Design of high extinction ratio silicon electro optic modulator based on coupled hybrid plasmonic waveguide using graphene

In this paper, a high extinction ratio (ER) and a low power silicon-plasmonic hybrid electro-optic modulator based on graphene has been proposed and designed. The proposed modulator has three coupled waveguides, two silicon waveguides, and one hybrid plasmonic waveguide. A hybrid plasmonic waveguide has two coupled graphene layers. Two-dimensional hexagonal boron nitride (hBN) and hafnium oxide (HfO₂) are used in the plasmonic waveguide. The high performance and quality modulator is obtained with this combination of materials. By electrically adjusting the graphene refractive index as low as a noble metal, the hybrid plasmonic waveguide support the high lossy surface plasmon polariton (SPPs) waves. Therefore, the propagating optical mode experiences high power attenuation. In addition, the coupling length between waveguides is changed, which causes further attenuation of light. The designed modulator has a high ER (11.01 dB/μm), wide f_3dB modulation bandwidth (72.2 GHz), and low power consumption (19.36 fJ) at 1.55 μm wavelength. The finite-difference time-domain (FDTD) method is used to investigate the proposed modulator characteristics.