Study On Multi-mode Nonlinear Dynamical Characteristics Of Erbium Doped Fiber Laser

Focusing on the phenomena of complicated multi-mode oscillation of erbium-doped fiber ring laser(EDFRL)system in practical engineering applications,based on optical heterodyne experimental measurement,the real time multi-channel output of EDFRL in frequency and time domain can be obtained,which breakthrough traditional experimental technology.The multimode dynamics and total output intensity of EDFRL can be obtained and analyzed,the analysis on multi-mode dynamics of EDFRL from low dimension to higher,which make it possible to study the complicated correlation and relationship between single mode and total output.This thesis adopts erbium-doped fiber ring laser(EDFRL)as the main research object.Based on theory analysis and experimental detection,we try to study on multi-mode high dimension dynamical characteristics of EDFRL.In numerical analysis part,multi-mode EDFL model has been developed according to saturable absorption of ions in the gainmedium of laser system,together with cross coupling factor and anisotropic mechanism among modes.The dynamical output of dual-mode and multi-mode systems have been analyzed in time intensity domain and state space.In this model we also have discussed quantificationally the dynamical output of laser system by altering pump intensity,cross coupling parameter and ion concentration.Under such condition,a great variety of dynamics can be observed deponding on the parameters of ion pair concentration,cross coupling and pump.Moreover,a sine modulation has been added in this model,which leads this model to behave multi-periodic,quasi-periodic and chaotic dynamics.In experimental part,based on optical heterodyne method and radio frequency analyzer,dynamical multi-mode outputs of EDFRL in free running and modulation states have been measured and analyzed in real-time.In experiment,output of EDFRL system has been divided into two parts,one of the parts is regarded as monitoring the total mode intensity,the other is used for monitoring multi-mode dynamics of laser system.Incidental mode hopping and complex multi-mode oscillation of EDFRL have been obtained according to the methods above.Moreover,we have added a sine voltage signal into the pump of laser system,by altering frequency and modulation depth of sine voltage signal,we have studied multi-mode oscillation phenomena when the total mode intensity operates at multi-periodical state and chaotic state.Trying to investigate the dynamical evolution of these modes,time series of different modes have been analyzed.According to nonlinear testing for single mode,we have proved that EDFRL is a nonlinear system for sure.Based on space reconstruction method,We have observed that both chaotic and random operation can be existed in multi-mode oscillation.After adding the modulation in laser system,the maximum likelihood estimation of correlation dimension of single mode is as large as 4.6,which proves multi-mode and high dimension characteristics in erbium-doped fiber ring laser system.According to the methods above,we have proved on theory and in experiment that multi-mode optical field of EDFRL exhibits distinct chaotic characteristics.