Design and analysis of heterostructure based tunable nanophotonic resonators with high Q and low mode volume

Abstract

The primary purpose of this thesis is to design a high quality factor (Q) and low mode volume nanophotonic resonator which can be tuned using external stimuli, e.g., voltage. Based on the existing designing algorithms as well as novel observations, several nanophotonic resonators are designed and their confinement capabilities are compared using a series of FDTD calculations. Different electro-optic materials are adopted as base materials of the resonators in order to implement tunability. The suitability of the used materials for the resonators are discussed In order to implement tunability, it is vital to know the detailed material properties. The optical properties of BaTiO3 are not available in sufficient detail among the published literature. First principle calculations are employed to calculate the detailed optical properties of BaTiO3. A brief primer on the first principle calculation followed by the detailed results of the calculations are presented. Then, suitable analytical method of calculating the optical properties of Graphene is selected from literature and presented along with a discussion regarding the incorporation of Graphene in photonic crystal calculations. Once the base materials are discussed, a detailed analysis of a novel defect based nanophotonic resonator is presented, which is superior to traditional L3 cavities. The resonant properties of the designed cavity is analyzed and optimized. Then, a defectless band-edge cavity is designed by confining the slow light modes. It is shown that the band-edge resonator is superior to the defect based cavity. After that, a double heterostructure (DH) cavity is defined on a rectangular lattice. This cavity is unique because it can confine modes of both transverse electric and transverse magnetic symmetry. Subsequently, extending the concept of heterostructure, an analytical design for a multi-heterostruture (MH) nanophotonic resonator is presented. It is shown that the MH cavity is superior to the other cavities in terms of confinement capabilities. Finally the designed resonators are studied for possible tunability in the presence of applied voltage. It is observed that when ferroelectric BaTiO3 is used, the tuning is switch-like, with two stable resonant modes, between which the resonator can be switched using applied voltage. On the other hand, when is Graphene is used, the tuning is continuous. The resonant properties of the resonator change gradually with applied voltage. However, the highly conductive Graphene greatly reduces the Q of the resonator. The study shown that gradual confinement in theMH and bandedge resonator produces much better confinement performance. Furthermore, ferroelectric materials produce switching like tunability where as Graphene produces continuous tunability – at the cost of lowered confinement capabilities.