Abstract-Terahertz electromagnetically-induced transparency of self-complementary meta-molecules on Croatian checkerboard

Zhenyu Zhao, Xiaobo Zheng, Wei Peng, Jianbing Zhang, Hongwei Zhao, Wangzhou Shi

https://www.nature.com/articles/s41598-019-42038-8

A terahertz (THz) electromagnetically-induced transparency (EIT) phenomenon is observed from two types of self-complementary meta-molecules (MMs) based on rectangular shaped electric split-ring resonators (eSRR) on Croatian checkerboard. Each MM contains a couple of identical size eSRRs and a couple of structural inversed eSRRs twisted π/2 in checkerboard pattern. In the first type of MM (type-I), the gap is in the middle line of eSRR. In the second type of MM (type-II), the gap is on the two arms of eSRR. Both types of MMs exhibit EIT effect. A maximum 20 ps group delay is observed at the transparency window of 0.63 THz in type-I MM; while a maximum 6.0 ps group delay is observed at the transparent window of 0.60 THz in type-II MM. The distribution of surface currents and electrical energy reveals that only CeSRR contribute to the transparency window as well as the side-modes in type-I MM, where the current leakage via contact point contributes to the low-frequency side-mode, and the coupled local inductive-capacitive (LC) oscillation in CeSRRs contributes to the high-frequency side-mode. In type-II MM, however, the localized dipolar oscillator of CeSRR contributes to the low-frequency side-mode; while the hybridization of dipole oscillation on eSRR and LC resonance on CeSRR contributes to the high-frequency side-modes. Our experimental findings manifest a new approach to develop THz slow-light devices.

Abstract-Dual terahertz slow light plateaus in bilayer asymmetric metasurfaces

Zhenyu Zhao, Zhidong Gu, Hui Zhao, Wangzhou Shi,

Fig. 1 (a) Schematic diagram of THz radiating on the bilayer asymmetric metasurface, KTHz refers to the wavevector of incident THz pulse. ETHz and HTHz refer to the electrical components and magnetic components respectively. (b) The sandwich structure of bilayer metasurface is 125 μm × 125 μm, in which L = 98 μm, D = 2.5 μm, t= 0.2 μm, w1 = 5 μm, w2 = 6 μm, a = 32 μm, g = 6 μm, respectively.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-4-1608

This work theoretically proposed dual terahertz (THz) slow light plateaus by tuning the destructive interference between a toroidal magnetic momentum and magnetic dipole momentum. The metasurfaces are in a sandwich structure. A metallic cut-wire is patterned on one side of polyimide thin-film, and a rectangular split-ring resonator (SRR) on the other side with asymmetric layout. By translating the SRR along the cut-wire from the top terminal to the bottom terminal of the cut-wire, dual slow light plateaus are found in the transparency window at a certain range of displacement. A maximum of 40.4 ps group delay is achieved as the displacement achieves 9 μm. The numerical mapping of electromagnetic field indicates that the electrical dipole on metallic cut-wire results in a localized toroidal magnetic momentum, while the inductive-capacitor oscillation of SRR results in a magnetic dipole momentum. These two momentums have opposite directions, which will repel each other at certain displacement, creating the transparency windows. Furthermore, an electrical coupling takes place in between the bilayer metasurface so that the slow light achieves a maximum, with the aforementioned two mechanisms working in coincidence.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Maximization of terahertz slow light by tuning the spoof localized surface plasmon induced transparency

Zhenyu Zhao, Yana Chen, Zhidong Gu, and Wangzhou Shi

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-8-2345

This work numerically investigates a localized terahertz (THz) slow light phenomenon by tuning the spoof localized surface plasmon-induced transparency (PIT). A binary meta-molecule supports the interaction of the spoof localized surface plasmon (spoof-LSP), which is composed of a metallic arc and a textured circular cavity of periodic grooves. By tuning the central angle θ of the arc from 90 degrees to 170 degrees, a slow light plateau is found in the transparency window at certain frequency range. A maximum of 46 ps group delay is achieved at the θ of 135. The numerical mapping of the electromagnetic field indicates a new-born dipolar spoof-LSP that appears at the transparency windows on the circular cavity with opposite polarity to the spoof-LSP on the metallic arc. These two spoof-LSPs of opposite direction lead to a fake quadrupole, which will repel each other in magnetic dipole momentum. The slow light achieves maximum with the induced spoof-LSP and is the same as the origin spoof-LSP on the metallic arc in oscillation strength. This work paves a new way for the maximization of THz slow light.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Graphene patterns supported terahertz tunable plasmon induced transparency

