The Study on the Theoretical Perspectives of Soliton and Its Applications

Abstract

A soliton is a strongly stable, nonlinear, self-reinforcing, localised wave packet that propagates freely at a constant speed and keeps its shape even after colliding with other similar localised wave packets. Its exceptional stability arises from the balanced cancellation of nonlinear and dispersive effects in the medium. In engineering, a soliton wave is a self-reinforcing solitary wave packet that keeps its shape as it travels at a steady speed. It results from the medium\'s non-linear and dispersive effects cancelling each other out. Many systems exhibit dispersive effects, in which the wave frequency controls the wave\'s speed of propagation. It was then demonstrated that soliton solutions provide stable solutions for a wide class of dispersive partial differential equations that are weakly nonlinear and describe physical systems. Solitons are preferred for high-speed, long-distance transmissions because of their self-restoring characteristics. Given that transmission speeds over longer distances are now close to 40 Gbit per second, the strain on networks is rapidly approaching a critical threshold. Solitons may provide interesting alternatives in the future. Non-linear wave equations that describe how waves propagate in specific physical systems are solved to get soliton solutions. These waves appear as solutions in mathematical models of various systems, such as optical wave-guides, crystal lattice vibrations, and water waves.

Introduction

I. INTRODUCTION

A generally agreed definition of soliton is difficult to come up with. Drazin & Johnson provide solitons three features (1989, p. 15) [1]. They possess three qualities: they can interact with other solitons, they are confined within a region, and they have a permanent form. They also survive collisions intact, with the exception of a phase shift.More formal formulations are available, although they need a significant amount of mathematics. Moreover, a few of scientists label occurrences that do not meet these three requirements as soliton phenomena (for example, even though they lose energy during interaction, the "light bullets" in nonlinear optics are occasionally referred to as solitons).[2]Dispersion and nonlinearity can interact to produce both permanent and localised wave patterns. Imagine a pulse of light travelling through glass. We could suppose that this pulse is composed of multiple light frequencies. The dispersion of glass causes these distinct frequencies to travel through it at different speeds, which causes the pulse's shape to change over time. However, there is also the nonlinear Kerr effect, where a material's refractive index at a given frequency is determined by the amplitude or brightness of the light. A properly formed pulse has a stable shape throughout time because the Kerr effect precisely cancels out the dispersion effect. As such, the pulse is a soliton [3]. Numerous models that are completely solvable are solved by solitons, including the coupled nonlinear Schrödinger equation, the Korteweg–de Vries equation, the sine-Gordon equation, and the nonlinear Schrödinger equation. The integrability of the field equations—which is typically accomplished via the inverse scattering transform—is responsible for the stability of the soliton solutions. The mathematical theory of these equations is a broad and active field of mathematical study.[3] A train of solitons follows a wavefront in some "undular" tidal bore occurrences that are found in a few rivers, including the River Severn. More solitons are produced as underwater internal waves driven by the topography of the seafloor spread out along the oceanic pycnocline. There are further atmospheric solitons. As an illustration, consider the morning glory cloud in the Gulf of Carpentaria, which is produced by enormous linear roll clouds that are brought about by pressure solitons passing over a layer of temperature inversion. In the recently constructed, but not widely accepted, soliton model of neuroscience, pressure solitons are used to explain the signal conduction within neurons [3].A topological soliton, often called a topological defect, is any solution of a system of partial differential equations that is persistent against decay to the "trivial solution". Topological restrictions, not the integrability of the field equations, are the source of soliton stability. Constraints are almost always present because the differential equations must adhere to a set of boundary conditions and maintain the nontrivial homotopy group of the boundary. As a result, homotopy classes can be used to group differential equation solutions [3].

Specifically, soliton transmission in optical fibres counteracts two primary types of pulse degradation in order to improve the quality of data transmission. One type of degradation is the dispersion that happens when pulses travel over long fibre stretches. The other is the nonlinear effects that arise from signals interacting in a power-dependent way with the fibre and with each other. Generally, the combined effect of the two effects makes the situation worse; but, for certain optical pulse forms and powers, the effects can cancel each other out, at least to a first-order approximation. Soliton is the term used to describe these types of pulses.The inherent durability of solitons for long-distance high-speed gearboxes is one of their main advantages. Over long fibre lengths, soliton can be made intrinsically stable despite soliton attenuation. This offers a way to stop dispersion and nonlinear effects from deteriorating signal quality, which is a major problem at 10 Gbit/s and gets worse at higher transmission speeds. Due to these features, scientists are developing soliton systems for long-haul 10-Gbit/s and upcoming 40-Gbit/s systems [4].

