Nanoantenna-coupled broadband and ultra-compact plasmonic waveguide modulator based on graphene

Surface plasmon polaritons (SPPs) are propagating electromagnetic waves formed by the coupling of light with free electron collective oscillations. With the characteristics of breaking the diffraction limit and realizing subwavelength constraint, devices based on plasmonic architecture would have promising applications in on-chip optoelectronic integrated systems. In this paper, we report an antenna-coupled plasmonic slot waveguide modulator based on graphene. The modulator integrates gold nanoantenna and plasmonic slot waveguide. The antenna couplers are utilized to efficiently excite SPPs in the nanoscale, achieving broadband high coupling efficiency. The plasmonic slot waveguides allow strong modal confinement with large in-plane electric field around the graphene region, which greatly enhances the interaction between light and graphene. Compared to conventional grating-coupled graphene modulators, our design achieves a more compact footprint and wider optical bandwidth. Our proposed modulator can obtain high modulation efficiency (0.85 dB/μm), broad modulation bandwidth (81.52 GHz), and low energy consumption (5.77 fJ/bit). The device also demonstrated a uniform electro-optic modulation with 500 nm optical bandwidth with wavelength from 1200 to 1700 nm. Our work provides a feasible approach for the design of ultra-compact nanoscale devices for future high-density integrated photonic chips.