  An electro-absorption optical modulator concept based upon a dual-graphene
layer is presented. The device consists of a silicon-on-insulator waveguide
upon which two graphene layers reside, separated by a thin insulating region.
The lower graphene acts as a tunable absorber, while the upper layer functions
as a transparent gate electrode. Calculations based upon realistic graphene
material properties show that 3-dB bandwidths over 100 GHz (30 GHz) are
possible at near- (\lambda=1.55 \mu m) and mid- (\lambda=3.5\mu m) infrared
bands. The effect of background doping and potential fluctuations on the
bandwidth, modulation depth and insertion loss are also quantified.
