Study On Optical Phenomena In Micro-and Nano-photonic Structures Based On Scattering Theory

With the development of nanotechnology,micro-and nano-photonic structures have made unprecedented progress in recent thirty years and become one of main topics in the fields of photonics.Micro-and nano-photonic structures aim to control the transmission,absorption and emission of light through the structural design of materials.Among all of the micro-and nano-photonic structures,that composed of micro-and nano-particles occupy an important position.Micro-and nano-particles can exhibit strong Mie scattering with external excitation.The multipolar resonances of the particles and their coupling can be tuned through the structural design,which allows us to realize many interesting phenomena,for example,plasmonic cloaking and lasing in core-shell particles,strong toroidal response in nanoparticle clusters,et al.So far,the structures composed of micro-and nano-particles have been widely investigated.However,there are still many questions that need further investigation,such as theoretical analysis for plasmonic modes.In this paper,according to the complexity of the structures,we investigate three different micro-and nano-photonic structures:dielectric-graphene core-shell nanoparticle,metal nanoparticle clusters and periodic array of dielectric rods.Based on the scattering theory,we study the interaction between the multipoles of particles and explain the optical phenomena.The main structure of this paper is arranged as follows:In the first chapter,we briefly introduce the Mie scattering theory and summarize the research status of the three micro-and nano-photonic structures: particles,clusters and periodic structures.Meanwhile,the optical phenomena involved in this paper are described in detail.In the second chapter,we introduce the theoretical methods which are applied in our work,including multipole expansion,coupled-dipole equation and layer effective medium theory.At last,we briefly introduce the simulation software used in this paper.In the third chapter,we propose a tunable terahertz cloaking and lasing by the optically pumped graphene wrapped on a dielectric cylinder.Based on the scattering cancellation of dipole resonances of graphene and dielectric cylinder,we realize the terahertz cloaking.According to the gain effect of graphene under optical pump,we realize the terahertz lasing with the strong interaction of the localized surface plasmon mode and gain amplification of graphene.Besides,because the gain of graphene can be continuously tuned by pumping light,the cloaking and lasing are tunable,meanwhile,the cloaking and lasing can also be transformed in one structure.In the fourth chapter,we study the angular dependence of plasmonic modes of plasmonic nanoparticle clusters with rotational symmetry.The optical response of the clusters is investigated based on the analytical solutions of plasmonic modes obtained with the eigen-decomposition method.With the analytically obtained excitation efficiency and extinction cross section of the plasmonic modes,the angular dependent optical response of the nanoparticle clusters can be explained clearly: if the particle number of clusters is odd,all of the plasmonic modes are angle-independent,while for even number cases,there is a non-degenerate antisymmetric mode which is very sensitive to the incident angle and others are angle-independent.In the end,we analyze the reason of the presence of negative extinction cross section and the realization of directional scattering.In the fifth chapter,we study the interface states and bound states in the continuum(BICs)in two photonic crystals(Ph Cs)with different lattice constants.We find a band folding effect of interface states in the common band gap of the two Ph Cs,and we demonstrate that the existence of interface states can be determined by the surface impedance of the two Ph Cs.Because the lattice constants of the two Ph Cs along the interface direction are different,the projected band structures will be folded.Therefore,some part of interface states penetrates the region of folded bulk bands and turns to guided resonance modes.However,because the interface state at the(38)point and the corresponding bulk mode are in different symmetries,the interface state at the(38)point is perfectly localized and forms a symmetry-protected BIC.These findings may provide a general scheme for designing BICs based on the interface states.In the last chapter,we summarize the works during Ph D study time and give an outlook for further researches.