Optical solitons via the collective variable method for the classical and perturbed Chen-Lee-Liu equations - De Gruyter

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Optical solitons via the collective variable method for the classical and perturbed Chen-Lee-Liu equations - De Gruyter
Open Physics 2021; 19: 559–567

Research Article

Reyouf Alrashed, Aisha Abdu Alshaery*, and Sadah Alkhateeb

Optical solitons via the collective variable
method for the classical and perturbed
Chen–Lee–Liu equations
https://doi.org/10.1515/phys-2021-0065                                    munication and optical fibers. In addition, solitary wave
received July 03, 2021; accepted August 13, 2021                          solutions or solitons are important structures of evolution
Abstract: In this article, the collective variable method to              equations with fascinating characteristics that occur in
study two types of the Chen–Lee–Liu (CLL) equations, is                   various forms and have great uses. One of the renowned
employed. The CLL equation, which is also the second                      equations in this category is the Chen–Lee–Liu (CLL)
member of the derivative nonlinear Schrödinger equa-                      equation [8] which emerged in 1979. CLL equation which
tions, is known to have vast applications in optical                      is also the second member of the derivative nonlinear
fibers, in particular. More specifically, a consideration                   Schrödinger equations is known to have many applica-
to the classical Chen–Lee–Liu (CCLL) and the perturbed                    tions in optical fibers and in the sub-picosecond soliton
Chen–Lee–Liu (PCLL) equations, is made. Certain gra-                      propagation, in particular. Due to its interesting applica-
phical illustrations of the simulated numerical results                   tions, CLL model has over the years undergone various
that depict the pulse interactions in terms of the soliton                extensions, modifications, and perturbations in relation
parameters are provided. Also, the influential parameters                  to different situations and applications [9–14]. Besides,
in each model that characterize the evolution of pulse                    optical soliton perturbation is one of the most energetic
propagation in the media, are identified.                                  areas of study in the areas of telecommunication technology
                                                                          and physics [15–22]. Furthermore, there exist various com-
Keywords: CLL equations, perturbation term, collective                    putational, semi-analytical, and analytical techniques to
variables method, solitons                                                treat different forms of nonlinear Schrödinger equations
                                                                          including the computational Adomian’s method [23–25],
                                                                          tanh function expansion method [26,27], certain integra-
                                                                          tion schemes [28], Kudryashov method [29], rational (G/G)-
1 Introduction                                                            expansion method [30], trial equation approach [31],
                                                                          sine-Gordon equation approach [32], and many more
Nonlinear Schrödinger equations are complex-valued time-                  [33,34] to mention a few.
evolving equations that are known to have a variety of                         Furthermore, a method of interest in this article is the
applications in nonlinear sciences including biological                   collective variable method [35–43]. In the given refer-
models, optics, fluid dynamics, plasma physics, among                      ences, different researchers have over a time employed
other fields [1–7]. Hyperbolic function solutions of these                 the collective variable method to examine various evolu-
equations or rather solitary wave solutions which are also                tion and Schrödinger equations. This method is relatively
referred to as solitons are found to play a vital role in                 a new technique that splits the complex-valued wave
many pulse propagation processes in modern telecom-                       function into two components and thereafter introduces
                                                                          new variables to characterize the dynamics of soliton
                                                                          propagation. Additionally, the method which was first
                                                                          introduced by Boesch et al. [44] is a mixture of an analy-
                                                                        tical process with a computational technique or semi-ana-
* Corresponding author: Aisha Abdu Alshaery, Department of                lytical process to analyze the model under consideration.
Mathematics, Faculty of Science, University of Jeddah, Jeddah,
                                                                          Above and beyond, the method gives the dynamics of each
P.O. Box 80327, Saudi Arabia, e-mail: aaal-shaery@uj.edu.sa
Reyouf Alrashed, Sadah Alkhateeb: Department of Mathematics,
                                                                          of the pulse parameter by utilizing the Gaussian ansatz to
Faculty of Science, University of Jeddah, Jeddah, P.O. Box 80327,         get hold of the resulting dynamical equations of motions
Saudi Arabia                                                              for the subsequent examination. The resulting equations

   Open Access. © 2021 Reyouf Alrashed et al., published by De Gruyter.         This work is licensed under the Creative Commons Attribution 4.0
International License.
Optical solitons via the collective variable method for the classical and perturbed Chen-Lee-Liu equations - De Gruyter
560        Reyouf Alrashed et al.

