Abstract
Stability dynamics of dipole solitons have been numerically investigated in a nonlocal nonlinear medium with self-focusing and self-defocusing quintic nonlinearity by the squared-operator method. It has been demonstrated that solitons can stay nonlinearly stable for a wide range of each parameter, and two nonlinearly stable regions have been found for dipole solitons in the gap domain. Moreover, it has been observed that instability of dipole solitons can be improved or suppressed by modification of the potential depth and strong anisotropy coefficient.
Keywords
- dipole solitons
- nonlinear response
- nonlocal nonlinear medium
- quintic nonlinearity
1. Introduction
Many phenomena in nature are modeled mathematically using nonlinear differential equations. Traveling wave solutions of nonlinear partial differential equations play a significant role in nonlinear wave propagation problems that are observed in various fields such as nonlinear optics, fluid dynamics, plasma physics, elastic media, and biology [1]. Some of the solutions to such nonlinear wave propagation problems are called solitons, which are localized wave solutions.
Optical solitons are formed because of the balance between the medium’s diffraction and the self-phase modulation [2]. As a consequence of this, an optical field that does not change its shape occurs during propagation [3]. Recently, spatial solitons that can be used for optical switching and processing applications [4] have been extensively investigated in nonlinear optical systems with external optical lattices. There is a considerable amount of research about this subject in the literature. In 2003, Segev et al. experimentally observed spatial solitons in optically induced periodic potentials [5]. Fundamental and vortex solitons with real or complex lattices have been investigated in optical media with the cubic Kerr-type [6, 7, 8, 9, 10], the saturable [11], and competing nonlinearities [12]. Moreover, the existence of solitons has been observed in aperiodic or quasicrystal lattice structures [13, 14, 15, 16, 17, 18] and the lattices that possess defects [19, 20] and dislocations [21, 22].
The dynamics of solitons are governed by nonlinear Schrödinger (NLS) type equations in optical media with nonlinearities and/or external potentials as in the referred studies. Additionally, the cubic nonlinear NLS equation needs to be modified to describe nonlinear optical materials that have both cubic and quadratic nonlinear responses [23, 24, 25, 26, 27, 28, 29], such as potassium niobate (
NLSM equations were first studied by Benney and Roskes for water of finite depth in the free surface conditions in 1969 [32]. Later, in 1974, Davey and Stewartson derived the limiting integrable case, which is a reduced case of the Benney–Roske’s system by studying the evolution of a 3D wave packet for water of finite depth [33]. In 1975, Ablowitz and Haberman [34] studied the integrability of NLSM systems in the shallow water limit. The effects of surface tension were included in the results of Benney and Roskes by Djordevic and Reddekopp [35] in 1977. From the first principles, Ablowitz et al. [23, 36, 37] discovered that NLSM-type equations describe the evolution of the electromagnetic field in a quadratic nonlinear media. The general NLSM system is given by [23, 36, 37]
where
Wave collapses play a significant role in various branches of science. The peak amplitude of the wave solutions tends to infinity (blow-up) in finite time or finite propagation distance when a singularity occurs. This phenomenon is often called wave collapse [39]. In the NLS equation, it was first observed numerically by Kelley in 1965 [40]. In fact, this wave collapse phenomenon is similar for the NLSM systems. Wave collapse in the NLSM systems occurs with a modulated profile [41]. Merle and Raphael [42] analyzed the collapse behavior of the NLS equation and other related equations in detail. Moreover, Moll et al. investigated experimental observations of optical wave collapse in cubic nonlinearity and showed that the amplitude of the wave increases as the spatial extent decreases in a self-similar profile [43]. In Ref [39], Ablowitz and coworkers studied wave collapse that occurs with a quasi-self-similar profile in the NLSM system and found that collapse can be arrested by the small nonlinear saturation. Furthermore, in Ref [30], NLSM collapse was arrested by wave self-rectification. In this aforementioned study, they considered only the nonlinear evolution of beams with an initial Gaussian beam profile with several values of input power and/or beam ellipticity and found that the wave collapse can be arrested by increasing the coupling constant
More recently, Bağcı et al. [46] have numerically investigated stability dynamics of fundamental lattice solitons that are solutions of extended NLSM system in a nonlocal nonlinear medium with self-focusing and self-defocusing quintic nonlinearity. It has been shown that as the absolute value of
Dipole (two-phased) and higher-phase vortex solitons in the presence of an induced lattice have been studied analytically and experimentally in Bose-Einstein condensates (BECs) [47, 48] and in optical Kerr media [49, 50, 51, 52, 53, 54]. In recent years, these types of solitons have attracted considerable interest because of their unique features and potential applications [55].
