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Robustness of rogue waves: the route to improve the ultrafast propagation of pulses in wave guide structures

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Abstract

In this work, an adaptive control of instability is used to improve the ultrafast propagation of pulses in wave guide structures. One focuses on robust wave profiles with ideal shape and amplitude that can be useful for the ultrafast propagation without severe perturbations. The few perturbations observed are managed to catch up the stability of pulses and pick up the ultrafast propagation. To achieve this aim, a rich generalized model of nonparaxial nonlinear Schrödinger equation that improves the description of spontaneous waves in higher nonlinear and chiral media is derived, based on the theory of Beltrami-Maxwell formalism. The type of rogue wave ideal for the fast propagation is constructed with the modified Darboux transformation (mDT) method and its robustness to nonlinear effects is shown numerically through the pseudo-spectral method. This paper provides a framework to appreciate the efficiency of rogue waves in the improvement of ultrafast propagation of pulses in wave guides, biological systems and life-science.

© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

1. Introduction

The matter of instability has been a serious challenge that attracted the attention of many scientists in nonlinear sciences [13]. So far, it has been subject of many scientific discussions, based on frequency level of waves, quality of wave guide structures and transmission with few losses [4,5]. Moreover, the wave propagation phenomenon has been studied in optical fibers with ultrashort pulses, and the consistency of the instability was also observed. A methodology was proposed to solve this matter [6], the equilibrium between the dispersion and nonlinearity of a certain level till the needed balance [2]. In this work, we suggest an adaptive control [6] of the instability with the parameters of the system and the balance control if necessary to achieve the study aim. Therefore, the generalized cubic-quintic nonparaxial chiral nonlinear Schrödinger equation is derived from the theory of Beltrami-Maxwell formalism to catch up the stability of robust waves traveling in micro-structures with fast motion, and that are capable to face nonlinear phenomena responsible of the instability of pulses in wave guide structures [7]. This approach is a framework to improve the ultrafast propagation with robust waves related to special rogue waves [8] in micro-structures. Rogue waves were found useful and benefit in other systems although their powerful destructive nature in ocean [9,10], this according to their remarkable properties of localization in both space and time [10], their robustness to nonlinear effects [11], their appearance and disappearance in short-time delay [12]. In optics, rogue wave events have been studied with a diversity of analytical and numerical methods through the standard nonlinear Schrödinger (NLS) equation. More specifically, a variety of NLS models were used to investigate on the predictability of rogue wave events whose occurrence have been observed in Bose-Einstein condensates [11,13,14], laser-plasma interactions [15], superfluids [16], in the atmosphere [17],…, etc. The enlightenment on the properties and controllability of different types of rogue waves such as the Peregrine soliton [18], Kuznetsov-Ma soliton [19] and Akhmediev breathers [20] were made possible through a nonlinear management with several nonlinear models from scalar to vectorial ones, [21,22], describing rogue waves in physical systems.

In optical communication, the miniaturization of devices in multiplexed systems can generate non-negligible nonlinear effects such as the optical activity and nonparaxial phenomena in optical systems. Hence, our investigation on robustness of rogue waves in a chiral medium, where we assume that the control of chiral level can help to define the sufficient quantity of optical activity, necessary for the good performance of devices, their better configurations, as well as the types of spontaneous waves, robust to nonlinear effects and compatible for the fast propagation in optical systems. To ensure the stability of robust wave propagating in wave guides, an adaptive control is applied to improve the ultrafast propagation of pulses, this, by choosing adequately the parameters that will insure the fast propagation of rogue waves and their robustness to nonlinear effects.

The paper is organized as follows. In Section 2 the generalized cubic-quintic nonparaxial chiral nonlinear Schrödinger equation is derived. In Section 3 the modulation instability is investigated to find the existence condition of robust waves with ideal shape useful for the ultrafast propagation. In Section 4 the rogue wave solutions are constructed and their stability during the propagation in wave guides filed with chiral material is exhibited . In Section 5 the robustness of rogue wave against nonlinear effects is exhibited through the analytical and numerical methods. Section 6 is devoted to the summary of main results and comments.

2. Derivation of the cubic-quintic nonparaxial chiral nonlinear Schrödinger equation

The concept of chirality, known as optical activity in optics, is the ability to rotate plane polarized light, either to the right or left-hand side called, respectively dextrorotatory and levorotatory [23]. This phenomenon is governed by two main effects, the optical rotatory dispersion (ORD) and circular dichroism (CD). Both have been used in the literature as optical characterization techniques of molecules [24]. The optical activity is extremely microscopic and can not occur naturally and should therefore be constructed in the form of artificial composite materials, which can then be considered at appropriate wavelengths to be an effectively chiral medium [25]. Chiral materials are different from ordinary dielectric or magnetic materials through the constitutive relations

$$\begin{gathered} \vec D = {\varepsilon _0}\vec E + {\varepsilon _0} {T_c}\vec \nabla \times \vec E, \quad \vec B = {\mu _0}\left( {\vec H + {T_c}\vec \nabla \times \vec H} \right), \end{gathered}$$
where $\vec E$ and $\vec H$ are electric and magnetic fields, respectively. $\vec D$ is the electric displacement and $\vec B$ is the magnetic intensity. ${\varepsilon _0}$ is the dielectric constant known as the linear permittivity and the parameter ${\mu _0}$ is the magnetic permeability in the free space. To avoid confusion, we set ${T_c}$ as the chiral parameter that is nil for non chiral materials and non zero for chiral material. In this work, the transmission support is a wave guide tailored with specific properties among which, the chiral distribution that involve left and-right circularly polarized (LCP and RCP) fields that propagate through the wave guide with different speeds. Considering an electromagnetic field propagating in the nonlinear chiral medium, the permittivity takes the form [26]
$${\varepsilon _n} = {\varepsilon _0} + {\varepsilon _2}{\left| {\vec E} \right|^2} + {\varepsilon _4}{\left| {\vec E} \right|^4},$$
where ${\varepsilon _2}$ and ${\varepsilon _4}$ are the nonlinear permittivity of the cubic and quintic nonlinearity, respectively. Therefore, the constitutive relations take the form [26]
$$\begin{gathered} \vec D = {\varepsilon _n}\vec E + {\varepsilon _0} {T_c}\vec \nabla \times \vec E, \quad \vec B = {\mu _0}\left( {\vec H +{T_c}\vec \nabla \times \vec H} \right). \end{gathered}$$

Under the same assumption, the Beltrami-Maxwell formalism taken in the presence of current density ($\vec J=\sigma \vec E$) and charge density (${\rho _V}$) is given by [27]

$$\begin{gathered} \vec \nabla \cdot \vec D = {\rho _v},\quad \vec \nabla \cdot \vec B = 0, \quad \vec \nabla \times \vec E ={-} \frac{{\partial \vec B}}{{\partial t}},\quad \vec \nabla \times \vec H = \sigma {\mu _0}\vec E + \frac{{\partial \vec D}}{{\partial t}}. \end{gathered}$$

Here, the main idea is to improve the ultrafast propagation of pulses in wave guides with the help of robust waves that are capable to keep their shapes and amplitude under a chiral distribution in the medium. To manage the perturbations of rogue waves in the above medium, one investigates the stability of robust waves to improve it whenever weak through an adaptive control or balance control. The adaptive control is achivable through the level of optical activity in the medium and also through a meticulous choice of parameters of the model that are perfectly sensible and determinist to a sudden change as nonparaxial parameter ($d$). To achieve this aim under a theoretical approach, one derives a new model, based on the above theory of Beltrami-Maxwell formalism. Substituting Eq. (3) into Eq. (4), one derives the wave equation as follows

$$\begin{gathered} {{\vec \nabla }^2}\vec E + {\mu _0}{\varepsilon _0}{T_c}^2\frac{{{\partial ^2}{\nabla ^2}\vec E}}{{\partial {t^2}}} = {\mu _0}\sigma \frac{{\partial \vec E}}{{\partial t}} + {\mu _0}{\varepsilon _0}\frac{{{\partial ^2}\vec E}}{{\partial {t^2}}} + {\mu _0}{\varepsilon _2}{\left| {\vec E} \right|^2}\frac{{{\partial ^2}\vec E}}{{\partial {t^2}}} + {\mu _0}{\varepsilon _4}{\left| {\vec E} \right|^4}\frac{{{\partial ^2}\vec E}}{{\partial {t^2}}} + \hfill \\ {\mu _0}\sigma {T_c}\vec \nabla \times \frac{{\partial \vec E}}{{\partial t}} + 2{\mu _0}{\varepsilon _0}{T_c}\vec \nabla \times \frac{{{\partial ^2}\vec E}}{{\partial {t^2}}} + {\mu _0}{\varepsilon _2}{T_c}{\left| {\vec E} \right|^2}\vec \nabla \times \frac{{{\partial ^2}\vec E}}{{\partial {t^2}}} + {\mu _0}{\varepsilon _4}{T_c}{\left| {\vec E} \right|^4}\vec \nabla \times \frac{{{\partial ^2}\vec E}}{{\partial {t^2}}}. \end{gathered}$$

Considering the optical field $\vec E$ represented by the right-(R) (positive sign (+)) and left-hand (L) (negative sign (-)) polarization in the z direction as

$$\begin{gathered} \vec E(\vec r,t) = (\hat x \mp j\hat y)\vec A(\vec r,t)\exp \left[ { - j({k_ \pm }z - {\omega _0}t)} \right] = {{\vec \psi }_{R,L}}\exp \left[ { - j({k_ \pm }z - {\omega _0}t)} \right], \end{gathered}$$
where ${{\vec \psi }_{R,L}}$ is the complex envelope of the optical field in the nonlinear chiral medium, ${k_ \pm }$ the wave number of the right- and left-hand polarization of the optical wave, respectively and ${\omega _0}$ is the frequency of the medium. Considering that the wave is propagating in the $z$ direction, we obtain after a series of derivation and simplification, the cubic-quintic nonparaxial chiral nonlinear Schrödinger equation below
$$\begin{gathered} - \frac{1}{{2{K_0}}}\frac{{{\partial ^2}\phi }}{{\partial {{z'}^2}}} + j\frac{{\partial \phi }}{{\partial z'}} + \frac{1}{2}\left( {{{K'}^\prime } - \frac{{{{K'}^2}}}{K_0}} \right)\frac{{{\partial ^2}\phi }}{{\partial {{t'}^2}}} - j\frac{1}{6}{{K'}^{\prime \prime }}\frac{{{\partial ^3}\phi }}{{\partial {{t'}^3}}} + j\frac{{\omega \alpha }}{{2{K_0}}}\left( {1 \pm {K_0}{T_c}} \right)\phi \hfill \\ \mp {{K_0}^2}{T_c}\phi - \frac{{\beta {\omega ^2}}}{{2{K_0}}}\left( {1 \mp {K_0}{T_c}} \right){\left| \phi \right|^2}\phi - \frac{{{\beta _1} {\omega ^2}}}{{2{K_0}}}\left( {1 \mp {K_0}{T_c}} \right){\left| \phi \right|^4}\phi + \frac{\alpha }{{2{K_0}}}(1 \pm {K_0}{T_c} \pm {\omega}{K'}{T_c})\frac{{\partial \phi }}{{\partial t'}} \hfill \\ \pm j\frac{{2{{K_0}^2}{T_c}}}{\omega }({1+\frac{{K'}{\omega}}{2{K_0}}})\frac{{\partial \phi }}{{\partial t'}} + j\frac{{\omega \beta }}{{{K_0}}}(1 \pm {K_0}{T_c} \pm \frac{{\omega}{K'}{T_c}}{2}){\left| \phi \right|^2}\frac{{\partial \phi }}{{\partial t'}} \hfill \\ + j\frac{{\omega {\beta _1} }}{{{K_0}}}(1 \pm {K_0}{T_c} \pm \frac{{\omega}{K'}{T_c}}{2}){\left| \phi \right|^4}\frac{{\partial \phi }}{{\partial t'}}=0. \hfill \\ \end{gathered}$$
where $K'$ is the inverse of group-velocity, ${{K'}^\prime }$ is the coefficient of the group-velocity dispersion (GVD) which can take the plus and minus signs $(\pm )$, representing the anomalous and normal dispersion regimes, respectively. The parameter ${{K'}^{\prime \prime }}$ is the third-order dispersion (TOD). The attenuation coefficient $\alpha$ is weighted towards the chiral parameter ${T_c}$. The fifth term represents the gain or loss term of the induced optical activity. Then, the sixth and seventh terms, stand for the cubic and quintic nonlinearity, respectively. The term ${{K_0}^2}{T_c}\phi$ occurs as an additional correction of the optical activity in the wave guide. The expressions at the ninth and tenth positions are the differential gain or loss term and the walk-off effect, respectively. The two last terms have the physical sense of self-steepening (SS) and are related to the third-and fifth-order nonlinearity, respectively. These terms are useful to improve the description of rogue waves that can be favorable for the ultrafast propagation. In addition, the model given in Eq. (7) verifies the conditions of time-reversal symmetry, reciprocity and controllability. Such a model which takes into account the artificial and induced optical activity has the ability to assure the total reflexion of ultrashort pulses in optical systems. Moreover, this model can help to define the sufficient level of the optical activity necessary to improve the functionalities of devices.

