Stationary quantum states of asymmetrical molecules have the permanent dipole moment. Under considered conditions the ordinary pulse component excites quantum transitions between stationary states. The extraordinary component, besides, causes a dynamic chirp of frequencies of these transitions. The new solitonic modes of propagation of the half- and single-period pulses are found. The solitonic mechanism of simultaneous generation of the second and zero harmonics in the modes of “bright” and “dark” solitons is analyzed.

Controllable soliton propagation based on phase-front curvature in asymmetrical nonlocal media**Project supported by the National Natural Science Foundation of China (Grants Nos. 11547007 and 11304024), the Innovation Personnel Training Plan for Excellent Youth of Guangdong University Project (Grant No. 2013LYM_0023), and the Yangtze Fund for Youth Teams of Science and Technology Innovation (Grant No. 2015cqt03).

The influence of phase-front curvature on the dynamical behavior of the fundamental mode soliton during its transmission in asymmetrical nonlocal media is studied in detail and the phase-front curvature can be imposed on the fundamental mode soliton by reshaping or phase imprinting technologies. By changing the phase-front curvature or its imposed position, controllable soliton propagation in asymmetrical nonlocal media can be achieved.