Research On Terahertz Amplitude And Polarization Modulated Metasurface Based On Vanadium Dioxide

Terahertz waves have extensive prospects in the fields of biomedicine,nondestructive testing,security check,and wireless communication due to their many unique physical properties.The emergence of efficient terahertz sources has accelerated the application of terahertz technology in various fields,and the rapid development of related technologies has put forward higher requirements for terahertz modulators.In recent years,the research of terahertz devices that can flexibly and efficiently manipulate terahertz waves has become a hot topic.In this context,the amplitude and polarization modulation devices in the terahertz regime are selected as the research direction of this paper.Three amplitude/polarization modulated metasurface devices based on vanadium dioxide(VO₂)at the terahertz frequency are proposed by combining the reversible metal-insulator phase transition of VO₂ with the metasurface and the optimization design and analysis are carried out.Firstly,a wide-band terahertz metasurface absorber with tunable absorption rate based on VO₂ is proposed and optimized by using electromagnetic field simulation software HFSS.The metasurface realizes the absorption rate tuned from 50%to 98%and the absorption bandwidth of over 90%reaches 0.75THz by changing the temperature to control the phase transition of VO₂ embedded in the gap of a positive cross element of the unit cell.The absorbing mechanism of the absorber is studied by using the impedance matching theory and observing the distributions of surface field and current.Then,the polarization-insensitive and wide-angle characteristics of the absorber are discussed.Secondly,a narrowband switchable terahertz metasurface filter based on VO₂ is proposed and optimized by using electromagnetic field simulation software CST.The switchable filter can be switched between"ON"and"OFF"states through the electrically-controlled phase transition of VO₂.In the"ON"state,the highest transmittance of the filter is 92%,and the corresponding-3d B bandwidth is 0.14THz.In the"OFF"state,the transmittance is close to 0 in the whole simulation frequency band.The transmission mechanism of the filter is studied by using the surface electric field and current distributions,and the equivalent circuit model of the filter is obtained.The sample of filter is made by the micro-machining technology,and the transmittance is measured by a terahertz time-domain spectrometer.The results show that the test results are in good agreement with the simulation results.Finally,a VO₂-based broadband switchable multi-functional metasurface is proposed after the simulation optimization of CST.The metasurface realizes switching between wave absorption and linear-to-linear polarization conversion by electrically controlling the phase transition of VO₂ in the structure.Meanwhile,the linear-to-circular polarization is realized based on the size adjustment of the structure.The polarization conversion mechanism of multifunctional metasurface is analyzed by combining the polarization conversion theory with the magnitude and phase difference of the reflected electric field obtained by simulation.The absorption mechanism is analyzed by the impedance matching theory,the surface current and cross-section field distributions.Finally,the polarization-insensitive and wide-angle incident properties of the metasurface are investigated.