Numerical Study Of Supercontinuum Generation Based On High Nonlinear Fiber

Because of the advantages of high brightness,wide spectrum,good stability,and low price,supercontinuum has extremely important application value and development prospects in spectral analysis,high precision optical frequency measurement,optical fiber communication,and white light source.Compared with the traditional silica fiber,chalcogenide fiber and photonic crystal fiber have received more and more attention because of their characteristics of high nonlinear coefficient and extremely high infrared transmittance.Currently,the generation of supercontinuum has been a hot topic.In this thesis,the supercontinuum generation based on chalcogenide fiber and photonic crystal fiber,respectively,are studied numerically.The study includes the following aspects:(1)Based on the Maxwell's equations,the propagation equation of the optical pulse in the optical fiber is gradually derived,and the generalized nonlinear Schr?dinger equation is finally obtained,and then the split-step Fourier method is used to solve the equation numerically.Based on this,a theoretical model for the evolution of optical pulse propagation in optical fiber is constructed.(2)Based on the established theoretical model of the optical pulses propagation in the optical fiber,the effect of input pulse parameters(including peak power,pulse width,initial frequency chirp)and the reference fiber length on the supercontinuum generation in the chalcogenide fiber are numerically studied.The research results show that within a certain range,the output spectral width increases with the increase of the peak power and pulse width of the input pulse;positive chirp is beneficial to spectral broadening,while negative chirp is just the opposite.In addition,when the initial frequency chirp is less than 30,the supercontinuum bandwidth increases with the initial frequency chirp.When the incident pulse with initial frequency chirp of 30,peak power of 1000 W,and pulse width of 500 fs,a supercontinuum with good flatness as well as a wide range spanning from the near infrared region to the mid infrared region can be obtained.The corresponding spectral width is 2300 nm.The width and flatness of the supercontinuum do not always increase with increase of the reference fiber length,but there is an optimal reference fiber length.(3)The photonic crystal fiber is selected as the reference fiber,and the finite energy Airy pulse(FEAP)is selected as the input pulse.Based on the established theoretical model of the optical pulse propagation in the optical fiber,the propagationcharacteristics and the influence of all kind of parameters such as truncation coefficient and chirp parameters on the supercontinuum generation are studied.The results show that FEAP will decelerate with the increase of the input pulse's peak power during propagation;higher-order nonlinear effects are conducive to obtaining supercontinuum with better width and flatness;supercontinuum becomes wider with the decreasing of the truncation coefficient;in addition,compared with the negative initial frequency chirp,positive frequency chirp is conducive to the generation of supercontinuum.When the frequency chirp is 0.9,the width of the supercontinuum obtained by numerical simulation is 458 nm.