Abstract-Polarization-independent and angle-insensitive tunable electromagnetically induced transparency in terahertz metamaterials

 

Xiaoyu Shi, Yuanwei Tong,  Yaqiong Ding

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-60-25-7784

A metamaterial with a polarization-independent and angle-insensitive electromagnetically induced transparency (EIT)-like effect is theoretically investigated in the terahertz regime. The proposed metamaterial is composed of square rings and split isosceles triangle rings, which behave as bright elements and quasi-dark elements, respectively. An EIT-like phenomenon, which is caused by the destructive interference between different scattering paths via the bright and quasi-dark elements, is observed with a transparent window. This EIT mechanism is revealed with simulated field distributions as well as the analysis based on coupled-mode theory. Full wave simulations show that EIT-like phenomenon in the proposed metamaterial is independent of polarization and is robust to the angle of the incident light. This structure may have potential applications in terahertz detectors, sensors, and modulators.

© 2021 Optical Society of America

Abstract-Bifunctional terahertz modulator for beam steering and broadband absorption based on a hybrid structure of graphene and vanadium dioxide

 

Wenwen Liu, Jiashuai Xu, Zhengyong Song

Schematic diagram of the proposed structure. (a) The whole 3D structure. (b) Schematic of 3D unit cell. (c) Top view of graphene patch.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-15-23331&id=453128

A bifunctional metamaterial is proposed based on a hybrid graphene and vanadium dioxide (VO2) configuration, which can realize a dynamic switch between beam steering and broadband absorption. The structure consists of a VO2 square, graphene patch, topas spacer, VO2 film, topas spacer, and metal substrate. When VO2 is in the metallic state, the structure serves as a coding metamaterial. By engineering different sizes of the top VO2 square and adjusting the Fermi energy level of graphene, the incident wave is scattered in different patterns. When VO2 is in the dielectric state, the structure serves as a broadband absorber. By changing the Fermi energy level of graphene from 0.0 eV to 0.9 eV, absorptance can be gradually changed and working bandwidth widens. There is an absorption band with near 100% absorptance from 0.9 THz to 1.35 THz when the Fermi energy level is 0.73 eV. And the designed broadband absorber is polarization-insensitive within the incident angle of 50°. Our work may show great potential in applications such as terahertz switching and modulation.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Graphene-enabled active metamaterial for dynamical manipulation of terahertz reflection/transmission/absorption

Yin Zhang. Yijun Feng, Junming Zhao,

                                       

https://www.sciencedirect.com/science/article/abs/pii/S0375960120307076

Arbitrarily controlling the reflection/transmission/absorption state of electromagnetic waves, especially their dynamical manipulation, is on high demand due to the growing development of practical optical devices and application systems. In this work, we present a scheme to dynamically manipulating terahertz wave reflection/transmission/absorption using the active metamaterial composed of a layer of metallic structural and two graphene sandwich structures as well as polymer spacers. By adjusting the Fermi level of graphene, this tunable metamaterial can achieve electronically reconfigurable terahertz reflection, transmission and absorption in a highly efficient manner. Furthermore, it also enables continuous dynamical modulation between any two among the three states. The presented metamaterial is a promising candidate for exploring active terahertz devices for dynamically controlling the state of light-matter interactions and have potential applications in optoelectronic devices, wireless communication and frequency selective surface.

Abstract-Graphene-based tunable multi-band metamaterial polarization-insensitive absorber for terahertz applications

Prince Jain, Shonak Bansal, Krishna Prakash, Neha Sardana, Neena Gupta, Sanjeev Kumar, Arun K. Singh

https://link.springer.com/article/10.1007/s10854-020-03742-8

This paper presents a graphene-based tunable polarization-insensitive metamaterial absorber (MMA) at terahertz (THz) frequencies. The absorber consists of top patterned gold (Au) layer followed by single layer of graphene, dielectric spacer, and Au layer at bottom. The proposed MMA demonstrates multi-band absorption with the characteristics of both broad- and dual-band absorption by optimizing dimensions (parametric analysis). Broad-band absorption reaches over 90% for the range of 4.57–6.45 THz with the relative absorption bandwidth of 34%, and the absorption peak at 6.86 and 7.20 THz having 98.9 and 95.2% absorption. The normalized impedance and constitutive electromagnetic parameters of the MMA are calculated using the Nicolson–Ross–Weir (NRW) method to validate the absorption rate. Furthermore, proposed absorber is polarization-insensitive upto 90° for transverse electric wave. The tunable characteristic of MMA is achieved by tuning the Fermi energy of graphene with the application of bias voltage. Accordingly, the proposed multi- and broad-band absorbers find its potential applications in spectroscopy detection, imaging, and sensing.

