Preparation And Characterization Of High Nonlinear Photonic Crystal Fiber

The excellent properties of photonic crystal fiber include the endless single mode,large mode area,adjustable dispersion property,high birefringence and nonlinear.It is widely used in the field of fiber sensing.Dispersion and high nonlinear characteristics are two important research directions in photonic crystal fibers(PCFs)The study of nonlinear characteristics of photonic crystal fiber with double zero dispersion wavelength and full positive dispersion crystal fiber without zero dispersion point has become one of the most important research points.In this paper,the nonlinear characteristics of optical fiber are studied theoretically and experimentally.The main contents are as follows:Firstly,based on the nonlinear theory of PCF,a split-step Fourier method for the propagation of laser pulses in optical fibers is derived to solve the nonlinear propagation equation,and the propagation spectra of femtosecond laser pulses in PCF are numerically simulated.The dispersion and nonlinear effects of fiber(group velocity dispersion,self-phase modulation,cross-phase modulation,four-wave mixing,soliton,stimulated Raman scattering,etc.)are studied.The theoretical basis for the subsequent experimental study is provided.Secondly,the fabrication technology of photonic crystal fiber is studied,and the fiber products with excellent characteristics are fabricated according to the fiber structure designed by theoretical simulation.The theoretical simulation of the fiber used in the experiment is carried out by using the finite element method.It is found that the fiber has the characteristics of high nonlinearity and double zero dispersion point.The femtosecond laser pulse of Ti: sapphire laser is incident into the high nonlinear PCF,and the nonlinear spectrum experiment is carried out.The high efficient broad band dispersion wave is obtained,the conversion efficiency is higher,the spectrum band is stable and smooth,not only the high efficiency broadband blue shift dispersion wave is obtained,but also the wide band red shift dispersion wave in the long band normal dispersion region is obtained.The red-shift dispersion wave in the near infrared band is connected with the soliton wave to form a supercontinuum spectrum with a bandwidth of 628 nm.The blue-shift dispersion wave of the bandwidth 309 nm is obtained and the conversion efficiency is up to 99.6%.The effect of the central wavelength,input power and polarization angle on the range of the central wavelength,the intensity and the conversion efficiency caused by the high efficiency broadband dispersion wave generated by the PCF and the influencing factors are further studied.Finally,the femtosecond laser pulse incident full positive dispersion high nonlinear photonic crystal fiber of Ti gem laser is studied.The fiber has no zero dispersion point and the whole band is normal dispersion region.The femtosecond laser pulse incident into the fiber is studied experimentally.The 203 nm dispersion flat hypercontinuum spectrum is obtained.By adjusting the incident wavelength and increasing the initial power,the supercontinuum spectrum can be further broadened.The supercontinuum spectrum broadening is mainly due to self-phase modulation and optical wave splitting,because only dispersion is introduced in the transmission process,and no optical solitons are produced,and the characteristics of single pulse are always maintained,and there is no pulse splitting.Therefore,the obtained supercontinuum spectrum is very stable and flat.Visible light band has good spatial coherence and stable time-domain pulse waveform.It has important applications in the generation of frequency comb and broadband time-resolved spectroscopy in ultra-high resolution spectroscopy.