Research Of Terahertz Planar Lens Based On Phase Gradient Metasurface

With the rapid development of the communications industry,spectrum resources are becoming increasingly tight,and terahertz has gained increasing attention as a frequency development gap.In the past ten years,with the strong support of the country,the development of terahertz has made great progress.Terahertz waves have huge potential applications in security imaging,radar communication,and biological monitoring.Although the research on terahertz has achieved staged development,there is still a further development in the regulation of terahertz waves.In this paper,we study the regulation of terahertz waves,including modulation of terahertz phase,amplitude,angular momentum,etc.The response of various metamaterial unit structures to terahertz waves was studied.A variety of planar devices were designed to achieve the modulation of terahertz waves by combining phase gradient metasurfaces and phase change materials vanadium dioxide?VO₂?.The terahertz wave is controlled through design simulation and experimental analysis.The main task is as follow:first part is the design theory of gradient phase metasurface is studied.The response of terahertz wave to the structure of metamaterials is analyzed by CST electromagnetic simulation software,and the electromagnetic analysis of various metamaterial microstructures is carried out.The influence can be adjusted and controlled by the structural parameters.Second part is the performance of the phase change material VO₂ was studied.The terahertz time-domain spectroscopy system?THz-TDS?was used to experimentally test VO₂.It was found that VO₂ can change the transmission of terahertz waves under light and temperature.The response of VO₂ to light and temperature is analyzed,and the transitions between the medium state and the metal state of the material can be achieved.Then,a terahertz plane lens with dynamically controllable focus was designed by combining the phase gradient metasurface and VO₂again,and the phase of the terahertz wave was adjusted to achieve a plane lens with adjustable focus.In the VO₂ medium state,the plane lens focuses the terahertz beam at a focal length of 3mm;in the VO₂ metal state,the plane lens focuses the terahertz beam at a focal length of 10mm.Experiments show that temperature control can achieve adjustable focal length.Finally,the existing flexible materials are used to study the flexible terahertz dynamic planar device,and the modulation effect of the planar device on the terahertz wave under the condit sensitive and insensitive are designed respectively.Aiming at the insensitivity of the curved surface,a flexible amplitude modulator was designed to modulate the amplitude of the terahertz wave to realize the on-off modulation of the terahertz beam;for the sensitivity of the curved surface,a flexible flat lens was designed to modulate the amplitude of the terahertz wave to achieve Plane lens dynamic focal length adjustment and beam state adjustment.Through the above four parts,this paper verifies the modulation effect of the terahertz plane device based on the gradient surface from the aspects of theory,design and experiment.The response of flexible planar devices to terahertz waves was also studied.Designed focus dynamic control plane lenses and flexible plane devices,which have huge potential applications in terahertz optical systems and conformal optical systems.