In this chapter, we numerically study the existence and stability of dipole soliton solutions of the NLSM system in a nonlocal nonlinear medium with the self-defocusing quintic nonlinear response by adding an external lattice. In fact, this study is about the dynamics of dipole solitons instead of fundamental solitons in the problem that Bağcı and coworkers have addressed in recent book chapter [46]. The purpose of this study is to numerically investigate the effects of the strength of quintic nonlinearity that specify characteristics of the model and variation of potential depth on the existence and stability of dipole solitons. In several applications, many optical materials such as chalcogenide glasses are required quintic and seventh-order effects in addition to cubic nonlinear effects [56], and effective higher-order nonlinearities can reveal with pure Kerr materials in an inhomogeneous propagation media [57, 58, 59].
The chapter is outlined as follows: In Sec. 2, we present the model equations, and the squared-operator method is explained so that it is modified for the model. The dipole solitons are computed by this numerical method. Nonlinear evolution of the dipole solitons is examined to perform stability analysis, In Sec. 3. Finally in Sec. 4, results of this study are outlined.
2. The model
In this chapter, we modify the NLSM system (1) as follows to describe the dynamics of lattice solitons in a nonlocal nonlinear medium with cubic and quintic nonlinearity
where
where
2.1 Numerical solution for the dipole solitons
Yang and Lakoba developed an iterative numerical method called the squared-operator method (SOM) [60]. The idea of this method is to iterate a modified differential equation whose linearization operator is square of the original equation together with a preconditioning (or acceleration) operator. To obtain the soliton solution of the (2+1)D NLSM model, this method is modified as follows:
Soliton solutions are sought in the form
where
Applying the Fourier transform to the eigenequations system (5) yields
where
Taking the inverse Fourier transform of Eq. (7), we get
where
To obtain operator
where
Now, we should obtain operator
where
where
where
Substituting perturbations in Eq. (12) and Eq. (15) into Eq. (13) and only terms of
Substituting
Applying the Fourier transform to the first perturbed equation in Eq. (17) and the inverse Fourier transform to the obtained equation, we get
Using Eq. (5) and the second equation in Eq. (17), following equation is obtained
Applying Fourier transform to Eq. (19) and isolating
Taking the inverse Fourier transform of
Substituting Eq. (8) and Eq. (21) into Eq. (18) yields
After grouping the terms, Eq. (22) can be written as
Hence,
From Eq. (9), we know that the first bracket is identically zero. Consequently, we obtain
Moreover, Eq. (24) satisfied
where
To obtain soliton solution
where
where
Consequently, in Eq. (28)
Using the forward Euler method, steady-state solution
where Δ
In this chapter, to obtain dipole solitons, the initial condition of the SOM algorithm is chosen as a multi-humped Gaussian function which is given by
where
where (
Here
Unless otherwise stated, parameters in the NLSM model (2) are fixed to
It is noted that
Dipole solitons of the NLSM model (2) are calculated by the SOM method. In Figure 2, 3D views (first column), phase structures (second column), and contour plots of dipole solitons on the underlying lattice (third column) are displayed for self-defocusing (
3. Stability analysis
The stability dynamics of dipole solitons obtained by the SOM method are studied by the power analysis and direct simulation of the nonlinear evolution.
The power of solitons plays an important role in the stability analysis and it is calculated by
Vakhitov and Kolokolov proved a necessary condition for the linear stability of solitons in Ref [62]. They demonstrated that a soliton is linearly stable only if its power increases as propagation constant (or eigenvalue)
Moreover, Weinstein and Rose [63, 64] proved that a necessary condition for the nonlinear stability of solitons is also the slope condition given in Eq. (38).
