Research On Nonlinear Effects In Ultra-long-haul High-power Optical Fiber Transmission Systems Without Repeaters

With the development of communication technology,non-relay,ultra-long-distance,high-power optical fiber transmission systems have become more and more widely used.For optical fiber communication systems,the improvement of non-relay transmission distance faces many difficulties.The main limiting factors include: power limitation,optical signal-to-noise ratio limitation,chromatic dispersion limitation and nonlinear limitation.Among them,nonlinear effect limitation is the most complicated and difficult problem to solve.Various non-linear effects are widely present in optical fiber communication systems.On the one hand,these non-linear effects will destroy the communication quality and limit the transmission distance without relay.On the other hand,non-linear effects such as stimulated Raman effect can also be applied to optical fiber communication systems to increase the non-relay transmission distance of the system.This article designs experiments to study the nonlinear effects in optical fiber transmission systems,mainly including the following two innovations:(1)The first part of this paper studies the use of the distributed gain characteristics of the forward Raman amplifier can increase the equivalent fiber power of the system and break the limit of the system's stimulated Brillouin scattering threshold.According to the theory of nonlinear effects,a theoretical model of signal light transmission in optical fibers under Raman gain is established,and the system's stimulated Brillouin scattering threshold and optical signal-to-noise ratio are considered comprehensively,and the single-wave 1544 nm,1550nm and 1558 nm transmission systems are optimized respectively.The equivalent incoming fiber power breaks the limit of the system's stimulated Brillouin scattering threshold,and the equivalent incoming fiber power of the system exceeds the SBS threshold of 4.1d B,4.1d B,and 5.5d B respectively.(2)It is proposed that the in-band four-wave mixing phenomenon will impose a threshold limit on the increase of the incoming fiber power of the optical transmission system.When the incoming fiber power exceeds a certain threshold,a spectrum shoulder phenomenon appears in the spectrum,which limits the non-relay transmission distance.The second part of this article is based on the theory of nonlinear effects in optical fibers.This article establishes a simulation model and compares the experimental results to analyze the causes of spectral distortion.When the incoming fiber power exceeds 20 d Bm,the four-wave mixing effect between the signal light and the modulated light causes the generation of a spectral shoulder phenomenon,which causes noise interference to the signal light.As a result,the optical signal-to-noise ratio at the receiving end of the system is reduced,resulting in a limited transmission distance without relay.In this paper,experiments are carried out to verify the non-linear effects in the non-relay ultra-long-distance optical fiber communication system,and the MATLAB software is used for simulation calculation,and the problem is quantitatively analyzed.The simulation and experimental results are in good agreement.