Research On Optical Waveguide Based On Bound States In The Continuum Of Photonic Crystal

In recent years,it has found that it is a canonical way to realize abnormal refraction phenomena by utilizing the spatial dispersion of the photonic crystal,including but not limited to the comprehensive manipulation of space-time wave packet,self-collimation non-diffraction transmission,super prism and negative refraction.At the same time,all dielectric photonic crystals with topological properties can be realized by utilizing the liner dispersion relation of Dirac cone in photonic crystal band structure.Due to the unidirectional light guiding and robustness to disorder effect,topological photonic crystals have received extensive attention recently.Although various types of optical waveguides based on photonic crystal have been demonstrated,negative refraction photonic crystal waveguides are still strictly dependent on the total internal reflection(TIR),which would superimpose a cutoff frequency and affect the further application of negative refraction waveguides on optical chips.In addition,all-dielectric topological photonic crystal generally relies on two photonic crystals with different topological properties to form light guiding interfaces.Although it has a high unidirectional guide light capability,its large size will hamper it from chip scale application.Therefore,in order to break these limitations,this thesis aims to focus on new guiding wave mechanisms working beyond the light cone and their applications,which might provide new prospective for the on-chip application of photonic crystal optical waveguides beyond the light cone.Specific studies are as follows:(1)Aiming at the limitation of cutoff frequency in negative refraction waveguides based on TIR,we design a negative refraction waveguide operated beyond the light cone,whose guiding mechanism is provided by the bound states in the continuum(BIC).Because of the high-quality factor of BICs,the light can be localized in the waveguide even in the radiation continuum,which provides the possibility for the design of a new type optical waveguide.Firstly,we use finite element method(FEM)to carry out the numerical simulation,and then verify the numerical results through microwave experiments.This kind of negative refraction waveguide would provide a new research idea for mode coupler and multiplexing technology in the future.(2)Aiming at the volume limitation of topological photonic crystals that is too large for onchip integration applications.Combining the concept of BIC with traditional topological photonic crystals,we propose a new concept of bound topological edge state in the continuum,where a topological photonic crystal waveguide works beyond the light cone.Firstly,we design the topological crystal by using FEM and analyze the possibility of realizing bound topological edge state in the continuum through numerical simulation.Finally,the numerical results are verified by using microwave experiments.The proposed bound topological edge states in the continuum will facilitate the development of topological single-mode lasing,sensors and other topological photonic devices.