To analyze nonlinear stability of the NLSM model (2), we examine the direct simulation of dipole solitons obtained by the SOM method. A finite-difference discretization scheme is used in the spatial domain (
The power diagrams of dipole solitons are displayed for varied
The dipole solitons are found to be nonlinearly stable for self-defocusing quintic nonlinearity (
In Figure 4, nonlinear evolution of peak amplitudes, 3D views of the evolved dipole solitons, and the phase structures of evolved dipole solitons are plotted for the dipole solitons that are shown in Figure 2. The effect of quintic nonlinearity (
Figure 4(b) shows that peak amplitudes of dipole solitons oscillate mildly (first column), and the 3D profile (second column) and phase structure (third column) of dipole solitons are preserved for
In previous studies [6, 14, 24], it is found that modification of the depth of potential can suppress nonlinear instabilities. More recently, Bağcı and coworkers [46] have demonstrated that nonlinear stability of fundamental solitons in an NLSM system (2) with quintic nonlinearity can be improved by the modification of lattice depth
It is also known that when the quadratic [15, 24, 44] and quintic [46] electro-optic effects are strong, the instability of fundamental solitons can be improved by increasing the anisotropy parameter. To examine the effect of anisotropy coefficient
4. Conclusions
In this chapter, the existence and nonlinear stability dynamics of dipole solitons have been investigated for a nonlocal nonlinear medium with quintic nonlinear response. This medium was characterized by the (2+1)D NLSM system with a periodic external lattice. Dipole solitons were obtained for self-defocusing (
Nonlinear evolution of the dipole solitons showed that the dipole solitons are stable for the weak self-focusing and self-defocusing quintic nonlinearity. In other words, as an absolute value of
In conclusion, the existence and stability properties of dipole solitons have been numerically explored in a nonlocal nonlinear medium with quintic nonlinear response, and it has been demonstrated that the instability of dipole solitons can be suppressed by modification of the lattice depth and increased anisotropy coefficient.
References
- 1.
Ablowitz MJ. Nonlinear Dispersive Waves: Asymptotic Analysis and Solutions. Cambridge University Press; 2011 - 2.
Stegeman GIA, Christodoulides DN, Segev M. Optical spatial solitons: historical perspectives. IEEE Journal of Selected Topics in Quantum Electronics. 2000; 6 (6):1419-1427. DOI: 10.1109/2944.902197 - 3.
Yuri S, Agrawal GP. Optical Solitons: From Fibers to Photonic Crystals. Academic Press; 2003 - 4.
Andersen DR, Allan GR, Skinner SR, Smirl AL. Observation of fundamental dark spatial solitons in semiconductors using picosecond pulses. Optics Letters. 1991; 16 (3):156-158. DOI: 10.1364/OL.16.000156 - 5.
Fleischer JW, Segev M, Efremidis NK, Christodoulides DN. Observation of two-dimensional discrete solitons in optically induced nonlinear photonic lattices. Nature. 2003; 422 :147 - 6.
Ablowitz MJ, Antar N, Bakırtaş İ, Ilan B. Band-gap boundaries and fundamental solitons in complex two-dimensional nonlinear lattices. Physical Review A. 2010; 81 :033834 - 7.
Bağcı M. Impact of the lattice period on the stability dynamics of defect solitons in periodic lattices. Physical Review A. 2022; 105 :043524 - 8.
Christodoulides DN, Yang J. Parity-Time Symmetry and Its Applications. Singapore: Springer; 2018 - 9.
Yang J, Musslimani ZH. Fundamental and vortex solitons in a two-dimensional optical lattice. Optics Letters. 2003; 28 (21):2094-2096. DOI: 10.1364/OL.28.002094 - 10.
Kartashov LTYV, Egorov AA, Christodoulides DN. Stable soliton complexes in two-dimensional photonic lattices. Optics Letters. 2004; 29 (16):1918-1920. DOI: 10.1364/OL.29.001918 - 11.
Göksel İ, Bakırtaş İ, Antar N. Nonlinear lattice solitons in saturable media. Applied Mathematics and Information Sciences. 2014; 9 :377-385 - 12.
Göksel İ, Antar N, Bakırtaş İ. Two-dimensional solitons in PT-symmetric optical media with competing nonlinearity. Optik. 2018; 156 :470-478 - 13.
Mark J, Ilan B, Schonbrun E, Piestun R. Solitons in two-dimensional lattices possessing defects, dislocations, and quasicrystal structures. Physical Review E. 2006; 74 :035601 - 14.
Ablowitz MJ, Antar N, Bakırtaş İ, Ilan B. Vortex and dipole solitons in complex two-dimensional nonlinear lattices. Physical Review A. 2012; 86 :033804 - 15.
Bağcı M. Soliton dynamics in quadratic nonlinear media with two-dimensional pythagorean aperiodic lattices. Optics Letters. 2021; 38 :1276 - 16.
Qidong F, Wang P, Huang C, Kartashov YV, Torner L, Konotop VV, et al. Optical soliton formation controlled by angle twisting in photonic moiré lattices. Nature Photonics. 2020; 14 (11):663-668 - 17.
Huang C, Ye F, Chen X, Kartashov YV, Konotop VV, Torner L. Localization-delocalization wavepacket transition in pythagorean aperiodic potentials. Scientific Reports. 2016; 6 (1):32546 - 18.
