Preparation And Properties Of Metal Wire Grid Terahertz Polarizers

Terahertz(THz)wave has many advantages such as low photon energy,rich spectral information and strong penetrability.It has potential applications in biomedicine,semiconductor,security inspection,military defense,information and communication,basic science and other fields.The effective control and modulation of terahertz waves is a precondition for the wide applications of terahertz technology.Therefore,research on functional devices such as waveguides,polarizers,modulators,antennas,switches,band-stop/band-pass filters,etc.,is particularly important.In recent years,with the development of microfabrication technology and the understanding of the interaction mechanism between electromagnetic waves and subwavelength microstructures,subwavelength microstructures demonstrate outstanding electromagnetic control capabilities due to their surface plasmon polariton designability for fabricating terahertz devices,attracting more and more people's attention.In this thesis,I mainly study the utilization of femtosecond laser micromachining technology and magnetorheological fluids to prepare subwavelength metal wire grid terahertz polarizers.Combined with FDTD simulation and time domain terahertz spectrometer performance tests,a comprehensive study on the performance parameters of the polarizers was performed.The research work has innovations in processing technology and preparation methods.The main contents of the thesis include:(1)First,I introduced the classification of terahertz waves according to their polarization states,the generation method of polarized terahertz waves,the design theory of terahertz polarizers,and the research status of processing and manufacturing technologies in the world.The advantages and disadvantages of the polarizers fabricated using these methods were compared and analyzed.(2)Introduction on the time-domain terahertz spectroscopy system,and the advantages of femtosecond laser micromachining and its application examples in terahertz device processing.(3)Through a comprehensive experimental operation test of the femtosecond laser micromachining system,the influence of processing parameters(laser power and processing speed,etc.)on the machining accuracy was analyzed,and the wire grid polarizer was made.Finite difference time domain(FDTD)method was used to simulate and analyze the effect of the structural parameters(line width and period)of the wire grid terahertz polarizer on the polarization characteristics.With thickness change of the aluminum foil,resonant features in the THz spectra were observed.The new phenomenon was attributed to the resonant coupling between the upper and lower surface plasmons on the foil.(4)The polarization characteristics of the fabricated metal wire-grid terahertz polarizers were experimentally verified by the home-made terahertz time-domain spectroscopy system,and the characteristic parameters such as transmittance,polarization degree and extinction ratio were calculated.(5)Different from the conventional preparation methods,I invented a low-cost THz polarizer based on a microphysical phenomenon in which magnetic particles are arranged in chains under a magnetic field to form a metal-like wire grid structure.Its polarization characteristics were verified by a time-domain terahertz spectroscopy system.