The Effect Of Self-steepening On Soliton Spectral Tunneling In Photonic Crystal Fibers

The photonic crystal fiber(PCF)overcomes the limitations of the traditional optical fiber,and provides new opportunities for many new scientific research.Its good characteristics,for instance,controllable group velocity and high nonlinear properties,have brought new possibilities for nonlinear optical research.By adjusting the geometric structure of the PCF,a dispersion curve with multiple zero dispersion wavelengths can be obtained.When the ultrashort optical pulse pumped in the anomalous dispersion regime of PCF,the nonlinear effect and high-order dispersion effects are the prominent factors that greatly affect the ideal periodic high-order soliton evolution.Consequently,the higher-order soliton can break up into red-shifted fundamental solitons through soliton fission.During the soliton fission process,dispersive wave is emitted due to the energy transfer from soliton to narrow-band resonance in the normal dispersion regime.When fundamental solitons,undergoing Raman-induced frequency shift,approaches one of the zero dispersion wavelengths,may tunnel through a forbidden region of the normal group velocity dispersion between two anomalous dispersion regions and transfer its energy to a new soliton in the latter anomalous-dispersion region.In this paper,we mainly use the numerical methods to detailedly simulate the influence of the effect of self-steepening on soliton spectral tunneling(SST)in PCF with three zero dispersion wavelengths.The main research contents are listed below:Firstly,based on the Maxwell equations,the nonlinear Schrodinger equation is derived for the transmission of light pulses in PCF,and we use the standard split-step Fourier method solve the generalized nonlinear Schrodinger equation,and analyze the calculation accuracy of the algorithm.Then we study the time-frequency characteristics of the ultrashort pulse by cross-correlation frequency-resolved optical gating technique(X-FROG),and get the evolution process of the SST.Secondly,we analyze the interaction between dispersion and major nonlinear effects in PCF with three zero dispersion wavelengths.The influence of the self-steepening on the SST effect is mainly studied.The numerical simulation results show that the spectral energy can be redistributed by changing the self-steepening coefficient of the initial pulse.As the self-steepening coefficient increased,more energy transfers from the solitons in first anomalous dispersion region and red-shifted dispersive waves in long wavelength normal dispersion region to the new soliton generated in the second anomalous dispersion region.Consequently,the new soliton forms at a shorter distance and has a higher energy accumulation which makes the SST effect more obvious,contributing to the reshaping of the supercontinuum.Furthermore,the enhanced energy of blue-shifted dispersive waves can extend the blue edge of supercontinuum.Therefore,the numerical simulations and analysis presented here has great research value of the optical soliton dynamics,may open up the possibility of obtaining a high power spectral component at flexible wavelength,which shape the SC spectrum uniquely.It has potential application in ultra-short pulse compression,optical sensing,or multi-channel communication light source,etc.