of motions are set to be numerically examined with the       2.2 Perturbed Chen–Lee–Liu (PCLL)
help of fourth-order Runge–Kutta numerical technique.            equation
Moreover, different methods have been utilized in the lit-
erature to examine various forms of evolution equations      The governing CLL equation in the presence of perturba-
as cited in the above references and references therein;     tion terms is expressed in dimensionless as follows [13,14]:
besides, most of these methods used to examine the CLL
                                                                 iqz + aqtt + ib∣q ∣2 qt = i[αqt + β (∣q∣2 q )t + γ (∣q∣2 )t q]. (2)
models gave only sets of exact soliton solutions to the
model via various analytical approaches.                          Clearly, equation (2) emanates from equation (1) due
     However, we employ in this study the collective vari-   to the presence of perturbation terms with q = q (z , t )
able method to investigate two forms of the CLL equa-        being the complex-valued wave function that depends
tions. Specifically, we will examine the CCLL and the         on the spatial and temporal variables z and t , respec-
PCLL equations. Also, certain graphical illustrations of     tively. Similarly, the real constants a and b represent
the simulated numerical results will be depicted to          the coefficients of the group-velocity dispersion and non-
portray the pulse interactions, in addition to identifying   linearity term, respectively. Furthermore, going to the
the influential parameters in each model that charac-         other side of the equation, the real constant α denotes
terize the evolution of pulse propagation in the media.      the coefficient of inter-modal dispersion; while the real
Additionally, we arrange the present study as follows:       constants β and γ denote the coefficients of self-stee-
Section 2 gives the two models of interest; while Section    pening and nonlinear dispersion, respectively. Moreover,
3 gives the basic outline of the adopted methodology.        the subscripts in equations (1) and (2) are partial deriva-
Section 4 considers a particular pulse configuration func-    tives in the respective spatial and time variables.
tion f through the Gaussian ansatz to construct the
resulting equations of motions for both models; while
Sections 5 and 6 present the numerical results and con-
clusion, respectively.                                       3 Collective variable methodology
                                                             This section presents the method collective variable
                                                             approach [35–43] based on the initial work by Boesch
2 Governing equations                                        et al. [44]. First, the method starts off by splitting the
                                                             complex-valued wave function (solution) of the given
In this section, we consider the two famous dimension-       nonlinear Schrödinger equation into two parts. The first
less types of the governing CLL equation to be analyzed      part constitutes the soliton solution that is called the pulse
in the present study.                                        configuration; while the second part is called the residual
                                                             field function. Mathematically, we express the complex-
                                                             valued wave function q (z , t ) after splitting as
                                                                                 q (z , t ) = f (z , t ) + g (z , t ) ,          (3)
2.1 Classical Chen–Lee–Liu (CCLL) equation
                                                             where f (z , t ) is the pulse configuration and g (z , t ) is the
The governing CCLL equation that is known for its var-       residual field function. Moreover, the pulse configuration
ious applications in optical fibers is given in dimension-    function f (z , t ) is further assumed to depend on N vari-
less form as follows [8–12]:                                 ables symbolically represented by Xj , for j = 1, 2, … , N .
                                                             Thus, the above equation in the presence of these new
                 iqz + aqtt + ib∣q ∣2 qt = 0,          (1)
                                                             variables can be expressed as
where q = q (z , t ) is the complex-valued wave function                 q (z , t ) = f (X1 , X2 , … , XN , t ) + g (z , t ) ,   (4)
that depends on the spatial and temporal variables z
and t, respectively. Furthermore, the real constant a        where the collection of these new variables stands for the
represents the coefficient of group-velocity dispersion;       soliton’s amplitude, central position, inverse-width, chirp,
while b is a real constant that denotes the coefficient of     frequency, and the phase among others. Additionally, the
nonlinearity. Additionally, it is very clear for one to      introduction of these new variables in the pulse configura-
obtain a regular CLL equation from equation (1) by simply    tion function f increases the degree of freedom, which
setting a = 1 and b = 1.                                     results in the available phase space of the dynamical
Optical solitons via the collective variable method for the classical and perturbed Chen-Lee-Liu equations - De Gruyter
Optical solitons via the collective variable method for the CCLL and PCLL equations                              561

