Electrical Tunable Reflective THz Polarizer Based Dirac Semimetal Metamaterial

Metamaterial is an artificial electromagnetic medium which is composed of sub-wavelength and periodical units.It has many electromagnetic properties that natural materials do not possess.Metamaterials/metasurfaces have attracted great attention in many fields such as communication and image processing recently.Traditionally,metamaterials is composed of single or multiple layers of periodic metal units which are fabricated on a semiconductor substrate so as to realize the amplitude or phase control of electromagnetic waves.But this traditional metamaterial cannot realize the frequency tune of electromagnetic waves.In recent years,the advent of Dirac semimetal metamaterials has brought new opportunities to development of tunable metamaterials.The Dirac semimetal has all the advantages of graphene and could easier coupled to electromagnetic waves because of it's a bulk material.In this dissertation,two different types of terahertz polarization converters are designed using Dirac semi-metal,and the transmission characteristics of the two types of polarization converters are studied.It can dynamically tune the frequency of polarization converter by changing Fermi energy and which lay the foundation for the development of high-performance polarization converter and polarization switches.The main innovations of this article are as follows:(1)A reflective terahertz polarization converter is designed:firstly,we design its structure and simulated its electromagnetic tuning characteristics using CST Studio Suite.The results show that when the thickness of the intermediate medium is 22?m,the thickness of Dirac semimetal is 0.2 ?m,and the Fermi level is 60 meV,the polarization conversion rate is about 100%at two resonance frequencies of 2.072 THz and 2.428 THz.The polarization conversion rate is more than 0.85 in the frequency range of 2.026-2.481THz.The polarization converter also has good oblique incidence performance when the incident angle changes from 0°to 30°,the average polarization conversion efficiency is still higher than 70%.When the Fermi level is increased from 55meV to 70meV,the device can be dynamically tuned in the range of 1.88-2.52THz.(2)A transmissive terahertz orthogonal polarization converter is designed.We firstly optimize the structure and simulated using CST Studio Suite.The results show that when the thickness of the intermediate dielectric silica is 25 ?m,the thickness of Dirac semi-metal is 0.2?m,and the Fermi level is 200 meV,the orthogonal polarization conversion efficiency is as high as 90%in the frequency range of 0.9-2.5 THz.We have also studied the effect of Fermi level on polarization conversion efficiency.As the Fermi level increases from 120meV to 240meV,the spectrum at low frequencies undergoes redshift and the spectrum at high frequencies undergoes blueshift.The polarization converter can be dynamic tuned in the range 0.7-2.6THz.