Magneto-optic Effect Enhancement And Nonreciprocal Transmission Based On Gyromagnetic Metasurface

Electromagnetic nonreciprocity refers to the different transmission properties of electromagnetic waves in forward and reverse channels,which has been one of the academic frontiers and research hotspots.It is worth noting that waves have reciprocity during propagation in conventional media,and lorentz reciprocity theorem makes it impossible to generate nonreciprocal electromagnetic responses in non-magnetic,linear and time-invariant media.The urgent demand of non-reciprocal devices stimulates the active exploration of new nonreciprocal mechanisms in the academic world and promotes the continuous development of integrated devices with strong isolation performance.The realization of electromagnetic nonreciprocity is highly dependent on the time reversal symmetry breaking of the system.In order to break the electromagnetic reciprocity,scientists have proposed various design methods in optical and microwave bands,such as magneto-optic effect,refractive index space-time modulation,nonlinear modulation and photoelectric control.Magneto-optic effect is extensively used technique,which destroys the time reversal symmetry of magneto-optic crystal by applying external static magnetic field to the gyromagnetic material.The breaking can generate magneto-optic effect and realize the purpose of nonreciprocal electromagnetic wave transmission.Despite its success in industrial production,it is incompatible with mature semiconductor technology and has significant loss problems.In addition,with the rapid development of two-dimensional artificial subwavelength structures,new concepts such as Snell’s law,Huygens’ metasurface,surface impedance holography,reconfigurable and programmable metasurface are proposed,which provide new theoretical methods for manipulating electromagnetic fields and waves.In this dissertation,we combine the design concept of metasurface and the nonreciprocal properties of gyromagnetic materials to explore the magneto-optical effect enhancement mechanism and nonreciprocal transmission devices.We discuss the application of gyromagnetic metasurface in nonreciprocal isolators and nonreciprocal antennas.The following is a summary of the innovation points and research content of this dissertation:1.We propose theoretically that magnetic resonance(hereinafter referred to as magnetic particles)generated by optically doped(In this dissertation,doping refers to the addition of micro-structured particles with specific electromagnetic modes to the background material)gyromagnetic materials can enhance the magneto-optic effect of the gyromagnetic materials,enabling nonreciprocal transmission enhancement without changing the chemical composition of the materials.This concept originated from photonic doping of near-zero medium,which is similar to the doping method in semiconductor.We can introduce doped elements into near-zero medium to improve the macroscopic effective permeability and dielectric constant of the medium.In this dissertation,we extend the doping theory to the field of nonreciprocity.We analyze the optical rotation characteristics of magnetically doped gyromagnetic materials,and draw the conclusion that both the gyromagnetic and gyroelectric properties will be enhanced at the same time.The magneto-optic effect is tuned in low bias magnetic media with a spin-magnetic ratio close to zero,and a nonreciprocal isolator with low bias field,thin thickness and strong robustness to external field disturbances is realized.We analyze the design method of nonreciprocal enhancement based on magnetic photonic crystal.In the magnetic photonic crystal material,the applied bias magnetic field causes the band structure to split and produce a nonreciprocal one-way surface state,which is robust to obstacles and defects.2.In recent years,with the development of metasurface,the design of various electromagnetic devices using spatial wave and field has been greatly promoted.In this dissertation,a design method of electromagnetic wave nonreciprocal transmission using metasurface with external bias magnetic field is proposed.The designed magneto-optic metasurface consists of a nearly zero-rotating magnetic material plate doped with magnetic resonance impurities.The results of microwave measurement show that the metasurface has strong magnetic resonance effect and can be used as a circular polarization chiral isolator.We also prove its signal isolation capability to circularly polarized antennas and realize the application of circularly polarized nonreciprocal antennas.3.A metasurface with nonreciprocal polarizing filter is realized based on gyromagnetic materials.The design of nonreciprocal polarizing filter polarizer with chirality reversal is explored.The selective reflection or absorption of different circularly polarized electromagnetic waves is realized.The reflection is nonreciprocal.The simulation design of the metasurface and the experimental verification is carried out in microwave band.The experimental data show the effectiveness of this method.It has great potential application in the space isolation design of receiving and transmitting components in advanced electrical systems.To sum up,some research achievements have been made in the basic properties of gyromagnetic materials,enhancement magneto-optical effects and nonreciprocal devices by the design of metasurface and magnetic dope.