equations. Thus, in view of the objectionable effect, the                                    Therefore, on using Dirac’s theory, a function is
constraints and the residual free energy expressed as                                   nearly not zero for all parameters, if its variations can
                 ∞                  ∞                                                   be set to zero [35–43]. Hence, Cj is minimum when
         E=      ∫    ∣g∣2 dt   =   ∫ ∣q − f (X1, X2 , … , XN , t )∣2 dt ,        (5)                                              Cj ≈ 0                              (10)
                 −∞                 −∞
                                                                                        and
should be minimized. Now, if Cj designates the partial                                                                             Ċj ≈ 0.                            (11)
derivative of the residual free energy with respect to
(w.r.t.) Xj , then                                                                          Thus, on using either of the governing models given
                                     ∞                      ∞
                                                                                        in equations (1) and (2), we have
                 ∂E     ∂                              ∂                                                               N
            Cj =
                 ∂Xj
                     =
                       ∂Xj
                                     ∫    ∣g∣2 dt   =
                                                      ∂Xj
                                                            ∫ gg∗dt ,                                          qz =    ∑
                                                                                                                           ∂f dXj
                                                                                                                                   +
                                                                                                                                     ∂g (z , t )
                                                                                                                                                 ,                     (12)
                                     −∞                     −∞                                                             ∂Xj d z      ∂z
                      ∞                     ∞                                     (6)                                  j=1
                                                                   ∗
                =     ∫    ∂
                          ∂Xj
                              gg ∗dt =      ∫ ⎛ ∂∂Xgj g∗ + g ∂∂gXj ⎞dt.
                                                ⎜                      ⎟
                                                                                        or equally
                                           −∞ ⎝                        ⎠                             N
                     −∞                                                                                  ∂f dXj   ∂g (z , t )
                                                                                                    ∑           +             = τr ,                   r = c, p,       (13)
      Additionally, since                                                                            j=1
                                                                                                         ∂Xj dz      ∂z

g (z , t ) = q (z , t ) − f (X1(z , t ) , X2 (z , t ) , … , XN (z , t ) , t ) ,   (7)   where r = c corresponds to the CCLL equation given in
                                                                                        equation (1), and r = p stands for the PCLL equation
we could rewrite equation (6) as
                                                                                        given in equation (2).
                 ∂g ∗         ∂g ∗                                                           Therefore, the CCLL equation given in equation (1)
        Cj =         , g + g,
                 ∂Xj          ∂Xj                                                       coupled to equation (12) reveals from equation (13) the
                                                                                        following:
                 ∂g ∗                ∂g ∗
            =        ,g +                ,g ,                                                     τc = iaftt + iagtt − b∣f + g∣2 ft − b∣f + g∣2 gt .                   (14)
                 ∂Xj                 ∂Xj
                 ∂g ∗                ∂g ∗                                                    Similarly, combination of the PCLL equation given in
            =         ,g        +         ,g                                            equation (2) to equation (12) yields via equation (13) the
                 ∂Xj                 ∂Xj
                                                                                        following:
                ⎛ ∂g ∗              ⎞
            = 2R⎜      ,g           ⎟,                                                         τp = iaftt + iagtt − b∣f + g∣2 ft − b∣f + g∣2 gt + αft
                  ∂Xj                                                             (8)
                ⎝                   ⎠                                                                                                                                  (15)
                                                                                                    + αgt + β (∣f + g∣2 f )t + β (∣f + g∣2 g )t
                ⎛ ∂(q (z , t ) − f (X1 , X2 , … , Xn , t ))∗     ⎞
            = 2R⎜                                            , g ⎟,                                 + γ (∣f + g∣2 )t ( f + g ) .
                                    ∂Xj
                ⎝                                                ⎠
                                                                                              Thus, we express from equation (13) the following:
                ⎛ ∂q∗(z , t )   ∂f ∗(X1 , X2 , … , Xn , t )                 ⎞
            = 2R⎜             −                             ,g              ⎟,                                  N
                    ∂Xj                    ∂Xj                                                           ∂g        ∂f dXj
                ⎝                                                           ⎠                               = −∑          + τr ,                     r = c, p.         (16)
                                                     ∞
                                                                                                         ∂z    j=1
                                                                                                                   ∂Xj dz
                  ⎛ ∂f ∗     ⎞       ⎛    ∂f ∗      ⎞
            = − 2R⎜
                    ∂Xj
                         , g ⎟ = − 2R⎜
                                     ⎜    ∂Xj       ⎟
                                                     ∫
                                               g dt ⎟ ,                                       On putting equation (16) into equation (9), we thus obtain
                  ⎝          ⎠       ⎝ −∞           ⎠                                                            ∞
                                                                                                         ⎛N      ∂f ∗ ∂f
                                                                                                                                                N
                                                                                                                                                    ∂ 2f ∗ ⎞ dXk
                                                                                              C˙ j = − 2R⎜ ∑ ⎛⎜−
                                ∞
with ⟨.,.⟩ denoting ∫ (⋅ ) and R denotes the real part of
                     −∞                                                                                  ⎜ k=1
                                                                                                                 ∫
                                                                                                                 ∂Xj ∂Xk
                                                                                                                         +                     ∑           g ⎟dt
                                                                                                                                                   ∂Xk ∂Xj ⎠ dz
the given expressions. Therefore, the rate of change of Cj                                               ⎝ −∞  ⎝                               k=1

