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.