Research On Transmission Characteristics Of Dielectrically Chiral Photonic Crystal Fiber With Bandgap

Due to the promising application in optical communication, photonic crystal fiber (PCF) with some unique properties arouses more and more attentions recently. In fact, most of existing PCF are fabricated by achiral material while chiral PCF do not received adequate emphasis. In this thesis, a concept of dielectrically chiral PCF with bandgap is proposed. By using numerical simulations, the effects of chirality are investigated on the photonic bandgap and guidance characteristics.In this thesis, two current algorithms, namely the plane wave expansion (PWE) method and the Finite-difference Frequency-domain (FDFD) method, are improved and applied to photonic structure with dielectric chirality. Through two typical examples, namely the chiral fiber and index-guided PCF, two above methods are proved. The improved FDFD method may be utilized to study a regular chiral waveguide with arbitrary structure. The improved PWE method has two forms: the conventional chiral PWE method and the chiral PWE method for waveguide, the former is suitable for the PCF with bandgap structure, while, by incorporating the supercell approximation, the latter can be used to study simple chiral PCF.By using the chiral PWE method, the effects of chirality are investigated on the mode distribution, polarization distribution, bandgap width and effective indices in the cladding. Based on two structures with triangular lattices and honeycomb lattices, the eigenmodes are calculated for specific wave vector directions, the circularly polarized modes are found, and the phenomenon of suppression of bandgap width arising from chirality is analyzed.Based on the chiral FDFD method, the hollow PCF with triangular lattices and the PCF with honeycomb lattices of bandgap type are simulated. The polarization characteristics, effective indices and confinement loss are discussed. A mechanism of bandgap guidance in chiral PCF is validated. In the two types of PCF mentioned above, guided modes with quite pure circular polarization are revealed. Based on the difference in loss and indices for right-/left-handed circularly polarized modes, a possibility of selective transmission is discussed for a given circular polarization.