w.r.t. z is expressed as follows:                                                                          ∞
                                                                                                                   ∗           ⎞
                dCj
                                                                                                      +   ∫ ∂∂fXj τr dt ⎟⎟,
       C˙ j =                                                                                             −∞                   ⎠                                       (17)
                dz                                                                                          ∞
                                                                                                          N
                                                                                                                      ∂f ∗                  ∂ 2f ∗     dX
                                                                                                               ∫ ⎛ ∂Xj ∂∂Xfk
                                ∞
                 ⎧d⎛    ∂f ∗      ⎞⎫                                                             = 2R ∑           ⎜                   −          g ⎟⎞dt k
           = − 2R     ⎜
                 ⎨ dz ⎜ ∂Xj
                                ∫
                             g dt ⎟ ,
                                  ⎟⎬                                              (9)                    k=1
                                                                                                               −∞ ⎝
                                                                                                                                          ∂Xk ∂Xj ⎠ dz
                 ⎩ ⎝ −∞           ⎠⎭                                                                             ∞
                                                                                                                           ∗
                 ⎛
                          ∞
                      ∂f ∗ ∂g
                                                N
                                                    ∞
                                                         ∂ 2f ∗
                                                              ∂Xk      ⎞                              − 2R      ∫ ∂∂fXj τr dt ,
           = − 2R⎜
                 ⎜
                          ∫
                      ∂Xj ∂z
                              dt +              ∑   ∫  ∂Xj∂Xk ∂z
                                                                  g dt ⎟ .
                                                                       ⎟
                                                                                                                −∞
                                                k=1
                 ⎝ −∞                               −∞                 ⎠
                                                                                        for j ∈ {1, 2, 3, … , N } .
Optical solitons via the collective variable method for the classical and perturbed Chen-Lee-Liu equations - De Gruyter
562         Reyouf Alrashed et al.

    Alternatively, equation (17) can equally be expressed                                         The equations of the collective variables otherwise
in compact form as follows:                                                                   called the dynamical equations of motions are deter-
                                 ∂C ˙                                                         mined through the application of the theory of lowest
                            C˙ =    X + R,                                             (18)   order collective variable, also referred to as the bare
                                 ∂X
                                                                                              approximation (theory). Thus, with this development,
with                                                                                          the residual field function g (z , t ) becomes zero.

                    ⎛ ∂C1                  ∂C1
                                               ⋯
                                                                   ∂C1 ⎞
                    ⎜ ∂X1                  ∂X2                     ∂XN ⎟
                    ⎜ ∂C2                  ∂C2                     ∂C2 ⎟
               ∂C                              ⋯                                              4.1 Dynamical equations of motions for CCLL
                  = ⎜ ∂X1                  ∂X2                     ∂XN ⎟,
               ∂X ⎜                                                                               equation
                       ⋮                    ⋮                       ⋮ ⎟
                    ⎜ ∂C                                           ∂CN ⎟
                        N                  ∂CN
                                               ⋯                                       (19)
                    ⎜                                                  ⎟                      To determine the resulting dynamical equations of motions
                      ∂
                    ⎝ 1X                   ∂X2                     ∂XN ⎠
                                                                                              of the CCLL equation given in equation (1), we first compute
                      ⎡ X˙ 1 ⎤                     ⎡ R1 ⎤                                     the entries of the matrix R with the help of Maple soft-
                      ⎢ ⎥
                 X˙ = ⎢ X˙ 2 ⎥,                R = ⎢ R2 ⎥,                                    ware as
                        ⋯                          ⎢⋯⎥
                      ⎢ ⎥                          ⎢ RN ⎥
                       X ˙
                      ⎣ N⎦                         ⎣ ⎦                                                                      R1 = 0,                           (22)

