Plasmon Resonance Coupling Properties Of Monolayer Graphene Sheet Arrays

Graphene exhibits excellent surface plasmon properties in Terahertz band,and it has attracted great attention in recent years due to the advantages of high localization,low loss,and tunability.A large number of graphene devices,such as plasmon waveguides,absorbers,polarizers,sensors,and metamaterials,were explored for optical communication,biological detection,and security imaging,etc.In this thesis,we propose the single-layer graphene periodic arrays with different cell structures where the plasmon induced transparencies(PIT)and Fano resonance are achieved by the couplings of the plasmon modes in the graphene arrays.We further clarify the corresponding physical mechanisms and modulation factors of the PIT and Fano resonance.The main contents and results of this thesis are as follows:(1)We establish a single-layer graphene periodic array where each periodic cell includes a graphene rectangular sheet connected with a thin graphene strip.The transmission spectra of the graphene arrays are calculated by using the finite element method.It is found that,under the irradiation of the incident light,the local surface plasmon resonance(LSPR)of the graphene rectangular sheet could excite the SPP dark mode of the graphene strip.Then this SPP dark mode couples with the LSPR bright mode of the graphene rectangular sheet,resulting in the PIT phenomenon in the transmission spectrum.We carefully study the effects of the length of the graphene rectangular sheet,the width of the graphene strip,and the periodic parameter on the plasmon couplings between the bright dark and modes.In addition,it is found that the transmission of the PIT peak can be improved by increasing the carrier mobility of the graphene.The Fermi energy level of the graphene can be increased with the external bias voltage,resulting in the increase of group delay time and the blue-shift of the spectrum.(2)We propose a single-layer graphene composite structure consisting of an ellipse sheet and a graphene rectangular sheet.It is found that the Fano resonance could be achieved in this graphene composite structure by separately rotating the graphene ellipse sheet.The longitudinal component of the bright LSPR mode of the rotated graphene ellipse sheet could excite the dark LSPR mode of the graphene rectangular sheet.The couplings of the bright and dark modes result in a low energy bonding mode and a high energy anti-bonding mode.The interference of two new coupling states forms a Fano resonance.We further carefully investigate the influences of the rotation angle of the graphene ellipse sheet and the periodic parameter on the Fano resonance.Finally,we study the influences of the Fermi level and carrier mobility of the graphene on the group delay time of the single-layer graphene array.It is found that,with increasing the Fermi energy level,the peaks of the group delay time are enhanced and show blue-shifts.With increasing the carrier mobility of the graphene,the group delay time of the array structure can be effectively improved.