Tunable Multispectral Plasmon Induced Transparency And Nanoantennas Based On Graphene Plasmons

Graphene is a two-dimensional(2D)form of carbon where the atoms are arranged in a hexagonal honeycomb lattice.The band structure of electrons in graphene is formed as a Dirac cone,leading to the electrons behave as massless Dirac fermions.Graphene has many unique properties: high carrier mobility,low transmission loss,and tunable interband and intraband conductivities,etc.Due to the unique electrical and optical properties,graphene has great potential in the integration of photonic devices.Graphene has an extremely high quantum efficiency for light-matter interactions,is strongly optically nonlinear and contains plasmons with unusual properties.Furthermore,it can be modified by gating,by doping.Not only does graphene possess intrinsic plasmons that are tunable and adjustable,but a combination of graphene with noble-metal nanostructures promises a variety of exciting applications for conventional plasmonics.The main research works and conclusions in this dissertation are as following:(1)The tunability of multispectral EIT-like responses are realized in two different kinds of periodically patterned graphene double layers separated by a dielectric layer in the terahertz frequency range.The coupled Lorentz oscillator model,incorporating the near-field coupling in different graphene layers and the bright-dark coupling in the same graphene layer,is employed to explain multispectral EIT-like responses.The resonances in multiple PIT windows are controlled by changing the Fermi energy of graphen or the structural parameters,which is demonstrated by the simulated transmission based on the FDTD solutions.(2)A tunable dual-band plasmonically induced transparency(PIT)device based on hybrid metal-graphene nanostructures is proposed theoretically and numerically at mid-infrared frequencies,which is composed of two kinds of gold dolmen-like structures with different sizes placed on separate graphene interdigitated finger sets respectively.The coupled Lorentz oscillator model is used to explain the physical mechanism of the PIT effect at multiple frequency domains.The FDTD solutions are employed to simulate the characteristics of the hybrid metalgraphene dual-band PIT device.The simulated spectral locations of multiple transparency peaks are separately and dynamically modulated by varying the Fermi energy of corresponding graphene finger set.(3)A graphene-based V-shaped metallic nanoantenna is demonstrated theoretically and numerically to realize active control of unidirectional side scattering of light in the mid-infrared region.Based on the two point-dipoles model,two localized surface plasmonic resonance(LSPR)modes in the metallic nanoantennna constructively and destructively interfere with each other in opposite directions.The simulated far-field scattering intensity distributions by the FDTD solutions exhibit the unidirectional side scattering of the graphene-based V-shaped metallic nanostructures is actively controlled by the gate voltage applied on the graphene layer,as well as changing the V-angle of the nanoantenna.