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本文提出一种新型超表面结构，通过改变工作温度能够实现透反双模态极化转换与超宽带吸收等功能切换。当二氧化钒为金属态且碲化锗为晶态时，太赫兹波沿-z方向入射，该超表面在7.96~17.76THz频带表现为超宽带吸收器，吸收率大于90%。太赫兹波沿+z方向入射，该超表面在2.04~4.44THz频带表现为对x-/y-偏振波的反射极化转换，极化转换率大于0.9。当二氧化钒为介质态且碲化锗为非晶态时，该超表面在0.65~5.07THz频带表现为对x偏振波的透射极化转换，极化转换率大于0.9。研究结果表明该超表面结构对太赫兹波操控具有双向、可切换和多功能特点，在太赫兹波传感、成像和通信领域具有广阔的应用前景。In this paper, we propose a vanadium dioxide and germanium telluride composite metasurface. The conductivity of vanadium dioxide and germanium telluride is changed by changing the temperature, which enables the switching of functions such as ultra-broadband absorption, reflective-type polarization, and transmissive-type polarization . When vanadium dioxide is metallic and germanium telluride is crystalline, the terahertz wave is incident along the -z direction, and the metasurface can be used as a broadband absorber, with an absorption rate greater than 90% in the frequency range of 7.96~17.76 THz, and the absorption bandwidth reaches 9.8 THz, with a relative bandwidth of 76.2%. In addition, the designed metasurface absorber is polarization insensitive and exhibits good absorption performance at large incidence angles. Terahertz waves are incident along the +z direction, and this metasurface can be used as a reflective polarization converter with a polarization conversion ratio greater than 0.9 for x- and y-polarized waves in the frequency band from 2.04 to 4.44 THz. The effects of incidence angle and structural parameters on polarization conversion performance are also investigated. When vanadium dioxide is in the dielectric state and germanium telluride is in the amorphous state, the metasurface can be used as a transmissive polarization converter, with a polarization conversion rate of greater than 0.9 in the 0.65~5.07 THz band. And the high polarization conversion performance can be maintained over a wide range of incidence angles. Finally the physical mechanism of polarization conversion is analyzed using surface currents. The results show that the metasurface structure has bi-directional, switchable and multi-functional characteristics for terahertz wave manipulation, and has broad application prospects in terahertz wave sensing, imaging and communication.
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Keywords:
- Reflective polarization conversion /
- Transmissive polarization conversion /
- Ultra-broadband absorption /
- Metasurface
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