| The optical fiber communication system is a pivotal support in the contemporary communication industry.How to improve the communication quality and capacity of optical fiber communication system is one of the hot research issues at present.In optical fiber,the nonlinear effect would lead to phase distortion and interference of adjacent channels which should be solved urgently.The optical soliton is an optical pulse carrier generated by the balance of the nonlinear effect and dispersion,which can keep its shape and velocity unchanged over long distances.The optical soliton communication has higher transmission rate and larger transmission capacity compared with other communication methods.In particular,the information transmission rate of double-hump solitons is higher than that of single-hump solitons.By studying nonlinear equations in the optical fiber communication system,the internal mechanism,transmission properties and applications of optical solitons are calculated and analyzed via symbolic computation and Hirota bilinear method.Based on the research experience of single-hump soliton,the collision dynamic characteristics of the doublehump soliton are further explored by adjusting the nonlinear effect and other physical factors.Moreover,the flat-top soliton with strong antiinterference ability is found.These researches give the theoretical basis for optical fiber communication system to modulate optical pulse and improve communication quality and capacity.The work of this paper specifically includes the following aspects:(1)Research on single-hump solitons in inhomogeneous optical fiber communication systems.Two nonlinear Schrodinger equations with variable coefficients and one Kundu-Eckhaus equation are analytically explored for optical fiber communication systems.New types of bright and dark solitons are constructed by adjusting the nonlinear effect,group velocity and group velocity dispersion.Bright soliton structures include parallel transmission solitons,parabolic solitons,butterfly-shaped structures and dromion-like structures.The amplification and attenuation of solitons in bound state are studied.Moreover,the effects of phase shift,oscillation and incident angle on soliton transmissions are found.Moreover,dark solitons with periodic oscillation,dark solitons with increasing oscillation amplitude in the positive or negative direction relative to the point of z=0 are found.New dark soliton molecules are further found.The methods to control soliton interactions are given.(2)Research on single-hump dark solitons in inhomogeneous birefringence optical fiber communication systems.The coupled nonlinear model should be considered because of the birefringence in the fiber.The dark soliton propagation described by the(2+1)-dimensional and(3+1)-dimensional nonlinear coupled Schrodinger equations with variable coefficients are studied.The parabolic dark solitons,parabolic dark solitons with oscillation,m-type anti-dark solitons,w-type anti-dark solitons,s-type anti-dark solitons with two different curvature,anti-dark solitons with peaks are constructed based on the analytical soliton solutions.These can meet the needs of different paths,phase shift and pulse width control.In addition,the method to control the interval and interaction intensity of two anti-dark solitons is discussed.(3)Research on double-hump bright solitons in inhomogeneous twomode optical fiber communication systems.Optical solitons with doublehump structure can improve the data carrying capacity.Based on the research experience of single-hump soliton,some new types of doublehump soliton transmitted along curves,including v-type,parabolic,stype and double-hump solitons with phase shifts have been found,via the analytical study of variable-coefficient coupled Manakov equations.The energy exchanges and amplitude change between two peaks within the double-hump soliton are analyzed.Elastic and inelastic collisions between double-hump solitons are also discussed.The different transmission characteristics of double-hump solitons in two modes are also studied.(4)Research on double-hump dark solitons with high-order effects in two-mode fiber.The capacity of the transmission system with high bit rate can be improved when the pulse width of optical pulse is compressed into femtosecond.The ultrashort pulses transmitting in the form of three double-hump dark soliton structures are found for the first time.The elastic collisions of multiple double-hump dark solitons,double-hump dark solitons and anti-dark solitons,double-hump dark solitons and anti-dark soliton molecules have been studied in two modes.A new type of solitons composed of anti-dark solitons,kink solitons and anti-kink solitons is also found.The influences of self-steepening effect,third-order dispersion and group velocity dispersion on the transmission characteristics of doublehump dark solitons and the different collision dynamics between doublehump dark solitons in two modes are further analyzed.(5)Research on flat-top solitons in Alfven model.Flat-top solitons are more efficient than bright solitons in pump-comb conversion efficiency.A flat-top soliton structure based on the Alfven model has been constructed.In order to verify its anti-interference ability,the flat-top soliton is once or twice truncated.Finally,it is proved that the flat-top soliton can restore the initial state after truncations.Hence it has strong anti-interference ability. |