Abstract-An Ultra-Wideband Terahertz Metamaterial Absorber Utilizing Sinusoidal-Patterned Dielectric Loaded Graphene

Milad Nourbakhsh, Ehsan Zareian-Jahromi, Raheleh Basiri, Valiollah Mashayekhi

https://link.springer.com/article/10.1007/s11468-020-01203-w

In this paper, a non-structured graphene sheet loaded with a sinusoidal-patterned dielectric is introduced as an ultra-wideband metamaterial absorber in terahertz regime. Regardless of conventional structures with multilayered-graphene, a single layer sheet of non-structured graphene is used whereas the proposed structure benefits from dielectric width modulation and cavity method in order to excite continuous graphene plasmon resonances. The structure comprises four layers that two Fabry-Perot cavity mirrors are constructed by upper sinusoidal-patterned dielectric and a gold film. Full wave simulation results demonstrate that a broadband over 90% absorption with absolute bandwidth of 6.58 THz and central frequency of 3.97 THz is achieved under normal TE/TM incident plane wave. The designed structure yields 166% relative bandwidth. According to the symmetric configuration, the absorption spectra of mentioned polarizations are thoroughly close to each other resulting to a polarization insensitive structure. The stability of bandwidth and absorbance of the structure versus angle of incidence, θ, up to 35°/65° for TM/TE polarizations, respectively, and azimuth angle, φ, shows an interesting capability for utilization as detectors and sensors. The simple geometry of utilized graphene layer results in easy fabrication. The designed structure has wideband absorption in THz regime. Moreover, it is more compact than conventional broadband THz absorbers.

Abstract-Topological flexible metamaterials with isotropic dual-frequency terahertz-band absorption

Jianli Cui, Binzhen Zhang, Hong Cheng Xu, Huixia Sun, Guirong Shao



https://www.sciencedirect.com/science/article/abs/pii/S0030401819301439

This study demonstrates an isotropic flexible absorptive metamaterial structure for terahertz wave bands based on topological-optimization design. One rotationally symmetric absorbing element consists of a polarization-sensitive metamaterial cell arranged with a counterclockwise topology. A flexible topological metamaterial absorber is formed from crystalline elements through an infinite periodic arrangement using Floquet’s theorem. This artificial material achieves dual-frequency absorption with peak absorptions of 94% and 99.9% at 0.136 and 0.143 THz, respectively. The independent polarization angle of the two absorption peaks exceeds 45°under an oblique incident-wave process operation and in bending measurement, which indicate polarization isotropy. The equivalent electrical thickness corresponding to the minimum resonance point is close to one-ninth. The proposed ultra-thin flexible artificial material not only possesses perfect conformity with complex surfaces but also achieves larger angle electromagneticabsorption. The study results can present this material a potential candidate for polarized manipulation in electromagnetic stealth and electromagnetic control in the terahertz technology.

Abstract-Selective excitation of resonances in gammadion metamaterials for terahertz wave manipulation

DaCheng WANG,  Qin HUANG,  ChengWei QIU,  MingHui HONG,

http://engine.scichina.com/publisher/scp/journal/SCPMA/58/8/10.1007/s11433-015-5674-7?slug=fulltext

A gammadion terahertz (THz) metamaterial embedded with a pair of splits is experimentally investigated. By introducing the pair of splits at different arms, the transmitted amplitude at the resonance frequency can be manipulated from 61% to 24%. Broadband static resonance tunability from 1.11 to 1.51 THz is also demonstrated via varying the relative split positions at certain arms. The amplitude change and static resonance tunability are attributed to the introduced split pairs, which enable selective excitation of different resonance modes in the gammadion metamaterials. This work promises a new approach to design THz functional devices.

