The Research Of Terahertz Two Dimensional Photonic Crystal Filter

Terahertz?THz?has been developing rapidly in the fields of medical technology,information and communication and national defense security because of its low energy,coherence and penetration.Terahertz filter occupies an irreplaceable position in these applications.The filtering performance of the photonic crystal filter can be improved by introducing different defects or impurities in the photonic crystal.The design of two-dimensional photonic crystal filters for terahertz communication window?has certain practical value and significance.First of all,the plane wave expansion method and the finite element method are used to analyze the energy band structure of the two-dimensional photonic crystal under the electrical polarization and magnetic polarization modes.The intrinsic equations and the linear equations are obtained.According to the two methods for solving the speed of equations,the plane wave expansion method with fast solution is chosen.And the band structures of photonic crystals with three kinds of lattice structures with honeycomb,square and triangle are analyzed by the plane wave expansion method.The two-dimensional photonic crystal with square lattice structure has been chosen.Then,the size of photonic crystal is determined according to the terahertz communication window?.Next,the filtering theory of photonic crystal filter with direct coupling and side coupling mode is analyzed,and their filtering characteristics are obtained.Then,the direct coupled photonic crystal filter with band-pass characteristics is selected The terahertz two-dimensional photonic crystal bandpass filter based on cylindrical point defects is designed by introducing defects and impurity into square two-dimensional photonic crystals.Its central frequency is 338GHz,the 3dB bandwidth is 70.72GHz,the S₁₁ is lower than-12.42dB,the insertion loss is less than 0.39dB,the band ripple is0.2dB,the edge is steep and the rectangular coefficient is good.So,it can be effectively used in terahertz communication window?.Aiming at broadening the bandwidth of the filter,the terahertz two-dimensional photonic crystal filter with improved cylindrical point defect is designed.By optimizing the structure parameters of the device,the 3dB bandwidth is increased to 74.21GHz,the insertion loss is reduced to 0.35dB.So,it can be applied to the terahertz atmospheric wireless communication system.In order to further widen the bandwidth of the filter to better cover the frequency range of the terahertz communication window?,the terahertz two-dimensional photonic crystal filter with hollow cylindrical point defect is designed.By analyzing the relationship between the structural parameters and the filtering performance,the structural size is optimized to widen the working bandwidth to 75.32 GHz.And the bandpass is flat,the rectangular coefficient is good.It shows a comprehensive good filtering performance.In conclusion,the terahertz filters based on two-dimensional photonic crystal are designed in this thesis have good filtering performance.So,it can be effectively used in the terahertz communication window?communication system.