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Terahertz (THz) wave usually refers to the electromagnetic wave with a frequency between 0.1—10.0 THz. It has potential applications in wireless communication, biomedical image processing, nondestructive testing, military radar, and other fields. However, owing to function limitation of the natural material, multifunctional terahertz devices are difficult to design and fabricate, which becomes a bottleneck for THz technology. The emergence of metamaterials fills the gap in the electromagnetic materials in the THz frequency band, and now they are widely used in THz functional devices, such as THz modulators, THz absorbers, THz filters, THz sensors, and THz slow-light devices. However, the above-mentioned THz devices all have a single function. For practical application, multifunction integrated THz devices have broader application prospects. As is well known, the Ge2Sb2Te5 (GST) is a typical phase transition material. Under excitation of light or electronic field, GST can realize a reversible phase transition between insulating state and metallic state. In order to achieve a switchable multifunctional THz device, in this work we design a THz metamaterial based on the phase transition material GST and realize a switchable function with slow-light and absorption functions. The THz metamaterial consists of a microstructure layer, which is composed of gold rings arranged periodically, and a GST thin film spaced by an SiO2 dielectric layer. When GST is in an insulating state, the two gold rings are coupled to each other under the excitation of the THz pulse. Then, we can observe the EIT-like effect. The THz pulses propagating in the metamaterial we proposed can be slowed down, and a maximum group delay of the THz pulse can reach 3.6 ps. However, when GST is in a metallic state, we can observe two absorption peaks in the spectrum of the proposed THz metamaterial, and the absorption rate is 97% at a frequency of 0.365 THz and 100% at a frequency of 0.609 THz. Furthermore, we also investigate the polarization properties of the proposed THz metamaterial, and find that it has polarization insensitive characteristic. When the polarization angle of the incident THz light pulse changes from 0° to 90°, the slow-light and absorption properties of the THz metamaterial are unaffected. The proposed THz metamaterial has potential applications in THz biomedical image processing, THz optical switching, and THz optical buffer.
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Keywords:
- metamaterials /
- terahertz /
- slow light /
- absorber /
- phase change materials
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图 1 THz超材料结构示意图 (a) THz超材料阵列; (b) 微结构单元俯视图; (c) 微结构单元侧视图
Figure 1. Schematic structure diagram of the THz metamaterials: (a) THz metamaterial array; (b) top view of microstructure cells; (c) side view of microstructure units.
图 2 (a) GST薄膜处于绝缘状态时, 外环、内环和双环结构的透射光谱图; (b)—(d) 0.453, 0.547, 0.834 THz处超材料结构的表面电流分布
Figure 2. (a) Transmission spectrum of outer ring, inner ring, and double ring structures with GST films in an insulating state; (b)–(d) surface current distribution of metamaterial structures at 0.453, 0.547, and 0.834 THz.
图 3 (a) THz超材料的类EIT效应的理论计算与仿真结果; (b) THz光脉冲在超材料中传输时的相位变化和相对群延迟
Figure 3. (a) Theoretical calculation and simulation results of EIT-like effects of THz metamaterials; (b) phase change and relative group delay of THz light pulse transmission in metamaterials.
图 4 (a) THz超材料的透射、反射和吸收光谱; (b) THz超材料的外环、内环和双环微结构的吸收光谱
Figure 4. (a) Transmission, reflection, and absorption spectra of THz metamaterials; (b) absorption spectra of the outer ring, inner ring, and two-loop microstructures of THz metamaterials.
图 5 (a)—(c) SiO2层厚度h = 24 μm时, THz超材料结构的介电常数 (a)、磁导率(b)和等效阻抗(c); (d)不同SiO2层厚度时THz超材料结构的吸收光谱
Figure 5. (a)–(c) Permittivity(a), permeability (b) and equivalent impedance (c) of THz metamaterial structure at SiO2 layer thickness h = 24 μm; (d) absorption spectrum of THz metamaterial structure at different SiO2 layer thickness.
图 6 吸收光谱与入射角的关系
Figure 6. Dependence of the absorption spectra on the incidence angle.
图 7 入射光的偏振角从0°到90°变化时, THz超材料的透射光谱(a)、群延迟(b)和吸收光谱(c)
Figure 7. Transmission spectrum (a), group delay (b), and absorption spectrum (c) of the THz metamaterials, when the polarization angle of the incident light varies from 0° to 90°.
表 1 三种相态GST材料的Drude模型参数
Table 1. Drude model parameters of the GST materials for the three phases.
