Investigation On Transmission Characteristics And Application Of Unidirectional Edge Modes In Two Dimensional Photonic Crystals

Recently,investigations on transmission characteristics and application of one-way edge modes in photonic crystals have been popular with widely researchers in the world.The paper mainly has studied the nonreciprocal phenomena for unidirectional edge modes of electromagnetic wave in the photonic crystals based on Quantum Hall effect.We have presented couple model of one-way edge modes,and realized the unidirectional air waveguide with great transmission characteristics.According to waveguide-cavity interaction,we have constructed two waveguide ring resonators with dynamically manipulation for photonic energy.Furthermore,we have proposed a all-dielectric topological photonic crystals structure,achieved a robust unidirectional helical edge states,etc.Mainly study contents as the following:?1?The breaking of the magneto-optical photonic crystals system time-reversal symmetry with the external magnetic field applied,photonic crystals system could realize unidirectional edge modes.Based on the transmission features of unidirectional edge modes,such as completely suppressed backscattering,immunizing from defect surface imperfections,and edge modes couple theory,presented coupling models of two one-way edge modes.The one were constructed in two semi-infinite two-dimensional magneto-optical photonic crystals with a triangle lattice,a unidirectional air wavuguide with extra-broad operation bandwidth,low-loss,single-mode was achieved.The unidirectional air wavuguide was realized by the same propagation group velocities by applied opposite magnetic fields to two semi-infinite parts.To study the influence of edge modes coupling effect on line waveguide width,calculated projected band dispersion curves of model along the wavevectork_x.Additionally,to test the unidirectional air wavuguide achieved transmission features,employed S parameter calculating the transmission energy loss,get the waveguide working bandwidth,the optimum working frequency parameters.The other one were constructed in two semi-infinite two-dimensional magneto-optical photonic crystals with honeycomb,a unidirectional air wavuguide with energy-condensed,low-loss,strong-stability,great nonreciprocity was achieved.Similarly,based on the same analysis methods,have studied coupling effect of self-guiding edge modes.Results showed,the unidirectional air wavuguide realized by the modeling were extra-stability,zero-loss.?2?Based on the waveguide-cavity interaction,we have proposed a coupling model between a line defect waveguide and two cavities with one-way rotating states in a gyromagnetic material and a ordinary material.Here we have calculated photonic band gaps,projected band dispersion curves of a line defect waveguide,the dispersion curves of waveguide-cavity interaction,and systematically analyzed the relation among them.By emulating simulations based on finite element method,have observed a series of relevant interesting coupling resonance phenomena of waveguide-cavity.By taking advantage of propagation direction of one-way edge modes controlled by the direction of external magnetic field applied,have designed a configuration that can realize dynamically storing and discharging of photonic energy in optical circuits.?3?Based on topological properties of topological photonic crystals fully preserving the graphene C_6VV symmetry,such as topological symmetry,topological phase invariability,we have induced and demonstrated photonic pseudo-time-reversal?TR?symmetry analogizing to that of electric system.By expanding and compressing the scale of graphene cell under fully preserving the graphene C_6VV symmetry,have realized the doubling Dirac zone separation at the?38?in the First Brillouin Zone,opening photonic bands,modes inversion.Here we have performed an investigation on the influence of frame parameters,such as lattice constant,dielectric permittivity of cylinders,dielectric cylinder radii,scaling factor,etc.on the bandgaps of topological PCs structure,and proposed a topological photonic crystals structure supporting robust unidirectional helical edge states interface between a topological trivial and non-trivial photonic crystal.We have achieved a robust unidirectional helical edge states with broad operation bandwidth,supporting topological protect and robustness,its transmission direction depended on the orbital angular momentum of electromagnetic wave.Furthermore,we have tested the robustness and tunability unidirectional helical edge states for different cases,such as t Z-shaped channel,defect structure,sharp bend.