Research On Graphene Surface Plasmons And Its Application In THz Modulator

Graphene not only has excellent physical properties such as stable, high-strength, and high conductivity, but also has unique band structure with zero band gap, conductivity shift as the carrier density changed. Plasmons supported by graphene which can be controlled via an electric bias, thus providing an advantage for graphene over plasmons in metal-dielectric interface. The remarkable properties possessed by graphene, which make it an ideal material for adjustable devices.The dispersion properties of surface plasmons in graphene are studied, and the tunability of plasmons with an electric bias are mainly discussed. By the Maxwell equations and the boundary conditions, the dispersion relationship can be obtained. The TE and TM modes plasmons in graphene are discussed, and the confinement and loss in electric biased graphene are analyzed. The results show that in Graphene-Si O2-Si structure, plasmons shows small loss, and better confinement compared with metal, which can strongly confine energy at sub-wavelength scales.Based on the analysis of propagation characteristics and tunability of surface plasmons in graphene, and using the structure of graphene plasmonic waveguide, a terahertz modulator based on graphene plasmons is designed and analyzed. Firstly a modulator based on single graphene ribbon is designed. The signal can be modulated by the propagation loss in graphene ribbon controlled via a bias voltage. This modulator has modulation depth about 28%. The RC constant and the modulation speed is calculate by the equivalent circuit, and the 3d B modulation bandwidth can be achieved 45 MHz. The modulator based on the coupling structure is designed in order to improve the modulation depth. The coupling coefficients and propagation loss can be modulated via a bias voltage. In this scenario, the modulation depth can reach about 76% and with a 40 MHz modulation bandwidth.