Research On Refractive Index Based On Topological Photonic Crystal

Topological photonic crystals are a new type of material different from traditional photonic crystal.This material does not depend on certain defective modes in the photonic band gap,but use the topological phase transition of matter to achieve the operation and control of photons.This material exhibits extremely high unidirectionality,robustness,single-mode output effects,and is highly valuable for applications in chip development,biosensing,and military communications.At present,the theoretical models of topological photonic crystals are gradually matured,but the applications of topological photonic crystal are still need to be developed.Therefore,the thesis mainly focuses on the applications of topological photonic crystals in the field of refractive index sensing,which provides important clues for the development of topological photonics in optical devices.Thesis analyzes the basic principle of topological photonic crystal formation and realizes topological photonic crystals in two different dimensions.In thesis,topological photonic crystals are used for the development of refractive index sensors and the sensing performance analysis is completed.The results show that the edge states generated by topological photonic crystals play an important role in the sensors.The research work in thesis is as follows:(1)A refractive index sensor based on a one-dimensional topological photonic crystal is designed.First,the SSH model is studied,and a one-dimensional topological grating structure is implemented on the basis of the SSH model.It is concluded that having phase transition points with different winding numbers in the energy band is an important prerequisite for the generation of topological edge states.The design and optimization of the topological photonic crystal is completed around 1550 nm in the communication band.The topological resonance peak in the forbidden band of the photon is confirmed by the TMM with a transmission rate close to 100%,a very narrow halfpeak full width and a stable Lorentzian line shape.Combined with the actual optical device development needs,thesis design a topological photonic crystal bas on a flat waveguide structure for refractive index sensors.The electric field map and transmittance spectrum of the structure are calculated using FDTD method.The results show that the incident light is confined at the topological interface.Next,the refractive index sensor is studied using a flat waveguide structure.The results show a red shift of the topological resonance peak with the change of refractive index under the sample to be measured in the refractive index range(1.33-1.43),with a good linear and stable output.The sensing sensitivity is 489 nm/RIU,which is five times higher than that of refractive index sensors designed with ordinary photonic crystals.(2)A refractive index sensor based on a two-dimensional topological photonic crystal is designed to realize the development of the sensor in the three-dimensional direction.To investigate the mechanism of topological edge state generation in twodimensional photonic crystals,we find that there are Dirac points in silicon photonic graphene,and a two-dimensional topological photonic crystal can be realized by breaking the symmetry inside the lattice.Determining the structural dimensions of the twodimensional topological photonic crystal,the electric field map and transmittance spectrum of the structure are observed by the FDTD method.Finally,we select a small circular air hole with a zigzag shape and a flat plate thickness of 0.5a in the vertical direction as the basic form of the structure,which extinction ratio exceeds-30 d B.The designed structure is used for refractive index sensing and shows a sensing effect with higher sensitivity than the ordinary photonic crystal flat plate refractive index sensor,and is almost unaffected by defects in the detection process,possessing high defect immunity.