Study On Chalcogenide Glass Micro-structured Optical Fibers

Micro-structured optical fiber（MOF）,also named photonic crystal fiber（PCF）,is a novel special fiber proposed about 20 years ago.Because of its variable optical fiber structure,MOF has excellent optical characteristics such as no cut-off single-mode transmission,high nonlinear coefficient and tunable dispersion.Therefore,it has attracted much attention in the field of broadband and flat supercontinuum generation and Raman amplification.The traditional silica glass MOF is difficult to produce high nonlinear effect in the mid-infrared region due to the limitation of its infrared cut-off wavelength and the smaller nonlinear coefficient.However,chalcogenide glass has received extensive attention from researchers because of its excellent mid and far infrared transmittance,high refractive index,high nonlinear coefficient and excellent thermal stability.Nonlinear coefficients and dispersion are important parameters involved in the application of MOFs,especially the high nonlinear coefficient&dispersion flattened MOF is the key device for the generation of supercontinuum.Therefore,the research on the related structure design appears constantly,however their work are mainly aimed at one particular structural parameter.In this thesis,the effective index guidance MOF with two different structures,suspended-core fiber and stacked fiber,is studied.The influence of structural parameters on nonlinear coefficients and dispersion is studied by simulation,data fitting and analysis by changing the different structural parameters of MOF.According to the analysis results,the structural parameters of the chalcogenide MOF with high nonlinearity and dispersion flattened are obtained.Finally,the stacked fiber has been fabricated successfully.The main contributions of this dissertation are listed as follows:1)A method of effective refractive index fitting is proposed to obtain the dispersion of MOF.The use of a unified custom fitting function can greatly reduce the influence of the system error on the fitting function in the fitting process,and the R-square is greater than 0.9998 and the SSE is not more than 6.57e^-5;2)By using the finite element method（FEM）,the effective refractive index and nonlinear coefficient of the 3-hole suspended-core fiber（SCF）,with different structural parameters（internal&external circle diameter of air hole and thickness of bridge）,are obtained in the operating wavelengths from 0.6 to 11.6μm.The corresponding dispersion curves of the MOF are obtained by means of a custom fitting method.Finally,the influence of structural parameters on the nonlinear coefficients and dispersion curves of fiber with this structure is systematically analyzed.It is found that when t=1μm,d1=40μm,d=1.7μm,the nonlinear coefficient can reach up to 17.48 m-1W-1,and there are two zero dispersion points of 1.944μm and 3.65μm in the MOF;3)A stacked As₂S₃ MOF with inner hexagonal tube is designed.By means of FEM,the effective refractive index and nonlinear coefficient of the fiber with different structure parameters（inner& outer diameters of capillary,the number of layers）are obtained by systematically simulating in the operating wavelengths from 0.6 to 11.6μm,and their dispersion curves are fitted by a custom fitting method.It is found that d1 has the greatest influence on the nonlinear coefficient and dispersion of the MOF.When d1=6μm,d2=2μm,N=2,the MOF has an ultra flat dispersion region in the range of 7.5-11.6μm,with a dispersion value of only about 10 ps/（km·nm）,and the nonlinear coefficient of 2.24543 m^-1W^-1.Moreover,with the decrease of d1,the nonlinear coefficient will increase gradually.4)The As2S3 stacked MOF with inner hexagonal tube and diameter of 400μm has been successfully fabricated by the combination of extrusion and stacking-capillary method.Through the fabrication of glass,preform and optical fiber,the three processes have been explored in terms of the fabrication of stacked MOF.And the improvement of the fabrication process of the stacked MOF is proposed by micro-fiber-end inspector,near field test and loss test.