3. Instability and existence condition of robust waves with ideal shape favorable in ultrafast propagation

The goal to achieve is to provide a framework useful for an adaptive control of nonlinear effects in wave guide structures. As assumption, we consider a section of wave guide highly filled with chiral materials along the core. In addition, this wave guide should favor the wave propagation with few losses that can be corrected by an adaptive control and should be compatible to spontaneous wave propagation, means, waves with short-life time as rogue waves or rogons. Moreover, the wave propagating in the wave guides should be robust against perturbations. In consequence, the prototypes of rogue waves are of special interest due to their spontaneous behavior. Their disappearance and reappearance with the same shape and amplitude have been shown in the literature [10,28]. One denotes three main prototypes of spontaneous waves with finite backgrounds. The Peregrine soliton (PS) known as usual rogue wave due to its localization in both space and time [18], and unusual rogue waves, that are, the Kuznetsov-Ma soliton (KM), localized in temporal dimension with periodicity along the propagation direction [29,30] and finally, the Akhmediev Breathers (ABs), localized along the propagation direction with periodicity in temporal dimension [19]. So far, other derivative prototypes such as the chirp PS and three sisters were found in the literature [31,32]. To find the appropriate prototype of rogue waves for ultrafast propagation, one rewrites the model derived and expressed in Eq. (6) in an appropriate form. For the better understanding of the calculation and simplification of Eq. (5) into Eq. (7) and Eq. (8), see the Appendix A from Eq. (A3) to Eq. (A25) of our previous work [33] where a similar derivation was done with the same terms, except the quintic ones. So doing, we arrive at

$$\begin{gathered} d{\psi _{\xi \xi }} + j{\psi _\xi } + P{\psi _{\tau \tau }} - j\gamma {\psi _{\tau \tau \tau }} + j\mu \psi - {C_2}{\left| \psi \right|^2}\psi - {\Omega _3}{\left| \psi \right|^4}\psi + D\psi + j{\alpha _3}{\left| \psi \right|^2}{\psi _\tau } \hfill \\ + j{C_3}{\left| \psi \right|^4}{\psi _\tau } + {\eta _3}{\psi _\tau } +j{\sigma _3}{\psi _\tau } = 0, \hfill \\ \end{gathered}$$
where $\xi$ and $\tau$ ($z'$ and $t'$) are the scaled (unscaled) coordinates in the propagation direction and temporal dimension, respectively. $\psi \left ( {\xi,\tau } \right )$ is the complex envelope field of the forward (RCP) and backward (LCP) components of the optical field in the wave guide. The coefficients of Eq. (8) are derived from the relations between the scaled and unscaled variables given in Eq. (9) where $\phi$ is the unscaled complex envelop field. For more details, see Appendix A of the Ref. [33]. These coefficients are expressed in relation (10).
$$\begin{gathered} \psi = \frac{{{\omega _0}^{2/3}{\beta ^{1/3}}}}{{{{(2{K_0})}^{1/3}}}}\phi,\quad \ \xi = \frac{{{\beta ^{1/3}}{\omega _0}^{2/3}}}{{{{(2{K_0})}^{1/3}}}}z',\quad \ \tau = \frac{{{\omega _0}^{1/3}{\beta ^{1/6}}}}{{{{K''}^{1/2}}{{(2{K_0})}^{1/6}}}}t'. \end{gathered}$$
$$\begin{gathered} d = \frac{{ - \omega _0^{2/3}{\beta ^{1/3}}}}{{{{(2{K_0})}^{4/3}}}},\quad \ P = \frac{1}{2}\left( {1 - \frac{{{{K'}^2}}}{{{K_0}K''}}} \right), \quad \gamma = \frac{{K'''}}{{6{{K''}^{3/2}}}}\frac{{{\omega _0}^{1/3}{\beta ^{1/6}}}}{{{{(2{K_0})}^{1/6}}}},\quad \ \mu = \frac{{{C_2}\alpha {\omega _0}^{1/3}}}{{{\beta ^{1/3}}{{(2{K_0})}^{2/3}}}}, \hfill \\ {C_2} = 1 \pm {K_0}{T_c},\quad \ {\Omega _3} = \frac{{{C_2}{\beta _1}{{(2{K_0})}^{2/3}}}}{{\omega _0^{2/3}{\beta ^{1/3}}}}, \quad \ D ={\mp} \frac{{K_0^2{{(2{K_0})}^{1/3}}{T_c}}}{{{\omega _0}^{2/3}{\beta ^{1/3}}}},\quad \ {\eta _3} = \frac{{\alpha \left( {{C_2} \pm {\omega _0}K'{T_c}} \right)}}{{\omega _0^{1/3}{\beta ^{1/6}}{{(2{K_0})}^{5/6}}}}, \hfill \\ {\alpha _3} = \left( {{C_2} \pm \frac{{{\omega _0}K'{T_c}}}{2}} \right)\frac{{{{(2{K_0})}^{5/6}}{\beta ^{1/6}}}}{{{K_0}{{K''}^{1/2}}\omega _0^{2/3}}}, \quad \ {C_3} = {\beta _1}\left( {{C_2} \pm \frac{{{\omega _0}K'{T_c}}}{2}} \right)\frac{{{{(2{K_0})}^{3/2}}}}{{{K_0}{{K''}^{1/2}}\omega _0^{4/3}{\beta ^{3/2}}}}, \hfill \\ {\sigma _3} ={\pm} {K_0}{T_c}\left( {1 + \frac{{{\omega _0}K'{T_c}}}{2}} \right)\frac{{{{(2{K_0})}^{7/6}}}}{{{{K''}^{1/2}}\omega _0^{4/3}{\beta ^{1/6}}}}, \hfill \\ \end{gathered}$$
where
$$\begin{gathered} \alpha = {\mu _0}\sigma ,\quad \ \beta = {\mu _0}{\varepsilon _2},\quad \ {\beta _1} = {\mu _0}{\varepsilon _4}, \quad K' =\frac{1}{{{v_g}}},\quad \ K'' = \frac{{{\partial ^2}K}}{{\partial {\omega ^2}}},\quad \ K''' = \frac{{{\partial ^3}K}}{{\partial {\omega ^3}}}. \end{gathered}$$

In Eq. (8), the coefficient $d$ is the nonparaxial parameter, $P$ the GVD, $\gamma$, the TOD, $\mu$, the gain/loss term, ${C_2}$ and ${\Omega _3}$ are the third-and fifth-order nonlinearity coefficients, respectively. The coefficient $D$ is the linear birefringence, ${\eta _3}$, the differential gain/loss term, ${\alpha _3}$ and ${C_3}$ have the physical sense of SS related to the cubic and quintic nonlinearity, respectively. The parameter ${\sigma _3}$, is the walk-off coefficient. In Eq. (11), $\alpha$ is the attenuation coefficient that influences the gain/loss term ($\mu$) and differential gain/loss term (${\eta _3}$). We mentioned that the vectorial model derived and written in the scalar form for simplification as presented in Eq. (8), can be developed into two equations when considering the plus and minus signs ($\pm$) of the coefficients $\mu$, ${C_2}$, ${\Omega _3}$, $D$, ${\eta _3}$, ${\alpha _3}$, ${C_3}$ and ${\sigma _3}$ (see the expressions given in Eq. (10)). Thus, ${\psi _-}$ is the LCP component of the wave and ${\psi _+}$ represents the RCP component of the wave. The next step consists to do an investigation of the modulation instability (MI) to find the existence condition of rogue waves through the model given in Eq. (8).

To achieve that, we consider the background under the propagation of a plane wave solution in the form

$$\psi \left( {\xi ,\tau } \right) = a\exp \left\{ {j\left( {{k_0}\xi - {\omega _0}\tau } \right)} \right\}$$
where $a$ is the amplitude of the constant background, ${k_0}$, the wave number and ${\omega _0}$, the frequency. The substitution of Eq. (12) into Eq. (8) gives in the real and imaginary parts, respectively, the following equations
$$\begin{gathered} - {\Omega _3}{a^4} + {C_3}{a^4}{\omega _0} + \gamma \omega _0^3 + {\alpha _3}{a^2}{\omega _0} - {C_2}{a^2} - P\omega _0^2 - dk_0^2 + {\sigma _3}{\omega _0} + D - {k_0} = 0, \hfill \\ \mu - {\eta _3}{\omega _0} = 0,\;\;\;with\;\;\;a \ne 0. \hfill \\ \end{gathered}$$

Relation (13) gives the conditions to have an exact plane wave solution with constant background. The first equation allows to obtain the RCP $({k_{0 + }})$ and LCP $({k_{0 - }})$ components of the wave number ${k_0}$ as follow

$$\begin{gathered} {k_{0 + }} = \frac{{ - 1 - \sqrt {1 + 4dQ} }}{{2d}},\;\;\;{k_{0 - }} = \frac{{ - 1 + \sqrt {1 + 4dQ} }}{{2d}}, \hfill \\ with\;\;Q ={-} {\Omega _3}{a^4} + {C_3}{a^4}{\omega _0} + \gamma \omega _0^3 + {\alpha _3}{a^2}{\omega _0} - {C_2}{a^2} - P\omega _0^2 + {\sigma _3}{\omega _0} + D, \hfill \\ \end{gathered}$$
where the sign of nonparaxial coefficient $d$ defines better the components of the wave number (RCP or LCP). The second equation gives the expression of the frequency of the plane wave
$${\omega _0} = \frac{\mu }{{{\eta _3}}}.$$

