Design Of Unidirectional Photon Transmission Device Based On Topological Protection

In the process of photon information transmission system designing,the on-chip system will be affected by optical path bending,local defe cts and other factors.So it is very important to develop a technical means to control the photon at the micro-nano scale.Topological photonics,being similar to the concept of topological insulators in electronics,can construct optical paths with hi gh robustness in the boundaries.In this paper,the topological phases of electrons are obtained based on valley Hall quantum effect and Hall spin quantum effect without breaking the symmetry of time inversion.In this paper,we design a two-dimensional photonic topological insulator based on ordinary hexagonal silicon substrate under the valley Hall quantum effect.The proposed structure has primitive cells with in-plane C3 rotational symmetry composed of air holes etched on a silicon substrate.By obtaining mirror symmetry with respect to the protocell,Dirac point is placed on the point K.The mirror symmetry is broken by moving the air block to the hexagonal lattice angle.Open the degeneracy at the Dirac point,and creat different topological states in the valley in the sum points K and K' that depend on the direction and intensity of the movement.In addition,the valley topology boundary states between the two topological structures have non-monotone dispersion,indicating that different wave vector topology edge states exist at the same frequency.The influence of the valley hall effect on the direction of unidirectional transmission and the existence of a beat-like propagation due to the degeneracy of edge states are studied.A two-dimensional photonic topological insulator based on ordinary quadrilateral lattice air substrate is designed under the Hall spin quantum effect.Build photonic crystals by embedding in the background of air dielectric cylinder and get degeneracy by folding bands in cells when placing dielectric cylinders periodically.Then the space symmetry is broken by changing the minimum periodic element of the photonic crystal cell to achieve different pseudo spin Chern numbers and finally the topological boundary state at the interface is realized.By simply changing the diameters of the constituent cylinders,important topological phase transitions of the cylinder and its edges can be realized.In addition,the influence of local defects of photonic crystals on the transmission effect is also studied on the basis of the structure,which proves the high robustness of this design.Our results not only provide an alternative method to control the state transmission at the edge of the topology,but also provide a topological method to guide and capture electromagnetic waves.