Graphene-based optical phase modulation of waveguide transverse electric modes

In this paper we report TE-mode phase modulation obtained by inducing a capacitive charge on graphene layers embedded in the core of a waveguide. There is a biasing regime in which graphene absorption is negligible but large index variations can be achieved with a voltage–length product as small as VπLπ≃0.07  V  cm for straight waveguides and VπLπ≃0.0024  V  cm for 12 μm radius microring resonators. This phase modulation device uniquely enables a small signal amplitude <1  V with a micrometer-sized footprint for compatibility with CMOS circuit integration. Examples of phase-induced changes are computed for straight waveguides and for microring resonators, showing the possibility of implementing several optoelectronic functionalities as modulators, tunable filters, and switches.