Transmission Regulation Of Anti-Scattering Electromagnetic Wave Based On Topological Artificial Electromagnetic Structure

Artificial electromagnetic structures exhibit unique advantages in controlling the transmission of electromagnetic waves due to their periodicity and the presence of electromagnetic band gaps.However,during the transmission of electromagnetic waves,severe scattering may occur when encountering bending or defects.With the development of on-chip micro-nano technology,micro-nano devices based on photonic crystal have made great progress in manipulating terahertz and optical waves.However,waveguide with sharp bends and defects may exist due to integration factors and manufacturing deficiency,which will result in scattering losses that limit the development of photonic devices.In recent years,inspired by topological insulators in condensed matter systems,the concept of topology has been introduced into photonic crystals.Topological photonic crystals,as analogues of electronic topological materials,exhibit unique topological phenomena in electromagnetic characteristics,particularly in terms of unidirectional,defect-immune,and scattering-free propagation of electromagnetic waves.The paper is mainly focused on constructing topological artificial electromagnetic structures analogous to the quantum valley Hall effect.By maintaining the time-reversal symmetry and breaking the spatial inversion symmetry,we aim to control the transmission of light and manipulate the localization of light.The main research contents are as follows:1.Topological valley photonic crystals based on two-dimensional composite lattice structures are realized in analogy with quantum valley Hall effect.In the two-dimensional honeycomb lattice structure,the spatial inversion symmetry is broken by adjusting the size of the petal-like aperture to realize the transformation of valley topological phase,and the topologically protected edge states appear at the interface between two distinct topological structures with different valley Chern number.The relationship between the topological invariants and the perturbations in the Hamiltonian is studied theoretically,besides the conditions for the existence of valley edge states are revealed.The relationships between the berry curvature distribution,the valley Chern numbers and the degree of symmetry breaking of valley photonic crystals are analyzed by numerical calculations.The existence of the topological edge states is verified by constructing the valley topological waveguide structure,and the characteristics of edge states with different interface types are analyzed.These topological edge states with robustness to sharp bends and immunity to defects and disorders are analyzed.At the same time,valley transmission in terahertz regime is realized by using the valley photonic crystal plate.In metal photonic crystals,the topological phase transition of metal valley photonic crystals is also realized by rotating the Kagome lattice structure to break the mirror symmetry.Two different topological structures through rotating different angles are used to construct an ultra-wideband topological waveguide with robustness to backscattering.In addition,the topological higher order states are realized,and the topological corner states with high locality are found at the 60° corner of the triangular interface constructed by two different topological structures.2.Based on nematic liquid crystals(LCs),topological valley photonic crystals with reconfigurable electromagnetic pathways are proposed under electronically controlling.Compared with the previous reconfigurable photonic topological insulators realized by mechanical controlling,this scheme of reconfigurable electromagnetic pathways is more flexible and convenient.The direction of the long axis of the liquid crystal molecule will be deflected under the applied bias voltage,and then the aniso-tropic permittivity of nematic LCs is tunable under different bias voltages.In the designed honeycomb lattice,the spatial inversion symmetry of the lattice is broken by changing the permittivity of nematic LCs filled in the dielectric cylinders to realize the topological phase transition by electronically controlling.The elements “0” and “1” of the supercell in the array structure are digitally encoded,and these two elements can be switched between each other by the programmable device under the electronically controlling.Then programmable valley topology photonic crystal with reconfigurable electromagnetic pathways is designed.3.Based on nematic liquid crystals,the valley photonic crystal with reconfigurable edge states and corner states is proposed under electronically controlling.The nematic liquid crystals are filled into the aperture of petal-shaped valley photonic crystal.The refractive index of LCs filled in the apertures is varied under electrically controlling to adjust the band gap of the valley photonic crystal,and further manipulate the working band.Then the tunable optical switch and energy splitter are designed.At the same time,the topological higher order states are discovered in the designed structure,and the operating frequency of the topological corner state can be adjusted by electronically controlling,and the transformation between edge states and the corner states are also realized.In topological photonic devices with fixed configuration,the edge states and corner states can be controlled flexibly by electronically controlling,then the dynamic regulation of electromagnetic wave is realized,which will have some potential values for exploring integrated topological photonic devices.4.A wide channel terahertz waveguide with quasi-two-dimensional topological waveguide states is proposed.These two-dimensional topological waveguide states are realized based on artificial surface plasmon photonic crystals.Through the three-layer sandwich structure,the traditional one-dimensional topological edge state can be extended in space,and then these quasi-two-dimensional topological waveguide states with the freedom of aperture width are implemented.These topological waveguide states have unique unidirectional backscattering-immune features under bending and beam splitting.Note only does the designed terahertz topological waveguide structure improve the transmission efficiency of terahertz surface waves,but also realizes the high flux transmission of terahertz surface waves.