Abstract-Electrically Tunable Broadband Terahertz Absorption with Hybrid-Patterned Graphene Metasurfaces

Longfang Ye,  Xin Chen, Guoxiong Cai , Jinfeng Zhu,  Na Liu, Qing Huo Liu

http://www.mdpi.com/2079-4991/8/8/562

We numerically demonstrate a broadband terahertz (THz) absorber that is based on a hybrid-patterned graphene metasurface with excellent properties of polarization insensitivity, wide-angle, and active tunability. Our design is made up of a single-layer graphene with periodically arranged hybrid square/disk/loop patterns on a multilayer structure. We find that broadband absorption with 90% terahertz absorbance and the fractional bandwidth of 84.5% from 1.38 THz to 3.4 THz can be achieved. Because of the axisymmetric configuration, the absorber demonstrates absolute polarization independence for both transverse electric (TE) and transverse magnetic (TM) polarized terahertz waves under normal incidence. We also show that a bandwidth of 60% absorbance still remains 2.7 THz, ranging from 1.3 THz to 4 THz, for a wide incident angle ranging from 0° to 60°. Finally, we find that by changing the graphene Fermi energy from 0.7 eV to 0 eV, the absorbance of the absorbers can be easily tuned from more than 90% to lower than 20%. The proposed absorber may have promising applications in terahertz sensing, detecting, imaging, and cloaking

Abstract-Hybridization-induced broadband terahertz wave absorption with graphene metasurfaces

Nanli Mou, Shulin Sun, Hongxing Dong, Shaohua Dong, Qiong He, Lei Zhou, Long Zhang,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-9-11728

Electromagnetic (EM) wave absorption plays a vital role in photonics. While metasurfaces are proposed to absorb EM waves efficiently, most of them exhibit limited bandwidth and fixed functionalities. Here, we propose a broadband and tunable terahertz (THz) absorber based on a graphene-based metasurface, which is constructed by a single layer of closely patterned graphene concentric double rings and a metallic mirror separated by an ultrathin SiO2 layer. Plasmonic hybridization between two graphene rings significantly enlarges the absorption bandwidth, which can be further tuned by gating the graphene. Moreover, the specific design also makes our device insensitive to the incident angle and polarization state of impinging EM waves. Our results may inspire certain wave-modulation-related applications, such as THz imaging, smart absorber, tunable sensor, etc.

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

Abstract-Broadband Tunable THz Absorption with Singular Graphene Metasurfaces

Emanuele Galiffi,  John B. Pendry, Paloma A. Huidobro, 

http://pubs.acs.org/doi/abs/10.1021/acsnano.7b07951

By exploiting singular spatial modulations of the graphene conductivity, we design a broadband, tunable THz absorber whose efficiency approaches the theoretical upper bound for a wide absorption band with a fractional bandwidth of 185%. Strong field enhancement is exhibited by the modes of this extended structure, which is able to excite a wealth of high-order surface plasmons, enabling deeply subwavelength focusing of incident THz radiation. Previous studies have shown that the conductivity can be modulated at GHz frequencies, which might lead to the development of efficient high-speed broadband switching by an atomically thin layer.

Abstract-Broadband Tunable THz Absorption with Singular Graphene Metasurfaces

Emanuele Galiffi, John B. Pendry, and Paloma A. Huidobro

http://pubs.acs.org/doi/abs/10.1021/acsnano.7b07951?journalCode=ancac3

By exploiting singular spatial modulations of the graphene conductivity, we design a broadband, tunable THz absorber whose efficiency approaches the theoretical upper bound for a wide absorption band with a fractional bandwidth of 185\%. Strong field enhancement is exhibited by the modes of this extended structure, which is able to excite a wealth of high order surface plasmons, enabling deeply subwavelength focussing of incident THz radiation. Previous studies have shown that the conductivity can be modulated at GHz frequencies, which might lead to the development of efficient high speed broadband switching by an atomically thin layer.

Abstract-Graphene-based Metasurfaces for Multimode Tunable Terahertz Modulators

Thomas A. Searles, Mehdi Rezaee, Amirhassan Shams-Ansari, Erin Strickland, Tina Brower-Thomas, Gary Harris, and Riad Yahiaoui

https://www.osapublishing.org/abstract.cfm?uri=cleo_at-2017-JW2A.105&origin=search

We present a hybrid graphene metasurface and its modulation by electrostatically tuning the conductivity of the graphene. Through modification of unit cell symmetry, multiple Fano-like resonances arise for additional modes over a 300 GHz range.

