Study On Tunable Terahertz Metasurface Design And Its Electromagnetic Induced Transparency Effect

Terahertz technology is a new science field in the 21 st century,it is widely used in physics,material science,medicine,communication and other fields.Terahertz metasurface is a hot topic in academic circles.This thesis will focus on the study of electromagnetically induced transparency(EIT)effect in terahertz metasurface.Terahertz metasurface devices with adjustable,polarization insensitive,multi-channel and other functions are designed.The main content includes the following parts:First,a metasurface is designed to achieve EIT effect in terahertz region.Based on the electric field distribution and transmission spectrum,the origin of EIT effect is discussed,and three different coupling modes at three special frequency positions are explained.The influence of structural parameters on EIT effect is studied.Photosensitive silicon is added to the metasurface.Thus the active modulation of EIT is realized.The mechanism of modulation is to regulate EIT by adjusting bright mode with external pump.More importantly,the transmission characteristics of the metasurface can be switched between the EIT effect and Lorentz resonance by changing the intensity of the pump light.In addition,the slow light effect of EIT supersurface is further studied.The group delay of 4.3ps is obtained at the peak frequency of EIT,and the group delay dispersion is optically tunable.Based on the research above,some changes are made to the structure of the metasurface unit.It is found that the peak transmittance of EIT can be increased by62.11% by properly configuring the metasurface unit structure.The regulation on dark mode is discussed by changing the filling area of photosensitive silicon.At this point,the EIT peak transmittance of the metasurface can be adjusted by changing the intensity of the pump light source,and the tunable rate can reach 95.47%.The slow light characteristics of the changed metasurface are studied.The result shows that the device has a high group delay at the EIT peak frequency,up to 7.1ps,and a high group delay dispersion is found near the EIT peak frequency.Futher more,two metasurfaces were designed to increase application range.The unit cell of the first metasurface is center-symmetric and the obtained EIT properties are extremely insensitive to polarization.This kind of polarization-independent metasurface device has certain applications.Another metasurface can realize the multiple EIT effect.Compared with single EIT devices,multiple EIT devices have more working bands and a wider range of applications.More importantly,the switch between multiple EIT and single EIT is realized by the introduction of photosensitive materials.At the same time,the study on the sensing property shows that this device has good sensing performance with the sensitivity of 200 GHz/RIU.