Broadband graphene modulator with high modulation depth based on tip plasmonic waveguide

Abstract

Broadband operation is a critical feature for high-speed electro-optic modulators in optical signal processing. To overcome the obstacle of material absorption-induced optical bandwidth shrinkage, graphene optical modulators based on the tip plasmonic concept have been proposed. The modulator is composed of buried double-layer graphene and Ag-SiO2-Si-SiO2-Ag hybrid structure with taper slots. Due to the tightened field confinement induced by the tip plasmonic effect, the light-graphene coupling is significantly enhanced. The direct metal layers contact with graphene is exploited to serve as the electrode. The simulation results based on the finite element method present a graphene modulator with a high modulation depth (MD) of 1.1 dB/μm and a relatively low propagation loss of 0.14 dB/μm. The power consumption is about 43.80 fJ/bit at the modulation length of 20 µm. The 3 dB-bandwidth is estimated to be around 340 GHz. Comparison with reported graphene modulators adopting hybrid plasmonic slot waveguide proves favorable modulation depth of proposed design, which promise its potentials in hybrid integration and on-chip signal processing.