Design and analysis of low loss plasmonic waveguide and directional coupler based on pattern-free suspended graphene sheets

Suspended graphene sheets exhibit promising characteristics such as very high carrier mobility and long relaxation time of carriers. It is highly desirable to realize high performance electronic and optical devices based on suspended graphene layers. For the first time in this paper, a feasible low loss plasmonic waveguide based on a pattern-free suspended graphene sheet is proposed. Using an analytical approach, the dispersion relation of surface plasmon polaritons in a suspended graphene-based structure is investigated and derived. The obtained dispersion relation is then used to justify the mode characteristics of the proposed structure. According to our calculations, the propagation length of the proposed suspended graphene plasmonic waveguide at the wavelength of 10 mm is obtained as long as similar to 9 mm that is 25 times longer than that in its unsuspended counterpart. The structure of a plasmonic coupler which is based on the proposed suspended graphene plasmonic waveguide is also introduced. An ultrashort coupling length of just 496 nm is obtained. The proposed structures are simulated using three-dimensional finite-difference time-domain method. We believe that our proposed suspended graphene-based structures could pave the way for taking the unique advantages of graphene in the future low loss mid-infrared and terahertz integrated circuits. (C) 2017 Elsevier Ltd. All rights reserved.