Terahertz Polarization Control Devices Based On Vanadium Oxide Reconfigurable Metamaterial

Polarization is an important characteristic of THz wave,and it is necessary to regulate the polarization state of THz wave in many fields.Metamaterials provide new materials and new ideas for the development of THz wave polarization control devices,especially the active regulating metamaterials combined with phase change materials,which can realize a wider range of functions and more important applications.As a phase change material with excellent performance,vanadium dioxide can be combined with metal to regulate the polarization state of THz waves.This paper focuses on the study of THz wave polarization control devices based on vanadium dioxide reconfigurable metamaterials,and the main contents are as follows:1.Studied the basic physical principle and mathematical formula of polarization optics,and described the polarization state of electromagnetic wave from the physical and mathematical perspectives;The theoretical models of metamaterials have been analyzed and applied to the design of THz polarization devices.2.A THz polarization active controller based on vanadium dioxide and metal monolayer structure was designed,and the sample was made by micromachining.The experimental results show that the device can achieve two functions: First,is to realize the function of phase shifter at the frequency of 0.72 THz for the incident THz wave in the direction of y polarization;Second,it can act as a switchable quarter wave plate.In the absence of impressed current,the amplitude components of the transmitted electric field at0.69 THz are both 0.45 in the polarization directions of x and y,and the phase difference between them is 80°.At this point,the transmitted wave is almost circularly polarized.When the impressed current is 0.46 A,the amplitude component tx of the transmitted electric field at 0.69 THz is 0.45,ty is 0.42,and the phase difference between them is 7.8°.At this point,the transmitted wave is almost a linearly polarized wave.By analyzing the surface current of the device,the equivalent circuit model is established,and the polarization regulation mechanism is studied.3.Two THz active polarization controllers based on vanadium dioxide and metal multilayer structure are designed.(1)A THz wave orthogonal polarization conversion controller based on the structure of split resonant ring(SRR)was designed.The device can rotate the polarization direction of linearly polarized wave by 90° in the frequency range of 0.5-2.5 THz,and thetransmittance of Txy can reach more than 65% and the highest 92% at 1.55 THz,and the polarization conversion rate is close to 100%.By controlling the phase transition of vanadium dioxide,the transmittance of Txy can be modulated from 92% to 2.5%,and the modulation depth can reach 97%.The dependence of structural transmittance on incident angle is studied.The influence of parameters on device function was investigated.In this paper,the interference theory of multilayer structure is used to study the reason of high efficiency polarization conversion regulation.(2)A THz wave orthogonal polarization conversion modulator based on L-shape structure was designed.The polarization conversion effect of the device is good in the range of 0.7-2.5 THz,and the Txy transmittance reaches 50% at 1.85 THz.By controlling the phase transition of vanadium dioxide,the transmittance of Txy can be increased from1% to 50%,and the modulation depth can reach 98.5%.The three active control devices of THz polarization designed in this paper are of great significance for the effective control of the polarization state of THz wave.