Analysis Of The Characteristics Of Highly Nonlinear Photonic Crystal Fibers And Study On Their Brillouin Scattering Effect

In recent years,as a kind of optical fiber with special structure design,photonic crystal fiber(PCF)has attracted more and more attention.The research and application of PCF have also made great progress.Because of the good controllability of the structure,PCF has some optical characteristics that ordinary single-mode optical fibers don't have,such as high nonlinear,controllable dispersion,low bending loss,and vacuum light guide can be realized.Especially in nonlinear characteristics,through rational design,the nonlinear coefficient of PCF can be one to two orders of magnitude higher than that of ordinary single-mode fiber.Stimulated Brillouin Scattering(SBS)is an important non-linear effect in optical fiber.It has potential application value in optical fiber communication.The early research on SBS was only carried out on ordinary single-mode optical fibers.With the advent of special optical fibers such as PCF,researchers have also researched the SBS effect in such optical fibers more and more deeply,and their applications have become increasingly widespread,such as Brillouin fiber amplifier,slow light implementation,coherent optical storage,distributed sensors,etc.In this paper,by analyzing the effect of structural changes in PCF on the transmission characteristics of PCF,a PCF with high nonlinearity and low loss is designed.Then,based on the theoretical basis of fiber Brillouin scattering,the frequency shift and gain of Brillouin scattering signals are analyzed.And other calculation methods,the influence of PCF structure parameters on Brillouin scattering characteristics was studied.The main research contents are as follows:First,this paper analyzes the two basic classifications of PCF and some typical characteristics,and introduces the current research progress of highly nonlinear PCF.The nonlinear effects in PCF are theoretically deduced,and several typical nonlinear effects are analyzed,including phase modulation,four-wave mixing,stimulated Raman scattering,and stimulated Brillouin scattering.The formation process of SBS,coupling equations,Brillouin frequency shift,Brillouin gain characteristics,etc.are analyzed in detail.The PCF is numerically simulated by the finite element method,and several important transmission characteristics of the PCF are explained,including nonlinear characteristics,loss-limiting characteristics,and dispersion characteristics,and their calculation methods are specifically analyzed.Then,through the FEM for simulation analysis,mainly by reducing the effective mode field area of the core to improve the nonlinear coefficient.The effects of various structural parameters on the nonlinearity and loss of PCF are mainly analyzed.By changing the various structural parameters in the PCF cladding,the non-linear coefficients and restrictions on the PCF in the cladding duty cycle,the number of pore layers,and the pore diameter of each layer are analyzed.Due to the influence of loss and dispersion characteristics,a three-clad structure PCF was first designed.The nonlinear coefficient at a wavelength of 1.55?m is 28.29 w-1km-1,and the confinement loss is 4.35×10-6dB/km.Further improvements were made to stagger the distribution of two different sizes of pores in the innermost pores,the nonlinear coefficient at the wavelength of 1.55?m is 35.63 w-1km-1,and the confinement loss is 8.72 × 10-6dB/km.It's a better high nonlinear PCF structure.Finally,the distribution of light and sound fields under different PCF structures is analyzed through simulation,and the two characteristic parameters in Brillouin scattering:Brillouin frequency shift and Brillouin gain are analyzed.Firstly,the conventional cladding structure PCF is simulated and analyzed,and the effects of pore diameter,pore spacing and number of air pore layers on the Brillouin scattering characteristics are discussed respectively;then,the structure of the graded cladding is analyzed and the inner pores are discussed The influence of the diameter,the pore diameter of the second and third layers,and the smaller and larger pores in the innermost layer on the Brillouin scattering characteristics.The Brillouin frequency shift and Brillouin gain in different PCF structures are calculated,and the variation rules of the two with the parameters of the cladding are analyzed.The results show that the highly nonlinear PCF designed in this paper has a certain effect on the Brillouin signal Gain effect.The PCF structure designed in this paper has the characteristics of high nonlinearity and low loss.It can be applied to SBS-based sensing systems,which can help to better detect the Brillouin scattering signal and provide subsequent performance improvement for distributed optical fiber sensing systems some help.