| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 93 === In order to comprehend the properties of photonic crystal fibers (PCFs), which play a more and more important role in photonics applications, a variety of PCFs are investigated by using a high-accuracy full-vectorial finite element (FE) mode solver and the finite element imaginary distance beam propagation method (FE-ID-BPM) based on curvilinear hybrid edge/nodal elements. Because of the utilization of the nonuniform element division and the curvilinear elements, PCFs having complex structures can be analyzed accurately. In this thesis, several PCFs are discussed in detail. First, the propagating characteristics and the coupling strength of twin-core PCFs are studied and explained. It is observed that the computed results of twin-core PCFs have similar trends with those of conventional fiber couplers. Next, the analysis of air-core photonic bandgap fibers (PBGFs) is performed through calculating the con nement losses, the group velocity dispersions, and the effective mode areas. It is demonstrated that the con nement losses can be reduced by increasing the number of air-hole rings, raising the diameter to hole pitch ratio, or appropriately designing the air-core shape. Finally, we analyze the loss spectra of PCFs especially at shorter wavelengths. The numerical results show that the loss spectra are strongly determined by the size of the cylinder inclusions and the refractive index of the liquid lled in these inclusions of the PCFs. Besides the numerical investigation, an analytical theory which treats the PCFs as antiresonant reflecting optical waveguides is adopted to explain the guiding mechanism. Calculated wavelength dependence of the effective refractive indices of the guided modes is well predicted by the analytical theory.
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