Wang P, Zheng Y, Chen X, Huang C, Kartashov YV, Torner L, et al. Localization and delocalization of light in photonic moiré lattices. Nature. 2020; 577 (7788):42-46 - 19.
Bağcı M, Bakırtaş İ, Antar N. Fundamental solitons in parity-time symmetric lattice with a vacancy defect. Optical Communication. 2015; 356 :472-481 - 20.
Bağcı M. Effects of lattice frequency on vacancy defect solitons in a medium with quadratic nonlinear response. Bitlis Eren Üniversitesi Fen Bilimleri Dergisi. 2022; 11 :344-351 - 21.
Bağcı M, Bakırtaş İ, Antar N. Vortex and dipole solitons in lattices possessing defects and dislocations. Optical Communication. 2014; 331 :204-218 - 22.
Martin H, Eugenieva ED, Chen Z, Christodoulides DN. Discrete solitons and soliton-induced dislocations in partially coherent photonic lattices. Physical Review Letters. 2004; 92 :123902 - 23.
Mark J, Biondini G, Blair S. Localized multi-dimensional optical pulses in non-resonant quadratic materials. Mathematical Computational Simulation. 2001; 56 (6):511-519 - 24.
Bağcı M, Bakırtaş İ, Antar N. Lattice solitons in nonlinear Schrödinger equation with coupling-to-a-mean-term. Optical Communication. 2017; 383 :330-340 - 25.
Bağcı M, Kutz JN. Spatiotemporal mode locking in quadratic nonlinear media. Physical Review A. 2020; 102 :022205 - 26.
Buryak AV, Di Trapani P, Skryabin DV, Trillo S. Optical solitons due to quadratic nonlinearities: from basic physics to futuristic applications. Physical Reports. 2002; 370 (2):63-235 - 27.
Hayata K, Koshiba M. Multidimensional solitons in quadratic nonlinear media. Physical Review Letters. 1993; 71 (20):3275-3278. DOI: 10.1103/PhysRevLett.71.3275 - 28.
Torner L, Sukhorukov AP. Quadratic solitons. Optical Photonic News. 2002; 13 (2):42-47 - 29.
Torruellas WE, Wang Z, Hagan DJ, VanStryland EW, Stegeman GI, Torner L, et al. Observation of two-dimensional spatial solitary waves in a quadratic medium. Physical Review Letters. 1995; 74 :5036 - 30.
Crasovan L-C, Torres JP, Mihalache D, Torner L. Arresting wave collapse by wave self-rectification. Physical Review Letters. 2003; 91 :063904 - 31.
Schiek R, Pertsch T. Absolute measurement of the quadratic nonlinear susceptibility of lithium niobate in waveguides. Optical Material Express. 2012; 2 (2):126-139 - 32.
Benney DJ, Roskes GJ. Wave instabilities. Studies in Application Mathematics. 1969; 48 :377-385 - 33.
Davey A, Stewartson K. On three-dimensional packets of surface waves. Proceedings of the Royal Society A. 1974; 338 :101-110 - 34.
Ablowitz MJ, Haberman R. Nonlinear evolution equations—two and three dimensions. Physical Review Letters. 1975; 35 :1185-1188 - 35.
Djordjevic VD, Redekopp LG. On two-dimensional packets of capillary-gravity waves. Journal of Fluid Mechanics. 1977; 79 (4):703-714. DOI: 10.1017/S0022112077000408 - 36.
Mark J, Biondini G, Blair S. Multi-dimensional pulse propagation in non-resonant materials. Physical Review Letters. 1997; 236 (5):520-524 - 37.
Mark J, Biondini G, Blair S. Nonlinear Schrödinger equations with mean terms in nonresonant multidimensional quadratic materials. Physical Review. E. 2001; 63 :046605 - 38.
Michael L. Sundheimer. Cascaded second-order nonlinearities in waveguides [PHD thesis]. 1994 - 39.
Ablowitz MJ. Wave collapse in a class of nonlocal nonlinear Schrödinger equations. Physica D: Nonlinear Phenomena. 2005; 207 (3):230-253 - 40.
Kelley PL. Self-focusing of optical beams. Physical Review Letters. 1965; 15 :1005-1008 - 41.
Papanicolaou G, McLaughlin D, Weinstein M. Focusing singularity for the nonlinear Schrödinger equation. In: Fujita H, Lax PD, Strang G, editors. Nonlinear Partial Differential Equations in Applied Science; Proceedings of The U.S.-Japan Seminar, Tokyo, 1982, volume 81 of North-Holland Mathematics Studies. North-Holland; 1983 - 42.
