Solid-Electrolyte-Gated Graphene-Covered Metal-Insulator-Silicon-Insulator-Metal Waveguide With a Remarkably Large Modulation Depth

Abstract

Silicon photonic modulators are an essential element in providing fast and massive connectivity to the data-centric world. Ever-increasing data usage requires them to be smaller, faster, and easier to fabricate. Graphene with exceptional properties has been emerging as a material for such next-generation silicon photonic modulators, and a variety of graphene-based photonic or plasmonic modulators have been realized and verified. However, due to weak light-graphene interaction in them, they have a modulation depth smaller than 0.16 dB/ $\mu \text{m}$ , which is similar to those of existing germanium-silicon electroabsorption modulators. This work reports a graphene-covered hybrid plasmonic waveguide that has truly strong light-graphene interaction. The hybrid plasmonic waveguide is realized with standard CMOS technology and efficiently coupled to a conventional Si waveguide. To prove the strong light-graphene interaction, solid-electrolyte gating is used to modulate the intensity of the waveguide although its modulation speed is slow. It is demonstrated that the waveguide has a remarkably large modulation depth of 0.276 dB/ $\mu \text{m}$ even though just one single-layer graphene covers the waveguide. This demonstration opens the door to the waveguide covered with a graphene-oxide-graphene capacitor, which may have a larger modulation depth and a large 3-dB bandwidth, and it is theoretically analyzed. This work may be the solid base for a graphene-based silicon photonic modulator which is theoretically expected to surpass current silicon photonic modulators.