Xiaoyong He, Feng Liu, Fangting Lin, and Wangzhou Shi

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-8-9931

The tunable plasmonic induced transparency has been theoretically investigated based on graphene patterns/SiO2/Si/polymer multilayer structure in the terahertz regime, including the effects of graphene Fermi level, structural parameters and operation frequency. The results manifest that obvious Fano peak can be observed and efficiently modulated because of the strong coupling between incident light and graphene pattern structures. As Fermi level increases, the peak amplitude of Fano resonance increases, and the resonant peak position shifts to high frequency. The amplitude modulation depth of Fano curves is about 40% on condition that the Fermi level changes in the scope of 0.2-1.0 eV. With the distance between cut wire and double semi-circular patterns increases, the peak amplitude and figure of merit increases. The results are very helpful to develop novel graphene plasmonic devices (e.g.sensors, modulators, and antenna) and find potential applications in the fields of biomedical sensing and wireless communications.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Tuning the terahertz trapped modes of conductively coupled Fano-resonators in reflectional and rotational symmetry

Xiaobo Zheng, Zhenyu Zhao, Wei Peng, Jianbing Zhang, Hongwei Zhao, and Wangzhou Shi

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-1-105&origin=search

We experimentally investigate the terahertz (THz) response of conductively coupled asymmetric split ring resonator-based meta-molecules in the layout of reflection and rotational symmetry. In the reflectional symmetry case, the horizontally polarized THz excites a couple of trapped modes: the low-order one is a coupled Fano-resonance, and the high-order one is a decoupled dipole oscillator. The vertically polarized THz excites an inductive-capacitor resonance as a low-order trapped mode below the frequency of a high-order intrinsic mode. The quality factors (Q factors) of trapped modes decrease with the displacement of top-and-bottom gap increasing. In the rotational symmetry case, the horizontally polarized THz excites a single trapped mode owing to coupled Fano-resonance. The vertically polarized THz excites a high-order trapped mode of coupled multiple dipole oscillations beyond the frequency of intrinsic low-order dipole oscillation. The Q factors of trapped modes increase with the displacement of the top-and-bottom gap increase. For the first time, our results reveal the trapped modes’ evolution owing to the interaction of Fano-resonators conductively coupled under different symmetry.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Plasmon-induced transparency-like behavior at terahertz region via dipole oscillation detuning in a hybrid planar metamaterial

Plasmon-induced transparency-like behavior at terahertz region via dipole oscillation detuning in a hybrid planar metamaterial

Zhenyu Zhao, Zhiqiang Song, Wangzhou Shi, and Wei Peng

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-6-7-2190

We investigate a plasmon-induced transparency (PIT)-like behavior at terahertz (THz) region induced by resonance detuning in a hybrid planar metamaterial (MM). Each unit cell of the MM contains two types of dipole oscillation resonators: a cut-wire and a couple of U-shaped resonators in mirror symmetry. The hybridization of above resonators splits the single resonance mode into two side modes in THz transmission spectrum. The side modes are found to induce negative group delays of incident THz wave-packet. The distribution of surface currents and electric energy reveals that the near-field coupling between cut-wire and U-shape resonators results in inductive-capacitive (LC) resonance, which dominates the low frequency side mode, while the high frequency side mode attribute to the triple dipole oscillations. The reduction of the length of cut-wire give rise to a dipole resonance detuning, which enhances the LC resonance via near-field coupling, while attenuates the constructive inference of triple dipole oscillators. The retrieved complex dielectric functions indicate the evolution of LC resonance and triple dipole oscillations. By controlling the dipole resonance detuning appropriately, a man-made transparent tip can be created in between the two side modes. However, such a transparent tip is unable to induce negative group delay. Aforementioned PIT-like behavior can support the design of hybrid planar MMs in application of two-band notch filters or multi-channel buffer in the THz-region.

© 2016 Optical Society of America

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Abstract-Investigation of graphene assisted tunable terahertz metamaterials absorber

Xiaoyong He, Xu Zhong, Fangting Lin, and Wangzhou Shi
http://proxy.osapublishing.org/ome/abstract.cfm?uri=ome-6-2-331

By using the graphene-SiO2-Si-dielectrics-metallic ground plane (GSiO2SiDM) structures, we investigate the tunable properties of graphene metamaterials (MMs) absorbers in the terahertz region, including the effects of operation frequency, Fermi level, and graphene structure patterns. The results manifest that the graphene tunable GSiO2SiDM structure can achieve net absorption by changing structure parameters and the Fermi level of graphene layer. The resonant absorption and reflection curves of the GSiO2SiDM structures can be shifted in a wide range via controlling the applied electric fields. The modulation depth of resonant amplitude and frequency can reach more than 60% and 30%, respectively. The resonant peak (dip) of the absorption (reflection) curves shift to high frequency with the increase of Fermi level of the graphene layer. Due to broad absorption curve, the graphene MMs absorbers structures are suitable for the fabrication of broad absorber. The results are very useful to design novel devices, such as thermal detectors, imager, and biosensors.

