Manipulation Of Light Emission With Optical Antennas

The manipulation of light emission with an optical antenna and its applications are the hotspots in the research of micro-nano optics. An optical antenna is a nano device that efficiently converts propagating lights into local modes or vice versa and thus makes a bridge between near field and farfield. Because of the highly localized field enhance-ment and good directivity, optical antennas are used in the high efficient and directional radiation of localized quantum emitter. Optical antennas are applied in the progress of electromagnetic energy coupling, converting and coherent control and have wide appli-cations in fields as single molecule sensing, localized lasing. nano photoelectron chips and quantum manipulation. This thesis focuses on the ability of spontaneous emission enhancement of optical antennas along with the radiation efficiency and directivity. The nonlocal effects in small gaps are also taken into consideration.The main research works of this thesis are summarized as follows:1. Based on multisphere dyadic Green’s function, the interaction between a dipole source and a metal lo-dielectric hybrid optical antenna is investigated. In order to charac-terize spontaneous emission enhancement and radiation efficiency simultaneously, the parameter of radiation enhancemnet is introduced. The metal lo-dielectric hybrid optical antenna is formed by combining dielectric nanospheres with silver nanospheres. It can achieve high Purcell factor as well as high radiation efficiency for broadband operation.2. The mode features and manipulation of light emission of optical patch anten-nas are investigated. A silver nanosphere is coupled to hyperbolic metamaterial(HMM) multilayers to form a optical patch antenna. By tailoring the radius of the silver nanosphere and the ratio of silver and silicon layers in the multilayers, the excitation of the bulk mode of the HMM multilayers is enhanced. Nonocuboid optical patch antennas are de-signed to support different gap modes. Among them, the interaction between electric and magnetic mods provides a new means to tailor the properties of light emission. By placing a electric dipole at an asymmetric position in the gap of the nanocuboid optical patch antenna, electric and magnetic modes are both excited. And by tailoring the ge-ometry of the nanocuboid patch, an in-plane unidirectional radiation is realized when the electric and magnetic modes overlap with each other.3. The nonlocal effect on the spontaneous emission enhancement of a silver nanocuboid dimer is investigated using a local analogue model. Magnetic as well as electric dipole excitations are introduced to excite different gap modes. The nonlocal response of elec-tric and magnetic modes on various gap parameters(width and refractive index) are in-vestigated and compared to the local responses.Highlights of the thesis are as following:1. To overcome the dilemma that metallic optical antennas provide high Purcell factor as well as high loss and dielectric antennas are free of metal loss but have low Purcell factor, a metallo-dielectric hybrid optical antenna is introduced. By exploring the dependence of the radiation enhancement of the system on different geometry pa-rameters, high Purcell factor as well as radiation efficiency is achieved for both single peak and broadband operation.2. A silver nanocuboid optical patch antenna is designed to control the radiation directivity. By introducing the asymmetric excitation, the interaction between electric and magnetic modes is achieved in the simple design of a single nanocuboid optical patch antenna. And in-plane unidirectional radiation is therefore realized.3. Nonlocal effect in very narrow gaps are investigated under magnetic dipole excitation as well as electric dipole excitation. Not only the width of the gap but also the refractive index is considered when assessing the strength of the nonlocal effect.