It can be seen from Eq. (15), regarding the expressions of ${\mu }$ and ${\eta _3}$ in relation (10) that the attenuation parameter is vanished, leaving the total influence of the gain/loss and differential gain/loss terms on the frequency. The components of the wave number $({k_{0 + }}, {k_{0 - }})$ depend on the cubic and quintic nonlinearity, respectively of the Kerr and SS effects, then, to the second-and third-order dispersion, and also on the linear birefringence and walk-off effect. Hence, the richness of the wave number depending on nine parameters of the system compare to the frequency that depend only on two parameters. This information is capital in the choice of the variable of the dispersion relation. Therefore, the investigation of the MI on the amplitude allows to introduce a small perturbation $\chi \left ( {\xi,\tau } \right )$ such as

$$\psi \left( {\xi ,\tau } \right) = \left[ {a + \chi \left( {\xi ,\tau } \right)} \right]\exp \left[ {j\left( {{k_0}\xi - {\omega _0}\tau } \right)} \right],$$
with $\chi \left ( {\xi,\tau } \right ) << a$. Assuming
$$\begin{gathered} \chi \left( {\xi ,\tau } \right) = {A_1}\exp \left[ {j(K\xi - \Omega \tau )} \right] + {A_2c}\exp \left[ {j(K\xi - \Omega \tau )} \right] + cc, \end{gathered}$$
where the cc is given by the expression
$$cc = {A_{c1}}\exp \left[ { - j(K\xi - {\Omega _c}\tau )} \right] + {A_{2}}\exp \left[ { - j(K\xi - {\Omega _c}\tau )} \right].$$

Here, ${A_1}$ and ${A_2}$ are the complex constant amplitudes of the perturbation. $K$ is the wave number and $\Omega$, the frequency of the perturbed background. The letter $cc$ represents the complex conjugate of the quantity it carries. Considering the perturbation of the background, the substitution of Eq. (16) into Eq. (8) gives the following system

$$\left( {\begin{array}{cc} {{\lambda _1} - d{K^2} - {\lambda _0}K} & {{\delta _1}} \\ {{\delta _1}} & {{\lambda _2} - d{K^2} + {\lambda _0}K} \end{array}} \right)\left( \begin{gathered} {A_1} \hfill \\ {A_2} \hfill \\ \end{gathered} \right) = 0$$
where
$$\begin{gathered} {\lambda _1} = {C_3}{a^4}(\Omega + 3{\omega _0}) - 3{\Omega _3}{a^4} + {\alpha _3}{a^2}(\Omega + 2{\omega _0}) + \gamma ({\Omega ^3} + 3{\omega _0}{\Omega ^2} + 3\omega _0^2\Omega + \omega _0^3) \hfill \\ \;\;\;\;\;\;\;- ({k_0} + dk_0^2) + P( - {\Omega ^2} - 2{\omega _0}\Omega - \omega _0^2) + {\sigma _3}(\Omega + {\omega _0}) + D - 2{C_2}{a^2}, \hfill \\ {\lambda _2} = {C_3}{a^4}( - \Omega + 3{\omega _0}) - 3{\Omega _3}{a^4} + {\alpha _3}{a^2}( - \Omega + 2{\omega _0}) + \gamma ( - {\Omega ^3} + 3{\omega _0}{\Omega ^2} - 3\omega _0^2\Omega + \omega _0^3) \hfill \\ \;\;\;\;\;\;\; - ({k_0} + dk_0^2) + P( - {\Omega ^2} + 2{\omega _0}\Omega - \omega _0^2) + {\sigma _3}( - \Omega + {\omega _0}) + D - 2{C_2}{a^2}, \hfill \\ {\delta _1} = 2{C_3}{a^4}{\omega _0} - 2{\Omega _3}{a^4} + {\alpha _3}{a^2}\omega _0^2 - {C_2}{a^2}, \quad {\lambda _0} = (1 + 2d{k_0}). \hfill \\ \end{gathered}$$

The components of the perturbed frequency issue from the imaginary part take the form

$$\begin{gathered} {\Omega _-} = {\omega _0} - \frac{\mu }{{{\eta _3}}} \;\;\;\;\;\;\; {\Omega _+} = \frac{\mu }{{{\eta _3}}} -{\omega _0} . \end{gathered}$$

The system given in Eq. (19) admits the plane wave solutions with the perturbed wave number $K$ and frequency $\Omega$ if the dispersion relation is

$${K^4} + A{K^2} + BK + C = 0,$$
with
$$\begin{gathered} A ={-} \frac{{\left( {d({\lambda _1} + {\lambda _2}) + \lambda _0^2} \right)}}{{{d^2}}},\;\;B = \frac{{({\lambda _1} - {\lambda _2}){\lambda _0}}}{{{d^2}}}, \quad C = \frac{{{\lambda _1}{\lambda _2} - \delta _1^2}}{{{d^2}}}. \end{gathered}$$

The dispersion relation has the reduced form of the quartic equation and is known as the biquadratic equation. Using the Cardan’s solution for quartic equation, Eq. (22) is transformed to a cubic equation

$$\begin{gathered} {Z^3} + {a_1}{Z^2} + bZ + c = 0, \quad where\;{a_1} ={-} A,\;b ={-} 4C,\;c = 4AC - {B^2}.\; \hfill \\ \end{gathered}$$

Using the Cardan’s solution, the cubic equation is transformed to the reduced form

$$\begin{gathered} {y^3} + {p_1}y + {q_1} = 0, \quad with\;{p_1} ={-} \frac{{a_1^3}}{3} + b,\;\;{q_1} = 2{\left( {\frac{{{a_1}}}{3}} \right)^3} - \frac{{{a_1}b}}{3} + c, \end{gathered}$$
and where the roots are given by
$$\begin{gathered} {y_1} = {A_2} + {B_2}, \quad {y_2} ={-} \frac{{({A_2} + {B_2})}}{2} + j\frac{{({A_2} - {B_2})\sqrt 3 }}{2}, \quad {y_3} ={-} \frac{{({A_2} + {B_2})}}{2} - j\frac{{({A_2} - {B_2})\sqrt 3 }}{2}, \end{gathered}$$
with the given parameters
$$\begin{gathered} {A_2} = \sqrt[3]{{ - \frac{{{q_1}}}{2} + \sqrt {{Q_2}} }},\quad \;{B_2} = \sqrt[3]{{ - \frac{{{q_1}}}{2} - \sqrt {{Q_2}} }}, \quad \;{Q_2} = {\left( {\frac{{{p_1}}}{3}} \right)^3} + {\left( {\frac{{{q_1}}}{2}} \right)^2}, \end{gathered}$$
where ${Q_2}$ is the discriminant of the third-order. Now, the roots of Eq. (24) are deduced from the roots of Eq. (25) under the form $Z = y - {a_1}/3$. We should keep in mind that for both ${Q_2}\,>\,0$ and ${Q_2}\,<\,0$, the roots of the dispersion equation are all complex, with real and imaginary parts. So, the two cases should be taken into account for the evaluation of the roots of Eq. (22). Thus, for ${Q_2}\,>\,0$, the roots of Eq. (24) take the forms
$$\begin{gathered} {Z_1} = \;{A_2} + {B_2} - \frac{{{a_1}}}{3}, \quad {Z_2} = \; - \left[ {\frac{{({A_2} + {B_2})}}{2} + \frac{{{a_1}}}{3}} \right] + j\frac{{({A_2} - {B_2})\sqrt 3 }}{2}, \hfill \\ {Z_3} ={-} \left[ {\frac{{({A_2} + {B_2})}}{2} + \frac{{{a_1}}}{3}} \right] - j\frac{{({A_2} - {B_2})\sqrt 3 }}{2}, \hfill \\ \end{gathered}$$
and in the case where ${Q_2}\,<\,0$, we have
$$\begin{gathered} {Z_4} = 2\sqrt { - \frac{{{p_1}}}{3}} \cos \left[ {\frac{1}{3}\arccos \left( { - \frac{{{q_1}}}{2}\sqrt { - \frac{{27}}{{p_1^3}}} } \right)} \right] - \frac{{{a_1}}}{3}, \hfill \\ {Z_5} = 2\sqrt { - \frac{{{p_1}}}{3}} \cos \left[ {\frac{1}{3}\arccos \left( { - \frac{{{q_1}}}{2}\sqrt { - \frac{{27}}{{p_1^3}}} } \right) + \frac{{2\pi }}{3}} \right] - \frac{{{a_1}}}{3}, \hfill \\ {Z_6} = 2\sqrt { - \frac{{{p_1}}}{3}} \cos \left[ {\frac{1}{3}\arccos \left( { - \frac{{{q_1}}}{2}\sqrt { - \frac{{27}}{{p_1^3}}} } \right) + \frac{{4\pi }}{3}} \right] - \frac{{{a_1}}}{3}. \hfill \\ \end{gathered}$$

As we can see, the roots ${Z_1},{Z_2},\ldots,{Z_6}$ are the solutions of the cubic equation and by the way, the intermediate solution of the dispersion relation. The dispersion relation can be transformed as follows

$$\begin{gathered} \left( {{K^2} + {A_3}K + {B_3}} \right)\left( {{K^2} + {A_4}K + {B_4}} \right) = 0,\;where \quad \left\{ \begin{gathered} {A_3} = jz \hfill \\ {B_3} = \frac{{jB}}{{2z}} + {\phi _0} \hfill \\ \end{gathered} \right.,\;\;\;\left\{ \begin{gathered} {A_4} ={-} jz \hfill \\ {B_4} = \frac{{ - jB}}{{2z}} + {\phi _0} \hfill \\ \end{gathered} \right.,\; \hfill \\ with\;\;\left\{ \begin{gathered} z = {\left( { - {a_1} - 2{\phi _0}} \right)^{1/2}} \hfill \\ {\phi _0} = {Z_1},{Z_2},\ldots,{Z_6} \hfill \\ \end{gathered} \right.. \hfill \\ \end{gathered}$$

Therefore, the four roots of the wave number are expressed as follows

$$\begin{gathered} {K_1} = \frac{{ - {A_3} + \sqrt {A_3^2 - 4{B_3}} }}{2},\;\;{K_2} = \frac{{ - {A_3} - \sqrt {A_3^2 - 4{B_3}} }}{2}, \hfill \\ {K_3} = \frac{{ - {A_4} + \sqrt {A_4^2 - 4{B_4}} }}{2},\;\;{K_4} = \frac{{ - {A_4} - \sqrt {A_4^2 - 4{B_4}} }}{2}, \hfill \\ \end{gathered}$$
where the discriminants of each polynomial in relation (31) are given, respectively by
$${\Delta _1} = A_3^2 - 4{B_3},\;\;{\Delta _2} = A_4^2 - 4{B_4}.$$
We found useful in this work to represent the gain map of the system, to reveal the existence domain of MI (the necessary condition of existence of rogue waves) that occurs wherever the root of the dispersion relation has a negative imaginary part $Im(K)\,<\, 0$, with ${\Omega _1} = 0$ in the gain band $0 \leqslant {\Omega _1} \,<\, \Omega \,<\, {\Omega _2}$ as shown in the literature by many scientists [28,34], and focus on baseband MI (the sufficient condition of existence of rogue waves) where multiple rogue waves can be excited, for the purpose of rational and suitable choice of robust waves among them. According to the baseband MI theory, $\Omega = 0$. This relation is verified according to relations (15) and (21). This relation satisfies the assumption that MI arises for non-real value of $K$.
$$\begin{gathered} So\;for\;{\phi _0} = {Z_1},{Z_2},\ldots,{Z_6} \Rightarrow \;G(\Omega) = \operatorname{Im} ({K}) \hfill \\ \end{gathered}$$
where $G(\Omega )$ is the expression of the gain for the different roots of the dispersion relation. The marginal stability is obtained for ${\Delta _{1,2}} = 0$. Therefore, the wave numbers take the form
$${K_{1,2}} ={-} j\frac{z}{2}\;,\;{K_{3,4}} = j\frac{z}{2},\;where\;z = {\left( {A - 2{\phi _0}} \right)^{1/2}}.$$