Merle FH, Raphael P. On universality of blow-up profile for l2 critical nonlinear schrödinger equation. Inventiones Mathematicae. 2004; 156 :565 - 43.
Moll KD, Gaeta AL, Fibich G. Self-similar optical wave collapse: Observation of the townes profile. Physical Review Letters. 2003; 90 :203902 - 44.
Bağcı M. Partially PT -symmetric lattice solitons in quadratic nonlinear media. Physical Review A. 2021; 103 :023530 - 45.
Bağcı M. Vortex solitons on partially PT -symmetric azimuthal lattices in a medium with quadratic nonlinear response. Journal of Mathematical Sciences and Modelling. 2021; 4 :117-125 - 46.
Bağcı M, Horikis TP, Bakırtaş İ, Antar N. Lattice solitons in a nonlocal nonlinear medium with self-focusing and self-defocusing quintic nonlinearity. In: Antar N, Bakırtaş İ, editors. The Nonlinear Schrödinger Equation. Rijeka: IntechOpen; 2022 - 47.
Abo-Shaeer JR, Raman C, Vogels JM, Ketterle W. Observation of vortex lattices in bose-einstein condensates. Science. 2001; 292 :476-479 - 48.
Matthews MR, Anderson BP, Haljan PC, Hall DS, Wieman CE, Cornell EA. Vortices in a bose-einstein condensate. Physical Review Letters. 1999; 83 :2498 - 49.
Bartal G, Fleischer JW, Segev M, Manela O, Cohen O. Two-dimensional higher-band vortex lattice solitons. Optics Letters. 2004; 29 :2049 - 50.
Fleischer JW, Bartal G, Cohen O, Manela O, Segev M, Hudock J, et al. Observation of vortex-ring “discrete” solitons in 2d photonic lattices. Physical Review Letters. 2004; 92 :3 - 51.
Freedman B, Bartal G, Segev M, Lifshitz R, Christodoulides DN, Fleischer JW. Wave and defect dynamics in nonlinear photonic quasicrystals. Nature. 2006; 440 :7088 - 52.
Kartashov YV, Malomed BA, Torner L. Solitons in nonlinear lattices. Reviews of Modern Physics. 2011; 83 :247-305 - 53.
Yuri S. Dark optical solitons: physics and applications. Physics Reports. 1998; 298 :81-197 - 54.
Leblond H, Malomed BA, Mihalache D. Spatiotemporal vortex solitons in hexagonal arrays of waveguides. Physical Review E. 2011; 83 :063825 - 55.
Izdebskaya YV, Shvedov VG, Jung PS, Krolikowski W. Stable vortex soliton in nonlocal media with orientational nonlinearity. Optics Letters. 2018; 43 :66 - 56.
Chen Y-F, Beckwitt K, Wise FW, Aitken BG, Sanghera JS, Aggarwal ID. Measurement of fifth- and seventh-order nonlinearities of glasses. Journal of Optical Society America B. 2006; 23 (2):347-352 - 57.
Azzouzi F, Triki H, Grelu P. Dipole soliton solution for the homogeneous high-order nonlinear schrödinger equation with cubic-quintic-septic non-kerr terms. Applied Mathematical Modelling. 2015; 39 :3-1300 - 58.
Komarov A, Leblond H, Sanchez F. Quintic complex ginzburg-landau model for ring fiber lasers. Physical Review E. 2005; 72 :025604 - 59.
Alidou Mohamadou CG, Tiofack L, Kofané TC. Wave train generation of solitons in systems with higher-order nonlinearities. Physical Review E. 2010; 82 :016601 - 60.
Yang J, Lakoba TI. Universally-convergent squared-operator iteration methods for solitary waves in general nonlinear wave equations. Studies in Applied Mathematics. 2007; 118 (2):153-197 - 61.
Yang J. Nonlinear Waves in Integrable and Nonintegrable Systems. Philadelphia: SIAM; 2010 - 62.
Vakhitov NG, Kolokolov AA. Stationary solutions of the wave equation in a medium with nonlinearity saturation. Radiophysics and Quantum Electronics. 1973; 16 (7):783-789 - 63.
Harvey A, Weinstein MI. On the bound states of the nonlinear schrödinger equation with a linear potential. Physica D: Nonlinear Phenomena. 1988; 30 (1):207-218 - 64.
Michael I. Weinstein, Modulational stability of ground states of nonlinear schrödinger equations. SIAM Journal on Mathematical Analysis. 1985; 16 (3):472-491