Research Article Application of the G /G Expansion Method in Ultrashort Pulses in Nonlinear Optical Fibers

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1 Advances in Optical Technologies Volume 013, Article ID 63647, 5 pages Research Article Application of the G /G Expansion Method in Ultrashort Pulses in Nonlinear Optical Fibers Jiang Xing-Fang, Wang Jun, Wei Jian-Ping, and Hua Ping School of Mathematics and Physics, Research Institute of Photoelectric Technology, Changzhou University, Changzhou 13164, China Correspondence should be addressed to Jiang Xing-Fang; xfjiang @hotmail.com Received 18 July 013; Revised 5 November 013; Accepted 11 November 013 Academic Editor: Zoran Ikonic Copyright 013 Jiang Xing-Fang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. With the increasing input power in optical fibers, the dispersion problem is becoming a severe restriction on wavelength division multiplexing (WDM). With the aid of solitons, in which the shape and speed can remain constant during propagation, it is expected that the transmission of nonlinear ultrashort pulses in optical fibers can effectively control the dispersion. The propagation of a nonlinear ultrashort laser pulse in an optical fiber, which fits the high-order nonlinear Schrödinger equation (NLSE), has been solved using the G /G expansion method. Group velocity dispersion, self-phase modulation, the fourth-order dispersion, and the fifth-order nonlinearity of the high-order NLSE were taken into consideration. A series of solutions has been obtained such as the solitary wave solutions of kink, inverse kink, the tangent trigonometric function, and the cotangent trigonometric function. The results have shown that the G /G expansion method is an effective way to obtain the exact solutions for the high-order NLSE, and it provides a theoretical basis for the transmission of ultrashort pulses in nonlinear optical fibers. 1. Introduction It is understood that a soliton is excited by a nonlinear field, and its energy is relatively concentrated in a small area. The elastic scattering phenomenon occurs during the interaction between two solitons. The energy is nondispersed, sothattheshapeandspeedcanremainunchangedduring its propagation. The history of the studies of solitons can be traced back to 1834, when James Scott Russell, a British scientist, accidentally observed that a bulge of water in Edinburgh-Glasgow Canal was propagating undistorted over several kilometers [1]. In 1973, Hasegawa and Tappert [] first proposed the idea of applying optical solitons to photonic communication. After rigorous theoretical and mathematical deduction, he predicted that both bright and dark soliton pulses were present in an optical fiber. He also proved that any nondestructive optical pulse could travel as stable as a soliton during its transmission in an optical fiber. As an intrinsically nonlinear phenomenon, a soliton is the product of the optical fiber dispersion and the nonlinear interaction. It obeys the NLSE and is controlled by the optical fiber dispersion and the nonlinear effects of self-phase modulation. In 1980, bright solitons were observed for the first time in an optical fiber by Mollenaure [3] and his colleagues during their experiments at the Bell Laboratory of the United States. In 1987, Emplit observed dark solitons in a fiber by using an amplitude technique and a phase filtering technique. In mathematics, the progress of the soliton theory has been achieved mainly by finding a large number of soliton solutions for nonlinear partial differential equations, so as to gradually establish a systematic theory of solitons. The special properties of a soliton, the related mathematical description of its rich structure, and the deep physical origins have profoundly expanded the applications of soliton theory and methods. The study of the exact solutions for the NLSEs has become an important research and development direction. The G /G expansion method [4], one of the methods for obtaining exact solutions for NLSE, has attracted much attention recently [4 6]. In particular, it plays an important role in deriving the propagation wave solution of NLSE. Therefore, a good understanding of the G /G expansion method is of great significance to the transmission application of ultrashort pulses in nonlinear optical fibers. This paper presents the method in detail with examples for obtaining multiple soliton solutions.