© 2016 Optical Society of America

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Abstract-Terahertz response of fractal meta-atoms based on concentric rectangular square resonators

Zhiqiang Song^1,a), Zhenyu Zhao^1,a),b), Wei Peng² and Wangzhou Shi¹
 HIDE AFFILIATIONS
1 Department of Physics, Shanghai Normal University, Shanghai 200234, China
2 State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
a) Z. Song and Z. Zhao contributed equally to this work.
b) Electronic mail: zyzhao@shnu.edu.cn
J. Appl. Phys. 118, 193103 (2015); http://dx.doi.org/10.1063/1.4936217

http://scitation.aip.org/content/aip/journal/jap/118/19/10.1063/1.4936217?TRACK=RSS

We investigate the terahertz electromagnetic responses of fractal meta-atoms (MAs) induced by different mode coupling mechanisms. Two types of MAs based on concentric rectangular square (CRS) resonators are presented: independent CRS (I-CRS) and junctional-CRS (J-CRS). In I-CRS, each resonator works as an independent dipole so as to result in the multiple resonance modes when the fractal level is above 1. In J-CRS, however, the generated layer is rotated by π/2 radius to the adjacent CRS in one MA. The multiple resonance modes are coupled into a single mode resonance. The fractal level increasing induces resonance modesredshift in I-CRS while blueshift in J-CRS. When the fractal level is below 4, the mode Q factor of J-CRS is in between the two modes of I-CRS; when the fractal level is 4 or above, the mode Q factor of J-CRS exceeds the two modes of I-CRS. Furthermore, the modulation depth (MD) decreases in I-CRS while it increases in J-CRS with the increase in fractal levels. The surfacecurrents analysis reveals that the capacitive coupling of modes in I-CRS results in the modesredshift, while the conductive coupling of modes in J-CRS induces the mode blueshift. A high Q mode with large MD can be achieved via conductive coupling between the resonators of different scales in a fractal MA.

Abstract-Theoretical investigation of semiconductor supported tunable terahertz dielectric loaded surface plasmons waveguides

• Chunlin Liu, 
• Xiaoyong He, 
• Zhenyu Zhao, 
• Hao Zhang, 
• Wangzhou Shi

• Department of Physics, Mathematics & Science College, Shanghai Normal University, No. 100 Guilin Road, Shanghai 200234, PR China

Received 16 April 2015, Revised 12 July 2015, Accepted 21 July 2015, Available online 30 July 2015

http://www.sciencedirect.com/science/article/pii/S0030401815006604

The tunable propagation properties of semiconductor-based dielectric loaded surface plasmons (DLSPs) structures have been theoretically investigated in the THz regime, including the effects of temperature, operation frequency, and the thermo-optic effect of dielectric stripe materials. The results show that the waveguide properties of DLSPs structure can be modulated in a wide range via changing the temperature. For instance, when the temperature is changed in the range of 300–600 K, the modulation depth of propagation length can reach more than 80%. With the increase of refractive index of the dielectric stripe, the modulation depth of the effective indices and propagation lengths increase. In addition, the propagation length and figure of the merit can be improved obviously with the hybrid dielectric stripe structure (by coating Si on the SiO₂ layer). The results are very helpful to design novel waveguide devices, such as modulators, switchers, sensors and polarizers.

Abstract-Teeter-totter effect of terahertz dual modes in C-shaped complementary split-ring resonators

Zhiqiang Song¹, Zhenyu Zhao^1,a), Hongwei Zhao², Wei Peng³, Xiaoyong He¹ and Wangzhou Shi¹
http://scitation.aip.org/content/aip/journal/jap/118/4/10.1063/1.4927845
1 Department of Physics, Shanghai Normal University, Shanghai 200234, China
2 Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China
3 State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
a) Electronic mail: zyzhao@shnu.edu.cn
J. Appl. Phys. 118, 043108 (2015); http://dx.doi.org/10.1063/1.4927845

A teeter-totter effect of terahertz (THz) resonant modes in C-shaped complementary split-ringresonators (CSRRs) is observed. The dual resonant mode transmission enhancement was investigated using THz time-domain spectroscopy. The intensity of the lower-frequency resonance modes increases monotonically with the CSSR gap width, which is accompanied by a monotonic decrease in the intensity of the higher-frequency resonance modes. The origin of the dual resonant modes is numerically explained by the electromagnetic energy density distribution and surface current analysis. The inductive-capacitive resonance dominates the lower frequency mode, while the dipole oscillation dominates the higher frequency mode. By tuning the gap of the CSRR, an equilibrant transmittance of above dual resonance modes can be designed. This teeter-totter effect promises a possible application of CSSRs as potential dual-bandpass filters in the THz-region.