© 2017 OSA

Abstract-Giant cross-polarization conversion of terahertz radiation by plasmons in an active graphene metasurface

O. V. Polischuk1, V. S. Melnikova2 and V. V. Popov1,2,3
http://scitation.aip.org/content/aip/journal/apl/109/13/10.1063/1.4963276
1 Saratov Branch, Kotelnikov Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Saratov 410019, Russia
2 National Research Saratov State University, Saratov 410012, Russia
3 Saratov Scientific Center of the Russian Academy of Sciences, Saratov 410028, Russia
Appl. Phys. Lett. 109, 131101 (2016); http://dx.doi.org/10.1063/1.4963276

Results of theoretical investigation of the cross-polarization conversion of terahertz (THz) radiation by the graphene metasurface formed by a periodic array of graphene nanoribbons located at the surface of a high-refractive-index dielectric substrate are presented. Giant polarization conversion at the plasmonresonance frequencies takes place without applying external DC magnetic field. Pumping graphene by its direct optical illumination or diffusion pumping allows for compensating the Drude losses in grapheneand leads to further enhancement of the polarization conversion. It is shown that the total polarizationconversion can be achieved in the total internal reflection regime of THz wave from the graphenemetasurface at room temperature.

Nanosphere lithography makes graphene moiré metasurface

A new type of graphene metasurface containing moiré patterns that can be made using cost-effective and scalable nanosphere lithography has been developed by researchers at the University of Texas at Austin. The surface, which boasts multiband plasmonic resonance peaks that can be tuned from the mid-infrared to the terahertz range, could be used in applications like ultrathin light modulators, biosensors, flexible optoelectronics and photodetectors.

Making moiré patterns

 http://nanotechweb.org/cws/article/tech/65983

When two pieces of fine mesh are placed one on top of the other and then rotated, new, more complicated patterns appear. As you keep on twisting, the patterns change like in a kaleidoscope and so-called moiré patterns form. Such patterns have been recently observed in scanning tunnelling microscope (STM) images of stacked layers of graphene (a sheet of carbon just one atom thick) with the twists causing dramatic changes in the material’s electronic properties.

Graphene also has extraordinary optical properties thanks to the fact that it supports strong surface plasmon polaritons. A polariton is a particle-like entity (or quasiparticle) that can be used to describe how light interacts with semiconductors and other materials that have been made to resonate at certain frequencies. It has two different components: an electron-hole pair (or exciton) and a photon, which is emitted when the electron and hole recombine. When a photon is emitted, it is immediately reabsorbed to reform an exciton, so the cycle is repeated. This continuous exchange, or coupling, of energy between photons and excitons can be described in terms of polariton states.

Tunable plasmonic resonance bands

Polaritons will play an important role in future photonics devices that exploit light instead of electricity to process information. Such devices will be much faster and use less energy than their electronic counterparts and the strong coupling of polaritons will be crucial for the success of this new photonics.

“Graphene metasurfaces show plasmonic resonance bands that can be tuned from the mid-infrared to the terahertz regimes,” explains Maruthi Nagavalli Yogeesh, who is a member of Deji Akinwande’s team in Texas. “These plasmonic bands could be exploited for biosensing, spectroscopy, light modulation and communications applications.”

Multiband surfaces are better

The problem is that current graphene plasmonic metasurfaces are usually single band and it would better to be able to make multiband surfaces for more advanced applications such as single-molecule detection, surveillance and communication.

Now, the Austin researchers have succeeded in making such a surface using a cheap and simple technique to pattern large area graphene into moiré metasurfaces having tunable multiband resonance peaks.

Obtaining various moiré patterns

“In this work, we patterned graphene grown by chemical vapour deposition into moiré metasurfaces by combining moiré nanosphere lithography (MNSL) and oxygen reactive ion etching (RIE),” explains Zilong Wu, a member of Yuebing Zheng’s team in Texas. “In brief, we self-assemble colloidal polystyrene (PS) nanospheres into a monolayer on substrates with the graphene. We then deposit a second monolayer of PS nanospheres on top of the first one using a similar process. We can control the relative rotation angle between the first and second layers to obtain various moiré patterns.”

An additional RIE step creates voids between closely packed nanospheres and etches away graphene that has been exposed to the plasma. “After removing the residual nanospheres, graphene sheets with moiré patterns are then left on the substrates,” adds Wu.

Towards protein biosensors

“By varying the relative rotational angle between the top and bottom monolayers of PS nanospheres during MNSL, we are able to significantly change the size and shape of the graphene nanostructures in the metasurfaces. This means that we can tune the multiband resonance peaks in the material from the infrared to the terahertz.” team member Wei Li tellsnanotechweb.org.

The team, reporting its work in Advanced Optical MaterialsDOI: 10.1002/adom.201600242, says that it is now working on making protein biosensors from the graphene metasurface. “We also hope to integrate it with THz photodetectors,” says Zheng.

