Analysis On Race-track Two-dimensional Photonic Crystal Ring Resonators And Their Applications

Optical ring resonators have been widely used in these areas like optical communications, optical sensors and laser spectrum due to their merits of large free spectral range, high spectral selectivity and high quality factor (Q). They can be typically demonstrated based on optical fiber and planar waveguide technique. In general, optical fiber ring is bulky and incompatible with photonic integration. For planar waveguide ring limited by the total internal reflection (TIR) mechanism, its propagation loss increases exponentially with the reduction of ring radius. Moreover, its performance is greatly affected by the air gap between the bus waveguide and ring, as well as surface roughness, which creates new manufacturing challenge. On the other hand, photonic crystals (PCs) offer potential for ultra-compact photonic integration due to their unique properties in controlling the flow of light at optical wavelength scale. In the past few years, photonic crystal ring resonators (PCRRs) have attracted great attention owing to their potential scalable ring sizes, flexible coupling and size-independent propagation loss. However, the reported PCRR configurations are mostly based on a dielectric-rod standard quasi-ring, i.e, equilateral polygon like square rings, which can easily provide single mode operation with large range of frequency. Additionally, dielectric-rod PCRR creates fabrication difficulty without vertical confinement and is inherently leaky as compared to air-hole type PCRR. But air-hole PCRR is very easy to stimulate multimode operation especially at the bent corner of waveguide and finally lead to poor dropping efficiency and low sidelobe suppression. Therefore, it is very significant to further enrich the PCRR family and improve the dropping efficiency of air-hole PCRR.In this thesis, we utilized silicon material and proposed three new types of PCRRs including race-track PCRR based on square-lattice cylindrical silicon rods in air, polarization-independent race-track PCRR based on honeycomb-lattice cylindrical silicon rods in air and high-drop race-track PCRR based on square-lattice air hole in silicon. The characteristics of proposed configurations were numerically analyzed by using plane-wave expansion method (PWE) and finite-difference time-domain technique (FDTD). The major research achievements have been summarized as follows:1. A new channel drop filter (CDF) was proposed based on a race-track PCRR composed of square-lattice cylindrical silicon rods in air. By using a two-dimensional (2D) FDTD numerical technique, the modal behavior of two representative CDFs, parallel and perpendicular, has been analyzed. The analyses included the impact of additional scatterer size, scatterer amount and their position on the performance of proposed CDFs, such as drop efficiency and quality factor (Q).2. A new polarization beam splitter (PBS) was demonstrated based on race-track ring resonator composed of2D honeycomb-lattice cylindrical silicon rods in air. By using2D FDTD numerical technique, we realized the PBS at the same wavelength where TM polarization light propagates through the forward port and TE polarization light enters through the backward port. Besides, the impact of the refractive index and surrounding period d and L on the characteristics of proposed devices was also studied.3. A high-drop air-hole-type PCRR was proposed based on2D square-lattice configuration. The single mode operation can be realized by compressing the width of bus waveguide. The impact of number of rows of holes on the propagating field intensity distribution was also analyzed. The physical parameters like dropping wavelength, dropping efficiency and spectral Q affected by changing the localized refractive index of inner ring and coupling strength between bus waveguide and PCRR were numerically demonstrated based on2D FDTD technique.The key contributions of this work are summarized. First of all, we described a comprehensive study of the modal behavior of a race-track PCRR-based CDF composed of square-lattice cylindrical silicon rods in air. Then, for the first time we demonstrated a race-track PCRR-based PBS composed of2D honeycomb-lattice cylindrical silicon rods combing the effect of line defect and perfect PC bandgap. Finally, a high-drop air-hole-type racetrack PCRR based on2D square lattice configuration was designed. All these findings offer a designed guideline for nano-scale photonic devices.