2 Advances in Optical Technologies. G /G Expansion Method The nonlinear equation with two variables x and t could be written as P(u(x, t), u x, u t, u x, u x t, u,...)=0. (1) t The first step of the G /G expansion method is to assume avariableξ=x Vt; thus,u = u(x, t) = u(ξ);itcanthenbe expressed as a G /G power polynomial: u (ξ) =α m ( G m G ) +α m 1 ( G m 1 G ) + +α 0, () in which G=G(ξ)satisfies the second-order linear ordinary differential equation: G +λg +μg=0, (3) where α m,α m 1,...,α 0,λ,μin () and(3) are undetermined parameters, in which, α m =0, and the general solution of (3) is expressed as G (ξ) =Ae ( λ+ λ 4μ)ξ/ +Be ( λ λ 4μ)ξ/. (4) The derivative of G(ξ) canbederivedfrom(4): G = ( λ ) e( λ/)ξ [ λ 4μ (A+B) cosh ( ξ) [ λ 4μ + (A B) sinh ( ξ) ] ] + e ( λ/)ξ [ λ 4μ (A+B) sinh ( ξ) [ λ 4μ. λ 4μ + (A B) cosh ( ξ) ] ] The ratio of G(ξ) and G (ξ) is expressed as [6] G G = λ λ 4μ + (A+B) sinh (( λ 4μ/)ξ)+(A B) cosh (( λ 4μ/)ξ). (A+B) cosh (( λ 4μ/)ξ)+(A B) sinh (( λ 4μ/)ξ) (5) (6) 3. Applying the G /G Expansion Method to Solve NLSE for Ultrashort Pulses in Optical Fibers Many problems in the study of natural science can be related to nonlinear evolution equations, and the optical soliton is one of them. It is always problematic to find soliton solutions for nonlinear evolution equations by physicists and mathematicians. With the development of modern computers, many methods have been developed, such as the homogeneous balance method and the hyperbolic function method [7 9].ThisresearchusestheG /G expansion method to solve the high-order NLSE. The generalized NLSE is given by l=0 i l α l l ψ+ x l m=0 i m β m m ψ m! tm + γ n ψ n ψ=0. n=0 Considering the case when l=1, m =, 3, 4, andn=1,, the corresponding coefficients are nonzero and the rest of the coefficients are zero. Assuming the coefficient α 1 = 1 and allowing the variable x to be replaced by z and the function ψ to be replaced by q, the high-order NLSE (with items included, namely, the group velocity dispersion, the selfphase modulation effect, the fourth-order dispersion, and the fifth-order nonlinear term) can then be expressed as i q z β q t +γ q q = i β q t q 4 t 4 q 4 q, in which β, β 3,and arethesecond-,third-,andfourthorder dispersion coefficients and γ and are the third- and fifth-order nonlinear coefficients. The second-order dispersion coefficient β is also known as the group velocity dispersion coefficient. With increasing optical power in a fiber, it is necessary to take the third-order nonlinear term into account, which represents the phase equilibrium between the groupvelocitydispersionandthenonlineareffect.thiswill allow the maintaining of unchanged properties for soliton pulses in an optical fiber, which is necessary for long distance transmission, and is also beneficial to WDM. Other methods, such as the extended tanh-function method, the subsidiary ordinary differential method, and the extended hyperbolic auxiliary equation method, have been used in order to find the exact solutions for (8)[10 1]. It has been found that there is no solution for (8)whenβ 3 ] =0. In order to obtain the exact solution, ] =β 3 / is assumed and (8) is then converted to a real equation after its real part and imaginary part are separated. The G /G expansion method is then used for solving the equation. (7) (8)