More specifically, the instability is obtained when the discriminant of the quartic equation is negative. Thus, by setting $\Omega = 0$, this implies that ${\lambda _1} = {\lambda _2} = \lambda$. Therefore, the MI condition becomes

$$\lambda \,<\,{\pm} {\delta _1}\;,\;16\left[ {16{d^4}{{\left( {{\lambda ^2} - \delta _1^2} \right)}^2} - 8{{\left( {2\lambda d + \lambda _0^2} \right)}^2}\left( {{\lambda ^2} - \delta _1^2} \right) + {{\left( {2\lambda d + \lambda _0^2} \right)}^4}} \right] \,<\, 0$$

Here, we consider as the existence domain of MI, the gain band where $G\left ( \Omega \right ) = - \operatorname {Im} \left ( K \right ) > 0$ and as the grow rate or explosive rate, the area where perturbations grow exponentially as $\exp \left ( {G\left ( \Omega \right )\;\xi } \right )$ at the expense of the pump. As the cubic nonlinearity parameter ${C_2}\,>\,0$ with $-{C_2} \,<\, 0$, in relation (8), we are working under the defocusing regime in which rogue waves exist whenever the MI is present, mostly when the baseband MI is present. We should keep in mind that the existence domain of the MI can be represented for all the four roots of the dispersion relation when considering all the six solutions of ${\phi _0}$ given by ${\phi _0} = {Z_1},{Z_2},\ldots,{Z_6}$. Here, we mainly focus on the solutions for the case, ${\phi _0} = {Z_1}$. So doing, Figure 1 reveals the MI maps $\left ( {\Omega,d} \right )$ and $\left ( {\Omega,a} \right )$ with sensible parameters of the system, that are, the nonparaxial parameter $d$ and the amplitude $a$ of the background, respectively. The same conclusion is obtained when operating with the maps $\left ( {\Omega,{\omega _0}} \right )$ and $\left ( {\Omega,{T_C}} \right )$ with other sensible parameters as the frequency of the background ${\omega _0}$, and and optical activity or chiral parameter $Tc$ that are not represented here. The presence of baseband MI is well-observed in Fig. 1(a), confirming the assumption of the presence of rogue waves that mostly appear whenever the baseband MI is present. These maps exhibit the influence of nonparaxial coefficient on the existence domain of MI. View the shapes of the existence domain of MI through the maps ($\Omega$ and $d$), ($\Omega$ and $a$), we can conclude that the assumption done on the nonparaxial parameter $d$, and the amplitude of the background $a$ are effectively sensitive parameters and can be chosen for an adaptive control of MI in the system. The same conclusion it also applied for the frequency ${\omega _0}$ and the chiral coefficient $Tc$. Thus, any perturbation susceptible to affect the stability of rogue waves during their propagation, can therefore be managed by an adjustment of the above sensitive parameters of the medium to pick up the ultrafast propagation. Now that the baseband MI that coincides with the existence condition of rogue waves can be localized on different maps, let us find the rational solutions related to rogue waves via the model derived earlier to select the ones that are more adequate for the fast propagation, based on their shape and robustness under perturbation.

 figure: Fig. 1.

Fig. 1. Gain maps: $\left ( {\Omega,d} \right )$ in Fig. 1(a) and $\left ( {\Omega,a} \right )$ in Fig. 1(b) with ${\phi _0} = {Z_1}$

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4. Construction of rogue wave solution of the cubic-quintic nonparaxial chiral nonlinear Schrödinger equation

Among the variety of rogue wave solutions that are known in the literature, the Peregrine soliton (PS) is of special interest according to the exceptional characteristic of its both localization in space and time, comparatively to other rogue wave prototypes that are either localized in the propagation direction with periodicity in the transverse direction (Akhmediev Breathers (ABs)) or localized in temporal dimension with periodicity along the propagation direction (Kuznetsov–Ma (KM)). This additional property has many applications in medical sciences. Hence, the importance to test the ability of PS under perturbations. Thus, let find the rogue wave solutions of the cubic-quintic nonparaxial chiral nonlinear Schrödinger equation given in Eq. (8). That equation can be rewritten as follows

$$\begin{gathered} d{\psi _{\xi \xi }} + j{\psi _\xi } + P{\psi _{\tau \tau }} - {C_2}{\left| \psi \right|^2}\psi + j{\alpha _3}{\left| \psi \right|^2}{\psi _\tau } - j\gamma {\psi _{\tau \tau \tau }} + {r_1}\left( {D + j\mu } \right)\psi + {r_2}\left( {\eta + j{\sigma _3}} \right){\psi _\tau } \hfill \\ - {\Omega _3}{\left| \psi \right|^4}\psi + j{C_3}{\left| \psi \right|^4}{\psi _\tau } = 0. \hfill \\ \end{gathered}$$

This model verifies the condition of controllability of higher-order NLS equation [35,36] throughout the coefficients ${\alpha _3}$ and ${C_3}$, that are, respectively, the SS related to the cubic nonlinearity and quintic nonlinearity. It can be seen that the model is non integrable and it is of crucial interest to reduce Eq. (36) into an integrable model. Based on the well-known integrability conditions of the Hirota equation [37] and on our previous work [37], the integrability of the model is satisfied for $d = - 10\nu$, $P = 1/2$, ${C_2} = - \sigma$, ${\alpha _3} = -6\nu \sigma$, $\gamma = 6\nu \sigma$, ${r_1} = {r_2} = 1$, $\mu = D = - 3\nu$, ${\eta _3} = {\sigma _3} = - 3\nu$, ${\Omega _3} = - 5\nu \sigma /2$, ${C_3} = -3\nu \sigma$. Therefore, if we set $\nu = 0$, Eq. (36) is reduced to the standard NLS equation. Let consider ${r_1} = {r_2} = 1$, to find the integrability constraints of the model through the similarity reduction method, that is, the envelope field in the form [14]

$$\psi \left( {\xi ,\tau } \right) = A(\xi )V\left[ {Z(\xi ),T\left( {\xi ,\tau } \right)} \right]\exp \left\{ {j\rho \left( {\xi ,\tau } \right)} \right\},$$
that would reduce Eq. (36) to the cubic-quintic NLS equation below
$$\begin{gathered} j{u_\xi } + \frac{1}{2}{u_{\tau \tau }} + j\frac{\gamma }{{6\sigma }}{u_{\tau \tau \tau }} + j\gamma {\left| u \right|^2}{u_\tau } + \sigma {\left| u \right|^2}u + 6{\sigma ^2}{\varepsilon _4}^\prime {\left| u \right|^4}u + 30{\sigma ^2}{\varepsilon _5}{\left| u \right|^4}{u_\tau } = 0, \end{gathered}$$
where ${\gamma }$, $\sigma$, ${\varepsilon _4}^\prime$ and ${\varepsilon _5}$ are parameters of integrabiltity.

The first step is to find the integrability conditions of the parameters related to the envelope field among which, the amplitude of the wave, $A(\xi )$, the effective propagation distance, $Z(\xi )$, the similitude variable, ${T\left ( {\xi,\tau } \right )}$, the complex field, $V\left [ {Z(\xi ), T\left ( {\xi,\tau } \right )} \right ]$, and the phase of the wave ${\rho \left ( {\xi,\tau } \right )}$. The substitution of Eq. (37) into Eq. (36) gives a system of two partial differential equations with constant coefficients

$$\begin{gathered} d({A_{\xi \xi }}V + 2{A_\xi }{Z_\xi }{V_Z} + 2{A_\xi }{T_\xi }{V_T} + 2A{Z_\xi }{T_\xi }{V_{ZT}} + A{Z_{\xi \xi }}{V_Z} + A{T_{\xi \xi }}{V_T} + A{Z_\xi }^2{V_{ZZ}} \hfill \\ + A{T_\xi }^2{V_{TT}} - A{\rho _\xi }^2V) - AV{\rho _\xi } + P(A{V_{TT}}{T_\tau }^2 + A{V_T}{T_{\tau \tau }} - AV{\rho _\tau }^2) + \gamma (3A{V_T}{T_{\tau \tau }}{\rho _\tau } \hfill \\ + 3A{V_T}{T_\tau }{\rho _{\tau \tau }} + 3A{V_{TT}}{T_\tau }^2{\rho _\tau } + AV{\rho _{\tau \tau \tau }} - AV{\rho _\tau }^3) + DAV - {C _2}{A^2}{\left| V \right|^2}AV \hfill \\ -{\Omega_3}{A^4}{\left| V \right|^4}AV- {\alpha _3}{A^2}{\left| V \right|^2}AV{\rho _\tau } - {C _3}{A^4}{\left| V \right|^4}AV{\rho _\tau } + {\eta _3} A{T_\tau }{V_T} - {\sigma _3} AV{\rho _\tau } =0, \hfill \\ \end{gathered}$$
$$\begin{gathered} d(AV{\rho _{\xi \xi }} + 2{A_\xi }{\rho _\xi }V + 2A{Z_\xi }{\rho _\xi }{V_Z} + 2A{\rho _\xi }{T_\xi }{V_T}) + {A_\xi }V + A{V_Z}{Z_\xi } + A{V_T}{T_\xi }+ P(AV{\rho _{\tau \tau }} \hfill \\ + 2A{V_T}{T_\tau }{\rho _\tau }) - \gamma (A{V_T}{T_{\tau \tau \tau }} + 3A{V_{TT}}{T_\tau }{T_{\tau \tau }} + A{V_{TTT}}{T_\tau }^3 - 3A{V_T}{T_\tau }{\rho _\tau }^2 - 3AV{\rho _{\tau \tau }}{\rho _\tau }) \hfill \\ + \mu AV + {\alpha _3}{A^2}{\left| V \right|^2}A{V_T}{T_\tau } + {C _3}{A^4}{\left| V \right|^4}A{V_T}{T_\tau } + {\eta _3}AV{\rho _\tau } + {\sigma _3} A{T_\tau }{V_T} =0, \hfill \\ \end{gathered}$$
where the scripts of differential equations are simplified as $A\left ( \xi \right ) = A$, $Z\left ( \xi \right ) = Z$, $T\left ( {\xi,\tau } \right ) = T$, $\rho \left ( {\xi,\tau } \right ) = \rho$ and $V\left [ {Z(\xi ),T\left ( {\xi,\tau } \right )} \right ] = V$. By connecting the solution of Eq. (36) to the one of Eq. (38), the complex field $V\left [ {Z(\xi ),T(\xi,\tau )} \right ]$ should satisfy the integrable form of Eq. (38) [12,35,37] for the correspondence $\gamma = 6\nu \sigma$, ${\varepsilon _4}^\prime = \frac {\nu }{{2\sigma }}$, ${\varepsilon _5} = \frac {{3\nu }}{{5\sigma }}$, $\tau \to \frac {1}{{\sqrt 2 }}\;T\left ( {\xi,\tau } \right )$ and $\xi \to Z\left ( \xi \right )$, in the form
$$j{V_Z} + {V_{TT}} + \sigma {\left| V \right|^2}V + j2\sqrt {2\;} \nu {V_{TTT}} + j6\sqrt 2 \;\nu {\left| V \right|^2}{V_T} + 3\nu \sigma {\left| V \right|^4}V + j18\sqrt 2 \;\nu \sigma {\left| V \right|^4}{V_T} = 0,$$

