Abstract-Investigation of multiband plasmonic metamaterial perfect absorbers based on graphene ribbons by the phase-coupled method

Hongju Li, Chuansheng Ji, Yongze Ren, Jigang Hu, Meng Qin, Lingling Wang,

https://www.sciencedirect.com/science/article/pii/S0008622318309138

We develop an original phase-coupled method to realize multispectral metamaterial near-unity absorbers based on spatially separated graphene ribbon arrays with mid-infrared plasmonic resonances. The results both from the coupled-mode theory and finite-difference time-domain simulations reveal that in addition to the single-band absorption enabled by the bi-layer identical ribbon arrays, the outstanding dual-band perfect absorption is observed with the change in the phase between bi-layer ribbons only by varying the spacer thickness. The spectral positions of absorption peaks are tuned handily by small changes in ribbon widths and chemical potentials of graphene. Moreover, the triple-band absorber is achieved handily by the same principle and such absorbers are robust for nor-normal incident angles. The transfer matrix method is also utilized to uncover further the underlying physics of the phased-coupled-induced multispectral absorbers. Theoretical analysis are in excellent agreement with numerical calculations. The phase-coupled method thus provides new opportunities for obtaining multi-channel metamaterial perfect absorbers.

Abstract-Graphene-based terahertz tunable plasmonic directional coupler

Meng-Dong He^1,a), Kai-Jun Wang¹, Lei Wang¹, Jian-Bo Li¹, Jian-Qiang Liu²,Zhen-Rong Huang³, Lingling Wang³, Lin Wang⁴, Wei-Da Hu⁴ and Xiaoshuang Chen⁴
http://scitation.aip.org/content/aip/journal/apl/105/8/10.1063/1.4894090
1 Institute of Mathematics and Physics, Central South University of Forestry and Technology, Changsha 410004, People's Republic of China
2 College of Science, Jiujiang University, Jiujiang 332005, People's Republic of China
3 Key Laboratory for Micro-Nano Optoelectronic Devices of Ministry of Education, Hunan University, Changsha 410082, People's Republic of China
4 National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Science, Shanghai 200083, People's Republic of China
a) Author to whom correspondence should be addressed. Electronic mail: hemendong@sohu.com
Appl. Phys. Lett. 105, 081903 (2014); http://dx.doi.org/10.1063/1.4894090

We propose and numerically analyze a terahertz tunable plasmonic directional coupler which is composed of a thin metal film with a nanoscale slit, dielectric grating, a graphene sheet, and adielectric substrate. The slit is employed to generate surface plasmon polaritons (SPPs), and the metal-dielectric grating-graphene-dielectric constructs a Bragg reflector, whose bandgap can be tuned over a wide frequency range by a small change in the Fermi energy level of graphene. As a graphene-based Bragg reflector is formed on one side of the slit, the structure enables SPP waves to be unidirectionally excited on the other side of the slit due to SPP interference, and the SPP waves in the Bragg reflector can be efficiently switched on and off by tuning the graphene'sFermi energy level. By introducing two optimized graphene-based Bragg reflectors into opposite sides of the slit, SPP waves can be guided to different Bragg reflectors at different Fermi energy levels, thus achieving a tunable bidirectional coupler.