3 Advances in Optical Technologies Reduction Travelling Wave. Assume the form of the exact solution is q (z, t) =u(ξ) e i(lz Vt), ξ = kz ωt. (9) The parameters of k, L, ω, V are undetermined parameters. A series of expressions can be obtained based on (9). The key equation (10) can be obtained after the real part and the imaginary part of (8)areseparated: ω 4 u +(6β 3 ω β 3 + 1β ω )u + ( 1β β 3 β 4 + 4L )u 4γ u 3 4 u 5 =0. (10) (1β β 3 β 4 10 α 4 0 ]=0, 4L ) 7γ α 0 ω 4 (μλ 3 +8λμ )α 1 +(6β 3 ω β 3 + 1β ω )λμα 1 + ( 1β β 3 β 4 + 4L )α 0 4γ α 3 0 4α 5 0 =0. The parameter α 1 canbeobtainedfrom(13): (17) (18) 3.. The Exact Solution Obtained Using the G /G Expansion Method. The G /G expansion method was proposed for the exactsolutionsbywangetal.[4]. The method is effective to solve the exact solutions for the nonlinear partial differential equation. The form of the exact solution for (10)is u (ξ) = n i=0 α i ( G G ) i, (11) where G=G(ξ)and it satisfies (3). The result of n = 1 can be obtained by balancing the highest derivative u and the highest derivative with high nonlinearity u 5 in (10). The general expression for (10)canbe expressed as α 1 = 4 ω. (19) It was mistakenly written as α 1 = 5 ( / )ω in [6] The First Type Exact Solution. From (14) when λ=0, the result is α 0 =0: μ= 3 10 ω 3 [γ ( β 3 +β )ω], L= [γ ( β 3 +β )ω] u (ξ) =α 1 ( G G )+α 0. (1) Based on (1) and(10),andassumingthecoefficients of (G /G) i, i = 0, 1,, 3, 4, 5 are zero, a set of six algebraic equations can be obtained: α 1 ( ω 4 α 4 1 )=0, (13) α 1 ( ω 4 λ α 3 1 α 0)=0, (14) α 1 [ ω 4 (5λ + 0μ) + (6β 3 ω β 3 + 1β ω ) 1γ α 1 10α 1 α 0 ]=0, (15) α 1 [ ω 4 (5λ 3 + 0λμ) + (6β 3 ω β 3 + 1β ω )λ 4γ α 1 α 0 80 α 1 α 3 0 ]=0, (16) [ 3γ 5 ω 3 β β 50 ω 5 ω + 1 β β 3 3 0ω (β 3 ) 3β 10 ω ] The exact solution of (1)basedon(6)is q 1 = 4 ω μ. (A+B) sinh (( 4μ/) ξ) + (A B) cosh (( 4μ/) ξ) (A+B) cosh (( 4μ/) ξ) + (A B) sinh (( 4μ/) ξ) e i(lz Vt). Consider the following. (0) (1) α 1 [ ω 4 (λ 4 + λ μ + 16μ ) +(6β 3 ω β 3 + 1β ω )(λ + μ) (a) When μ<0and A=B=1,thekinkwavesolutionis q 11 = 4 ω μ tanh ( 4μ ξ) e i(lz Vt). ()

4 4 Advances in Optical Technologies (b) When μ<0and A= B=1, the inverse kink wave solution is q 1 = 4 ω μ coth ( 4μ ξ) e i(lz Vt). (3) (c) When μ 0and A=B=1, the solitary wave solution of the tangent trigonometric function is q 13 = ω 4 μ tan ( μξ) e i(lz Vt). (4) (d) When μ 0 and A = B = 1,thesolitarywave solution of the cotangent trigonometric function is q 14 = 4 μ ω cot ( μξ) e i(lz Vt). (5) 3... The Second Type Exact Solution. From (14)whenλ=0, the result is α 1 = ( 4 / )ω, α 0 = ( ω 4 λ/ α 3 1 ) = (λ/) ( 4 / )ω = (λ/)α 1, μ= 3 10 ( β 3 ω ) 3 5 β ( ω) + 3γ 5ω 1 + λ 4 ; (6) β 3 L=β + 3 3λ 8 3 +γ 4 ω +5 λ4 16 ω 4 λ β 3ω β 3 λ 1 β ω λ { 11 1 ω 4 λ + 1 β 3ω β 3 +β ω }μ 3 ω 4 μ. The exact solution of (6)basedon(6)is q =[ 4 ω ( λ + λ 4μ λ 4μ ((A+B) sinh ( ξ) λ 4μ + (A B) cosh ( ξ)) (7) + λ λ 4μ ((A+B) cosh ( ξ) λ 4μ + (A B) sinh ( ξ)) 4 ω] e i(lz Vt). 1 ) (8) The item of (λ/) in [6]waslostandtheitemofα 0 was not compensated. Consider the following. (a) When λ 4μ 0and A=B=1,thekinkwave solution is q 1 = β λ 4μ λ 4μ 4 4 ω tanh ( ξ) e i(lz Vt). (9) (b) When λ 4μ 0and A= B=1, the inverse kink wave solution is q = β λ 4μ λ 4μ 4 4 ω coth ( ξ) e i(lz Vt). (30) (c) When λ 4μ<0and A=B=1,thesolitarywave solution of the tangent trigonometric function is q 3 = ω β 4μ λ 4μ λ 4 4 tan ( ξ) e i(lz Vt). (31) (d) When λ 4μ<0and A= B=1,thesolitarywave solution of the cotangent trigonometric function is q 4 = 4 ω 4μ λ 4μ λ cot ( ξ) e i(lz Vt). (3) The application of the feature equations can be found in [13 17]. 4. Conclusions A G /G expansion method was applied to obtain the exact solutions for NLSE which is the governing equation for ultrashort pulse transmission in a nonlinear fiber. The items of the group velocity dispersion, self-phase modulation effect, the fourth-order dispersion, and the fifth-order nonlinearity