This integrable model can generate a rogue wave solution if $\sigma = 1$. Thus, for $V\left [{Z(\xi ),T(\xi,\tau )} \right ]$ satisfying the relation (41), the similarity reduction method gives the above differential equations

$$-3\gamma {T_\tau }{T_{\tau \tau }} = 0,$$
$${T_\xi } + 2P {T_\tau }{\rho _\tau } + {\sigma _3} {T_\tau }\ - \gamma \left( {{T_{\tau \tau \tau }} - 3{T_\tau }{\rho _\tau }^2} \right) = 0,$$
$${A_\xi } + A(d{\rho _{\xi \xi }} + P{\rho _{\tau \tau }} + 3\gamma {\rho _{\tau \tau }}{\rho _\tau } + \mu + {\eta_3 } {\rho _\tau }) = 0,$$
$$-\gamma {T_\tau }^3 + 2\sqrt 2 \nu {Z_\xi } = 0,$$
$$d{\rho_\xi }{A_\xi }V+\frac{1}{2}A{Z_\xi }{V_Z}+dA{\rho_\xi }{Z_\xi }{V_Z}+dA{T_\xi }{\rho_\xi }{V_T} = 0,$$
$${\alpha _3}{A^2}{T_\tau } + 6\sqrt 2 \nu {Z_\xi } = 0,$$
$${C _3}{A^4}{T_\tau } + 18\sqrt 2 \nu {Z_\xi } = 0,$$
$$d{T_{\xi \xi }} + P {T_{\tau \tau }} + 3\gamma \left( {{T_{\tau \tau }}{\rho _\tau } + {T_\tau }{\rho _{\tau \tau }}} \right) + {\eta_3 } {T_\tau } = 0,$$
$${Z_\xi } + d{T_\xi }^2 + P {T_\tau }^2 + 3\gamma {\rho _\tau }{T_\tau }^2 = 0,$$
$${\rho _\xi } + d{\rho _\xi }^2 + P {\rho _\tau }^2 + \gamma \left( {{\rho _\tau }^3 - {\rho _{\tau \tau \tau }}} \right) +{\sigma _3} {\rho _\tau } - D = 0,$$
$$\sigma {Z_\xi } - {A^2}\left( {{C_2} + {\alpha _3}{\rho _\tau }} \right) = 0,$$
$$3\nu{Z_\xi } - {A^4}\left( {{\Omega_3} + {C _3}{\rho _\tau }} \right) = 0,$$
$${A_{\xi \xi }}V + 2{A_\xi }{Z_\xi }{V_Z} + 2{A_\xi }{T_\xi }{V_T} + 2A{Z_\xi }{T_\xi }{V_{ZT}} + A{Z_{\xi \xi }}{V_Z} + A{Z_\xi }^2{V_{ZZ}} = 0,$$
where the constraints that play an important role in the choice of arbitrary parameters of the system are deduced from the above differential equations of which the simplified forms stand from Eq. (42) to Eq. (54), respectively as follows $A{V_{TT}} \ne 0$, $A \ne 0$, $A{V_T} \ne 0$, $V \ne 0$, $A{V_{TTT}} \ne 0$, $2 \ne 0$, $A{\left | V \right |^2}{V_T} \ne 0$, $A{\left | V \right |^4}{V_T} \ne 0$, $A{V_T} \ne 0$, $A{V_{TT}} \ne 0$, $- AV \ne 0$, $A{\left | V \right |^2}V \ne 0$, $A{\left | V \right |^4}V \ne 0$ and $d \ne 0$. These conditions play an important role in the sense that they are necessary to find the integrability constants of parameters related to the envelope field. To construct the analytical rogue wave solutions, one firstly find the parameters of the envelope field by solving the above differential equations. The integration is made from the simplest differential equation to the highly complex one. So doing, Eq. (42) yields for $-3 \gamma (\xi ) \ne 0$ and ${{T_\tau }T_{\tau \tau }} = 0$ to the similarity variable
$$T\left( {\xi ,\tau } \right) = {T_1}(\xi )\tau + {T_0}(\xi ),$$
where ${T_1}(\xi )$ is the inverse of wave width and ${T_0}(\xi )$ is the position of the center of mass, given by: $- \frac {{{T_0}\left ( \xi \right )}}{{{T_1}\left ( \xi \right )}}$. The variable ${T_1}(\xi )$ and ${T_0}(\xi )$ should be defined as free functions of $\xi$. One notice that $T_{\tau \tau } = 0$ is the second derivative condition of the similarity variable in the temporal dimension. Equation (45) gives the effective propagation distance
$$Z(\xi ) = \frac{{\sqrt 2 \gamma}}{{4\nu }}\int_0^\xi { {T_1}{{(s)}^3}ds},$$
which can be reduce for ${T_1}\left ( \xi \right ) = \sqrt 2$ to $Z\left ( \xi \right ) = \frac {\gamma }{\nu }\xi$. Then, for $\nu = \frac {1}{3}$, $\sigma = 1$, $\gamma = 6\nu \sigma = 2$, the particular solution of the effective propagation distance becomes $Z\left ( \xi \right ) = 6\xi$. The substitution of expressions (55) and (56) into Eq. (47) tends to
$$A(\xi ) = \sqrt {\frac{{ - 3\gamma {T_1}{{(\xi )}^2}}}{{{\alpha _3}}}},$$
with ${\alpha _3} \,<\, 0$ and $\gamma > 0$. Thus, for ${\alpha _3} = -\gamma$, the particular solution of the amplitude takes the form $A\left ( \xi \right ) = \sqrt 3 \;{T_1}\left ( \xi \right ) = \sqrt 6$. Then, the substitution of expressions (56) and (57) into Eq. (52) gives the phase of the envelope field which can be written as
$$\rho \left( {\xi ,\tau } \right) ={-} \left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(\xi )}}{{6\sqrt 2 \nu }}} \right)\tau + {\rho _0}\left( \xi \right).$$

For ${C_2} = - 1$, and ${\alpha _3} = - 2$, a particular solution of the phase of the envelope field is given by $\rho \left ( {\xi,\tau } \right ) = - \tau + {\rho _0}\left ( \xi \right )$, where ${\rho _0}(\xi )$ should be defined as well as ${T_0}\left ( \xi \right )$. The substitution of known relations into Eq. (43) gives

$$\begin{gathered} {T_0}\left( \xi \right) = \int_0^\xi {\left[ { - 3\gamma {{\left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(s)}}{{6\sqrt 2 \nu }}} \right)}^2} - {\sigma _3}} \right]{T_1}(s)ds} + \int_0^\xi {2P\left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(s)}}{{6\sqrt 2 \nu }}} \right)} {T_1}(s)ds. \end{gathered}$$

For $P = 1/2$, the particular solution of the arbitrary function ${{T_0}(\xi )}$ takes the form ${T_0}\left ( \xi \right ) = - 4\sqrt 2 \xi$. The substitution of variables and parameters into Eq. (43) shows that the first derivative of the phase ${\rho _{0\xi }}$ is a constant. This imply that the arbitrary function of the phase will take the form ${\rho _0}\left ( \xi \right ) = C\xi$, where $C$ is the unknown constant that is deduced from Eq. (51) as follow

$${\rho _0}\left( \xi \right) = \left[ {\frac{{ {{\left( {4d{C_4}} \right)}^{1/2}} - 1}}{{2d}}} \right]\xi,$$
where
$$\begin{gathered} {C_4} = P{\left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(\xi )}}{{6\sqrt 2 \nu }}} \right)^2} + \gamma {\left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(\xi )}}{{6\sqrt 2 \nu }}} \right)^3} + {\sigma _3}\left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(\xi )}}{{6\sqrt 2 \nu }}} \right) - D. \end{gathered}$$

For $\mu = {\eta _3} = -1$, $D = {\sigma _3} = -1$ and $d = \frac {{ - 5{\alpha _3}}}{{3{C_2}}} = - \frac {{10}}{3}$, the simplified form of ${\rho _0}\left ( \xi \right )$ becomes ${\rho _0}\left ( \xi \right ) = \frac {1}{2}\xi$. From Eq. (47), it can be seen that the SS coefficients related to the cubic nonlinearity, ${\alpha _3} = - \gamma$. Then, from Eq. (48), the SS coefficients related to the quintic nonlinearity is ${C_3} = \frac {{ - \alpha _3^2}}{{\gamma T_1^2(\xi )}}$. From Eq. (53), the quintic nonlinearity coefficient is given by

$${\Omega _3} = \frac{{\alpha _3^2}}{{6\sqrt 2 \gamma {T_1}(\xi )}} - \left( {\frac{{{C_2}}}{{{\alpha _3}}} + \frac{{\sigma {T_1}(\xi )}}{{6\sqrt 2 \nu }}} \right).$$

In view of great success of the Peregrine soliton in the modeling of some realistic problems, one investigates on the construction of rogue wave solutions. Based on the methodology applied on the infinite hierarchy of NLS equation which has a well-known rogue wave solutions in the focusing regime $(\sigma = 1)$, the finding of PS with the Darboux-dressing method is on special interest. Therefore, the complex field $V\left [ {Z(\xi ),T(\xi,\tau )} \right ]$ that is valid for $\sigma = 1$ in rogue wave finding is written as [38].

$$\begin{gathered} V\left[ {Z\left( \xi \right),T\left( {\xi ,\tau } \right)} \right] = a\exp \left\{ {jk'Z\left( \xi \right) + j\omega \frac{{\sqrt 2 }}{2}T\left( {\xi ,\tau } \right)} \right\} \times \hfill \\ \left[ {1 - \frac{{2j\eta 'Z\left( \xi \right) + 1/{a^2}}}{{\sigma {{\left( {\chi 'Z\left( \xi \right) - \frac{{\sqrt 2 }}{2}T\left( {\xi ,\tau } \right)} \right)}^2} + \eta '{a^2}{Z^2}\left( \xi \right) + 1/\left( {4{a^2}} \right)}}} \right] \hfill \\ \end{gathered}$$
where
$$\left\{ \begin{gathered} \eta ' = \sigma - \gamma \omega + 12\sigma {\varepsilon _4}^\prime (\sigma {a^2}) - 20{\varepsilon _5}\sigma \omega (3\sigma {a^2}), \hfill \\ k' = \eta '{a^2} - \frac{1}{2}{\omega ^2} + \frac{\gamma }{{6\sigma }}{\omega ^3} - {\varepsilon _4}^\prime (6{\sigma ^2}{a^4}) + {\varepsilon _5}\omega (30{\sigma ^2}{a^4}), \hfill \\ \chi ' = \omega + \gamma {a^2} - \frac{\gamma }{{2\sigma }}{\omega ^2} + 5{\varepsilon _5}(6{\sigma ^2}{a^4}). \hfill \\ \end{gathered} \right.$$

