Research On Terahertz Amplitude And Polarization Control Based On Vanadium Dioxide Metamaterials

Terahertz（THz）wave has great application prospects in broadband wireless communication,biosensor,security inspection and spectral imaging due to its low photon energy,strong penetration and wide frequency band.In terahertz communication,imaging,sensor detection and other applications,it is necessary to adjust the amplitude and polarization of terahertz wave.Due to the size limitation of traditional natural materials,the ability to adjust the amplitude and polarization of terahertz wave is limited.Metamaterial is a kind of artificial electromagnetic material composed of periodic sub wavelength structure.Terahertz devices based on metamaterial are flexible in design,small in size and easy to integrate,which has become one of the research focuses of terahertz wave control devices.Vanadium dioxide is a kind of thermal phase change material,which changes from dielectric state to metallic state at 68℃.This special property can be used to construct reconfigurable metamaterials and realize the dynamic control of terahertz wave parameters.This paper studies the modulation of THz amplitude and polarization based on vanadium dioxide,The main work is as follows:1.The theory of terahertz metamaterials is systematically studied,and the dispersion model of vanadium dioxide in terahertz band is analyzed and simulated.The metamaterials based on vanadium dioxide were constructed,and the influence of metamaterials on terahertz wave propagation and reflection was studied.2.The terahertz amplitude control device based on Vanadium dioxide was designed and manufactured.The sample was tested by THz time domain spectrum system.The results show that:（1）the transmission spectrum of the device is a pass band,the lower cutoff frequency is 0.33 THz,the upper limit cutoff frequency is 1.17 THz,the peak value at 0.7THz is 0.63,the full width of half peak is 0.58 THz;（2）When the device is powered on,vanadium dioxide undergoes a phase change at a current of 0.4 A,the terahertz wave transmission peak amplitude is reduced from 0.63 to 0.13,and the modulation depth reaches79%.After power off,it can be restored to the status before power on.At the same time,the hysteresis loop generated by vanadium dioxide in the device is obtained by processing the test data,and it is found that the hysteresis effect of the device is very small.Therefore,the device can realize the dynamic control of the transmission amplitude of the terahertz wave.3.A reflection terahertz wave cross polarization converter based on VO₂ was designed.The bandwidth of the cross-polarization conversion was changed by controlling the phase change of Vanadium dioxide.The cross-polarization conversion is realized in the range of1.58-2.08 THz,and the polarization conversion rate reaches 95%.The bandwidth of polarization conversion was changed from 0.5 THz to 0.04 THz by changing the conductivity of vanadium dioxide,and the relative bandwidth decreased from 27%to 1.9%.Through the analysis of the surface current of the device,it is found that the broadband polarization conversion is caused by the superposition of three resonant frequency points.The vanadium dioxide phase change causes the two resonances of the device to disappear and the bandwidth becomes narrow.At the same time,the influence of the thickness of the dielectric layer and the polarization angle of the incident wave on the reflection wave is also analyzed.The design ideas and methods in this paper are of great reference value to the research and development of terahertz active control devices.