The Influence Of Fourth-order Dispersion And Fifth-order Nonlinear Effects On The Performance Of Ultra-long Haul Optical Transmission System

With the rapid development of fiber communication technology,large-capacity and ultralong-haul optical transmission systems have gained more and more applications.However,the high-speed optical pulses transmitted in the ultra-long-haul fiber link engineering system will cause problems such as power jitter along the line and reduced bit error rate,traditional optical transmission theory cannot explain these phenomena.Based on Schrodinger equation including fourth-order dispersion and fifth-order nonlinear effects,this paper develops optical transmission simulation software and analyzes the influences of fourth-order dispersion and fifth-order nonlinear effects on the performance of ultra-long-haul optical transmission systems.Firstly,based on the nonlinear optical theory and Maxwell equations,an optical transmission equation considering fourth-order dispersion and third-fifth-order nonlinearity is established;and the fifth-order nonlinear self-phase and cross-phase modulation phenomena are analyzed.According to the theory of scalar light scattering,spontaneous scattering and stimulated scattering effects are discussed.The optical propagation equation considering the effect of stimulated scattering is given when the third and fifth-order nonlinear effects exist simultaneously.Secondly,based on optical transmission equation above,the overall framework and flow of the optical transmission analysis software are proposed.By symmetric split-step Fourier method,the optical transmission equation considering intrapulse Raman scattering is discretized and solved,and transmission analysis software is developed to realize the simulation analysis of the optical signal transmission in the single-mode fiber.The verification of the optical transmission analysis software is performed,and the error sources are analyzed.Then,the influences of the fifth-order nonlinear effect on the transmission of single pulse and pulse sequence in the fiber link are analyzed.It is found that the fifth-order nonlinear effect is greatly affected by the fifth-order nonlinear coefficient of single mode fiber,fiber input power and transmission distance.Through field emission scanning electron microscopy(SEM)and X-ray diffraction(XRD)experiments,the surface morphology and atomic composition of G.652 D and G.657A2 fiber core rods are obtained,and it provides a feasible method for further exploring the physical causes of the fifth-order nonlinear effects in the fiber core.Finally,the influence of the fifth-order nonlinear effect on the forward Raman amplification system is studied.It is found that the fifth-order nonlinear effect enhances with the increase of the pump power.When the pump power is constant,the limit transmission distance of the system is discussed.The optimal configuration of the first-order bi-directional Raman amplifiers is studied,reasonable pump wavelengths and pump power range are discussed,and the system performance of multi-wavelength balanced pumping is compared.Four different configurations of second-order Raman amplifiers are studied,the limit transmission distance of the system is given,and the performance parameters of the system are analyzed.