Contents 1. Introduction
Due to its unique electrical and optical properties of ultrahigh carrier mobility [1], wavelength-independent absorption [2], gate-tunable conductivity [3], and a high optical Kerr coefficient [4], graphene has shown great potential in photonics and optoelectronic applications. Most graphene-based photonic devices previously reported adopt a graphene on straight waveguide structures, but the interaction between graphene and light is too weak to obtain a significant change of optical absorption [5]. To elongate the graphene-light interaction length, resonant-enhanced cavity structure, such as microring resonators, can be an effective solution. Compared to silicon waveguides, silicon nitride waveguides have much lower losses, broader transparency windows, smaller thermal-optic effects and larger fabrication tolerance [6], [7]. Therefore, graphene-based device integrated on silicon nitride platform may obtain a higher performance.