                                                   π x12 (2 2 ax5(3x42x34 + 4x52x32 + 12) + b(x42x34 + 8x52x32 + 4)x12 )
                                 R2 = −                                                                                  ,                                    (23)
                                                                                   8x3

where the entries are explicitly computed using                                                                       R3 = − 2π ax12x4,                       (24)
                              ∞
                                           ∗                                                           π x12x3( 2 a(3x42x34 + 4x52x32 − 4) + 2bx12x5x32 )
             Rj = − 2R       ∫ ∂∂fXj τr dt                    and                             R4 =
                                                                                                                             32
                                                                                                                                                          ,   (25)
                            −∞
                                                                                       (20)
                           ∞
                                                                                                                      π x33x4(4 2 ax5x12 + bx14)
            ∂Ci                      ∗       2 ∗
                                ⎛⎜ ∂f ∂f − ∂ f g ⎞⎟dt .                                                      R5 =                                ,            (26)
            ∂Xj
                = 2R    ∫                                                                                                        8
                        −∞       ⎝ ∂Xi ∂Xj ∂Xi∂Xj ⎠
                                                                                                            π x12 ( 2 a(x42x34 + 4x52x32 + 4) + 4bx12x5x32 )
                                                                                                     R6 =                                                    . (27)
                                                                                                                                 4x3

                                                                                                 Therefore, the resulting dynamical equations of
4 Dynamical equations of motions                                                              motions are thus given by
This section determines the resulting dynamical equa-                                                                    X˙ 1 = −ax1x4,                       (28)
tions of motions of the two forms of CLL equations under
                                                                                                                          1
consideration via the outlined collective variable method.                                                          X˙ 2 = (8ax5 +     2 bx12 ) ,             (29)
                                                                                                                          4
First, by the Gaussian ansatz, we suppose the following
pulse configuration function f (X1 , X2 , X3 , X4 , X5 , X6) for                                                          X˙ 3 = 2ax3x4,                       (30)
both models as follows:
                                                                                                                             8a           2 bx5x12
                                                                                                              X˙ 4 = −2ax42 + 4 +                  ,          (31)
             f (X1 , X2 , X3 , X4 , X5 , X6)                                                                                  x3            x32
                           (t − X2 )2
                                                                                       (21)
                = X1e
                       −
                               x32      ei( 2 (t − X2)
                                            X4           2
                                                             + X5(t − X2 ) + X6   ),                                        Ẋ5 = 0,                          (32)

with the pulse characteristic parameters including the                                                                        2a   3bx5x12
                                                                                                                 X˙ 6 = ax52 − 2 −         .                  (33)
amplitude X1, central position X2 , inverse-width X3 , chirp                                                                  x3    4 2
X4 , frequency X5, and the phase X6 .
Optical solitons via the collective variable method for the CCLL and PCLL equations                 563

4.2 Dynamical equations of motions for                                    CCLL [8–11] and PCLL [12,13] models. Moreover, the
    PCLL equation                                                         obtained dynamical equations of motions via the appli-
                                                                          cation of the collective variable method [35–43] in both
To determine the resulting dynamical equations of motions                 cases and given in equations (28)–(33) and equations
of the PCLL equation given in equation (2), we first compute               (40)–(45), respectively, are simulated numerically for
the entries of the matrix R as follows:
                               R1 = 0,                            (34)

       2 2π x12 (x42x34(α − 3ax5) + 4x52x32 (α − ax5) + 4(α − 3ax5))        π x12 (x12 ((x32x42 + 8x52 )x32 ( −(b − β )) − 4b + 8γ + 12β ))
R2 =                                                                 +                                                                      ,   (35)
                                    8x3                                                                       8x3

                         R3 = −a 2π x12x4,                        (36)

                                   π x12x3( 2 a(3x42x34 + 4x52x32 − 4) − 2x32x5(2 2 α + x12 (β − b)))
                         R4 =                                                                         ,                                         (37)
                                                                   32

                                                        π x12x33x4(x12 (b − β ) − 2 2 (α − 2ax5))
                                               R5 =                                               ,                                             (38)
                                                                             8

                                   π x12 ( 2 (4x5x32 (ax5 − α) + ax42x34 + 4a) + 4x12x5x32 (b − β ))
                         R6 =                                                                        .                                          (39)
                                                                 4x3

