Design Of Compact Terahertz Wave Broadband Reflectors Based On Silicon Photonic Crystal Slabs

Terahertz (THz) waves with a frequency of0.1THz-10THz have been attracted intense interest in a wide range of potential applications like medical imaging, security screening, communications, chemical sensing, and radio astronomy due to their distinguished features of broad frequency bandwidth, ultrahigh temporal resolution, nondestructive and noninvasive inspection, as well as high directionality. There is an increasingly high need to control THz waves in a compact integrated circuit for those above applications, especially for compact THz sources and detectors. Broadband reflectors (BBRs) with high reflectivity are the essential components to construct the mentioned key devices. Therefore, it is very significant to design ultra-compact high-performance THz BBRs. On the other hand, photonic crystals (PCs) have become a promising technology to realize ultra-compact photonic integrated circuits owing to their extraordinary wavelength-scale light control capability. Its performance can be adjusted by introducing the defect or change of structure and can be similarly applied to THz range based on the scaling law of PCs.In this thesis, we propose a compact THz wave BBR based on the effect of guided mode resonance in two-dimensional (2D) photonic crystal slabs (PCSs). The PCSs consist of a square array of circular air holes in silicon. The rigorous coupled-wave analysis (RCWA) technique was applied to analyze the impact of parameters and structure configurations on the performance of designed THz-BBR. A compact broadband reflector was finally obtained. The primary contributions of this thesis are summarized as the followings:1. We design a THz reflector based on2D square-lattice photonic crystal on a single silicon layer. We neglect the requirement of low sidelobe initially. The performances of designed device under surface-normal incidence and oblique incidence as well as different polarizations have been numerically analyzed.2. We propose using dual-layer PCSs to further expand the relative bandwidth of reflector. Considering the concept of multiple dielectric films, a new configuration was proposed by partially etching the PCS and putting it on top of a separated simple planar waveguide. By optimizing those physics parameters like etching thickness and air gap between the two lays, a high-performance BBR with broad bandwidth and low sidelobe was finally obtained.The key contributions of our work are highlight here. First, we propose a compact THz BBR based on2D square-lattice Fano photonic crystal slab. The structure is simple with flexible selection of material as compared to the traditional reflectors based on stacked dielectric films which typically requires stringent physics parameters. Secondly, a novel method based on a map of localized bandwidth with defined reflectivity is introduced to analyze the impact of normalized thickness and hole size. Thirdly, we demonstrate low-sidelobe, high-reflectivity and broadband reflectors with the aid of multiple dielectric films, that is, partially etching photonic crystal slab and putting it on the top of a separated single planar waveguide.