Novel Photonic Quasi-crystal Fiber And Microscopic Mechanism Of Silica Fiber

With the rapid increase of the application of the supercontinuum light source in op-tical communication, spectroscopy, optical measurement, biomedical imaging and so on, there is an urgent demand of improving the performance of supercontinuum light source. Up to now, the main method to obtain the supercontinuum spectrum is based on high nonlinear fibers. Therefore, high nonlinear fibers with high nonlinear coefficient, special dispersion, and birefringence are crucial to improve the performance of supercontinuum spectrum source. Photonic quasi-crystal fibers (PQFs) have attracted the interests due to their unique characteristics and the flexibility of structure. It offers the opportunity of developing the fiber with novel characteristics. Based on the flexible structure of PQFs and the study of microscopic mechanism of silica-based optical fiber through dielectric materials amorphous SiO2and germanium doped amorphous SiO2, we focus on de-signing and optimizing the highly nonlinear PQF with special dispersion and high bire-fringence PQF to satisfy the demand of developing high performance of supercontinu-um light source in this dissertation. This work is supported by National Natural Science Foundation of China and excellent doctoral innovation fund of Beijing Jiaotong Univer-sity. The main achievements are summarized as the following.1. With the dual concentric core structure, a novel PQF with near-zero flattened dis-persion, highly nonlinear coefficient, and low confinement loss is proposed. By optimizing the structure parameter, the proposed PQF can achieve a nonlinear coef-ficient larger than33W-1km-1and near-zero flatten dispersion of0±3.4ps/nm/km with a near-zero dispersion slope of8.5×10-3ps/nm2/km at the wavelength of1550nm. Furthermore, two zero dispersion wavelengths (ZDWs) can be obtained in a wide wavelength ranger from1373to1725nm. The influence of deviation of each air hole diameter within3%is discussed to verify the robustness..2. An As2Se3-based highly nonlinear PQF with dual ZDWs is proposed. Numerical results demonstrate that the proposed PQF has dual ZDWs and stronger confine-ment ability in its guide mode and the nonlinearity coefficient is up to5000W-1km-1in the wavelength range from2to5.5μm. Due to the introduction of Ge-doped core into the fiber, the nonlinearity can be effectively enhanced. Meanwhile the two ZDWs would shift towards the longer wavelength and the confinement loss can be distinctly decreased. Furthermore, it is also verified the superiorities of this PQF to with the PCF structure.3. A novel design of highly birefringent PQF based on ZBLAN glass with twin grape-fruits air holes near the core is proposed. Numerical results show that the fiber maintains single mode operation in a wide wavelength range from1.8μm to2.2μm, and the birefringence is in the order of10-2which is two orders of magnitude larger than that of the conventional polarization-maintaining fibers and the same orders of magnitude with the elliptical hole PCF. But the proposed fiber is easier to fabricate than the elliptical hole PCF.4. A highly birefringent ZBLAN PQF with a rectangular array of four relatively small circular air holes in the core region is proposed. Through optimizing fiber structure parameters using a full-vector finite-element method combined with perfectly matched layers boundary condition, its birefringence is up to2.88×10-2and the confinement losses of both polarized modes are less than4.95×10-4dB/m at2μm. To the best of our knowledge, this is the first fiber with a birefringence of the order of10-2by all-circular-hole PQFs around2μm.5. On the one hand, we investigate the structural properties, thermodynamic proper-ties and mechanical properties of amorphous SiO2and amorphous SiO2with oxy-gen deficient center by using interatomic pair potentials. The calculated short-range structural parameters coincide well with experimental values and other calculations. The thermodynamic properties including specific heat, Debye temperature, vibra-tional entropy, and so on are obtained by the calculated phonon density. On the other hand, we investigate different stable geometric configurations of Ge doped amorphous SiO2. The most stable structures should be the structure in which Ge atoms tend to occupy the position far away from the center with the largest distance between them. In contrast to the results of doped metal compounds or crystal compounds, the stability of Ge doped amorphous SiO2can be reduced due to the doping of Ge.