Analysis of a planar silicon opto-electronic modulator based on the waveguide-vanishing effect

Silicon 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.