Polarization Properties Of Gradient Metamaterial

The development of metamaterials has been more than half a century.Its unique electromagnetic properties have made metamaterials become a research hotspot in many fields such as optics,electromagnetism and physics since its discovery.People try to use this special kind of material to achieve the manipulation of light.Gradient metasurface is an important branch in the field of metamaterials.The early research on gradient metamaterials is mainly based on the microwave band and the terahertz band.Recently,the research on metamaterials in the near infrared band has become a trend.We mainly designed two kinds of composite gradient metasurfaces and studiing the asymmetric transmission phenomena and optimize the reflection transmission efficiency in the optical band.Our main work is as follows:We have designed a two-layer hybrid rectangular gradient metasurface.In the range of 200 THz to 450 THz,we firstly study the transmission characteristics of the single-layer rectangular gradient metasurface under the incident of circularly polarized light,based on the study of single-layer structure.We further studied the reflection and transmission properties of the two-layer structure.Through the CST simulation calculation,we found that the gradient metasurface has an asymmetric transmission phenomenon for circularly polarized light.We also found that the reflected cross-polarization transmission efficiency of this two-layer gradient metasurface can reach more than 60%,while the transmission efficiency of the reflected co-polarization is close to zero.Further to scanne the structure parameters,and when the thickness of the metal layer and the thickness of the intermediate spacer layer are respectively increased from 40 nm to 100 nm,which can achieve a reflected cross-polarization transmission efficiency of 72% and reduce the reflected co-polarization transmission efficiency to zero.We designed a composite U-shaped gradient metasurface.Firstly,we studied the transmission characteristics of a single-layer U-shaped gradient structure in the optical band with circularly polarized incident.We found the single-layer U-shaped gradient metasurface with two resonance peaks in the transmission and reflection transmission efficiency between 200 THz and 450 THz.By comparing the transmission characteristics of these two kind of single-layer structure,it is found that their transmission curves have certain complementary symmetry.Then we studied the transmission characteristics of the composite U-shaped gradient metasurface.It was found that this structure has a strong asymmetric transmission phenomenon to the circularly polarized light,and the asymmetric transmission coefficient can reache 0.43.At the same time,we find that there is a big difference in the transmission of the reflected cross-polarization from the reflected co-polarization.At the resonant frequency,the transmission cross-polarization efficiency can reach 50% or more.At this time,the reflected co-polarization transmission efficiency is lower than 10%.We further optimize the parameters.The refiected cross-polarization efficiency can reache 78%,and the reflected co-polarization transmission efficiency can be reduced to zero.