Topological States Of Classical Light And Associated Phenomena In Micro- And Nano-Photonic Structures

When the sizes of components in photonic devices decrease to micrometer or nanometer scale,the electromagnetic waves(EM)perform different propagation characteristics as they do in traditional photonic structures.By using the micro-and nano-photonic structures,lots of theoretical results and practical applications have been made in manipulating the flow of the EM.In 2005,Haldane extended the concept of topology in electron systems to the realm of photonics and developed the study of the topological photonics.From then on,topological states in micro-and nano-photonic structures has always been the research hotspot in recent years.By now,different photonic topological states have been realized in these photonic structures in microwave,infrared and visible frequencies.In the fields of photonics and optoelectronics,it is theoretically and practically import to realize different topological states of the classical light in different micro-and nano-photonic structures.This thesis explore engineering of the photonic topological states in micro-and nano-photonic structures and the associated properties of these topological states.The main points are listed as below.First,based on the perturbation theory,we study the effects of changing of parameters on the eigen frequencies of the magnetic photonic crystals(MPCs),and propose a simple and effective mothed to engineer the topological edge states in two dimensional(2D)MPCs.According to the structure of the MPCs and the field distributions of the Bloch points on the edge of the dispersion band,it is easy to engineer topological edge states in 2D MPCs through altering their parameters.In some concrete examples,we construct different photonic topological band gaps and topological edge states in 2D MPCs.Second,through altering the parameters of the MPCs,we find two types of flatband with different topology in 2D MPCs.One has trivial topology,and the other has nontrivial topology.Through numerical simulations and physical analyses,we study the physical origin and topological properties of these flatbands.The topologically trivial flatband originates from single scattering resonances of scatters or cavity modes encircled by scatters in MPCs,and the topological flatband comes from strong gyromagnetic coupling interactions of fields among neighboring unit cells.The Berry curvatures of topologically trivial flatband is zero in the whole Brillouin zone(BZ),while the topological flatband possesses slowly varied Berry curvatures in BZ.Inside the 2D MPCs,the radiation excited by a point source with frequency at the topologically trivial flat band can be easily cloaked by metal obstacles.In contrast,non-trivial flatband states can bypass the metal obstacles and propagate in 2D plane.Third,we study the photonic topological states in 2D amorphous magnetic photonic lattices(AMPLs).For a certain kind of 2D AMPLs,by using the supercell method,we construct 2D MPCs to mimic the AMPLs.By enlarging the size of the supercell,the amorphous MPCs can be regarded as the approximate equivalent of the AMPLs.Thus,the topological states of the AMPLs can be characterized by the topological property of the 2D MPCs.Through calculating the band structure of the 2D supercell MPCs,together with the analyses and simulations of the one-way edge states,we find that there exist stable photonic topological edge states in AMPLs.Also,large Chern number of the topological edge states can be realized in these AMPLs by changing the parameters of the systems.At last,we introduce our method to tune the light absorption by using the graphene material,that is,using graphene wrapped dielectric sphere to realize tunable infrared light absorption.Due to the resonance of the surface plasmons,graphene wrapped dielectric spheres perform strong light absorption in infrared region.By either tuning the dielectric constant and size of the spheres,or changing the Fermi level and the damping of graphene,the infrared light absorption of graphene wrapped spheres can be tuned easily.