Abstract-Modulating Fundamental Resonance in Capacitive Coupled Asymmetric Terahertz Metamaterials

S. Jagan Mohan Rao, Yogesh Kumar Srivastava, Gagan Kumar & Dibakar Roy Chowdhury

https://www.nature.com/articles/s41598-018-34942-2

In this work, we experimentally investigate near-field capacitive coupling between a pair of single-gap split ring resonators (SRRs) in a terahertz metamaterial. The unit cell of our design comprises of two coupled SRRs with the split gaps facing each other. The coupling between two SRRs is examined by changing the gap of one resonator with respect to the other for several inter resonator separations. When split gap size of one resonator is increased for a fixed inter-resonator distance, we observe a split in the fundamental resonance mode. This split ultimately results in the excitation of narrow band low frequency resonance mode along with a higher frequency mode which gets blue shifted when the split gap increases. We attribute resonance split to the excitation of symmetric and asymmetric modes due to strong capacitive or electric interaction between the near-field coupled resonators, however blue shift of the higher frequency mode occurs mainly due to the reduced capacitance. The ability of near-field capacitive coupled terahertz metamaterials to excite split resonances could be significant in the construction of modulator and sensing devices beside other potential applications for terahertz domain.

Abstract-Broadband tunable terahertz polarization converter based on a sinusoidally-slotted graphene metamaterial

Jianfeng Zhu, Shufang Li, Li Deng, Chen Zhang, Yang Yang, and Hongbo Zhu

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-5-1164

A new wideband sinusoidally-slotted graphene-based cross-polarization converter (CPC) is proposed in this paper. The proposed polarization converter can realize a broadband terahertz polarization conversion from 1.28 to 2.13-THz with a polarization conversion ratio (PCR) of more than 0.85. Taking advantage of the gradient width modulation of the graphene-based unit structure, the continuous plasmon resonances are excited at the edges of the sinusoidal slot. Therefore, the proposed converter can achieve a broadband polarization conversion in a simplified structure. Furthermore, the polarization conversion characteristics of the CPC are insensitive to the incident angle. The PCR remains more than 0.85 with little bandwidth degradation even as the incident angle increases to as high as 50°. More importantly, the operating bandwidth and the magnitude of the PCR can be tuned easily by adjusting the chemical potential and the electron scattering times of the graphene. In a way, we believe this kind of graphene-based polarization converter can enrich the polarization conversion community for realizing broadband and tunable polarization conversion.

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

Abstract-Liquid crystal terahertz modulator with plasmon-induced transparency metamaterial

Jing Wang, Hao Tian, Yu Wang, Xueyan Li, Yujie Cao, Li Li, Jianlong Liu, Zhongxiang Zhou

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-5-5769

An electrically tunable terahertz (THz) modulator with large modulation depth and low insertion loss is performed with liquid crystal (LC) metamaterial. The modulation depth beyond 90% and insertion loss below 0.5 dB are achievable at normal incidence by exploiting plasmon-induced transparency (PIT) effect. The PIT spectra can be manipulated by actively controlling the interference between dipole mode and nonlocal surface-Bloch mode with LC. The incident angle tuning effect on PIT spectra shows that the large modulation depth and low insertion loss can remain over a wide range of working angles. The superior property and simplicity of design make this modulator promising in advanced terahertz communication.

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

Abstract-Investigation of graphene-supported tunable asymmetric terahertz metamaterials

Chenyuyi Shi, Xiaoyong He, Feng Liu, Fangting Lin, and Hao Zhang

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-35-3-575

By integrating a graphene layer with asymmetric split-ring metamaterial (MM) metal resonators, we investigated tunable propagation properties in the terahertz regime, including the effects of graphene Fermi levels, structural parameters, and operation frequencies. The results reveal that a sharp inductor-capacitor (LC) resonance can be observed at low frequency for the asymmetric MM structure, and its 𝑄$Q$ factor can reach more than 17.5. With the help of a graphene layer, the optical response is modulated efficiently. For instance, if the Fermi level changes in the range of 0.01–0.3 eV, for the semiconductor MM structure, the modulation depths (MDs) of amplitude and frequency are 27.0% and 43.4%, respectively. In addition, the resonant curves of indium antimonide (InSb) MMs can be modulated by changing the temperature; the amplitude MD is 56.2% as the temperature changes in the range of 350–800 K. The 𝑄$Q$ factor of the InSb MM structure is about 44.6. The results are helpful for designing novel graphene-based tunable terahertz devices, e.g., filters and modulators.

