Characteristic Analysis And Optimization Design Of Photonic Crystal Fibers And Polarization Splitter

Photonic crystal fiber?PCF? has the flexibility of structure design and many excellent optical properties. Therefore, compared with the the traditional fiber, photonic crystal fiber has incomparable superiority in design degrees of freedom or on the transmission characteristics. In addition, with the maturity of PCFs theory and the development of manufacture of PCFs, more and more PCFs which have different structures and different function are widely used in its development of filters, sensors, etc, so they have more and more important application values for the study of modern optics.This paper primarily researches on the PCF, and a novel high birefringence and high nonlinearity PCF and two kinds of dual-core PCF polarization splitters are proposed, the full vector finite element method?FEM? and coupled-mode theory are employed to investigate the relevant characteristics. The major contents are as follows:1. The PCF and its classification, fundamental characteristics and manufacture methods are1. The PCF and its classification, fundamental characteristics and manufacture methods are briefly introduced. After summarizing the present research situation of the PCF, the paper gives its main work arrangement and research innovation point.2. Several commonly used theoretical analysis methods of PCF are described, then focus on introducing the basic principles of the full-vector finite element method?FEM? and the simulation analysis process of the COMSOL Multiphysics software based on the full-vector finite element method?FEM?. In addition, the optical waveguide coupled-mode theory is present, and the mode coupling equations are solved.3. A new type of photonic crystal fiber with elliptic microstructure fiber core, high nonlinearity and high birefringence is designed which is based on quartz substrate, and the full-vector finite element method is used to investigate the relevant characteristics.Through the optimization of structure parameters, the minimum effective mode field area of the optical fiber is 2.18162mm, the nonlinear coefficient reaches as high as59.461km ¹ W^-1 and the birefringence value is 1.67910^-2 when the wavelength is1.55 mm. This design provides a new structure for obtaining excellent nonlinearity and high birefringence at the same time. In addition, it can be flexible to change the fiber nonlinearity and birefringence characteristics by adjusting the diameter of vertical air hole in the inner cladding, so we can choose the actual parameter according to the actual demand to study the performance metrics in practical applications.4. A novel kind of photonic crystal fiber polarization splitter based on quartz substrate is proposed, the full vector finite element method?FEM? and coupled-mode theory are employed to investigate the relevant characteristics. The results demonstrate that the coupling length of PCF can be reduced by enlarging the doped index of the central elliptical hole, reducing the ellipticity of the central elliptical hole or improving the ellipticity of 6 elliptical air holes which have the same size and symmetrical distribution.Through the optimization of structure parameters, the length of polarization beam splitter is 500 mm, the extinction ratio of the polarization beam splitter is-50.87 dB at the wavelength of 1.55 mm, and the bandwidth is 26 nm when the extinction ratio is less than-20dB.5. A novel kind of photonic crystal fiber polarization beam splitter is proposed based on tellurite and SF57 substrates. The performance difference of the polarization beam splitters are analyzed with the full-vector finite element method?FEM? and the coupled-mode theory. The results demonstrate that the relative coupling length increases whereas the birefringence remains practically unchanged with the increase of the ellipticity of the central elliptical hole. Compared with the SF57 glass polarization beam splitter, the tellurite glass counterpart exhibits higher extinction ratio and larger-20dB extinction bandwidth. The extinction ratio of the 0.161-mm-long tellurite glass polarization beam splitter is-59.26 dB at the wavelength of 1.55 mm, and the bandwidth is over 145 nm when the extinction ratio is less than^-20 dB.