Nonreciprocal Propagation Of Electromagnetic Waves Based On Magnetic Metasurfaces

Generally,conventional optical devices are based on the reflection,refraction,and diffraction of light,meanwhile,the light path is determined by the thickness of the device to achieve the purpose of phase control.The cumulative optical path is usually proportional to the thickness of the device itself.As a result,the size of traditional optical devices is hundreds of times longer than the operating wavelength.Therefore,it is of great significance to design a new ultra-thin planar optical material which can adjust electromagnetic waves flexibly.In this dissertation,we design a metasurface consisting of a magnetic metamaterial.By tuning the bias magnetic field or tailoring the gradient of the metasurface,we can realize the nonreciprocal propagating behavior of the electromagnetic waves.In the first chapter,we introduce the background and the concept of metasurface.Meanwhile,the related properties and some of the current applications are presented briefly.Finally,we present the main research contents and the basic framework of this dissertation.In chapter two,we introduce some historical literatures on nonreciprocal propagation of electromagnetic waves.The graded photonic crystals can be used to achieve nonreciprocal propagation of electromagnetic waves.The magnetic metamaterials can also be employed to achieve this purpose.Besides,some other methods for realizing nonreciprocal propagation of electromagnetic wave by using a traditional material structure is also introduced briefly.In chapter three,we present the theoretical methods used in the dissertation.For the two-dimensional system consisting of single-crystal yttrium-iron-garnet ferrite rods,we first use the cylindrical vector wave functions to expand the incident and scattering wave,and then use the Mie scattering theory to derive the scattering coefficients of a single ferrite cylinder.Finally,we use the multiple scattering theory to derive the scattering properties of magnetic metasurfaces by calculating the photonic dispersion curves and the field patterns.Finally,the Goos-Hanchen shifts on a variety of magnetic metasurfaces are obtained and analyzed.In chapter four,we demonstrate the nonreciprocal propagating behavior of electromagnetic waves by engineering a magnetic gradient metasurface consisting of an array of ferrite rods.We reveal the physical mechanism behind the phenomenon from the perspective of photonic band diagrams.Due to the dependence of the metasurface on the bias magnetic field,the nonreciprocal propagation of electromagnetic wave can be controlled by either tuning the bias magnetic field of the system or tailoring the gradient of the metasurface.Because of the time-reversal-symmetry breaking nature of magnetic system,for the Gaussian beam incident from one side there appears an obvious Goos-Hanchen shift,while for the Gaussian beam incident from the symmetric other side the Goos-Hanchen shift is vanished.This reflects the nonreciprocal property of the Goos-Hanchen shift,which is caused by the permeability tensor.Finally,we design a unidirectional waveguide by using the magnetic metasurface.In the last chapter,we summarize the results of the dissertation.An outlook on the future works and potential applications of the magnetic metasurface is presented.