© 2018 Optical Society of America

Abstract-Enhanced quadruple-resonant terahertz metamaterial with asymmetric hybrid resonators

Minglei Shi, Feng Lan, Pinaki Mazumder, Mahdi Aghadjani, Ziqiang Yang, Lin Meng, Jun Zhou,

https://www.sciencedirect.com/science/article/pii/S0925346717306997

This paper presents the design, fabrication and investigation of a quadruple-resonant terahertz metamaterial that comprises two different Electric-inductance capacitance (ELC) resonators in a vertical configuration. Owing to asymmetric electric field coupling between the two resonators, the combined structure exhibits better performance in terms of transmission minima and bandwidths than the individual particles. The distributions of the surface current and electric field reveal quasi-quadrupole resonance, electric dipolar resonance and coupling between these resonances at different resonant frequencies. Moreover, the resonant frequencies are tunable by adjusting the corresponding geometrical parameters. Above all, the excellent performance of the proposed structure makes it promising for application in multiband terahertz devices.

Abstract-Triple-band tunable perfect terahertz metamaterial absorber with liquid crystal

Ruoxing Wang, Li Li, Jianlong Liu, Fei Yan, Fengjun Tian, Hao Tian, Jianzhong Zhang,  Weimin Sun,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-32280

We report a compact triple-band tunable perfect terahertz metamaterial absorber (TMA) at the subwavelength scale of thickness, which is composed of a planar metallic disk resonator array above a conductive ground plane separated with liquid crystal (LC) mixture. The calculations of terahertz absorption spectra demonstrate triple near-unity absorption bands in the gap plasmonic resonance coupling regime. Three resonance frequencies of the absorber exhibit continuous linear-tunability as changing the refractive index of LC. Remarkably, each peak absorbance of the triple bands maintains at a level of beyond 99% in the whole tuning operation, and the absorbance can remain more than 90% over a wide range of incident angles. Our work suggests that the LC tunable absorber scheme has the potential to overcome the basic difficulty to perform simultaneously multiband spectral tuning and near-unity absorbance with wide angle of incidence and weak polarization dependence. The proposed LC-tunable multiband perfect TMA is promising in the application of biomolecular spectra-selective terahertz imaging and sensing.

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

Abstract-Single-layer plasmonic metasurface half-wave plates with wavelength-independent polarization conversion angle

Zhaocheng Liu, Zhancheng Li, Zhe Liu, Hua Cheng, Wenwei Liu, Chengchun Tang, Changzhi Gu, Junjie Li, Hou-Tong Chen, Shuqi Chen, and Jianguo Tian

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/acsphotonics.7b00491

Publication Date (Web): June 30, 2017

Copyright © 2017 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b00491?journalCode=apchd5

Manipulation of polarization state is of great fundamental importance and plays a crucial role in modern photonic applications such as optical communication, imaging and sensing. Metamaterials and metasurfaces have attracted increasing interest in this area because they facilitate designer optical response through engineering the composite subwavelength structures. Here we propose a general methods of designing half-wave plate, and demonstrate in the near-infrared wavelength range an optically thin plasmonic metasurface half-wave plates that rotate the polarization direction of the linearly polarized incident light with a high degree of linear polarization. The half-wave plate functionality is realized through arranging the orientation of the nanoantennas to form an appropriate spatial distribution profile, which behave exactly as in classical half-wave plates but over in a wavelength-independent way.

Abstract-Terahertz sensing of highly absorptive water-methanol mixtures with multiple resonances in metamaterials

Min Chen, Leena Singh, Ningning Xu, Ranjan Singh, Weili Zhang, and Lijuan Xie

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-13-14089

Terahertz sensing of highly absorptive aqueous solutions remains challenging due to strong absorption of water in the terahertz regime. Here, we experimentally demonstrate a cost-effective metamaterial-based sensor integrated with terahertz time-domain spectroscopy for highly absorptive water-methanol mixture sensing. This metamaterial has simple asymmetric wire structures that support multiple resonances including a fundamental Fano resonance and higher order dipolar resonance in the terahertz regime. Both the resonance modes have strong intensity in the transmission spectra which we exploit for detection of the highly absorptive water-methanol mixtures. The experimentally characterized sensitivities of the Fano and dipole resonances for the water-methanol mixtures are found to be 160 and 305 GHz/RIU, respectively. This method provides a robust route for metamaterial-assisted terahertz sensing of highly absorptive chemical and biochemical materials with multiple resonances and high accuracy.

