Study On The Generation Of Deep Ultraviolet Supercontinuum Spectrum Based On Subwavelength Fiber

Supercontinuum(SC)has the characteristics of wide spectrum,good stability and good coherence,and has become a research hotspot in the field of nonlinear optics technology.Ultraviolet(UV)SC light source has a wide range of applications in communication,military and environmental processing and other fields because of its special spectral characteristics.In recent years,the research on the generation of SC based on optical fiber media is mainly concentrated in the mid-infrared band,fewer in the UV range.Subwavelength fiber is an ideal medium for SC generation because it has many excellent characteristics,such as good dispersion controllability,high nonlinear effect,and strong optical field confinement.Therefore,it is of academic and practical value to carry out the related research.Firstly,photonic crystal fiber(PCF)and subwavelength fiber which can be used to produce UV supercontinuum medium are designed.The effective refractive index of the fundamental mode is obtained by using the full vector finite element method and the influence of structural parameters on loss and dispersion is studied.The structure is optimized continuously to make its dispersion zero point close to the UV band as much as possible.The study found that subwavelength fiber is easier to obtain low dispersion zero-point wavelength than PCF,which is conducive to the generation of SC.Through material selection and structural parameter optimization,subwavelength fiber with magnesium fluoride as the base material is selected,the core radius a=0.30 μm,the cladding radius b=2.40 μm,and the two dispersion zero wavelengths of the subwavelength fiber structure are: 424 nm and 642 nm,respectively.Then,the Schr?dinger equation is solved numerically by the Spilt-Step Fourier method.When the length of subwavelength fiber is 3 cm and a chirp-free hyperbolic secant pulse input with a center wavelength of 400 nm,and the initial pulse width is 300 fs,and the pulse peak power is 5 k W.The SC is broadened to an ultraviolet range of 250.10 nm～1023.00 nm,which has reached the UV band,and the average output power is-43.86 d B,and the output flatness is 0.963,and the flatness of the spectrum is good.To further obtain the extension to the deep UV supercontinuum,the multiple factors that affect the generation of SC are studied,including the length of fiber,and center wavelength,and peak power,and initial pulse width of the pump pulse.The results reveal that the SC is broadened to an deep ultraviolet range of 229.11 nm～2366.68 nm,and the average output power is-39.82 d B,and the output flatness is 0.945,when the length of subwavelength fiber is 4 cm,and the center wavelength of the pump light is 400 nm,and the initial pulse width is 350 fs,and the pulse peak power is 6 k W.The obtained UV supercontinuum light source can have corresponding applications in ultraviolet short-range high security communication,ultraviolet warning and environmental sewage treatment.