About the author

Belle Dumé is contributing editor at nanotechweb.org

Abstract-Frequency-tunable terahertz absorbers based on graphene metasurface

• Ming Chen^{a, b, , 1,} , 
• Wei Sun^b, 1, 
• Jianjin Cai^b, 
• Linzi Chang^b, 
• Xiaofei Xiao^b

• ^a Guangxi Key Laboratory of Precision Navigation Technology and Application, Guilin University of Electronic Technology, Guilin 541004, Guangxi, China
• ^b Guilin University of Electronic Technology, Guilin 541004, Guangxi, Chin
• 
  
• http://www.sciencedirect.com/science/article/pii/S0030401816306654

We present efficient designs of graphene-based thin absorbers, which are capable of near-unity absorption of the incident electromagnetic waves in the terahertz regime. Primarily, a single-frequency absorber is proposed. Subsequently, by simply stacking the double layer graphene metasurface with various geometric dimensions, the dual-frequency absorption and broadband absorption are realized respectively. Results demonstrate that the absorptivity of the single-frequency absorber reaches 99.51% at 2.71 THz when the Fermi energy is fixed at 0.9 eV. The dual-frequency absorber can simultaneously work at two frequencies with its absorptivity being 98.94% for 1.99 THz and 99.1% for 2.69 THz. The bandwidth of absorption rate above 90% expands three times when compared with the former single-frequency absorber. Additionally, it possesses the polarization-insensitive and large angle tolerance properties. More importantly, the absorption frequency can be dynamically controlled by adjusting Fermi energy levels without varying the nanostructure, which exhibits tremendous application values in many fields.

Abstract-Terahertz focusing of multiple wavelengths by graphene metasurfaces

Liming Liu^1,2,a), Yair Zarate¹, Haroldo T. Hattori², Dragomir N. Neshev^1,3, Ilya V. Shadrivov¹ and David A. Powell^1,3
 HIDE AFFILIATIONS
1 Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, ACT 2601, Australia
2 School of Engineering and Information Technology, University of New South Wales, Canberra, ACT 2612, Australia
3 Centre for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS), Australian National University, Canberra, ACT 2601, Australia
a) Author to whom correspondence should be addressed. Electronic mail:liming.liu@student.adfa.edu.au
Appl. Phys. Lett. 108, 031106 (2016); http://dx.doi.org/10.1063/1.4940231

http://scitation.aip.org/content/aip/journal/apl/108/3/10.1063/1.4940231?TRACK=RSS

Metasurfaces can achieve nearly arbitrary wavefront control based on manipulation of the wavephase profile. We propose a metasurface based on double graphene cut-wire resonatorswhich can cover the complete 2π phase region with high reflection efficiency. This full phase coverage is essential for efficient wavefront manipulation, without reflecting energy into unwanted channels. A mirror capable of focusing multiple wavelengths is demonstrated numerically based on the proposed structure. The mirror can effectively focus terahertz (THz)waves from 1.2 to 1.9 THz to the same focal point by changing the Fermi level of eachgrapheneresonator separately. The presented metasurface could provide a powerful platform for controlling THz waves, including focusing, beam steering, beam shaping, and holograph

Abstract-Dynamic Terahertz Beam Steering Based on Graphene Metasurfaces

Liming Liu, Yair Zarate, Haroldo T. Hattori

http://www.mathpubs.com/detail/1512.05425v1/Dynamic-Terahertz-Beam-Steering-Based-on-Graphene-Metasurfaces

A full (2π) phase modulation is critical for efficient wavefront manipulation. In this article, we propose a metasurface based on graphene long/short-strip resonators which are capable of implementing a dynamic 2π phase modulation by applying different voltages to different graphene resonators. The configuration is found to have high reflection efficiency (minimum 56%) and has a full phase modulation in a wide frequency range. Terahertz (THz) beam steering as large as 120 degrees (±60∘) is demonstrated in a broad frequency range (1.2 to 1.9 THz) by changing the Fermi levels of different graphene resonators accordingly. This metasurface can provide a new platform for effectively manipulating THz waves.

Abstract-Full-range Gate-controlled Terahertz Phase Modulation with Graphene Metasurfaces

Ziqi Miao, Qiong Wu, Xin Li, Qiong He, Kun Ding, Zhenghua An, Yuanbo Zhang, and Lei Zhou
https://www.osapublishing.org/abstract.cfm?uri=CLEO_AT-2015-AF2E.6

Combining metasurfaces with gate controlled graphene, we experimentally demonstrate ±180° phase modulation can be realized at certain frequencies in THz domain, and describe a practical scheme to achieve full-range active phase modulation with such graphene metasurfaces.

© 2015 OSA

PDF Article