Research On Terahertz Wave Polarization Dynamic Control Based On Vanadium Dioxide Metamaterial

Terahertz technology has become the cutting-edge technology in the field of information in the world.Polarization is an important parameter of the terahertz wave.The regulation of the terahertz wave polarization has become a research hotspot in the terahertz field,because it is necessary to dynamically regulate the polarization state of the terahertz wave in the fields of terahertz communication,imaging,sensing and detection.However,the traditional polarization converter realizes the polarization conversion by obtaining the phase accumulation through the wave plate.Its unit structure is fixed after processing,the polarization state cannot be dynamically controlled,and it is not conducive to the integration of the equipment.Metamaterial is an artificial material or structure consisting of periodic sub-wavelength unit structures.It is an excellent choice for the regulation of the terahertz wave parameters.Vanadium dioxide（VO₂）is a phase transition material.Under external excitation,the phase transition from insulating state to metallic state will occur.This property is very suitable for the dynamic regulation of the terahertz wave polarization state.This paper focuses on the terahertz wave polarization dynamic regulate devices based on VO₂metamaterial.The main contents are as follows:（1）The relevant theories,simulation methods and fabrication processes of the terahertz metamaterial are studied,the polarization states are classified and quantitatively described,and the phase transition mechanism and fabrication methods of VO₂ are discussed.（2）A mode switchable terahertz polarization converter based on VO₂ metamaterial is proposed.The device performance is simulated with the full-wave analysis software CST.The results show that,when the VO₂ is in insulating state,the device is a transmission polarization converter.The cross-linear polarization conversion can be realized in a broadband of 0.70 THz,and the transmission polarization conversion rate（PCR）is higher than 99%.Under thermal stimulus,the VO₂ changes from insulating state to metallic state,and the device is a reflective polarization converter.The linear-to-circular polarization conversion can be realized in a broadband of 0.50 THz,and the reflection PCR is higher than88%.And thus,realizing the dynamic regulation function of the terahertz wave polarization state successfully.（3）A bandwidth adjustable terahertz polarization converter based on VO₂ metamaterial is proposed.The full-wave simulation results show that,when the VO₂ is in insulating state,broadband cross polarization conversion effect can be realized in a broadband of 0.8 THz,and the reflection PCR is higher than 90%.Under thermal stimulus,VO₂ changes from insulating state to metallic state.The device can realize narrowband cross polarization conversion near two resonant frequencies,and the reflection PCR is close to 100%.And thus,realizing the bandwidth adjustable function in the polarization conversion process of the terahertz wave successfully.The two polarization converters proposed in this paper provide new ideas for the research of dynamic polarization regulation of the terahertz wave,and provide important reference values for the research of new terahertz functional devices.