Research On Terahertz Polarization Control Devices Based On Composite Metasurface

Metamaterials,artificial sub-wavelength scale structures,have attracted a great deal of research attentions due to their possibilities to engineer optical properties which cannot be obtained in nature materials,such as negative index,perfect lens and cloaking.By designing different metal structures on the interface of the dielectric layer,due to the discontinuity of the phase at the interface,electromagnetic waves will have abnormal refraction and reflection thereon,and the electromagnetic waves may be manipulated in accordance with people's wishes.Terahertz waves show many promising applications in imaging,sensing,and communications.High-performance polarization control devices have important significance for improving the channel capacity and anti-jamming capability of wireless communication systems,but they are still incapable of achieving polarization conversion efficiency,bandwidth,polarization modulation performance,isolation,insertion loss,and integration.Meet the requirements of the terahertz application system.Based on this background,in this paper,we focus on the technical development requirements of terahertz application systems,and we have designed reflective and broadband transmission polarization conversion devices by studying the artificial composite super-surface structures.The electromagnetic coupling and electromagnetic singularity control mechanism combined with ultra-thin artificial microstructure and phase shift material were studied.Using the combination of chiral metamaterial and phase shift material vanadium dioxide?VO₂?,a terahertz band reflective and transmissive polar design was designed.Regulatory devices are implemented to dynamically regulate the polarization of electromagnetic waves.The main research content includes the following aspects:Design of a reflective static polarization converter based on the chiral super surface structure.Improvement of Chiral Super Surfaces the“?”-shaped unit structure realize90°polarization conversion of linear polarization and circular polarization at 0.4 THz,and the polarization conversion ratio is all above 0.9,which is a high-speed wireless communication system for THz and a high-sensitivity detection system.The new system radar imaging system provides a new mechanism for signal control.In this dissertation,the combination of artificial microstructure and phase-shift material vanadium dioxideis also proposed.A dynamic polarization conversion control device has been designed.It has a wide range of polarization state modulation,high polarization modulation depth,and the advantages of high isolation and flexible design.Using the artificial electromagnetic super surface combined with VO₂,the design of the dynamic reflection polarization control device and the dynamic transmission polarization control device was completed.The temperature was used to control the conductivity to realize the dynamic control of polarization conversion.The designed structure has a pole.The advantages of wide range of state control,high depth and isolation of polarization modulation,and flexible design.Combining the chiral super surface micro-nano structure with a novel phase change material and applying an excitation source to control the refractive index variation of the device to realize dynamic and efficient polarization control of the incident terahertz wave is one of the innovation points of this thesis.Using the dynamic control of the refractive index of different polarized waves to achieve polar modulation and polarization isolation is the key to achieve terahertz signal transmission control.The working frequency band can be broadened by superimposing the multilayered metamaterial structure.In this paper,the polarization transducing characteristics of the broadband transmissive polarization device are studied using an artificial electromagnetic super-surface,the polarization conversion efficiency of the transmissive device is improved,and the bandwidth response range is broadened.