Broadband optical waveguide modulators based on strongly coupled hybrid graphene and metal nanoribbons for near-infrared applications

Abstract

In this paper, we numerically demonstrate a variety of broadband optical waveguide modulators based on the hybrid surface plasmon polariton (HSPP) concept for near-infrared applications. The modulator is composed of strongly coupled double-layer graphene and double rectangle cross-sectional metal nanoribbons separated by three Al₂O₃ spacers, which are interpolated in a SiO₂ waveguide. Owing to the unique strong coupling of HSPPs between metal nanoribbons, the subwavelength confinement, the in-plane electric field component, the light-graphene interaction, and the modulation effect of the modulator are significantly enhanced. The results show the proposed modulator achieves an outstanding performance with a modulation depth (MD) over 2.3 dB μm⁻¹ and a small normalized mode area of ∼10⁻⁵ in a wide range of wavelength from 1.3 to 1.8 μm. By optimizing the separation of the double rectangle metal nanoribbons at the telecommunication wavelength of 1.55 μm, the modulator exhibits a high MD of 3.12 dB μm⁻¹, a small footprint of 1.8 μm², an ultra-wide 3 dB modulation bandwidth of 380.23 GHz, and an ultra-low energy consumption of 29.39 fJ per bit. Furthermore, we also demonstrate a modulator based on two properly apart semicircular (rhombus) metal nanoribbons with a drastically enhanced MD of 11.3 (6.32) dB μm⁻¹ at 1.55 μm. Benefitting from the strong subwavelength confinement and excellent broadband modulation performance, the proposed optical waveguide modulators offer a significant potential to realize various long-wave near-infrared integrated modulators, interconnects and optoelectronic devices.