Thursday 28 Feb 2019: NEST Seminar: Graphene on waveguides: unexpected physics and innovative fabrication
Prof Nathalie Vermeulen - Vrije Universiteit Brussel
In recent years the integration of graphene on silicon-based waveguides has attracted much attention as it allows using well-established CMOS technology for constructing next-generation photonic integrated circuits. However, important challenges need to be overcome regarding the fabrication and patterning of graphene-covered waveguide devices. In addition, a more in-depth investigation of the fundamental optical properties of graphene-covered waveguides, and in particular their nonlinear optical characteristics, will be required. The latter are promising for, amongst others, generating spectrally broadband light useful for a wide range of application domains including telecommunications and sensing.
In this talk I present a novel approach for local patterning of graphene deposited on silicon waveguides, and provide new insights in the nonlinear optical properties of graphene on top of waveguides. Our patterning approach is chemicals-free and based on laser ablation and plasma etching, removing the graphene top layer without damaging the underlying silicon material. To better understand graphene’s nonlinear optical properties, we investigated the nonlinear-refraction process of self-phase modulation in graphene-covered waveguides, and found that the sign of graphene’s nonlinearity is negative, in contrast to what has been assumed so far. In addition, we recently showed by means of a paradigm-shifting theory that the underlying physics is not based on refraction induced by graphene’s conventional third-order susceptibility, but instead on a much more complex phenomenon that we call saturable photoexcited carrier refraction.