Longfang Ye,* Yao Chen
Institute of Electromagnetics and Acoustics, and Department of Electronic Science, Xiamen University, Xiamen 361005, China
Nano-Micro Conference, 2017, 1, 01009
Published Online: 05 October 2017 (Abstract)
Broadband terahertz absorbers have recently attracted considerable attention for their promising applications in terahertz trapping, sensing, imaging, and detecting. In this work, an efficient approach to achieve broadband terahertz absorber based on sinusoidally-patterned graphene with nearly 100% absorption is demonstrated . As shown in Figure 1(a), the proposed absorber is composed of a net-shaped periodically sinusoidally-patterned graphene sheet on the top, a thin gating layer embedded dielectric spacer in the middle, and a metallic reflecting plate on the bottom. We assume the material of the dielectric spacer, the gating layer and metallic plate are the polyethylene cyclic olefin copolymer (Topas) with the permittivity of εrt = 2.35 , and the polysilicon with the permittivity of εrp = 3 , and gold, respectively. The surface conductivity of the single-layered graphene is obtained from the Kubo formula . The polysilicon gating layer is placed beneath the graphene sheet to control the graphene conductivity via electrostatic doping of the graphene by applying a DC voltage Vg. By introducing such a unique gradient width modulation of the unit graphene sheet structure, the continuous plasmon resonances of the absorber can be excited, and over 65% normalized bandwidth of 90% terahertz absorbance can be achieved under normal incidence for both TE and TM polarizations. As one of the most exciting characteristics, the broadband absorption of this absorber are insensitive to the incident angles and the polarizations. The absorbance remains more than 70% even the incident angles reach 60o for both polarizations. Furthermore, compared to conventional multi-resonator or multi-layered structures, the continuous net-shaped single-layered graphene structure can greatly simplify the electrostatic gating structure in achieving flexible tunability. By controlling the chemical potential of the graphene, the peak absorbance can be continuously tuned from 14% to 100%, as shown in Figure 1(b). This work offers a new perspective on the design of graphene-based tunable terahertz broadband absorbers. The design scheme can be easily scaled to the infrared or visible regimes.
 L.F. Ye; Y. Chen; G.X. Cai; N. Liu; J.F. Zhu; Z.Y. Song; Q.H. Liu, Broadband absorber with periodically sinusoidally-patterned graphene layer in terahertz range. Optics Express. 25(10), 11223-11232 (2017). doi:10.1364/OE.25.011223
 P. D. Cunningham; N. N. Valdes; F. A. Vallejo; L. M. Hayden; B. Polishak; X. H. Zhou, Broadband terahertz characterization of the refractive index and absorption of some important polymeric and organic electro-optic materials. Journal of Applied Physics 109, 043505 (2011). doi:10.1063/1.3549120
J. S. Gómez-Díaz; J. Perruisseau-Carrier, Graphene-based plasmonic switches at near infrared frequencies. Optics Express 21(13), 15490 (2013). doi:10.1364/OE.21.015490
 G. W. Hanson, Dyadic Green’s functions and guided surface waves for a surface conductivity model of graphene. Journal of Applied Physics. 103, 064302 (2008). doi:10.1063/1.2891452
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