The Electromagnetic Characteristic Of THz Device

Terahertz(THz)technology has attracted much attention because of its potential application in many frontiers.Although great progress has been made in the generation and detection of THz wave source,the development of THz technology is slow due to the lack of THz devices.In recent years,the metamaterial has solved the problem of material which responses to THz wave.And with the rapid development of microstructure preparation,the fabrication of THz devices based on metamaterial has become possible.Therefore,the study of THz devices based on metamaterial is of great practical significance and academic value.In this paper,based on metal and black phosphorous metamaterial,two kinds of THz devices such as polarization converter and electromagnetic absorber are designed.The electromagnetic characteristics of the designed devices are analyzed by the simulation and the physical mechanisms are revealed by the current distribution and the interference theory.The main contents are as follows:(1)Based on metal metamaterial,two high-efficiency reflective ultra-wideband linear-to-circular(LTC)polarization converters at THz frequency are designed.The first is based on a double-split square ring,which can convert the linear polarization wave into circular polarization wave in the range of 0.60 THz and 1.41 THz,whose relative bandwidth is 80.6% and efficiency of polarization conversion is greater than 88%.In addition,the polarization converter can maintain good polarization conversion performance in a wide range of the incident angle.The LTC polarization conversion property of the polarization converter is analyzed according to the reflection of the two orthogonal components of the incident wave.The physical mechanism of the polarization conversion is illustrated through the current distribution on the metamaterial surface and the floor.Similarly,the other is based on a double-split hash(#)type metamaterial,which can convert the linear polarization wave into circular polarization wave in the range of 0.70 THz and 1.66 THz and the relative bandwidth is 81%.(2)Based on black phosphorous metamaterial,an ultra-wideband circular polarization converter is designed,which can convert the linear polarization wave into circular polarization wave in the range of 12.82 THz and 23.28 THz and the relative bandwidth is58%.Many factors,such as the polarization of the incident wave,the ridge arrangement of black phosphorus,the relaxation rate and the number of black phosphorus layers,have mainly been considered to investigate the polarization conversion property of the converter.The LTC polarization conversion property is analyzed according to the reflection of the two orthogonal components.(3)Based on black phosphorus metamaterial,a THz absorber is designed.This absorber consists of several dielectric layers,patterned black phosphorus layers and an optically thick gold mirror and then forms a sandwich-like structure.The sandwich-like structure forms a Fabry-Perot resonator to enhance the light-matter interaction.The simulation results demonstrate that the absorption rate of the proposed absorber is highly dependent on the number of layers in the sandwich-like structure.In addition,the electromagnetic response of black phosphorus metamaterial in the sandwich-like structure is investigated and the mechanism of its response is elaborated using interference theory.