Dynamically tuning the optical coupling of surface plasmons in coplanar graphene nanoribbons

We analyze the plasmonic resonant properties in engineered coplanar graphene nanoribbons by using the finite-difference time-domain (FDTD) method. A numerical analysis is introduced to calculate the coupling strength from frequency. Using this method, the coupling strengths of the first-order plasmon mode are calculated in two kinds of models, one is built with different doping concentration in graphene nanoribbons, the other is created with increasing period. As emulational examples of application of the method, a continuously tuning of the number of transmission dips from one to four is achieved for the first time, which is realized by severally varying the Fermi level of nanoribbons via electrostatic gating. Meanwhile, the novel hybridized plasmon resonances are realized based on periodic graphene nanoribbon pairs. The present paper is helpful for designing coupled plasmonic structures, which demonstrates much promise for applications in graphene-based optoelectronic nanodevices.