Research On The Dispersion And Nonlinearity For The Subwavelength Optical Fibers With Different Cladding Materials

In recent years,highly nonlinear optical fiber is widely used in super continuum spectrum generation.At present,the subwavelength optical fiber as one class of highly nonlinear fibers has become one of the hot research areas because of low absorption loss,large waveguide dispersion and highly nonlinearity.In this paper,we gain a flat normal dispersion curve by tuning the core radius and cladding material,and we use this fibers to gain the visible-to-near infrared spectrum with smooth spectral shape.The contents are as follows:Firstly,we investigate the group velocity dispersions and nonlinear parameter of the subwavelength optical fibers with air cladding under different core radius.The fibers with different core sizes are numerically simulated with 200 nm of radius interval,and then we choose two groups of dispersion curves with similar normal dispersion profiles.Based on these two group subwavelength fibers,we calculate the dispersion curves by setting the radius interval as 50 nm and obtain a group with relatively flattened dispersion profile.Secondly,the group velocity dispersions and nonlinearities are discussed for fibers with different cladding materials.Except the air-cladding fibers,we choose the heavy water,water and the index-matching oil as cladding materials,and simulated numerically based on the finite-element-methods of ware and Matlab.The results show that,for water-cladding subwavelength fibers,when the fiber core radius is 800 nm,the relatively flat dispersion curve can be obtained at wavelengths from 777 nm to 1685 nm.In the case of heavy water cladding,when the fiber core radius is 920 nm,the flat normal dispersion curve exists at wavelengths from 593 nm to 1800 nm;In the case of matching oil,when the fiber core radius is 1150 nm,the flat normal dispersion curve exists at wavelengths from 626 nm to 1800 nm.In order to improve the nonlinear parameters,the liquid-filled hollow-core subwavelength optical fiber is proposed and analyzed.Finally,numerical solutions based on the generalized nonlinear schrodinger equation are obtained for the evaluations of the ultrafast pulses along the subwavelength optical fibers.In the case of water cladding,when the fiber core radius is 800 nm,the spectrum with wavelength range of 645-1238 nm can be obtained.For the improved subwavelength optical fiber,given the same initial pumping pulses,the flat and smooth spectrum can be obtained in the wavelength range of 415-1355 nm at-3dB level.