Study On The Nonlinearity In Erbium-doped Fiber Lasers

As the third generation of lasers,fiber lasers possess technological advantages that are not access to other lasers.Fiber lasers have the characteristics of lower threshold,high efficiency,compact structure,light weight,reliable performance and can be compatible with modern communication system.As a result,fiber lasers have become the research hotspot,since its invention.At present,optical fiber doped with rare earth element are mainly used as the gain medium in fiber lasers.Due to that,the working wavelength of erbium-doped fiber lasers is around 1.55?m,which is corresponding to the lowest loss window in optical fiber communication system.It can serve as the ideal signal source for ultra long distance signal transmission,making people pay much attention on it.Further,nonlinear effect in fiber lasers is one of the most important issues.Therefore,study on the nonlinearity in erbium-doped fiber lasers has the important theoretical significance as well as the theoretical directions on both experiments and practical applications.Based on Ginzburg-Landau equation describing propagation of soliton pulse in erbium-doped fiber lasers,nonlinearity has been discussed in our paper.The main research contents of our paper are as follows:1.With the modified Hirota method,analytic soliton solutions for the generalized cubic complex Ginzburg-Landau equation(CGLE)with variable coefficients are derived.Based on the analytic solutions,optical solitons in erbium-doped fiber lasers are obtained by choosing corresponding parameters properly.2.Soliton amplification affected by the gain coefficient is discussed.Research shows that a higher value of gain efficient indicates a higher amplification of solitons along the fibers of propagation.3.Soliton amplification affected by the gain dispersion is also discussed.In contrast,the gain dispersion coefficient can weaken the amplification of solitons.That is to say,the existence of gain dispersion can bring about the attenuation during the propagation of solitons.In addition,stability analysis with white noise is proposed.We study the stability of soliton amplification by embedding white noise,which is subject to Gaussian distribution.We find that the white noise has little influence on soliton amplification.4.Analytic soliton solutions for the variable-coefficient cubic-quintic CGLE are derived.Four families(kink solitons,gray solitons,Y-type solitons and combined solitons)of exact soliton solutions for the variable-coefficient cubic-quintic CGLE are obtained.5.Influences of nonlinearity and spectral filtering effect are discussed in these obtained exact soliton solutions,respectively.Methods to amplify the amplitude and compress the width of soliton pulses are put forward.We hope our work can provide scientific guidance for future research on experiments.