Study On Transport Properties Of Topological Interface States In Photonic Crystals

In recent years,the topological photonics has entered a period of rapid development.By analogy with topological insulators in condensed matter physics,optical topological insulators can be realized by using photonic crystals which are artificial periodic structures.Photonic crystals have the advantages of simple fabrication and low loss,and become a good platform to achieve realize topological transport of edge state,which can be utilized to manipulate electromagnetic wave and design novel topological optical devices.The prominent feature of topological insulators is unidirectional transport of edge state,which immune to the defect and disorder.The flexibility and diversity of the photonic crystal structure also provide more possibilities for exploring new topological models.In this thesis,novel topological phenomena in optical systems have been observed by numerical simulation and microwave experiments using two-dimensional photonic crystal with hexagonal lattice,and new ideas and methods have been provided for the future development and design of photonic crystal devices.Firstly,the topological theory in condensed matter physics and the development of photonic topological insulators are introduced.Firstly,the development of Hall effect in condensed matter physics and the related concepts of topology are briefly discussed.Then,the development and properties of photonic crystals is reviewed.Finally,the typical models in photonic topological insulators are listed,such as quantum Hall effect,and quantum spin Hall effect.Secondly,the topological phase transition is realized by adjusting the coupling between the inter-and intra-distance of dielectric cylinders in unit cell of twodimensional topological photonic crystals with artificial honeycomb lattice.In addition,we study the interesting properties of topological photonic crystals.Based on the finite size effect,the band dispersions of interface states open a band gap.By changing the width of the photonic crystal in the transport of electromagnetic wave,the selective switch of interface states is also realized,and the phenomena of pseudo spin preserving and pseudo spin flipping are observed in microwave experiments.We also design a multi-tunneling device using a finite width photonic crystal.The design of pseudo spin switch provides a new possibility for controlling the transport of topological edge states and also paves the way for the design of optical devices.Then,we propose a two-dimensional amorphous photonic crystal structure with short range order and long-range disorder.By rotating the dielectric cylinder in a unit cell randomly,the long-range order of the lattice is changed,and it is proved that the edge state still maintains one-way transport under a certain disordered strength.In the proposed structure,we also study the energy division of edge states at the junction of four topological channels.This result is also observed in microwave near field scanning experiments.This study provides a platform for further study of amorphous topological photonic crystals and reduces the difficulty of optical devices in practical application.Finally,we summarize the main work of this thesis.The research in this thesis is mainly based on the knowledge of topological physics to design and control the propagation of electromagnetic waves in photonic crystals,and provides platform for the application of topological optical devices.