Transmission Properties And Sensing Applications Of Graphene-Assisted Waveguide

Waveguide is an important transmission line. The technology of waveguides in the optical and microwave regime has developed to be relatively mature. However, in the infrared and terahertz regime, the waveguiding technology is deficient. In recent years, graphene attracted much attention from researchers because it has exceptional properties and coud be used for waveguiding in the infrared and terahertz regime. The mechanism of graphene waveguiding is that realizing wave propagation by exciting the surface plasmon polaritons which can be regard as a kind of surface wave in the infrared and terahertz regime on the graphene surface. The factors, such as the geometry of waveguide, the parameters of graphene can influence the wave propagation. Therefore, the study on the transmission properties of graphene waveguide is meaningful to the design and the application of graphene waveguide.This work focuses on the transmission properties of graphene nano-ribbon waveguides and cylindrical graphene waveguides, and the molecular sensing applications based on graphene waveguide. The main results are as follows:1. The transmission properties of three kinds of graphene nano-ribbon waveguides are analyzed. Starting from deducing the dispersion relations of the waveguides, we analyzed the transmission properties and mode characteristics of monolayer graphene nano-ribbon waveguide, double layer graphene nano-ribbon waveguide and dielectric loaded graphene waveguide. Both monolayer and double layer graphene nano-ribbon waveguides have the waveguide mode and the edge mode. Due to the existence of the coupling effect, the double layer graphene nano-ribbon waveguide supports symmetric and anti-symmetric modes. The width of dielectric strip of dielectric loaded graphene waveguide has a strong impact on the mode behavior.2. The transmission properties of cylindrical graphene waveguides are studied. We introduce the transmission properties and mode characteristics of monolayer cylindrical graphene waveguides, whose waveguide mode exhibits a standing wave across the circle. Then the transmission properties of double layer cylindrical graphene waveguides are analyzed. An analytical model for eigen mode of the waveguide is presented and verified by finite element method simulations. We demonstrate the large tunabilities of the mode behavior, the performance of the waveguide and the cutoff characteristics by varying the Fermi level of graphene, the coupling distance between the two graphene sheets and the radius of the cylinder. Based on the principle that roolling up graphene do not affect the localization of the mode and the wave propagation theory, the relations between the radius of the cylinder and the modal cutoff frequencies of high order modes are derived from an analytical model and confirmed by numerical simulations.3. Based on strong light-matter interaction, a double layer cylindrical graphene waveguides as a platform for molecular sensing is designed and the properties of broadband and high sensitivity are demonstrated by the detections of ethanol and toluene molecules. Based on the same sensing idea, a corrugated metal parallel plate waveguide with gradually changed depth of corrugations is designed, and its transmission properties are analyzed. Then the waveguide is use to detect ethanol and toluene molecules, and the feasibility and broadband properties are proved. Finally, we do a comparison between the two sensing scheme.The analysis of the transmission properties and sensing application of graphene waveguide may help us have a deep insight in the mechanism of wave propagation on the garphene surface and provide theoretical guidance for the design and applications of graphene waveguide and the experiment in our work in the future.