ABSTRACTSilicon is the most diffused material for microelectronic industry and, in recent times, it is becoming more and more widespread in integrated optic and optoelectronic fields. We present the thermo-electro-optical analysis of an integrated waveguide-vanishing-based optical modulator based on free-carrier dispersion effect, realizable on standard SOI wafer. The optical behavior is based on the vanishing of the lateral confinement in the rib region, and consequent cut-off of the propagating mode. Results show that an optical modulation depth close to 100% can be reached with a bandwidth of about 154 MHz. Smart electrical driving, that is an injection overdrive of a few volts for a very short time, allows to reach total ON-OFF switching time of about 860 ps. For that bias scheme the fall transient is then limiting the whole dynamic and the resulting bit rate in a pure digital modulation scheme is about 1.2 Gb/s