Abstract-Tunable terahertz absorber using double-layer decussate graphene ribbon arrays

Fang Zeng, Longfang Ye,  Xiong Xu,  Xiaofan Yang,

https://ieeexplore.ieee.org/document/8400805

A tunable graphene-based terahertz perfect absorber consists of periodic double-layer decussate graphene ribbons is proposed. In the proposed absorber, the two arrays of graphene ribbons are separated by the dielectric zro2. From the bottom up, the multi-layer absorber structure is made up of Au/ zro2/graphene materials respectively. The reflection of all the electromagnetic waves is effectively restricted in the interlayer between the graphene ribbons and the metal plate, and the transmission of electromagnetic waves is also suppressed due to thick metal base. By varying the chemical potential graphene, the peak absorption frequency can be flexibly tuned. By changing the geometric parameters of the structure, more than 99% absorbance can be achieved. Moreover, the graphene absorber has a simple structure and can be easily manufactured by an existing manufacturing process, such absorber will benefit the fabrication of detecting, sensing and optoelectronic devices.

Abstract-Actively tunable broadband terahertz absorption using periodically square-patterned graphene

Longfang Ye, Xin Chen, Jianliang Zhuo, Feng Han,  Qing Huo Liu

http://iopscience.iop.org/article/10.7567/APEX.11.102201/pdf

We propose an actively tunable broadband perfect absorber using a square-patterned graphene–spacer–polysilicon–spacer–metal structure. The simulated results show that the absorber can reach nearly perfect broadband terahertz absorption with over 99.5% (90%) absorbance from 1.52 (1.27) to 2.23 (2.51) THz, corresponding to the normalized bandwidth of 37.5% (65.6%) under normal incidence with the graphene Fermi level of 0.7 eV. The absorption spectra show a clear independence of the polarization and the angle of incidence. By adjusting the graphene Fermi level from 0 to 0.7 eV, the peak absorbance can be continuously tuned from 15 to 100% without shifting the absorption frequency band.

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-Graphene-based hybrid plasmonic waveguide for highly efficient broadband mid-infrared propagation and modulation

Longfang Ye, Kehan Sui, Yanhui Liu, Miao Zhang, and Qing Huo Liu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-12-15935

In this paper, a graphene-based hybrid plasmonic waveguide is proposed for highly efficient broadband surface plasmon polariton (SPP) propagation and modulation at mid-infrared (mid-IR) spectrum. The hybrid plasmonic waveguide is composed of a monolayer graphene sheet in the center, a polysilicon gating layer, and two inner dielectric buffer layers and two outer parabolic-ridged silicon substrates symmetrically placed on both sides of the graphene. Owing to the unique parabolic-ridged waveguide structure, the light-graphene interaction and subwavelength SPPs confinement of the fundamental SPP mode for the hybrid waveguide can be significantly increased. Under the graphene chemical potential of 1.0 eV, the proposed waveguide can achieve outstanding SPP propagation performance with long propagation length of 12.1-16.7 μm and small normalized mode area of ~10−4 in the frequency range of 10-20 THz, exhibiting more than one order smaller in the normalized mode area while remaining the propagation length almost the same level with respect to the hybrid plasmonic waveguide without parabolic ridges. By tuning the graphene chemical potential from 0.1 to 1.0 eV, we demonstrate the waveguide has a modulation depth greater than 51% for the frequency ranging from 10 to 20 THz and reaches a maximum of nearly 100% at the frequency higher than 18 THz. Benefitting from the excellent broadband mid-IR propagation and modulation performance, the graphene-based hybrid plasmonic waveguide may open up a new way for various mid-IR waveguides, modulators, interconnects and optoelectronic devices.

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

Abstract-Multiple resonant excitations of surface plasmons in a graphene stratified slab by Otto configuration and their independent tuning

Jin Yao, Ying Chen, Longfang Ye, Na Liu, Guoxiong Cai, and Qing Huo Liu

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-4-377&origin=search

Multiple resonant excitations of surface plasmons in a graphene stratified slab are realized by Otto configuration at terahertz frequencies. The proposed graphene stratified slab consists of alternating dielectric layers and graphene sheets, and is sandwiched between a prism and another semi-infinite medium. Optical response and field distribution are determined by the transfer matrix method with the surface current density boundary condition. Multiple resonant excitations appear on the angular reflection spectrum, and are analyzed theoretically via the phase-matching condition. Furthermore, the effects of the system parameters are investigated. Among them, the Fermi levels can tune the corresponding resonances independently. The proposed concept can be engineered for promising applications, including angular selective or multiplex filters, multiple channel sensors, and directional delivery of energy.

© 2017 Chinese Laser Press

Abstract-Broadband absorber with periodically sinusoidally-patterned graphene layer in terahertz range

Longfang Ye, Yao Chen, Guoxiong Cai, Na Liu, Jinfeng Zhu, Zhengyong Song, and Qing Huo Liu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-10-11223

We demonstrate that a broadband terahertz absorber with near-unity absorption can be realized using a net-shaped periodically sinusoidally-patterned graphene sheet, placed on a dielectric spacer supported on a metallic reflecting plate. Because of the gradient width modulation of the unit graphene sheet, continuous plasmon resonances can be excited, and therefore broadband terahertz absorption can be achieved. The results show that the absorber’s normalized bandwidth of 90% terahertz absorbance is over 65% under normal incidence for both TE and TM polarizations when the graphene chemical potential is set as 0.7 eV. And the broadband absorption is insensitive to the incident angles and the polarizations. The peak absorbance remains more than 70% over a wide range of the incident angles up to 60° for both polarizations. Furthermore, this absorber also has the advantage of flexible tunability via electrostatic doping of graphene sheet, which peak absorbance can be continuously tuned from 14% to 100% by controlling the chemical potential from 0 eV to 0.8 eV. The design scheme is scalable to develop various graphene-based tunable broadband absorbers at other terahertz, infrared, and visible frequencies, which may have promising applications in sensing, detecting, and optoelectronic devices.

© 2017 Optical Society of America

Abstract-Plasmonic waveguide with folded stubs for highly confined terahertz propagation and concentration

Longfang Ye, Yifan Xiao, Na Liu, Zhengyong Song, Wei Zhang, and Qing Huo Liu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-2-898

We proposed a novel planar terahertz (THz) plasmonic waveguide with folded stub arrays to achieve excellent terahertz propagation performance with tight field confinement and compact size based on the concept of spoof surface plasmon polaritons (spoof SPPs). It is found that the waveguide propagation characteristics can be directly manipulated by increasing the length of the folded stubs without increasing its lateral dimension, which exhibits much lower asymptotic frequency of the dispersion relation and even tighter terahertz field confinement than conventional plasmonic waveguides with rectangular stub arrays. Based on this waveguiding scheme, a terahertz concentrator with gradual step-length folded stubs is proposed to achieve high terahertz field enhancement, and an enhancement factor greater than 20 is demonstrated. This work offers a new perspective on very confined terahertz propagation and concentration, which may have promising potential applications in various integrated terahertz plasmonic circuits and devices, terahertz sensing and terahertz nonlinear optics.

© 2017 Optical Society of America

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