Fabrication And Performance Test Of Substrateless Terahertz Filter

Terahertz(THz)generally refers to the electromagnetic wave between millimeter wave at0.1THz and far-infrared light at10 THz.It has some unique properties such as coherence,low energy,penetrability,and instantaneity,having a great application prospects in the field of nondestructive testing,biomedicine,security etc.THz technology is the key to the future 6G communication technology.Effective control and modulation of terahertz waves is a prerequisite for the widespread application of terahertz technology.Therefore,research on functional devices such as terahertz waveguides,polarizers,modulators,antennas,switches,high-pass,low-pass,band-pass and band-stop filters in terahertz systems is particularly important.Therefore,how to manufacture low-cost,high-performance terahertz devices has great research value.Current THz filtering devices are based on four different structure designs,including frequency selective surface(FSS),Metamaterial,waveguide and photonic crystals.FSS and metamaterial are the most widely used.However,because the wavelength of THz wave is short,and the structure sizes of these devices are small,ordinary machining techniques are usually not qualified.Femtosecond laser micromachining is widely used in the manufacture of microelectromechanical systems with its high precision,low cost and "cold" processing characteristics.Compared to the traditional ink-jet printing,photolithography,chemical vapor deposition and other micro processing technologies,it is simple,less processing,low-cost,via a single ablation operation,suitable for all kinds of microstructure and high precision processing.In this thesis,we have employed the Finite Difference Time Domain(FDTD)method to simulate and design the filter structure.Based on the self-built femtosecond laser micromachining platform,we have fabricated low-cost,large-area,high-performance substrateless terahertz filtering devices,including wire-grid polarizers,band-pass and high-pass filters.Time-domain terahertz spectroscopy system was used for performance testing.The main research contents of the thesis include:(1)The effects of various structural parameters,incident angle,and sidewalls of the cell on the performance of terahertz filters(band-pass,polarization,high-pass)were analyzed using FDTD simulation.We have found the coupling effect of surface plasmon polaritons in the thick cross filter and the double stopband effect in the high pass filter as a function of incident angle.(2)We have built a femtosecond laser micromachining system,which incorporated an automatic leveling device and laser shaping technology to improve the processing quality.The femtosecond laser automatic processing program,the autofocus program,and the matrix compensation program were adopted to achieve high quality processing.(3)A bold innovation in the design of wire grid polarizers was proposed by introducing a discontinuous short-line support structure to prepare large-area terahertz polarizers.(4)Experimental measurement,data analysis and discussion of the above filtering devices were performed using a time domain terahertz spectrometer.