Numerical Studies Based On The Generation Of Infrared Supercontinuum In Highly Nonlinear Fibers

Supercontinuous spectrum refers to the phenomenon that the incident pulse spectrum determined by the dispersion characteristics and complex nonlinear effects of optical fiber is broadened during the transmission of ultrashort laser pulses in the fiber.The mid-infrared supercontinuum light source is widely used in many fields because of the characteristics of ultra-wide spectrum,high brightness and high coherence.Therefore,it is very necessary to study the mid-infrared supercontinuum.light source.With the research and development of the optical medium used to produce the mid-infrared supercontinuum,and the improvement of the pump laser technology,it has been a truth that the long pulse,ultrashort pulse and pump wavelength are all adjustable,which will greatly promote the research of mid-infrared supercontinuum.The generation of the mid-infrared supercontinuum is very strict with the nonlinear coefficient of fiber,the dispersion characteristics and the transmission rate of infrared wavelengths.The soft glass fiber made with telluride,fluoride and chalcogenide is not only with very high nonlinear coefficient and excellent mid-infrared transmission performance,but also easier to meet the demand for pumped light sources by designing the structure of photonic crystal fiber that can transfer its zero dispersion wavelength to short wavelength,which is very beneficial to the generation of mid-infrared supercontinuum in broadband.At present,the use of soft glass photonic crystal fiber to produce mid-infrared supercontinuum has been a research hotspot in the field of supercontinuum.In this paper,the characteristics of mid-infrared supercontinuum generated by femtosecond pulse propagation in high-nonlinear suspended-core As2S3 microstructure fiber are simulated and analyzed.The split-step flourier method is used to numerically solve generalized nonlinear Schrodinger equation.What's more,the effects of the pump laser pulse parameters and the length of fiber on the generation of mid-infrared supercontinuum are studied numerically,including the laser pulse pump wavelength,pulse peak power,pulse width and the length of reference fiber.Combining the evolution of the time domain and frequency domain change with the length of fiber and the spectral output,the influence of different parameters on the generation of mid-infrared supercontinuum and the effect of various nonlinear effects on the spectral broadening are analyzed,the nonlinear effect when the fiber is in the normal dispersion region and in the anomalous dispersion region and its contribution to the spectral broadening are also analyzed.The simulation results show,by optimizing the parameters of pump pulse and the length of fiber,when the suspended-core As2S3 microstructure reference fiber length of 4 cm is used,of which the hyperbolic secant laser pulse pump wavelength is 2300 nm,the pulse peak power is 30 kW,the half full width of initial pulse is 300 fs,the ultra-wide mid-infrared supercontinuum is obtained,of which the spectral broadening is 9 ?m,the coverage of broadening wavelength is 1-10 ?m.What's more,the numerical simulation of the mid-infrared supercontinuum produced by telluride soft glass fiber and fluoride soft glass fiber was carried out.The feasibility of the mid-infrared supercontinuum produced by the telluride microstructure fiber and ZBLAN single mode fiber is analyzed.According to the simulation results,for the telluride microstructure fiber,when the pump wavelength is in the anomalous dispersion region of the fiber and close to the zero dispersion wavelength,selecting the appropriate peak power and incident pulse width can produce a wide range mid-infrared supercontinuum.For ZBLAN single-mode fiber,because its nonlinear coefficient is much smaller than that of Sulfide and Telluride fiber,so choosing a larger pulse peak power can produce broadband mid-infrared supercontinum.The results show that when the telluride microstructure reference fiber with the femtosecond pulse pumped of 10 cm is used,of which the pumped wavelength is 2000nm,the peak power is 30 kW,the pulse half full width is 100 fs,the wideband infrared supercontinuu of 1.2-4.7 ?m is obtained.When a femtosecond pulse with a peak power of 1 MW,a pump wavelength of 2000 nm and a pulse half full width of 100 fs was used to pump a 10 cm long ZBLAN single mode reference fiber,a broadband mid-infrared supercontinuum of 1.2-4 ?m was obtained.