    Thus, the resulting dynamical equations of motions                    the dynamics of pulse parameters with the help of fourth-
are as follows:                                                           order Runge–Kutta numerical technique. In doing so, we
                                                                          consider the following common initial conditions in both
                            X˙ 1 = −ax1x4,                        (40)
                                                                          the CCLL and PCLL models as:
                                 x 2 (b − 2γ − 3β )                                              X1 = X3 = 1,       at t = 0,                   (46)
               X˙ 2 = 2ax5 + α + 1                  ,              (41)
                                        2 2
                                                                          and
                            X˙ 3 = 2ax3x4,                         (42)
                                                                                          X2 = X4 = X5 = X6 = 0           at t = 0.             (47)
                             8a          2 x5x12 (b   − β)
              X˙ 4 = −2ax42 + 4 +                            ,    (43)          More so, Figure 1 depicts the discrepancy of the pulse
                              x3               x32
                                                                          characteristic parameters including the amplitude X1,
                               x 2 x 4 (γ + β )                           central position X2 , inverse-width X3 , chirp X4 , frequency
                       X˙ 5 = − 1               ,                 (44)
                                         2                                X5, and the phase X6 with respect to a specified distance z
                                                                          of the CCLL equation; while Figures 2 and 3 give similar
                          2a   x5x12 (3b + 4γ + β )                       depictions in relation to the PCLL equation. In Figure 1,
             X˙ 6 = ax52 − 2 −                      .             (45)
                          x3            4 2                               the influence of the pulse propagation parameters is not
                                                                          that visible for different values of a and b with regards to
                                                                          the CCLL equation; however, X4 seems to be an active
5 Numerical simulations and                                               parameter in the propagation having oscillates. Also, it
                                                                          is noted in Figures 2 and 3 that the pulse parameters
  discussion                                                              X1 , X3 , X4 , and X5 are the most influential parameters as
                                                                          the real constant b increases with regard to the evolution
In this section, we give some graphical depictions of the                 of pulse propagation associated with the PCLL equation
obtained computational results with regard to both the                    (see Figure 4 for b = 8).
564          Reyouf Alrashed et al.

Figure 1: Evolution of pulse characteristic parameters against the propagating distance when a = 0.1 , b = 10.

Figure 2: Evolution of pulse characteristic parameters against the propagating distance when a = 0.1 , b = 9, α = 0.25, β = 0.1 , and γ = 0.1 .
Optical solitons via the collective variable method for the CCLL and PCLL equations              565

Figure 3: Evolution of pulse characteristic parameters against the propagating distance when a = 0.1 , b = 15, α = 0.25, β = 0.1 , and γ = 0.1 .

Figure 4: Evolution of pulse characteristic parameters against the propagating distance when a = 0.1 , b = 8, α = 0.25, β = 0.1 , and γ = 0.1 .

6 Conclusion                                                             equation. The method is a very powerful technique that
                                                                         splits the complex-valued wave function into two com-
In conclusion, the collective variable method is employed                ponents and thereafter introduces new variables to char-
to investigate the evolution of pulse propagation via                    acterize the dynamics of soliton propagation. Additionally,
optical solitons of the two famous members of the CLL                    the method is a mixture of an analytical process with a
566           Reyouf Alrashed et al.

computational technique or a semi-analytical process.                       [10] Yildirim Y. Optical solitons to Chen–Lee–Liu model in bire-
More specifically, we extensively examined the classical                          fringent fibers with modified simple equation approach. Optik.
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fibers. Also, we provided supportive graphical depictions
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for the simulated numerical results of both models that                          Mod Phys Lett B. 2020;34:2050054.
depicted pulse interactions in terms of the soliton para-                   [12] Biswas A, Ekisi M, Sonimezoglu A, Alshomrani AS, Zhou Q,
meters. Finally, we identified the most influential para-                          Moshokoa SP, et al. Chirped optical solitons of Chen–Lee–Liu
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                                                                                 inverse variational principle. Optik. 2018;172:772–6.
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sibility for the entire content of this manuscript and                      [16] Biswas A, Kara AH, Alqahtani RT, Ullah MZ, Triki H, Belic M.
approved its submission.                                                         Conservation laws for optical solitons of Lakshmanan-
                                                                                 Porsezian-Daniel model. Proc Roman Acad Ser A.
                                                                                 2018;19(1):39–44.
Conflict of interest: The authors state no conflict of
                                                                            [17] Lakshmanan M, Porsezian K, Daniel M. Effect of discreteness
interest.                                                                        on the continuum limit of the Heisenberg spin chain. Phys Lett
                                                                                 A. 1988;133(9):483–8.
                                                                            [18] Alqahtani RT, Babatin MM, Biswas A. Bright optical solitons for
                                                                                 Lakshmanan-Porsezian-Daniel model by semi-inverse varia-
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