Tunable Terahertz Waveguide Narrowband Filters

Terahertz wave is located in the special area of the electromagnetic spectrum from electronics to photonics.And it has a wide range of applications in non-destructive testing,agriculture and food safety,spectral imaging,military,security inspection,biomedicine and wireless communication.With the continuous development of wireless communication technology,terahertz communication technology has become a research hotspot.However,the frequency bands available for terahertz communication are relatively scattered,and it is urgent to develop high-performance and easy-to-manufacture terahertz filters to solve this problem.In this paper,a periodic slab waveguide structure is designed based on Bragg resonance.A terahertz narrowband filter with narrow linewidth and high Q value is experimentally realized,and the tunability of the terahertz narrowband filter is realized by designing the slab waveguide structure.The main work of this paper is as follows:（1）The research background and significance of terahertz filters are introduced,and we have summarized the development status of different structural types of terahertz filters,the main content of this study is also been briefly introduced.（2）The propagation characteristics of terahertz waves in periodic flat plate waveguides were studied.based on defect structures,two types of terahertz narrowband filters were proposed.Starting from Maxwell’s equation,the propagation characteristics of terahertz waves in periodic undulating flat plate waveguides are analyzed theoretically,and the mechanism of mode generation is studied with the aid of the simulation,which provides a theoretical basis for the subsequent design of terahertz waveguide filters.（3）Single-defect waveguide filters are designed and fabricated based on the transmission characteristics of electromagnetic waves,and filters were experimentally studied using THz-TDS.The CO₂ laser marking machine is used to etch the groove on the PMMA plate,and the periodic undulating structure waveguide is obtained by plating the gold film on the structure surface by the ion sputtering instrument.And a terahertz waveguide narrowband filter was realized with a linewidth of 1.5 GHz and an extinction ratio of up to 29 d B.At the same time,the effect of plate spacing and number of cycles on filter performance is also deeply studied,and it is proposed that tunable narrowband filter can be realized through the design of waveguide structure parameters.（4）According to the influence of different defect lengths on the filtering performance,two various of tunable narrow-band filters with different shapes are designed.One is a step-type tunable narrow-band filter,which realizes three adjustable frequency positions by designing waveguides as a stepped shape,with a narrowest linewidth of 1 GHz and a maximum extinction ratio of 30 d B.The other is to design the defect structure into a wedge shape.Directly etch the groove on the aluminum alloy plate by the fiber laser marking machine to make a periodic undulating structure waveguide,which realizes a high-performance narrow-band filter with five frequency positions can be continuously adjusted.In summary,according to the structural characteristics of periodic undulating flat plate waveguides,this paper realizes a terahertz narrowband filter with superior performance,which has the advantages of simple structure,easy production and easy regulation,and it meets the performance requirements of terahertz communication system for filters.