5 Advances in Optical Technologies 5 were considered. Two kinds of the kink wave solution, inverse kink wave solutions, the solitary wave solution of the tangent trigonometric function, and the solitary wave solution of the cotangent trigonometric function were found by using the G /G expansion method. These results have important significance in optical fiber communication and its applications. Acknowledgments This work is supported by Open Issues of Jiangsu Key Lab for Solar Cell materials and technology, Changzhou University (0107). The authors acknowledge the support from the open issues of State Key laboratory of Satellite Ocean Environment Dynamics (no. SOED101). References [1] S. K. Yuri and P. A. Govind, Optical Solitons from Fibers to Photonic Crystals, Academic Press, 003. [] A. Hasegawa and F. Tappert, Transmission of stationary nonlinear optical pulses in dispersive dielectric fibers. I. Anomalous dispersion, Applied Physics Letters, vol. 3, no. 3, pp , [3] L. F. Mollenauer, R. H. Stolen, and J. P. Gordon, Experimental observation of picosecond pulse narrowing and solitons in optical fibers, Physical Review Letters, vol. 45, no. 13, pp , [4] M.Wang,X.Li,andJ.Zhang, The(G /G)-expansion method and travelling wave solutions of nonlinear evolution equations in mathematical physics, Physics Letters A, vol.37,no.4,pp , 008. [5] M.A.Akbar,N.H.M.Ali,andS.T.Mohyud-Din, Assessment of the further improved (G /G)-expansion method and the extended tanh-method in probing exact solution of nonlinear PDEs, Mathematical, Theoretical and Computational Physics, vol., article 36. [6] Y. Q. Shi, Solving the high-order dispersive nonlinear Schrödinger equation by the G /G-expansion method, Journal of Guangxi University of Technology, vol.0,no.3,pp.45 49, 009 (Chinese). [7] R. C. Yang and Y. Zhang, Exact combined solitary wave solutions in nonlinear metamaterils, the Optical Society of America B,vol.8,no.1,pp.13 17,011. [8] M. Wang, The solitary wave solutions for variant Boussinesq equations, Physics Letters A,vol.199,no.3-4,pp ,1995. [9] J.-H. He and X.-H. Wu, Exp-function method for nonlinear wave equations, Chaos, Solitons and Fractals,vol.30,no.3,pp , 006. [10] E. Fan, Extended tanh-function method and its applications to nonlinear equations, Physics Letters A, vol. 77, no. 4-5, pp. 1 18, 000. [11] J.-L. Zhang, M.-L. Wang, and X.-Z. Li, The subsidiary ordinary differential equations and the exact solutions of the higher order dispersive nonlinear Schrödinger equation, Physics Letters A, vol. 357, no. 3, pp , 006. [1] S.-D. Zhu, Exact solutions for the high-order dispersive cubicquintic nonlinear Schrödinger equation by the extended hyperbolic auxiliary equation method, Chaos, Solitons and Fractals, vol.34,no.5,pp ,007. [13] M. Mehdipoor and A. Neirameh, New exact solutions for nonlinear solitary waves in Thomas-Fermi plasmas with (G /G)- expansion method, Astrophysics and Space Science,vol.337,no. 1, pp , 01. [14] B.S.Bahrami,H.Abdollahzadeh,I.M.Berijani,D.D.Ganji,and M. Abdollahzadeh, Exact travelling solutions for some nonlinear physical models by (G /G)-expansion method, Pramana, vol.77,no.,pp.63 75,011. [15]H.A.Zedan, (G /G)-expansion method for the generalized Zakharov equations, Ricerche di Matematica,vol.60,no.,pp , 011. [16] S.K.Elagan,M.Sayed,andY.S.Hamed, Aninnovativesolution for the generalized FitzHugh-Nagumo equation by using the generalized (G /G)-expansion method, Applied Mathematics, vol., pp , 011. [17] H.Kheiri,M.R.Moghaddam,andV.Vafaei, Applicationofthe (G /G)-expansion method for the Burgers, Burgers-Huxley and modified Burgers-KdV equations, Pramana, vol.76,no.6,pp , 011.

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