II. LITERATURE REVIEW

The soliton phenomena was first documented in 1834 by John Scott Russell (1808–1882), who observed a single wave in Scotland's Union Canal. After he successfully duplicated the event in a wave tank, he dubbed it the "Wave of Translation". There are locally confined, strongly stable propagating solutions to the Korteweg–de Vries equation, which describes waves that resemble those observed by Russell. It was Zabusky and Kruskal who originally dubbed these solutions soliton. The word was meant to describe the solitary nature of the waves, with the suffix "on" reflecting its original usage to denote to particles such as hadrons, baryons, and electrons and reflecting their observed particle-like activity.[3].

The earliest known observation of a lone wave was made by a young engineer named John Scott Russell, who was hired for a summer project in 1834 to investigate methods to improve the designs for barges designed to traverse canals, notably the Union Canal in Edinburgh, Scotland. One day in August, the tow rope that was securing the mules to the barge broke, causing it to stop suddenly. Nevertheless, the water mass ahead of the barge's blunt prow rolled forward quickly, taking the shape of a sizable isolated elevation—a rounded, smooth, and well-defined mound of water—and continued down the canal without changing shape or pace. Russell (1844). After conducting further research into this coincidental finding, Russell rode up to the Wave of Translation and overtook it as it continued to roll at a speed of around eight or nine miles per hour, maintaining its original dimensions of about thirty feet by one foot to one and a half. He then used a wave tank in carefully controlled laboratory experiments, and in 1844 he reported the results (Russell, 1844). He provided four examples: He observed hyperbolic secant structure in single waves. If the starting water mass is sufficiently enormous, it can produce two or more waves that break apart gradually and become nearly solitary.Waves can flow past one another "without change of any kind" when they are isolated.A single wave with amplitude A moves at the speed of [g(A+h)]1/2 in a shallow water channel of height h, where g is the gravitational acceleration. It is a nonlinear phenomena where waves with greater amplitudes travel quicker than those with smaller amplitudes. Diederick Korteweg, a Dutch physicist, and his student Gustav de Vries (KdV) (de Vries, 1895) (Scott, 2005) devised a nonlinear partial differential equation (PDE) that is currently named after them in 1895. Korteweg and de Vries suggest that the KdV equation (1) could account for Russell's experiments. Equation (1) shows that the dispersive term, which allows waves of different wavelengths to travel at different velocities, the amplitude effect, and a nonlinear component add together to determine the rate of change of the wave's height over time. Korteweg and de Vries found a periodic solution in addition to a solitary-wave solution that matched the wave that Russell had pursued. These solutions resulted from a trade-off between dispersion and nonlinearity.

Up until 1965, when Norman Zabusky and Martin Kruskal published their numerical solutions to the KdV equation (and invented the phrase "soliton"), mathematicians, physicists, and engineers studying water waves ignored their work and Russell's discoveries (Zabusky, 1965). According to (1), Kruskal obtained a continuous description of the oscillations of unidirectional waves propagating on the cubic, Fermi–Pasta–Ulam (FPU) nonlinear lattice (Fermi, 1955; Porter, 2009b; Weissert, 1997). In parallel, Morikazu Toda created history when he became the first person to detect a soliton in what is now known as the Toda lattice, a discrete, integrable system (Toda, 1967).[5]

Gary Deem, Zabusky, and Kruskal (1965) made films showing interacting solitary waves in an FPU lattice, the KdV equation, and a modified KdV equation; see the discussion in the review paper (Zabusky, 1984). Using the KdV equation, we demonstrate the dynamics of solitons in Figure 1's space-time diagram. When Robert Miura realised the significance of this discovery, he found a precise transition between this modified KdV equation and equation (1) (Miura, 1976). When Clifford Gardner, John Greene, Martin Kruskal, and Robert Miura employed the inverse scattering approach to resolve the initial-value problem of the KdV equation in 1967 (Miura, 1968; Gardner, 1967; Gardner, 1974), this generated interest in the mathematical study of solitons. This led to the development of an appropriate notion of integrability for continuum frameworks. In 1972, Alexei Borisovich Shabat and Vladimir Zakharov extended the inverse scattering method by proving the existence of soliton solutions and the integrability of the nonlinear Schrödinger (NLS) problem. The sine-Gordon equation was one of several nonlinear PDEs that Mark Ablowitz, David Kaup, Alan Newell, and Harvey Segur proved to have soliton solutions for in 1973. This equation was already known to be integrable due to Albert Backlünd's 19th century investigations of surfaces with constant negative Gaussian curvature. Other researchers have since developed related soliton solutions and derived different integrable PDEs (in one and multiple spatial dimensions). A more complex definition of a "soliton" in several spatial dimensions is required, as the Kadomtsev–Petviashvili (KP) equation illustrates. Asymptotic analysis, variational approximations, and/or perturbative techniques are typically used in analytical approaches for investigating solitary waves in nonintegrable equations (Kivshar, 1989). (Scott, 2005) In optics, the coupled mode equations of the fibre Bragg grating are a prominent example of a nonintegrable system with precise solutions for isolated solitary waves.The study of solitons and solitary waves is currently one of the most active areas in mathematics and physics (Scott, 2005). It has impacted many fields, including pure mathematics and experimental science. This has led to important discoveries in nonlinear dynamics, biology, optics, supersymmetry, and integrable systems, among other domains.

