Transmission Of Double Layer Topological Resonance Loop Under Magneto-optic Effect And Coupled Mode Analysis For Magnetic Grating

Nonreciprocal transmission has become a new method to control optical flow,and provides an unprecedented means to develop various photonic components,including optical waveguides and optical isolators that are immune to structural defects.However,at present,the photonic crystal nonreciprocal waveguide based on the gyromagnetic medium can only work in the microwave band due to the serious absorption of the gyromagnetic medium in the optical band,and lacks the dynamic modulation method.On the other hand,the gyroelectric medium can work in the near-infrared or optical band,but the magneto-optical effect is very weak,and it is difficult to produce a strong robust nonreciprocal waveguide.Diffraction grating is an important component in modern optics,and rigorous coupled mode analysis is its basic research method.But so far,most of the grating materials are ordinary media,so their transmission characteristics are fixed and cannot be modulated.In this thesis,based on the principle of metamaterials,two-dimensional magneto-optical photonic crystals are designed using the gyroelectric background material and ordinary dielectric cylinders,which not only improve the magneto-optical effect of the structure,but also convert the working wavelength of the unidirectional boundary state from the microwave band to the near-infrared or optical band.We first study the topological properties of the photonic crystal through calculating and analyzing the number of its energy bands,and demonstrate the existence conditions of the edge state and the possibility of forming a circuit.In order to expand the application of nonreciprocal waveguide according to the optical flow control,a two-layer nested topological loop is designed.The group velocity of nonreciprocal mode is changed by the modulation of external magnetic field.As the transmission of the loop will result in conductive interference or deductive interference,the change of magnetic field will change the optical length of the loop for the nonreciprocal mode of a specific frequency,thus changing the interference phase of the loop.If a circuit meets the condition of conductive interference,it will be excited;If the structure has interference cancellation,it cannot be excited.Therefore,under the modulation of magnetic field,the optical signal of the system can circulate in different loops,realizing the purpose of dynamic modulation.For a fully closed cycle,the resonant mode has a high Q value.The structure model has two-fold functionalities: waveguide and resolator.This study provides a new method to the design of topological waveguide loops and dynamic modulation.At the same time,In order to realize the grating which can be dynamically modulated,a grating made of magnetic materials,called magnetic diffraction grating,is designed in this thesis.In order to promote the research of magnetic diffraction gratings,we developed a calculation formula of magnetic diffraction gratings based on rigorous coupled wave analysis and magnetic materials,which is used to analyze its transmission law and calculate the diffraction efficiency.Because of the existence of the non-diagonal dielectric tensor of magnetic materials,the traditional rigorous coupled mode formula needs to be corrected.In this thesis,all formulas are based on Maxwell equations,Floquet conditions and boundary conditions of periodic structures.Rigorous coupled wave analysis based on magnetic media will play an important role in modern optical research.The main results of this paper are as follows:1.Through the design principle of metamaterials,a new magneto-optical medium and a new topological waveguide are constructed.The waveguide not only has strong magneto-light effect,but also expands the working band from microwave segment to optical wave segment,which provides an important scheme for the design of future optical integrated loop.2.Design the two-layer topological loop,compared with previous studies,the design effectively expands the density of the channel.3.The transmission mechanism of the two-layer topological loop under magnetic field modulation is studied.Compared with previous studies,the transmission path and direction of the topological loop can be dynamically modulated by the external magnetic field or the frequency of the source,which effectively improves the application value of optical communication in the future.4.We deduce the formula of the theoretical calculation of magnetic grating,which provides an important reference for the development and design of magnetic grating.