Study Of Modulation Instability Analysis Of Nonlinear Multi-core Optical Fiber

In this paper,the characteristics of modulation instability in multi core fiber are studied.The influence of Raman scattering and four order dispersion in the double core fiber and the modulation instability of the isosceles symmetry plane in the three core fiber are analyzed in detail.The research work is of certain guiding significance to the study of the non linear effect of the multi core optical fiber based mode division multiplexing system.Through the nonlinear Schrodinger equation and the linear stability analysis method,it is found that the modulation instability gain spectrum does not exist only when the symmetric plane wave is in the normal dispersion under the first dispersion relation without Raman effect.The antisymmetric plane wave only exists in the anomalous dispersion region,however,the asymmetric wave has the gain spectrum always.The three plane waves have modulation instability gains in both anomalous and normal dispersion regions with the Raman effect,and the gain strength of the three waveforms exceeds the original gain under the effect of Raman scattering.The same method is used to analyze the influence of the four order dispersion on the modulation instability of the double core fiber.It is found that when the four order dispersion ?4>0,the gain is saturated and the strength is the same as the gain without the effect of ?4.When ?4<0,the gain strength increases with the increase of total power,and the gain strength is far greater than the gain strength without the effect of ?4.In the anomalous dispersion region,when ?4>0,the gain increases with the increase of total power,and the gain strength is less than the gain strength without the effect of ?4,but when?4<0,the gain strength and evolution trend is consistent with the gain without the effect of?4.Obviously,the modulation instability gain of asymmetric wave under the influence of the four order dispersion will change the original gain strength.The same method is used to analyze the modulation instability of isosceles symmetric plane waves in equilateral three-core fibers.The analysis shows that there are two forms of field distribution:the gain spectrum corresponding to the first field distribution is similar to the gain spectrum of the asymmetric planar wave of the double core fiber;the gain spectrum of the other field is completely different from the gain spectrum of the asymmetric planar wave in the double core fiber,and the significant feature is zero disturbance.In the normal and anomalous dispersion regions,the gain of instability can be generated in the normal and anomalous dispersion regions,and the gain of the zero perturbation frequency is the strongest in the normal dispersion region.On the other hand,the influence of the coupling coefficient dispersion on the gain spectrum is very weak in the normal and anomalous dispersion regions,which is very different from that in the double core fiber.