Local and Non-local Optically Induced Transparency Effects in Graphene-Silicon Hybrid Nanophotonic Integrated Circuits

Graphene is well-known as a two-dimensional sheet of carbon atoms arrayed in a honeycomb structure. It has many unique and fascinating properties, such as ultra-high carrier mobility at room temperature, zero-bandgap and electrochemically tunable Fermi level, broadband light absorption. All these make graphene very useful for realizing novel optoelectronic devices and applications, including photodetectors, solar cells, and modulators. In order to enhance light-graphene interactions, a promising approach is to combine a graphene sheet with optical waveguides, such as silicon nanophotonic wires considered here. In this paper we report local and non-local optically induced transparency (OIT) effects in graphene-silicon hybrid nanophotonic integrated circuits for the first time. A loss reduction of the hybrid nanophotonic wire is achieved over a broad wavelength range, when a pump light illuminates the graphene sheet both locally and non-locally. Moreover, the pump power density for the present OIT effect is extremely low, only ~2W/cm², which is several orders lower than the power density (up to 0.5~0.7×10⁶W/cm²) needed for the saturated absorption effect of graphene reported previously. This implies a totally new mechanism, involving light absorption by the silicon and photo-carrier transport through the silicon-graphene junction. The present OIT effect enables low power, all-optical, broadband modulation and switching locally and non-locally.