基于狄拉克半金属的宽带可切换双功能太赫兹极化转换器

Broadband Switchable Bifunction Terahertz Polarization Converter Based on Dirac Semimetal

提出了一种基于狄拉克半金属的宽带可切换双功能太赫兹极化转换器。该极化转换器由谐振结构和经聚乙烯环烯烃共聚物介质层隔开的金薄膜组成。通过调整狄拉克半金属的费米能级,设计的超表面可以从四分之一波片切换到二分之一波片。数值仿真结果表明:当费米能级为70 meV时,超表面为四分之一波片,可在1.955~2.071 THz频率范围内将入射的线极化波转换为左旋圆极化波,在2.606~3.490 THz频率范围内将入射的线极化波转换为右旋圆极化波,且在1.955~2.071 THz和2.606~3.490 THz两个频率范围内的椭圆率分别接近于±1;当费米能级为160 meV时,超表面为二分之一波片,在2.599~3.638 THz内可将y极化波转换为x极化波,极化转换率超过90%。此外,相比其他结构,该结构在较大的入射角下可以维持相同的性能,还可以通过改变狄拉克半金属的费米能级动态调节其极化转换性能。该设计方法可应用于无线通信、太赫兹传感和成像等领域中。

A broadband switchable bifunction terahertz polarization converter based on a Dirac semimetal is proposed in this paper.The polarization converter comprises a resonant structure and a gold film separated by a polyethylene cyclic olefin copolymer dielectric layer.By adjusting the Fermi energy level of the Dirac semimetal,the designed metasurface can be switched from a quarterwave plate to a halfwave plate.The numerical simulation results revealed that when the Fermi energy level is 70 meV,the metasurface is a quarterwave plate,which can convert the incident linearly polarized wave into a lefthanded circularly polarized wave at frequency ranging from 1.955-2.071 THz.The plate converts the linearly polarized wave into a righthanded circularly polarized wave at frequency ranging from 2.606-3.490 THz.Furthermore,the ellipticity associated with frequency ranging from 1.955-2.071 THz and 2.606-3.490 THz is close to±1.The metasurface behaves as a halfwave plate capable of converting ypolarized waves into xpolarized waves at frequency ranging from 2.599-3.638 THz.The corresponding polarization conversion rate exceeds 90%when the Fermi energy level is 160 meV.In addition,compared with other structures,the structure can maintain the same performance at a large incident angle,and its polarization switching performance can be dynamically tuned by changing the Fermi energy level of the Dirac semimetal.The design method can be employed in various fields including wireless communication,terahertz sensing,and imaging.