The coupled nonlinear Schrödinger (CNLS) equation including Raman gain has been utilized for birefringence fiber. Evolution process of the optical soliton pulse has been simulated by the fractional Fourier method when the optical soliton pulse transmission in a birefringence fiber has a different nature. Results show that the drift of soliton caused by nonlinear coupling effect can be suppressed by Raman gain, at the same time, the soliton pulse peak in the transmission is enhanced. The interaction between optical solitons can be effectively restrained by Raman gain in the birefringence fiber.

Using the nonlinear Schrödinger equation (NLSE) including Raman gain effect but ignoring fiber loss situation, the linear operator and nonlinear operator specific expression are obtained based on MATLAB fractional Fourier numerical algorithm. They are applied to the NLSE including Raman gain, and the evolutions of soliton pulse are simulated in optical fiber through changing parameters. The result shows that soliton propagation stability is destroyed compared with the case considering no Raman gain, leading to the rapid attenuation of optical soliton. The influence degree depends on input soliton pulse peak power. The effects of Raman gain on ground state soliton and high order soliton are not the same.

Under the condition that the light pulses meet the slowly varying function pulses, the higher-order nonlinear Schrödinger equation has been deduced by taking into consideration the Raman gain. The linear operator and nonlinear operator specific expressions are obtained using split-step Fourier numerical method. The Raman gain on the self-steepening of the Gaussian pulse has been simulated and then the result is compared with the self-steepening effect without taking into consideration the Raman gain when the pulse propagate in the isotropic optical fiber. Raman gain specific impact on the self-steepening of the Gaussian pulse has been obtained under different conditions. Results show that the Raman gain may affect the Gaussian pulse broadening, pulse peak attenuation as well as the oscillation of the edge. These influences depend on the parameters of self-steepening, input power, and dispersion coefficient.

In this paper, the linear polarization light satisfied nonlinear coupled differential equations containing the Raman effect are utilized in a low birefringence fiber. The coupling model equation satisfied by the Stokes parameters is derived by introducing the Stokes parameters. Poincaré sphere is used to analyze the influence of Raman scattering effect on the state of polarization evolution in the low-birefringence fiber. The results show that the state of polarization evolution can be changed and the polarization ellipticity can also be changed due to Raman scattering effect in the low birefringence fiber when between the input power and motion constants satisfy a certain relation.