© 2017 Optical Society of America

Abstract-Switchable metamaterial for enhancing and localizing electromagnetic field at terahertz band

Junxing Liu, Kailin Zhang, Xiankuan Liu, Zeyu Zhang, Zuanming Jin, Xiaoyong He, and Guohong Ma

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-13-13944

In this article, a novel metamaterial is designed aimed at generating a single electromagnetic hot spot, in order to realize the localization of the incident electromagnetic field at terahertz band, and this kind of metastructure is an ideal candidate for many research fields such as spintronics, nonlinear magnetic response, near-field optics, and optical antenna, etc. The specially tailored metamaterial takes the shape of diabolo with a metal triangle pair connected by a cubic gallium arsenide (GaAs) gap. We demonstrated by simulation that both electric- and magnetic-field of incident THz pulse can be confined in the small GaAs gap when a synchronized femtosecond laser pulse is illuminated. The numerical simulation results show that 2 orders of magnitude of field enhancement can be obtained for a 1-by-1 μm GaAs gap, and the field enhancement factor can also be further improved by tailoring the GaAs gap down to nanometer scale.

© 2017 Optical Society of America

Abstract-Enhanced spatial terahertz modulation based on graphene metamaterial

Dandan Sun, Mengqi Wang, Yuanyuan Huang, Yixuan Zhou, Mei Qi, Man Jiang, and Zhaoyu Ren

https://www.osapublishing.org/col/abstract.cfm?uri=col-15-5-051603

The plasmonic mode in graphene metamaterial provides a new approach to manipulate terahertz (THz) waves. Graphene-based split ring resonator (SRR) metamaterial is proposed with the capacity for modulating transmitted THz waves under normal and oblique incidence. Here, we theoretically demonstrate that the resonant strength of the dipolar mode can be significantly enhanced by enlarging the arm-width of the SRR and by stacking graphene layers. The principal mechanism of light–matter interaction in graphene metamaterial provides a dynamical modulation based on the controllable graphene Fermi level. This graphene-based design paves the way for a myriad of important THz applications, such as optical modulators, absorbers, polarizers, etc.

© 2017 Chinese Laser Press

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Abstract-Quad-band terahertz metamaterial absorber based on the combining of the dipole and quadrupole resonances of two SRRs

B. X. Wang
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=7442526&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D7442526

A new type of quad-band terahertz metamaterial absorber based on a common sandwich structure is investigated. In sharp contrast to the most previous studies focused on only combining of fundamental resonance (or LC resonance) of the metamaterial structure to obtain the quad-band response, we directly enable near-unity absorption in four distinct peaks by utilizing the dipole and quadrupole resonances of the patterns. The design also has the ability to tune the frequencies of the absorption peaks by merely changing the angle of polarization. The proposed platform has potential application perspectives in imaging, sensing, detection.

Abstract-Electrically controllable terahertz square-loop metamaterial based on VO2 thin film

Jun-Hwan Shin1,2, Kyung Hyun Park1,2 and Han-Cheol Ryu3

http://iopscience.iop.org/article/10.1088/0957-4484/27/19/195202/meta

An electrically controllable square-loop metamaterial based on vanadium dioxide (VO2) thin film was proposed in the terahertz frequency regime. The square-loop shaped metamaterial was adopted to perform roles not only as a resonator but also as a micro-heater for the electrical control of the VO2. A dual-resonant square-loop structure was designed to realize band-pass characteristics in the desired frequency band. The measured Q-factors of the basic and scaled-down metamaterials fabricated on VO2 thin films were 2.22 and 1.61 at the center frequencies of 0.44 and 1.14 THz in the passbands, respectively. The transmittances of the proposed metamaterial were successfully controlled by applying a bias voltage without an external heater. The measured transmittance on–off ratios of the metamaterials were over 40 at the center frequencies in the passbands. In the future, electrically controllable terahertz metamaterial based on VO2 metamaterial could be employed as high-performance active filters or sensors.

Abstract-Dual-band tunable perfect metamaterial absorber in the THz range

Gang Yao, Furi Ling, Jin Yue, Chunya Luo, Jie Ji, and Jianquan Yao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-2-1518

In this paper, a dual-band perfect absorber, composed of a periodically patterned elliptical nanodisk graphene structure and a metal ground plane spaced by a thin SiO2 dielectric layer, is proposed and investigated. Numerical results reveal that the absorption spectrum of the graphene-based structure displays two perfect absorption peaks in the terahertz band, corresponding to the absorption value of 99% at 35𝜇𝑚 and 97%at 59𝜇𝑚, respectively. And the resonance frequency of the absorber can be tunned by controlling the Fermi level of graphene layer. Further more, it is insensitive to the polarization and remains very high over a wide angular range of incidence around ±600. Compared with the previous graphene dual-band perfect absorption, our absorber only has one shape which can greatly simplify the manufacturing process.

© 2016 Optical Society of America

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