Electroabsorption modulator based on inverted-rib-type silicon waveguide including double graphene layers

We investigate, theoretically, a compact graphene-based electroabsorption modulator (EAM). The compactness of the EAM arises from an inverted-rib-type (IRT) silicon waveguide including a graphene–oxide–graphene stack. The EAM consists of input and output waveguides, which are conventional silicon strip waveguides, and the IRT waveguide efficiently connected to them through tapering regions. The stack is located in the region where the fundamental transverse electric mode of the IRT waveguide is mainly confined. Hence, the IRT waveguide mode strongly interacts with the graphene layers. Moreover, the IRT waveguide can be realized without complex high-precision processes. The calculated modulation depth of the IRT waveguide is 0.41 dB μm−1 when the chemical potential of graphene is tuned between 0.2 and 0.6 eV. It is more than two times larger than those of previous graphene-covered silicon waveguides. The EAM, with a 3 dB extinction ratio, employs an IRT waveguide of length 7–8 μm. This EAM is analyzed and found to have an optical bandwidth of 100 nm, an electrical bandwidth of up to 46.4 GHz, and energy consumption smaller than 630 fJ bit−1. Such EAMs based on IRT waveguides may play an important role in off-chip optical interconnection.