第二個方面我們將光子晶體做成有限厚度平板並以線偏振平面波正向入射，以RCWA (Rigorous Coupled-Wave Analysis)方法計算此平面波通過平板後的偏振態與原先偏振態的夾角以分析光子晶體作為偏振旋轉器的效果，並且我們也發現特定頻率的光會產生leaky guided resonance，這種共振會增強光子晶體的圓二色性進而使得在該頻率的偏振旋轉角度會特別大。 ;This thesis concerns the effective chirality of some three-dimensional dielectric photonic crystals consisting of two-dimensional-periodically arranged twisted rods. Through properly choosing the dielectric rod’s shape in a 2D unit cell, we can obtain a photonic crystal with nonzero chirality, overcoming the disadvantage of absorption of the chiral metamaterial consisting of metallic elements.
In our work we design three different types of photonic crystal and discuss their properties in two aspects. The first is calculating their band structures using the plane wave expansion method and check if their field vectors have the feature of circular polarization to confirm their chirality. We also developed a way to classify these propagating modes, and extracted the effective chirality parameters for the first two bands in the band structure.
In another aspect, we consider a photonic crystal slab with finite thickness and being illuminated by a normally incident linearly polarized plane EM wave, and use the RCWA (Rigorous Coupled-Wave Analysis) method to calculate the field distribution. We then compare the polarization states of the outgoing wave with the incident wave and analyze the effectiveness of the photonic crystal slab as a polarization rotator. We also found that at certain frequencies there occur resonances called leaky guided resonances. Such resonances enhance the circular dichroism of the photonic crystal slab, result in large polarization rotation angles.