The envelope field found is the rational solution related to rogue waves under its general form given by

$$\begin{gathered} \psi \left( {\xi ,\tau } \right) = a{\left( {\frac{{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}}} \right)^{1/2}} \exp \left\{ {jk'Z\left( \xi \right) + j\omega \frac{{T\left( {\xi ,\tau } \right)}}{{\sqrt 2 }} + j\rho \left( {\xi ,\tau } \right)} \right\} \hfill \\ \times \left[ {1 - \frac{{2j\eta 'Z\left( \xi \right) + 1/{a^2}}}{{\sigma {{\left( {\chi 'Z\left( \xi \right) - \frac{{T\left( {\xi ,\tau } \right)}}{{\sqrt 2 }}} \right)}^2} + {{\eta '}^2}{a^2}{Z^2}\left( \xi \right) + 1/\left( {4{a^2}} \right)}}} \right], \hfill \\ \end{gathered}$$
where the parameters are given in relations (56, 58, 60, 55, 59), and (64). The substitution of parameters of integrability of the model, $\gamma = 2$, ${\varepsilon _4}^\prime = \frac {1}{6}$, ${\varepsilon _5} = \frac {1}{5}$, $\sigma = 1$ into the expressions of $\eta '$, $k'$ and $\chi '$ gives the particular rational solution below related to rogue waves
$$\begin{gathered} \psi \left( {\xi ,\tau } \right) = \sqrt 6 a \exp \left\{ {j6k'\xi + j\omega \left( {\tau - 4\xi } \right) + j\left( { - \tau + \frac{1}{2}\xi } \right)} \right\}\hfill \\ \times \left[ {1 - \frac{{12j\eta '\xi + 1/{a^2}}}{{{{\left[ {6\chi '\xi - \left( {\tau - 4\xi } \right)} \right]}^2} + 36{{\eta '}^2}{a^2}{\xi ^2} + 1/\left( {4{a^2}} \right)}}} \right]. \hfill \\ \end{gathered}$$

This solution given in relation (66) is a particular solution whereas the solution given in relation (65) is more general to describe the fast propagation of ultrashort pulses in nonparaxial chiral media. Let reminds that the PS (66) found here is a compact form of a vectorial solution with two components, the LCP component represented by ${\psi _-}$ and the RCP component represented by ${\psi _+}$. More specifically, the vectorial status of this solution can help to examine the dynamical behavior of the LCP and RCP components of the waves under different aspects. At first glance, one can investigate the self-character of each component under a diversity of possibilities of focusing and defocusing interactions of the SPM nonlinearity. Afterwards, this solution offers a possibility to handle the control of nonparaxial effect responsible of the fast propagation, the linear goup velocity, the GVD, the TOD, the attenuation, the SPM, the SS and the linear and differential gain/loss parameters. Finally, this solution can be used to manage the characteristic properties of the device for it to shelter the transmission of categories of pulses. Therefore, one can assume that this vectorial PS solution has a multitask function and can provide a more convenient and controlled environment for further applications in optics and medical diagnostic analysis. Now, let examines the robustness of PS against perturbations.

5. Robust nature of rogue waves against perturbations

To illustrate the robustness of rogue waves against perturbations, one focuses the attention on the usual rogue wave, that is, the Peregrin Soliton (PS) constructed in section 4 and expressed in (65). To achieve this aim, two sensitive parameters of the system, that are, the frequency (${\omega _0}$) and the amplitude of the background (a) are of special interest. The variation of these parameters in the particular solution (66) exhibits through the analytical simulations presented in Figs. 2, 3 and 4, different single PS whose the forms and the shapes remain unchanged with a slightly change in size when the amplitude of the background increases as observed in Figs. 2, 3 and 4. It can be seen that the structures are identical one another, obeying to the properties of PS, that are based at the center of coordinates with one peak surrounding by two holes. For a range of frequency ${\omega _0}$ starting from $0.05$ to $10$, the same profiles are observed with a weak difference of the amplitude of the PS. Hence the evidence of stability of PS to these sensitive parameters. However, the perturbation of the amplitude of the background does not affect the structure of the PS even for hight values of the frequency as observed in Figs. 3 and 4. Hence, the robustness of the PS to nonlinear perturbations. A similar behavior is observed through a numerical simulation where profiles are represented in Figs. 5 and 6. These solutions are obtained with a pseudo-spectral method namely, difference-differential equation method [39]. The discrete Fourier transform is used to evaluate the spatial derivative of the model. Hence, ${\psi _{\xi \xi }}$ and ${\psi _\xi }$ are expressed into finite difference formulae with errors of second-order. The substitution of these derivatives into Eq. (8) allows to generate the difference-differential equation where we set $\psi =u$ to arrive at

$$\begin{gathered} {u_{n + 1}}(\tau ) = \frac{1}{{2d + i\Delta \xi }}[(4d - 2P\Delta {\xi ^2}\frac{{{\partial ^2}}}{{\partial {\tau ^2}}} + 2i\gamma \Delta {\xi ^2}\frac{{{\partial ^3}}}{{\partial {\tau^3}}}-2i\mu \Delta {\xi ^2} -2\Delta {\xi ^2}D + 2{C_2}\Delta {\xi ^2}{{\left| {{u_n}(\tau )} \right|}^2} \hfill \\ +2{\Omega_3}\Delta {\xi ^2}{{\left| {{u_n}(\tau )} \right|}^4} -2i{\alpha _3}\Delta {\xi ^2} {{\left| {{u_n}(\tau )} \right|}^2}\frac{\partial }{{\partial \tau }} -2i{C _3}\Delta {\xi ^2} {{\left| {{u_n}(\tau )} \right|}^4}\frac{\partial }{{\partial \tau }} \hfill \\ - 2\Delta {\xi ^2}\left( {{\eta _3} + i\sigma } \right) \frac{\partial }{{\partial \tau }}){u_n}(\tau ) - \left( {2d - i\Delta \xi } \right){u_{n - 1}}(\tau )],\hfill\\ \end{gathered}$$
with
$$\begin{gathered} {u_n}(\tau ) \equiv u\left( {n\Delta \xi ,\tau } \right),\quad {u_{n - 1}}(\tau ) \equiv u\left( {(n - 1)\Delta \xi ,\tau } \right),\quad {u_{n + 1}}(\tau ) \equiv f\left( {{u_n}(\tau ),{u_{n - 1}}(\tau )} \right). \end{gathered}$$

 figure: Fig. 2.

Fig. 2. Representation of PS in the focusing regime for ${C_2}=-1$, ${\sigma }=1$, ${\omega }=10$ and for $a=1$, and $a=0.5$,

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 figure: Fig. 3.

Fig. 3. Rogue waves representation for ${C_2}=-1$, ${\omega _0}=10$, $a=1$, ${\sigma }=1$, and for ${A_0} = a{\left ( {\frac {{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}} + 0.5} \right )^{1/2}}$ and ${A_0} = a{\left ( {\frac {{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}} + 3} \right )^{1/2}}$.

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 figure: Fig. 4.

Fig. 4. Rogue waves representation for ${C_2}=-1$, ${\omega _0}=10$, ${A_0} = a{\left ( {\frac {{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}} + 3} \right )^{1/2}}$, ${\sigma }=1$, and for $a=2$ and $a=3$.

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 figure: Fig. 5.

Fig. 5. Representation of rogue wave components (LCP, RCP) where ${\omega _0}=0.005$ with ${k_0} = \sigma '{a^2} + 1/2{\omega _0}$, $a=0.5$ and ${T_c}=0.8$.

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 figure: Fig. 6.

Fig. 6. 2D representation of rogue wave components (LCP, RCP) where ${\omega _0}=0.005$, with ${k_0} = - 1/2d$, $a=0.5$ and ${T_c}=0.1$.

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The explicit algorithm in the discretized domain is defined in Eq. (67) with the conditions of implementation of the index $n$ in Eq. (68). The transverse differential operators ${\partial ^2}/\partial {\tau ^2}$, ${\partial ^3}/\partial {\tau ^3}$ and $\partial /\partial \tau$ are computed through the fast Fourier transforms (FFTs) method. This numerical approach is in accordance with the flexibility and rapid convergence, in the modeling of nonparaxial NLS models [39]. Under this approach, the PS is used as initial condition to simulate the dynamical behavior of ultrafast pulses related to robust waves issue from the model, judged compatible to investigate the auto-amplification of pulses in a chiral core, on the one hand, and to improve the fast propagation of robust waves with negligeable losses, on the other hand. So doing, rogue wave profiles are illustrated in Figs. 5 and 6 for the following expressions of the initial wave number ${k_0} = - 1/2d$ and ${k_0} = \sigma '{a^2} + 1/2{\omega _0}$ with the seeding solution bellow, taken as initial condition [38]

$$\begin{gathered} U = {U_0}\left[ {1 - \frac{{\left( {i2\sigma '\xi + 1} \right)/{a^2}}}{{\sigma '{{\left( {{\omega _0}\xi - \tau } \right)}^2} + {{\sigma '}^2}{a^2}{\xi ^2} + 1/4{a^2}}}} \right], \; with\,{U_0} = a\exp \left[ {i\left( {{k_0}\xi + {\omega _0}\tau } \right)} \right]\,\; \sigma ' = 1. \end{gathered}$$

The parameters $K'$, $K''$, $K'''$, ${\mu _0}$, ${\varepsilon _2}$, ${\varepsilon _4}$, $\nu$, and $\sigma$ are chosen randomly for the computation. The coordinates ($\xi$, $\tau$) are bounded in the interval $\left [ { - 5,5} \right ]$. The spectral parameter $k$ is defined for a short length ($L= 10$) with $N=32$ iterations. The implementation of $n$ in Eq. (67) is done for 102 iterations in the propagation direction $\xi$ with $\Delta \xi = 0.05$. The initial condition used (Eq. (69)) introduces a single pulse in the waveguide filled with chiral material that generates an optical activity in the medium. In the literature, it is well-known that fibers with chiral core allow the propagation of two modes that are, the LCP (levorotatory: ${\psi _ - }$) and RCP (dextrorotatory: ${\psi _ + }$ ) components of the waves. Thus, the rotatory property of the chiral wave guide involves the degeneration of lobes of butterfly structures of the PS, exhibited in Fig. 5 for high value of chiral parameter (${T_c}=0.8$). This degeneration can involve a collision as the one observe in Fig. 5(a). Moreover, it has been noticed that a single wave introduce in a fiber can also split itself into two or four components of waves, depending on the number of wave field (i.e. ${\psi _1},\;{\psi _2}$ or ${\psi _ + },\;{\psi _ - }$ ) taken into account in the NLS model. These behaviors are known as phenomena of two-wave mixing observed in physical system described with scalar NLS model, and four wave mixing observed with vectorial NLS model. The model derived in Eq. (8) is in fact, a vectorial model with two components (LCP and RCP) but was written in a scalar form for simplification reasons. We noticed that the robustness of rogue waves increases with the increase of chiral parameter. Moreover, the increase of the optical activity favors the smoothness of the wave shape and involves the good stability of the robust waves during the ultrafast propagation. One denotes that the decrease of chiral parameter (${T_c}=0.1$), favors the degeneration of dark PS and the occurrence of usual PS at the center of coordinates as depicted in Fig. 6. This phenomenon is due to a transfer of energy from the vicinity to the center of coordinates. Therefore, one can conclude that, a good manipulation of chirality in chiral materials or biological systems can help to direct the energy in a particular area of physical systems. This theoretical framework can be used for further experimental investigation in medical science. More specifically, in the processes of transcription and replication of DNA, where the PS is used as inhibitory factor for local and short excitation of DNA strands.

