| As a kind of artificial microstructure material,photonic crystal has become a research highlights of many researchers because of its strong ability to control the photon path.In recent years,the research on the transmission characteristics of nonreciprocal waveguides has always been the research content with great potential for scientific application in the direction of photonic crystals.Unidirectional boundary states are the most important components of nonreciprocal optical waveguides.Based on the unidirectional boundary mode,this paper studies the unidirectional electromagnetic boundary mode in square lattice magneto-optical photonic crystal and its application,and further studies the unidirectional electromagnetic boundary mode in Sunflower quasi periodic magneto-optical photonic crystal by analogy.The main work of this paper is as follows:1.A Sunflower 8-fold quasi periodic magneto-optical photonic crystal structure is designed by finite element analysis.Taking YIG as the material,based on the material and structural parameters of two-dimensional square lattice magneto-optical photonic crystal with air line defects,the slow light waveguide and unidirectional air waveguide are realized in the Sunflower quasi periodic YIG magneto-optical photonic crystal structure with mirror symmetry but no translation symmetry in rectangular coordinate system by analogy.When the coupling distance is1.5a,the best slow light waveguide and unidirectional air waveguide can be realized.Because of the eight fold symmetry of the structure,this kind of line defect can be constructed in multiple channels to realize unidirectional air waveguide and slow light waveguide modes.2.Starting from the application of unidirectional waveguide,a Sunflower type cross waveguide model is constructed by constructing line defects in the horizontal and vertical directions of Sunflower type 8-fold quasi periodic magneto-optical photonic crystal structure.By controlling the applied bias magnetic field,two applications based on unidirectional air waveguide are realized.The first is the T-type beam splitter,which not only realizes the beam splitting of electromagnetic wave,that is,when the electromagnetic wave originally transmits from the left branch of the horizontal waveguide to the right branch of the horizontal waveguide,a right angle turn occurs in the center of the horizontal waveguide,and it transmits unidirectionally to the upper and lower branches of the vertical waveguide respectively.At the same time,in the process of beam splitting,the mode of electromagnetic wave is also converted from the unidirectional air waveguide mode in the left branch of the horizontal waveguide to two backward slow light waveguide modes.The second is a Sunflower type four port circulator,which has simple structure,easy integration and relatively high isolation.In a specific frequency range,the isolation can reach 100%,realizing the four port ring function.3.In the square lattice magneto-optical photonic crystal module matrix,the unidirectional air waveguide can be realized by controlling the applied bias magnetic field 1× 1?2×2?3×3 kinds of optical path splitters of type 3 matrix module structure.By coding the external bias magnetic field of each module,the optical transmission path can be accurately controlled,which can be used to achieve flexible control of the transmission path.Then,the same way was used to precisely control 4×4?5× 5...n×n-type optical path matrix.This kind of coding control process only needs to change the external magnetic field,so in the case of using DC to provide the magnetic field,the coding can be realized by controlling the electric switch,that is,it is easier to control through computer programming.This method provides a new idea for accurately controlling the transmission path of light,and helps to improve the speed of information transmission and processing. |
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