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 V pi L pi similar or equal to 0.07 V cm for straight waveguides and V pi L pi similar or equal to 0.0024 V cm for 12 mu m 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. (C) 2014 Chinese Laser Press