IV. APPLICATIONS OF SOLITON IN VARIOUS FIELDS

DNA and proteins may include solitons[9].[10] Low-frequency collective motion in proteins and DNA is associated with soliton dynamics.[11] According to a recently established neuroscience model, messages are conducted within neurons in the form of solitons and take the form of density waves.[12][13][14] Solitons are wave-like propagations of coupled conformational and electronic disturbances that transfer energy practically losslessly in biomolecular chains or lattices.[15].

In materials like ferroelectrics, solitons can also exist as domain barriers. Ferroelectric materials have electric dipoles, or spontaneous polarisation, that are connected to specific material structural configurations. When there are no outside pressures present and the structural configurations corresponding to opposing polarisations are equally favourable, domains of oppositely poled polarisations can exist within a single material. Regions of lattice dislocations make up the domain boundaries, or walls, that divide these local structural configurations.[16] Under applied pressures like mechanical stress or electric bias, the domain walls can spread as the polarisations, leading to local structural configurations switching inside a domain. As a result, the domain walls can be thought of as solitons, which are distinct dislocation zones with the ability to slip or propagate while keeping their breadth and length.[17][18][19] Ferroelectricity has been reported in twisted bilayers of van der Waal materials, including graphene and molybdenum disulfide, in recent literature.[16][20][21]

Different stacking orders of the atoms within the layers are produced by the moiré superlattice that results from the relative twist angle between the van der Waal monolayers. Ferroelectricity is made possible at the interface between these monolayers by the structural arrangements that these regions display, breaking inversion symmetry.  The domain walls dividing these areas are made up of partial dislocations where the lattice experiences various kinds of stresses and, consequently, strains. It has been noted that applied stress from an AFM tip on a fixed spot can start soliton or domain wall propagation across a moderate length of the sample ,order of nanometers to micrometres. Domain switching is made possible by the soliton propagation, which transfers the mechanical perturbation across the material with minimal energy loss.[18] It has also been shown that propagation characteristics like direction might be impacted by the kind of dislocations present at the walls.

For instance, depending on the kind of localised stacking order in twisted bilayer graphene, STM measurements revealed four forms of strains at domain walls with differing degrees of shear, compression, and tension. Variations in the strain types present at the domains lead to variable slip directions of the walls, which in turn affect the direction of propagation of the soliton network.[18] The propagation of soliton can also be affected by nonidealities such as surface contaminants and disturbances to the soliton network. In many ferroelectric twisted bilayer systems, domain walls can come together at nodes and become effectively pinned, generating triangular domains that are easily detected.[16] Furthermore, soliton propagation and the subsequent switching of polarisations across it can be prevented by complete loops of domain walls containing several polarisation domains.[18] Furthermore, van der Waal layers creases and surface inhomogeneities can serve as barriers to the spread of domain walls by causing them to collide.[18]

Other nonlinear waves and various forms of solitons can also be found in magnets.[22] The Landau-Lifshitz equation, the continuous Heisenberg model, the Ishimori equation, the nonlinear Schrödinger equation, and other magnetic equations are among the magnetic equations that these magnetic solitons are an exact solution of.

Solitonic behaviour can also be seen in atomic nuclei.[23] Here, it is anticipated that, under specific energy and temperature conditions, the entire nuclear wave function will exist as a soliton. It has been proposed that such conditions exist in the cores of some stars, where nuclei would collide but would not react, preserving their soliton waves as they passed through one another.A model of nuclei known as the Skyrme Model states that every nucleus is a topologically stable soliton solution of a field theory with a conserved baryon number.

Conclusion

In a non-linear dispersive medium, solitons light pulses can propagate over very long distances without broadening. As a result, they have drawn a lot of interest from the communications sector. Two effects that can balance each other out under the appropriate conditions are the reason solitons work in optical fibres. Chromatic dispersion is one of them; it happens when pulses with different wavelengths spread out as they move through an optical fibre. The alternative is referred to as self-phase modulation, or SPM, and it operates across a larger range of pulse spectrum wavelengths. Once the pulse finds equilibrium in the fibre, dispersion and SPM can counterbalance each other, allowing the pulse to keep its shape or dispersion. The pulse may potentially more severely expand or compress as a result of SPM. Conversely, attenuation reduces the pulse\'s strength and makes it more difficult for it to maintain its shape over the fibre span. Optical amplifiers have been constructed to balance attenuation and preserve pulse shapes. [24][25]. Solitons are obtained by solving non-linear wave equations that characterise the propagation of waves in certain physical systems. Mathematical models of a variety of systems, including water waves, crystal lattice vibrations, and optical waveguides, show these waves as solutions.

References

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Copyright © 2023 Muhammad Arif Bin Jalil. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.