The Research Of Terahertz Bandpass Filter Based On 2-Dimension Photonic Crystal

Terahertz(THz)frequency range(0.1-10 THz)lies in the transition zone between photonic technology and electronic technology.The terahertz technology in the applications of communication,biomedical,material identification,imaging are developing rapidly,and terahertz bandpass filters have important applications in these technologies.Photonic crystals are materials whose refractive index changes periodically.The application of photonic crystals to terahertz bandpass filters can effectively solve the problems of high loss and narrow transmission band of traditional filters.Based on the two-dimensional photonic crystals,the terahertz bandpass filters are designed in terahertz atmospheric transmission window by applying the two-dimensional photonic crystals originated from the optics into the THz frequency range.Firstly,the basic theory of photonic crystals is briefly introducted,and the band gap structure of photonic crystals is calculated by the Plane Wave Expansion Method.Secondly,under the guidance of waveguide and resonant cavity coupled theory,four terahertz photonic crystal bandpass filters are simulated by using CST MWS 2013 software,and the influences of various geometric and material parameters on the filtering performance are discussed.The first filter is a vertical waveguide terahertz bandpass filter,which can achieve a 3dB bandwidth of 50 GHz,and the in-band maximum insertion loss is 0.26 dB.The second filter is a parallel waveguide terahertz bandpass filter,which has a 3dB bandwidth of 55 GHz and the in-band maximum insertion loss is 0.24 dB.This filter achieves a wider 3dB bandwidth and lower insertion loss than the first filter.The third filter is a photonic crystal filter with graded dielectric columns,which can achieve a 3dB bandwidth of 52 GHz and the in-band maximum insertion loss is 0.72 dB.Compared to the previous two filters,it has a simpler structure and is easy to be fabricated.The fourth filter is an improved structure based on the previous three filters.It introduces a resonant cavity structure based on the third graded photonic crystal filter.The filter can achieve a 3dB bandwidth of 57 GHz,and the in-band maximum insertion loss is 0.15 dB.This filter exhibits a better in-band insertion loss characteristic.Finally,the third filter structure is fabricated and it is tested by using the terahertz time-domain spectrometer system.The experimental results and the simulation results are compared,and the test error is analyzed thoroughly.In summary,the terahertz photonic crystal bandpass filters presented in this thesis have good filtering performance,and have important potential applications in terahertz technology.