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 120 GHz (30 GHz) are achievable at near- (λ = 1.55 μm) and mid- (λ = 3.5 μm) infrared bands. The effect of background doping and potential fluctuations on the bandwidth, modulation depth, and insertion loss are also quantified.