Study On The Interactions Between Topological Photonic States Of Double-channel Magneto-optical Crystal Waveguides

Photonic crystals（PCs）are a kind of artificial microstructure which can regulate the behavior of photon transmission and the interaction between light and matter at the subwavelength scale.It is composed of the periodic arrangement of materials with different refractive indices in space.PCs generally have the basic properties of photonic bandgap and photonic localization,and in addition,their passband can produce novel physical effects such as slow light,negative refraction,self-collimation,and superprism effects under certain conditions.Due to the above unique properties,many designs of micro-nano photonic devices based on PCs have been proposed.Magneto-optic photonic crystals（MOPCs）are a special kind of PCs with magnetic response.They are usually composed of ferrite materials（such as yttrium iron garnet,YIG）arranged in a specific lattice type.In this paper,the slow light formation mechanism and the odd-even modes field characteristics of topological waveguide modes in MOPCs are studied.The coupling between two one-way boundary modes propagating in the same direction is studied,and the slow light state with zero-group velocity dispersion is obtained.In addition,the regulation of the insertion defect on the odd-even modes in the double-channel waveguide is studied,and the conversion between odd and even modes is realized.The main research work and conclusions are as follows:1.Study on the zero group velocity dispersion slow light effect based on the coupling of one-way topological photonic states.Firstly,a MOPC waveguide structure inserted with a metal layer is studied.A pair of degenerate band curves is found,which prove that there are two independent boundary topological states propagating in the same direction in the upper and lower sub-waveguides.Then,the metal layer is replaced by a double-channel Al₂O₃PC coupling layer,and the coupling effect of the upper and lower sub-waveguides in the double-channel waveguide is studied.It is found that the M1 fast and M2 slow waveguide modes can be obtained within the band gap by properly adjusting the radius of the Al₂O₃rods.It is found that the M1 mode is always a fast mode with large group velocity and large group velocity dispersion simultaneously,while M2 mode becomes a super slow light mode,which has the characteristics of near zero group velocity and zero group velocity dispersion at the same time.The physical origin of the slow light phenomenon is the strong coupling effect between the topological photonic states in the same direction in two sub-waveguides.Furthermore,the energy robustness（the property of anti-interference protection of energy transmission）of the two waveguide modes is studied.The results show that the energy robustness to the perfect electric conductor（PEC）defects is very strong,and the one-way transmittance is close to 100%.Finally,the transmission robustness（the property of anti-interference protection of the mode）of the slow light mode to the PEC is investigated.It is found that although the PEC defect can cause significant phase delay,the slow light transmission is not affected to some extent.In other words,the slow light mode still dominates the propagation process.These results bring new opportunities for many applications such as signal processing,optical modulation and the design of various topological devices.2.The studied of the characteristics and conversion of odd and even waveguide modes in double-channel MOPC waveguides.The MOPC structures of the double-channel waveguides with one-stranded and two-stranded Al₂O₃PC coupling layers are designed respectively.Different odd and even modes can be achieved by adjusting the strand number of Al₂O₃PC and the polarity of point light source.The energy band calculation and eigenfield analysis show that the one-stranded structure supports both odd mode and even mode,which are large group velocity waveguide modes.Although the two-stranded structure also supports odd mode and even mode,the odd mode is a fast-light mode,while the even mode is a slow-light mode.The energy transmittance of the super-cell structure was further studied,and it was found that the one-stranded structure was more sensitive to low frequency electromagnetic waves,while the two-stranded structure was more sensitive to high frequency light.The electromagnetic field distribution and odd-even model property of four waveguide modes are investigated.The effect of the defects of symmetrical and asymmetrical perfect electric conductor on the electromagnetic field distribution is studied.Combined with the analysis of the transmission robustness,it is found that the phase delay caused by the defect can have a certain effect on the electromagnetic wave transmission,but it can be adjusted by changing the defect parameters.Finally,by changing the length of the imperfection,the reversible conversion of the odd-even mode of the double-channel waveguide is realized.These results will provide important theoretical reference for mining novel properties of double-channel MOPC waveguides,and contribute to the design,optimization and application of micro-nano photonic devices in the future.