Bandwidth-tunable terahertz metamaterial half-wave plate component
doi: 10.37188/CO.2022-0198
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摘要:
基于二氧化钒（vanadium dioxide, VO2）的相变原理，提出了一种“树叶型”复合超构材料，能够实现带宽可调谐的半波片功能。VO2薄膜为绝缘态时，复合超构材料可以看作是空芯“树叶型”金属结构，能够实现双频带的半波片功能。在1.01~1.17 THz和1.47~1.95 THz 频带范围内能够将
y 偏振光转换成x 偏振光，偏振转换率大于0.9且平均相对带宽为26%。VO2 薄膜为金属态时，实芯“树叶型”金属结构的超构材料在1.13~2.80 THz范围内能够实现反射型的宽频带半波片功能，相对带宽为85%。利用瞬时表面电流分布和电场理论详细地分析了带宽可调谐半波片器件的工作原理。本文所提出的“树叶型”复合超构材料半波片器件在太赫兹成像、传感和偏振探测等领域具有潜在的应用前景。Abstract:We propose a “leaf-type” hybrid metamaterial to realize bandwidth-tunable half-wave plate based on vanadium dioxide (VO2) phase transition. The hybrid metamaterial is regarded as a hollow “leaf-type” metallic structure and act as a dual-band half-wave plate when VO2 film is in the insulating phase. Within 1.01−1.17 THz and 1.47−1.95 THz, it can accomplish
y - tox -polarization conversion with a polarization conversion rate over 0.9 and an average relative bandwidth of 26%. The metamaterial becomes a solid core “leaf-type” metallic structure when VO2 is in the metallic phase. Within 1.13−2.80 THz, it can act as a broadband half-wave plate with a relative bandwidth of 85%. The working principle of the bandwidth-tunable half-wave plate is explained by the instantaneous surface current distribution and electric field theory in detail. The proposed “leaf-type” hybrid metamaterial half-wave plate has potential application prospects in THz imaging, sensing and polarization detection.-
Key words:
- metamaterial /
- half-wave plate /
- bandwidth-tunable /
- terahertz /
- VO2
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图 1 “树叶型”复合超构材料的工作原理和结构示意图。（a）半波片工作原理图（偏振旋转角φ和倾斜入射角θ已在插图中标注）；（b）基本单元的结构参数图
Figure 1. Operation principle of “leaf-type” hybrid metamaterial and it’s structural diagram. (a) Schematic diagram of half-wave plate (The polarization angle φ and incident angle θ are marked in the inset); (b) structural parameters of a unit cell in the proposed metamaterial
图 2 VO2薄膜为不同相态时“树叶型”复合超构材料的反射偏振特性。（a）和（b）共偏振和正交偏振反射系数；（c）和（d）偏振转换率
Figure 2. Reflection polarization properties of “leaf-type” hybrid metamaterial when the VO2 film is in different phase states. (a) and (b) Reflection coefficients of co- and cross-polarization; (c) and (d) Polarization Conversion Ratio (PCR)
图 3 y偏振光激发下6个特定频率处的偏振椭圆
Figure 3. Polarization ellipses of reflected lights at the six specific frequencies under y-polarized illumination.
图 4 VO2薄膜为不同相态时，垂直入射的u偏振和v偏振激发“树叶型”复合超构材料的反射系数和相位频谱图。（a）和（b）反射系数ruu，rvv和ruv，rvu；（c）和（d）φuu和φvv及其相位差Δφ（u偏振和v偏振如插图所示）
Figure 4. Reflection coefficients and phases of the hybrid metamaterial for normal u and v polarization incidences when the VO2 film is in different phase states. (a) and (b) Reflection coefficients ruu , rvv and ruv , rvu; (c) and (d) reflection phases φuu , φvv and phase difference Δφ (normal u and v polarization incidences, as depicted by the inset)
图 5 关键频率处的瞬时表面电流分布图。VO2为绝缘态时，（a）1.22 THz、（b）1.68 THz、（c）2.10 THz、（d）2.61 THz；VO2为金属态时，（e）1.22 THz、（f）1.95 THz、（g）2.10 THz、（h）2.71 THz
Figure 5. Instantaneous surface current distributions at critical frequencies. (a) 1.22 THz, (b) 1.68 THz, (c) 2.10 THz, (d) 2.61 THz for VO2 film in the complete insulating state; (e) 1.22 THz, (f) 1.95 THz, (g) 2.10 THz, (h) 2.71 THz for VO2 film in the complete metallic state
图 6 VO2薄膜为绝缘态和金属态时，带宽可调谐半波片器件随入射角度θ的变化规律。（a）和（b）rxy；（c）和（d）PCR
Figure 6. Incident angle dependence of bandwidth-tunable half-wave plate components when VO2 film is in the complete insulating and metallic states. (a) and (b) rxy; (c) and (d) PCR
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