Study Of Terahertz Polarization Control Based On Meander-line Metamaterials

Metamaterials,as the artificial material with composite structures,have drawn substantial attention in the physics study.When the crystal constants of metamaterials become much smaller than wavelengths,these metamaterials possess some novel properties that never exist in natural materials.Based on metamaterials,various artificial sub-wavelength devices have been proposed.Especially,metamaterials are essential for terahertz applications,because of the absence of naturally functional material in the terahertz regime.The commonly used terahertz polarizers are manufactured based on the metal wire grid.However,these polarizers are fragile,inefficient and expensive.However,there are no other practical and efficient polarizers for terahertz applications.In this paper,we demonstrated a systematic study of an all dielectric metamaterial-based quarter-wave plate.The details of the design,simulation,fabrication and experimental verification were presented.In addition,several polarization control devices based on metal structures were also investigated.The main contents of this thesis are as follows:In chapter 1,the research background for terahertz waves was introduced firstly;the corresponding characteristics and applications of terahertz waves were described later;previous studies on metamaterials were referred in detail at last.Then,we presented the key point of this thesis,which is to investigate the terahertz polarization control devices.In chapter 2,theories for polarization optics were introduced.The polarization states of light and Stokes parameters were explained in detail.In chapter 3,standard photolithography process and terahertz time-domain spectroscopy system were introduced.In chapter 4,a terahertz quarter-wave plate based on dielectric meander-line metamaterials was demonstrated.Firstly,we introduced its design method,and then verified its performances by simulation and experiment.Additionally,the influences of the structure parameters and polarization direction of the incident terahertz wave were analyzed and theoretically explained.Finally,the principle of the quarter-wave plate was explained by the birefringence model and further discussions of quarter-wave plate were given.This all-dielectric(silicon)terahertz polarization device provides a novel avenue to control the polarization of terahertz wave,which has a great significance for terahertz applications.In chapter 5,several metallic meander-line terahertz wave plates were analyzed: 1)Metallic meander-line quarter wave plate with substrate;2)Metallic meander-line quarter wave plate without substrate;3)Metallic rectangle quarter wave plate.These works provide some new methods for design of terahertz polarization devices.