| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 95 === Photonic crystal fibers (PCFs) are photonic crystal modes consisting of a two dimensional periodic refractive index structure around the core. The novel fibers guide the light by total internal refraction (TIR) or photonic bandgaps (PBG) effect. We investigate properties of the PCFs and the photonic liquid crystal fibers (PLCFs) numerically by using the plane wave expansion method and the finite element method.
By destroying the symmetry of fiber structure, we demonstrate that the birefringence is increased by 80%. The intensified birefringence allows us to design the high birefringent PCF sensors. Details are discussed and the monochromatic and dynamic measurements are demonstrated.
PLCFs are the photonic crystal fibers filled with liquid crystals, which are thermal and electrical tunable anisotropic material. In this thesis, we focus on studying the birefringence and dispersions of the PLCFs guided by TIR and PBG effects, when the optical axis of nematic PCs are in different directions. Moreover, the effects of the anisotropism of liquid crystals to PCFs are addressed.
When the optical axial of LCs is parallel to the propagation direction, the birefringence is zero. For a positive uniaxial medium, we find the zero dispersive points shift toward the lower frequency with an increasing anisotropism. On the other hand, the anisotropism has weak influence on zero dispersive points. When the optical axial of LCs is perpendicular to the propagation direction, the birefringence aren’t zero and the anisotropism has weak influence on zero dispersive points. But, the power may be lost at other directional band.
Finally, a bi-guidance fiber which has two different guiding mechanisms at two polarization modes is proposed. According to the properties of bi-guide, we can design the optical switch and optical polarization selector. The present research gives a physical insight into PLCFs and is crucial for optoelectronic devices and biosensors.
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