Studies On Structure Design And Key Property Analysis Of Several Novel Microstructured Optical Fibers

The advent of Photonic Crystal brings up a new kind of fiber called Photonic Crystal Fiber or Microstructured Optical Fiber (MOF) which holds great potential to break the intrinsic limits of traditional silica fibers in terms of loss, dispersion, nonlinearity and polarization properties. Many unusual properties of MOFs have been identified such as endless single mode region, extremely versatile dispersion management, highly controllable nonlinearity and very large birefringence. In recent years, widespread research efforts have been paid to MOFs to explore "new structures, new materials and new applications".This dissertation aims to present some novel designs of MOFs for the advanced photonic networks or other fiber-related areas, involving highly birefringent MOFs, single-mode single-polarization (SMSP) MOFs, and highly nonlinear dispersion-flattented MOFs.It first presents a brief overview of the history and current state of the art in traditional optical fibers and MOFs.In chapter 2, a full-vector finite element mode solver based on the hybrid edge/nodal element is developed to conduct the numerical simulation of MOFs. Perfectly matched layer (PML) boundary conditions are incorporated into the mode solver to evaluate the leakage properties of MOFs. Mode characteristics of a multi-mode photonic crystal fiber are discussed in detail by using this mode solver. Furthermore, a nonlinear full-vector finite element mode solver is established for the steady-state analysis of highly nonlinear MOFs under high input power.Two types of highly birefringent MOFs, namely elliptical-high-index-core Bragg fibers (EHIC-BF) and high-index-elliptical-core Bragg fibers (HICE-BF), are proposed and numerically investigated in chapter 3. The results show that the mode birefringence of EHIC-BF and HICE-BF is on the magnitude of 10^-3 and even 10^-2, and the walkoff parameters exhibits quite unusual wavelength dependence different from that of conventional polarization-maintaining fibers. These unusual properties allow the flexible combination of high birefringence and large or zero walkoff at suitable wavelength. The dependence of mode birefringence and group velocity walkoff on the fiber structure parameters has been explored.The polarization properties of squeezed hexagonal photonic crystal fiber (SH-PCF) are dicussed in chapter 4. Confinement loss and its polarization dependency in SH-PCF are investigated for the first time. The results predict that SH-PCF can be used to perform SMSP transmission with proper design.A novel SMSP photonic crystal fiber using resonant absorption effect has been put forward in chapter 5. Numerical results show that very high bandwidth of SMSP operation can be obtained and high extinction ratio can be achieved with low loss penalty. The influence of structure parameters on the fiber performance has been investigated. Chapter 6 gives another novel design of SMSP fiber based on dual-core PCF. The numerical results predict that very efficient SMSP operation can be achieved with both high bandwidth and high extinction ratio at low loss penalty.Dispersion properties of high-index-core Bragg fibers are discussed in Chapter 7. The influence on dispersion properties induced by the low-index-layer thickness variance in different rings is also investigated. Confinement losses in dispersion-flattened high-index-core Bragg fibers are investigated, and an optimized design procedure is presented to achieve a dispersion-flattened MOF with low confinement loss.