6. Conclusion

The dynamics of ultrafast pulses related to robust waves is characterized by the cubic-quintic nonparaxial chiral NLS equation. This model is derived in this work to ensure the total reflexion of ultrafast pulses in optical systems due to the induced optical activity and the artificial one that adjust or correct the polarization in the system. This model improves the dynamics of ultrafast propagation of rogue waves in chiral wave guides, in the sense that it verifies the controllability of the system that exhibits the direct implications of nonlinearities, nonparaxiality, optical activity and more specifically, the robustness of rogue waves. Through the baseband MI theory, the range of frequencies susceptible to generate a rogue wave phenomenon can be determined. Through the integrability conditions of the model and symmetry reduction method, the solution of PS was constructed. The richness and the multitask function of the PS has been elucidated. It has been noticed that a such solution can offer a more convenient and controlled environment for further applications in optics and medical diagnostic analysis. The variation of chiral parameter, frequency and amplitude of the seeding solution has been used to enlighten the robustness of PS against perturbation. The prospective results are convincing through the numerical and analytical representations, showing the improvement of ultrafast propagation through the adjustment of optical activity, the frequency and the amplitude of the background. Therefore, a good management of the chirality in chiral materials or biological systems can help to direct the energy in a particular area of physical system. This theoretical framework can be used for experimental investigation in medical science. More specifically, in the processes of transcription and replication where the PS is used as inhibitory factor for local and short excitation of DNA strands. In addition, this work provides a novel approach to improve the ultrafast propagation and good transmission of PS in biological systems, as well as further consideration of total control of light in life-science and industry.

Acknowledgments

D. D. Estelle Temgoua is grateful to University of the Western Cape and I-Themba LABS, the National Research Foundation (NRF) of South Africa (SA) for research facilities and computer services. M. B. Tchoula Tchokonte thanks the SA - NRF (81296; UID 111174).

Disclosures

Compliance with ethical standards. The authors declare no competing ethical interest.

Data availability

Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.

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Figures (6)

Fig. 1.
Fig. 1. Gain maps: $\left ( {\Omega,d} \right )$ in Fig. 1(a) and $\left ( {\Omega,a} \right )$ in Fig. 1(b) with ${\phi _0} = {Z_1}$
Fig. 2.
Fig. 2. Representation of PS in the focusing regime for ${C_2}=-1$, ${\sigma }=1$, ${\omega }=10$ and for $a=1$, and $a=0.5$,
Fig. 3.
Fig. 3. Rogue waves representation for ${C_2}=-1$, ${\omega _0}=10$, $a=1$, ${\sigma }=1$, and for ${A_0} = a{\left ( {\frac {{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}} + 0.5} \right )^{1/2}}$ and ${A_0} = a{\left ( {\frac {{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}} + 3} \right )^{1/2}}$.
Fig. 4.
Fig. 4. Rogue waves representation for ${C_2}=-1$, ${\omega _0}=10$, ${A_0} = a{\left ( {\frac {{ - 3T_1^2(\xi )\gamma }}{{{\alpha _3}}} + 3} \right )^{1/2}}$, ${\sigma }=1$, and for $a=2$ and $a=3$.
Fig. 5.
Fig. 5. Representation of rogue wave components (LCP, RCP) where ${\omega _0}=0.005$ with ${k_0} = \sigma '{a^2} + 1/2{\omega _0}$, $a=0.5$ and ${T_c}=0.8$.
Fig. 6.
Fig. 6. 2D representation of rogue wave components (LCP, RCP) where ${\omega _0}=0.005$, with ${k_0} = - 1/2d$, $a=0.5$ and ${T_c}=0.1$.

Equations (69)