相态 ε τ σdc 非晶态(a-GST) 15.3 — 0 面心立方(c-GST) 38.2 1.61 382 六方(h-GST) 60.6 5.29 2230 
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[1] Tonouchi M 2007 Nat. Photonics 1 97
Google Scholar
[2] Yang X W, Zhao F 2022 Acta Opt. Sin. 42 0806002
Google Scholar
[3] Wang Y Y, Wang G Q, Xu D G, Jiang B Z, Ge M L, Wu L M, Yang C Y, Mu N, Wang S, Chang C, Chen T, Feng H, Yao J Q 2022 Acta Opt. Sin. 42 1017001
Google Scholar
[4] Shen Y C, Lo T, Taday P F, Cole B E, Tribe W R, Kemp M C 2005 Appl. Phys. Lett. 86 241116
Google Scholar
[5] Li H Y, Li Q, Xia Z W, Zhao Y P, Chen D Y Wang Q 2013 J. Infrared, Millimeter, Terahertz Waves 34 88
Google Scholar
[6] Zhou J F, Zhang L, Tuttle G, Koschny T, Soukoulis C M 2006 Phys. Rev. B 73 041101
Google Scholar
[7] Seddon N, Bearpark T 2003 Science 302 1537
Google Scholar
[8] Zhong Y J, Huang Y, Zhong S C 2021 Opt. Mater. 14 110996
Google Scholar
[9] Cai H 2018 Adv. Opt. Mater. 6 1800257
Google Scholar
[10] Zhu H L, Zhang Y, Ye L F, Li Y K, Xu Y H, Xu R 2020 Opt. Express 28 414039
Google Scholar
[11] Hu F R, Wang H, Zhang X W, Xu X L, Jiang W Y, Rong Q, Zhao S, Jiang M Z, Zhang W T 2019 IEEE J. Sel. Top. Quantum Electron. 25 4700207
Google Scholar
[12] Seo M, Park H R 2020 Adv. Opt. Mater. 8 1900662
Google Scholar
[13] Cui W, Wang Y X, He Z H, He H 2021 Results Phys. 26 104356
Google Scholar
[14] Gansel J K, Thiel M, Rill M S, Decker M, Bade K, Saile V, Freymann G V, Linden S, Wegener M 2009 Science 325 1513
Google Scholar
[15] Makino K, Kato K, Saito Y, Fons P, Kolobov A V, Tominaga J J, Nakano T, Nakajima M 2019 J. Mater. Chem. C 7 8209
Google Scholar
[16] Zhou K, Nan J Y, Shen J B, Li Z P, Cao J C, Song Z T, Zhu M, He B Q, Yan M, Zeng H P, Li H 2021 APL Mater. 9 101113
Google Scholar
[17] Guo L Y, Ma X H, Chang Z Q, Xu C L, Liao J, Zhang R 2021 J. Mater. Res. Technol 14 772
Google Scholar
[18] Fabio A, Brian K, Dragoslav G, Nickolay V L, Gamani K 2012 Appl. Phys. Lett. 100 111104
Google Scholar
[19] Sun H Y, Zhao L, Dai J S, Liang Y Y, Guo J P, Meng H Y, Liu H Z, Dai Q F, Wei Z C 2020 Nanomaterials 10 1359
Google Scholar
[20] Galván A M, Hernández J G 2000 J. Appl. Phys. 87 760
Google Scholar
[21] Manjappa M, Chiam S Y, Cong L Q, Bettiol A A, Zhang W L, Singh R J 2015 Appl. Phys. Lett. 106 181101
Google Scholar
[22] Meng F Y, Wu Q, Erni D, Wu K, Lee J C 2012 IEEE Trans. Microwave Theory Tech. 60 3013
Google Scholar
[23] Niakan N, Askari M, Zakery A 2012 J. Opt. Soc. Am. B 29 2329
Google Scholar
[24] Sun H, Hu Y Z, Tang Y H, You J, zhou J H, Liu H Z, Zheng X 2020 Photonics Res. 8 263
Google Scholar
[25] Bagcia F, Akaoglu B 2018 J. Appl. Phys. 123 173101
Google Scholar
[26] Suna Y B, Shi Y P, Liu X Y, Song J M, Lia M P, Wang X D, Yang F H 2021 Nanoscale Adv. 3 4072
Google Scholar
[27] Mattiucci N, Bloemer M J, Aközbek N, D’Aguanno G 2013 Sci. Rep. 3 3203
Google Scholar
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