Terahertz Filters Fabricated By Femtosecond Laser Micromachining

Terahertz radiation is located between the microwave and the far infrared,and the terahertz wave has significant research value in broadband mobile communication,satellite communication,military radar,object imaging,environmental monitoring and medical diagnosis.To truly realize the wide application of terahertz wave technology,effectively control and manipulate terahertz waves,research on terahertz system functional devices such as:terahertz waveguide,polarizer,modulator,antenna,switch,band-stop bandpass filter,is particularly important.In recent years,a variety of terahertz filter devices have been raised out,but its performance,processing costs are not satisfactory.The frequency selective surface is a metal two-dimensional periodic array structure with good filtering effect on the electromagnetic waves in the free propagation space.Femtosecond laser micromachining provides a low-cost manufacturing tool for high-precision machining of frequency-selective surfaces.Therefore,in this dissertation,the femtosecond laser micromachining technology is applied to the manufacture of terahertz filter devices.The terahertz filter based on the frequency selective surface is fabricated on the aluminum foil by combining the manufacturing process,the simulation analysis and the experimental test.It may be able to solve the problem of expensive terahertz devices,and to promote the extensive application of terahertz technology.This dissertation first introduces the development prospect of terahertz,and then introduces the theory and research status of terahertz filter and femtosecond laser micromachining.On this basis,the simulation design was carried out by using HFSS software,and the terahertz filter was processed and tested using a femtosecond laser micromachining system.The main contents of this dissertation are as follows:(1)A femtosecond laser micromachining system was built,as well as the automatic control software was developed.A series of experiments were carried out to debug the light path and optimize the control system.With 10 microns thick commercial aluminum foil as the experimental material,the influence of laser power and processing speed on the frequency selective surface processing was analyzed.The optimal combination of parameters suitable for processing was selected.(2)Four terahertz bandpass filters with circular openings in equilateral triangular lattice whose central frequency was 0.4THz,0.6THz,0.8THz,and 1THz respectively,were designed based on HFSS software.The transmission characteristics of the circular aperture cell frequency selective surface are analyzed for the arrangement mode of equilateral triangle.Furthermore,some new frequency selective surface elements are proposed,which extend the direction for the follow-up study.(3)The terahertz bandpass filters designed before were fabricated by the femtosecond laser micromachining system and tested by the terahertz time-domain spectroscopy system(THz-TDS)built in our laboratory.The experimental results show that:the circular aperture cell frequency selective surface with equilateral triangular lattice has better filtering performance,and the experimental test results are in good agreement with the HFSS simulation results,which make it suitable for rapid design and manufacturing as high performance terahertz bandpass filter.