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D = ε 0 E + ε 0 T c × E , B = μ 0 ( H + T c × H ) ,
ε n = ε 0 + ε 2 | E | 2 + ε 4 | E | 4 ,
D = ε n E + ε 0 T c × E , B = μ 0 ( H + T c × H ) .
D = ρ v , B = 0 , × E = B t , × H = σ μ 0 E + D t .
2 E + μ 0 ε 0 T c 2 2 2 E t 2 = μ 0 σ E t + μ 0 ε 0 2 E t 2 + μ 0 ε 2 | E | 2 2 E t 2 + μ 0 ε 4 | E | 4 2 E t 2 + μ 0 σ T c × E t + 2 μ 0 ε 0 T c × 2 E t 2 + μ 0 ε 2 T c | E | 2 × 2 E t 2 + μ 0 ε 4 T c | E | 4 × 2 E t 2 .
E ( r , t ) = ( x ^ j y ^ ) A ( r , t ) exp [ j ( k ± z ω 0 t ) ] = ψ R , L exp [ j ( k ± z ω 0 t ) ] ,
1 2 K 0 2 ϕ z 2 + j ϕ z + 1 2 ( K K 2 K 0 ) 2 ϕ t 2 j 1 6 K 3 ϕ t 3 + j ω α 2 K 0 ( 1 ± K 0 T c ) ϕ K 0 2 T c ϕ β ω 2 2 K 0 ( 1 K 0 T c ) | ϕ | 2 ϕ β 1 ω 2 2 K 0 ( 1 K 0 T c ) | ϕ | 4 ϕ + α 2 K 0 ( 1 ± K 0 T c ± ω K T c ) ϕ t ± j 2 K 0 2 T c ω ( 1 + K ω 2 K 0 ) ϕ t + j ω β K 0 ( 1 ± K 0 T c ± ω K T c 2 ) | ϕ | 2 ϕ t + j ω β 1 K 0 ( 1 ± K 0 T c ± ω K T c 2 ) | ϕ | 4 ϕ t = 0.
d ψ ξ ξ + j ψ ξ + P ψ τ τ j γ ψ τ τ τ + j μ ψ C 2 | ψ | 2 ψ Ω 3 | ψ | 4 ψ + D ψ + j α 3 | ψ | 2 ψ τ + j C 3 | ψ | 4 ψ τ + η 3 ψ τ + j σ 3 ψ τ = 0 ,
ψ = ω 0 2 / 3 β 1 / 3 ( 2 K 0 ) 1 / 3 ϕ ,   ξ = β 1 / 3 ω 0 2 / 3 ( 2 K 0 ) 1 / 3 z ,   τ = ω 0 1 / 3 β 1 / 6 K 1 / 2 ( 2 K 0 ) 1 / 6 t .
d = ω 0 2 / 3 β 1 / 3 ( 2 K 0 ) 4 / 3 ,   P = 1 2 ( 1 K 2 K 0 K ) , γ = K 6 K 3 / 2 ω 0 1 / 3 β 1 / 6 ( 2 K 0 ) 1 / 6 ,   μ = C 2 α ω 0 1 / 3 β 1 / 3 ( 2 K 0 ) 2 / 3 , C 2 = 1 ± K 0 T c ,   Ω 3 = C 2 β 1 ( 2 K 0 ) 2 / 3 ω 0 2 / 3 β 1 / 3 ,   D = K 0 2 ( 2 K 0 ) 1 / 3 T c ω 0 2 / 3 β 1 / 3 ,   η 3 = α ( C 2 ± ω 0 K T c ) ω 0 1 / 3 β 1 / 6 ( 2 K 0 ) 5 / 6 , α 3 = ( C 2 ± ω 0 K T c 2 ) ( 2 K 0 ) 5 / 6 β 1 / 6 K 0 K 1 / 2 ω 0 2 / 3 ,   C 3 = β 1 ( C 2 ± ω 0 K T c 2 ) ( 2 K 0 ) 3 / 2 K 0 K 1 / 2 ω 0 4 / 3 β 3 / 2 , σ 3 = ± K 0 T c ( 1 + ω 0 K T c 2 ) ( 2 K 0 ) 7 / 6 K 1 / 2 ω 0 4 / 3 β 1 / 6 ,
α = μ 0 σ ,   β = μ 0 ε 2 ,   β 1 = μ 0 ε 4 , K = 1 v g ,   K = 2 K ω 2 ,   K = 3 K ω 3 .
ψ ( ξ , τ ) = a exp { j ( k 0 ξ ω 0 τ ) }
Ω 3 a 4 + C 3 a 4 ω 0 + γ ω 0 3 + α 3 a 2 ω 0 C 2 a 2 P ω 0 2 d k 0 2 + σ 3 ω 0 + D k 0 = 0 , μ η 3 ω 0 = 0 , w i t h a 0.
k 0 + = 1 1 + 4 d Q 2 d , k 0 = 1 + 1 + 4 d Q 2 d , w i t h Q = Ω 3 a 4 + C 3 a 4 ω 0 + γ ω 0 3 + α 3 a 2 ω 0 C 2 a 2 P ω 0 2 + σ 3 ω 0 + D ,
ω 0 = μ η 3 .
ψ ( ξ , τ ) = [ a + χ ( ξ , τ ) ] exp [ j ( k 0 ξ ω 0 τ ) ] ,
χ ( ξ , τ ) = A 1 exp [ j ( K ξ Ω τ ) ] + A 2 c exp [ j ( K ξ Ω τ ) ] + c c ,
c c = A c 1 exp [ j ( K ξ Ω c τ ) ] + A 2 exp [ j ( K ξ Ω c τ ) ] .
( λ 1 d K 2 λ 0 K δ 1 δ 1 λ 2 d K 2 + λ 0 K ) ( A 1 A 2 ) = 0
λ 1 = C 3 a 4 ( Ω + 3 ω 0 ) 3 Ω 3 a 4 + α 3 a 2 ( Ω + 2 ω 0 ) + γ ( Ω 3 + 3 ω 0 Ω 2 + 3 ω 0 2 Ω + ω 0 3 ) ( k 0 + d k 0 2 ) + P ( Ω 2 2 ω 0 Ω ω 0 2 ) + σ 3 ( Ω + ω 0 ) + D 2 C 2 a 2 , λ 2 = C 3 a 4 ( Ω + 3 ω 0 ) 3 Ω 3 a 4 + α 3 a 2 ( Ω + 2 ω 0 ) + γ ( Ω 3 + 3 ω 0 Ω 2 3 ω 0 2 Ω + ω 0 3 ) ( k 0 + d k 0 2 ) + P ( Ω 2 + 2 ω 0 Ω ω 0 2 ) + σ 3 ( Ω + ω 0 ) + D 2 C 2 a 2 , δ 1 = 2 C 3 a 4 ω 0 2 Ω 3 a 4 + α 3 a 2 ω 0 2 C 2 a 2 , λ 0 = ( 1 + 2 d k 0 ) .
Ω = ω 0 μ η 3 Ω + = μ η 3 ω 0 .
K 4 + A K 2 + B K + C = 0 ,
A = ( d ( λ 1 + λ 2 ) + λ 0 2 ) d 2 , B = ( λ 1 λ 2 ) λ 0 d 2 , C = λ 1 λ 2 δ 1 2 d 2 .
Z 3 + a 1 Z 2 + b Z + c = 0 , w h e r e a 1 = A , b = 4 C , c = 4 A C B 2 .
y 3 + p 1 y + q 1 = 0 , w i t h p 1 = a 1 3 3 + b , q 1 = 2 ( a 1 3 ) 3 a 1 b 3 + c ,
y 1 = A 2 + B 2 , y 2 = ( A 2 + B 2 ) 2 + j ( A 2 B 2 ) 3 2 , y 3 = ( A 2 + B 2 ) 2 j ( A 2 B 2 ) 3 2 ,
A 2 = q 1 2 + Q 2 3 , B 2 = q 1 2 Q 2 3 , Q 2 = ( p 1 3 ) 3 + ( q 1 2 ) 2 ,
Z 1 = A 2 + B 2 a 1 3 , Z 2 = [ ( A 2 + B 2 ) 2 + a 1 3 ] + j ( A 2 B 2 ) 3 2 , Z 3 = [ ( A 2 + B 2 ) 2 + a 1 3 ] j ( A 2 B 2 ) 3 2 ,
Z 4 = 2 p 1 3 cos [ 1 3 arccos ( q 1 2 27 p 1 3 ) ] a 1 3 , Z 5 = 2 p 1 3 cos [ 1 3 arccos ( q 1 2 27 p 1 3 ) + 2 π 3 ] a 1 3 , Z 6 = 2 p 1 3 cos [ 1 3 arccos ( q 1 2 27 p 1 3 ) + 4 π 3 ] a 1 3 .
( K 2 + A 3 K + B 3 ) ( K 2 + A 4 K + B 4 ) = 0 , w h e r e { A 3 = j z B 3 = j B 2 z + ϕ 0 , { A 4 = j z B 4 = j B 2 z + ϕ 0 , w i t h { z = ( a 1 2 ϕ 0 ) 1 / 2 ϕ 0 = Z 1 , Z 2 , , Z 6 .
K 1 = A 3 + A 3 2 4 B 3 2 , K 2 = A 3 A 3 2 4 B 3 2 , K 3 = A 4 + A 4 2 4 B 4 2 , K 4 = A 4 A 4 2 4 B 4 2 ,
Δ 1 = A 3 2 4 B 3 , Δ 2 = A 4 2 4 B 4 .
S o f o r ϕ 0 = Z 1 , Z 2 , , Z 6 G ( Ω ) = Im ( K )
K 1 , 2 = j z 2 , K 3 , 4 = j z 2 , w h e r e z = ( A 2 ϕ 0 ) 1 / 2 .
λ < ± δ 1 , 16 [ 16 d 4 ( λ 2 δ 1 2 ) 2 8 ( 2 λ d + λ 0 2 ) 2 ( λ 2 δ 1 2 ) + ( 2 λ d + λ 0 2 ) 4 ] < 0
d ψ ξ ξ + j ψ ξ + P ψ τ τ C 2 | ψ | 2 ψ + j α 3 | ψ | 2 ψ τ j γ ψ τ τ τ + r 1 ( D + j μ ) ψ + r 2 ( η + j σ 3 ) ψ τ Ω 3 | ψ | 4 ψ + j C 3 | ψ | 4 ψ τ = 0.
ψ ( ξ , τ ) = A ( ξ ) V [ Z ( ξ ) , T ( ξ , τ ) ] exp { j ρ ( ξ , τ ) } ,
j u ξ + 1 2 u τ τ + j γ 6 σ u τ τ τ + j γ | u | 2 u τ + σ | u | 2 u + 6 σ 2 ε 4 | u | 4 u + 30 σ 2 ε 5 | u | 4 u τ = 0 ,
d ( A ξ ξ V + 2 A ξ Z ξ V Z + 2 A ξ T ξ V T + 2 A Z ξ T ξ V Z T + A Z ξ ξ V Z + A T ξ ξ V T + A Z ξ 2 V Z Z + A T ξ 2 V T T A ρ ξ 2 V ) A V ρ ξ + P ( A V T T T τ 2 + A V T T τ τ A V ρ τ 2 ) + γ ( 3 A V T T τ τ ρ τ + 3 A V T T τ ρ τ τ + 3 A V T T T τ 2 ρ τ + A V ρ τ τ τ A V ρ τ 3 ) + D A V C 2 A 2 | V | 2 A V Ω 3 A 4 | V | 4 A V α 3 A 2 | V | 2 A V ρ τ C 3 A 4 | V | 4 A V ρ τ + η 3 A T τ V T σ 3 A V ρ τ = 0 ,
d ( A V ρ ξ ξ + 2 A ξ ρ ξ V + 2 A Z ξ ρ ξ V Z + 2 A ρ ξ T ξ V T ) + A ξ V + A V Z Z ξ + A V T T ξ + P ( A V ρ τ τ + 2 A V T T τ ρ τ ) γ ( A V T T τ τ τ + 3 A V T T T τ T τ τ + A V T T T T τ 3 3 A V T T τ ρ τ 2 3 A V ρ τ τ ρ τ ) + μ A V + α 3 A 2 | V | 2 A V T T τ + C 3 A 4 | V | 4 A V T T τ + η 3 A V ρ τ + σ 3 A T τ V T = 0 ,
j V Z + V T T + σ | V | 2 V + j 2 2 ν V T T T + j 6 2 ν | V | 2 V T + 3 ν σ | V | 4 V + j 18 2 ν σ | V | 4 V T = 0 ,
3 γ T τ T τ τ = 0 ,
T ξ + 2 P T τ ρ τ + σ 3 T τ   γ ( T τ τ τ 3 T τ ρ τ 2 ) = 0 ,
A ξ + A ( d ρ ξ ξ + P ρ τ τ + 3 γ ρ τ τ ρ τ + μ + η 3 ρ τ ) = 0 ,
γ T τ 3 + 2 2 ν Z ξ = 0 ,
d ρ ξ A ξ V + 1 2 A Z ξ V Z + d A ρ ξ Z ξ V Z + d A T ξ ρ ξ V T = 0 ,
α 3 A 2 T τ + 6 2 ν Z ξ = 0 ,
C 3 A 4 T τ + 18 2 ν Z ξ = 0 ,
d T ξ ξ + P T τ τ + 3 γ ( T τ τ ρ τ + T τ ρ τ τ ) + η 3 T τ = 0 ,
Z ξ + d T ξ 2 + P T τ 2 + 3 γ ρ τ T τ 2 = 0 ,
ρ ξ + d ρ ξ 2 + P ρ τ 2 + γ ( ρ τ 3 ρ τ τ τ ) + σ 3 ρ τ D = 0 ,
σ Z ξ A 2 ( C 2 + α 3 ρ τ ) = 0 ,
3 ν Z ξ A 4 ( Ω 3 + C 3 ρ τ ) = 0 ,
A ξ ξ V + 2 A ξ Z ξ V Z + 2 A ξ T ξ V T + 2 A Z ξ T ξ V Z T + A Z ξ ξ V Z + A Z ξ 2 V Z Z = 0 ,
T ( ξ , τ ) = T 1 ( ξ ) τ + T 0 ( ξ ) ,
Z ( ξ ) = 2 γ 4 ν 0 ξ T 1 ( s ) 3 d s ,
A ( ξ ) = 3 γ T 1 ( ξ ) 2 α 3 ,
ρ ( ξ , τ ) = ( C 2 α 3 + σ T 1 ( ξ ) 6 2 ν ) τ + ρ 0 ( ξ ) .
T 0 ( ξ ) = 0 ξ [ 3 γ ( C 2 α 3 + σ T 1 ( s ) 6 2 ν ) 2 σ 3 ] T 1 ( s ) d s + 0 ξ 2 P ( C 2 α 3 + σ T 1 ( s ) 6 2 ν ) T 1 ( s ) d s .
ρ 0 ( ξ ) = [ ( 4 d C 4 ) 1 / 2 1 2 d ] ξ ,
C 4 = P ( C 2 α 3 + σ T 1 ( ξ ) 6 2 ν ) 2 + γ ( C 2 α 3 + σ T 1 ( ξ ) 6 2 ν ) 3 + σ 3 ( C 2 α 3 + σ T 1 ( ξ ) 6 2 ν ) D .
Ω 3 = α 3 2 6 2 γ T 1 ( ξ ) ( C 2 α 3 + σ T 1 ( ξ ) 6 2 ν ) .
V [ Z ( ξ ) , T ( ξ , τ ) ] = a exp { j k Z ( ξ ) + j ω 2 2 T ( ξ , τ ) } × [ 1 2 j η Z ( ξ ) + 1 / a 2 σ ( χ Z ( ξ ) 2 2 T ( ξ , τ ) ) 2 + η a 2 Z 2 ( ξ ) + 1 / ( 4 a 2 ) ]
{ η = σ γ ω + 12 σ ε 4 ( σ a 2 ) 20 ε 5 σ ω ( 3 σ a 2 ) , k = η a 2 1 2 ω 2 + γ 6 σ ω 3 ε 4 ( 6 σ 2 a 4 ) + ε 5 ω ( 30 σ 2 a 4 ) , χ = ω + γ a 2 γ 2 σ ω 2 + 5 ε 5 ( 6 σ 2 a 4 ) .
ψ ( ξ , τ ) = a ( 3 T 1 2 ( ξ ) γ α 3 ) 1 / 2 exp { j k Z ( ξ ) + j ω T ( ξ , τ ) 2 + j ρ ( ξ , τ ) } × [ 1 2 j η Z ( ξ ) + 1 / a 2 σ ( χ Z ( ξ ) T ( ξ , τ ) 2 ) 2 + η 2 a 2 Z 2 ( ξ ) + 1 / ( 4 a 2 ) ] ,
ψ ( ξ , τ ) = 6 a exp { j 6 k ξ + j ω ( τ 4 ξ ) + j ( τ + 1 2 ξ ) } × [ 1 12 j η ξ + 1 / a 2 [ 6 χ ξ ( τ 4 ξ ) ] 2 + 36 η 2 a 2 ξ 2 + 1 / ( 4 a 2 ) ] .
u n + 1 ( τ ) = 1 2 d + i Δ ξ [ ( 4 d 2 P Δ ξ 2 2 τ 2 + 2 i γ Δ ξ 2 3 τ 3 2 i μ Δ ξ 2 2 Δ ξ 2 D + 2 C 2 Δ ξ 2 | u n ( τ ) | 2 + 2 Ω 3 Δ ξ 2 | u n ( τ ) | 4 2 i α 3 Δ ξ 2 | u n ( τ ) | 2 τ 2 i C 3 Δ ξ 2 | u n ( τ ) | 4 τ 2 Δ ξ 2 ( η 3 + i σ ) τ ) u n ( τ ) ( 2 d i Δ ξ ) u n 1 ( τ ) ] ,
u n ( τ ) u ( n Δ ξ , τ ) , u n 1 ( τ ) u ( ( n 1 ) Δ ξ , τ ) , u n + 1 ( τ ) f ( u n ( τ ) , u n 1 ( τ ) ) .
U = U 0 [ 1 ( i 2 σ ξ + 1 ) / a 2 σ ( ω 0 ξ τ ) 2 + σ 2 a 2 ξ 2 + 1 / 4 a 2 ] , w i t h U 0 = a exp [ i ( k 0 ξ + ω 0 τ ) ] σ = 1.
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