Study On Unidirectional Waveguide In Two-dimensional Topological Photonic Crystal

In the field of electronic computers,diodes play a very important role in the construction of logic circuits.Correspondingly,the design of photonic diodes is also an important issue for the realization of optical logic circuits.In view of the development of photodiodes,the current implementation approaches involved mainly include adding nonlinear materials or isolator methods based on the Faraday effect.The main problems faced by these approaches are high energy consumption,large volume,and unfavorable integration.Realizing the one-way transmission of light waves under the energy of high,this is a new problem that people are facing,and new ideas are needed to solve it.The discovery of topological photon states has given people a new understanding of light wave transmission and scattering.At the same time,the introduction of topological concepts has given traditional photonic systems new characteristics,such as unidirectional propagation of boundary states,robustness of defect immunity,non-defect immunity and backscattering,etc.,these characteristics can provide a certain reference value for the design of new optical waveguides.Systems such as photonic crystals and metamaterials have become important optical topology research platforms.The main advantage of photonic crystals is that they are flexible in design.Various types of waveguides and various new optical devices can be easily prepared by changing their structure and parameters.Based on optical pseudospin and valley pseudospin,two photonic crystal structures that can realize wave unidirectional transmission are designed in the thesis.Since this structure does not need to use nonlinear effects,it does not require a high-energy background environment to activate the unidirectional transmission effect.Low application threshold;at the same time,the structure has the characteristics of small size and easy integration,and is suitable for integration in photonic circuits.The main contents are as follows:（1）Based on the optical pseudo-spin,by expanding and stretching the hexagonal honeycomb structure of Si material,two basic structures of photonic crystals with different topological properties are constructed,and the structural lattice constant,column dielectric constant,column radius and structure are studied.The influence of parameters such as the degree of expansion and contraction on the band gap.On the basis of the analysis results,a stable two-dimensional topological photonic crystal structure is proposed,which can realize the unidirectional propagation of impurity immunity and anti-scattering in the communication band.（2）Based on the pseudo-spin of the valley,two photonic crystals with different topological properties can be constructed by changing the sublattice materials Al₇₀Ga₃₀As and Si in the hexagonal honeycomb structure to break the symmetry of the structure.The two photonic crystals can be spliced together.One-way propagation of light is realized at its boundary,and by constructing a"Z"-shaped structure and randomly changing the position or size of multiple cylinders at the boundary,light can propagate along the original path,which verifies the stability of the structure and shows that the structure Immune to defects and impurities.