Thermo-opto-electrical analysis of an optical modulator integrated in a silicon planar structure

We propose numerical analysis of an integrated waveguide-vanishing-based modulator realized by ion implantation in SOI wafer. The active region is 3×3 µm2 and the lateral confinement is guaranteed by two highly-doped As (8×1019cm-3) and B (2×1019cm-3) implanted regions 1-µm-deep. This type of structure allows to obtain a planar device, avoiding structural steps which are harmful for photolithography processes. The resulting channel waveguide shows single mode operation and propagation losses of about 1.8 dB/mm, which are acceptable for short structures. The modulation is based on a lateral p-i-n diode, which injects free carriers into the rib volume between the doped regions. We have optimized the device for maximum injection efficiency for a given applied voltage. The resulting optical behavior can be explained by the lateral confinement vanishing that transforms the rib waveguide in a slab waveguide, once the rib is full of free carriers. This phenomenon occurs at driving voltage of about 1.0 V, with electrical power consumption below 1 mW, and implies a rapid variation of the propagating characteristics, and as consequence an optical beam lateral redistribution into the structure. Results show that an optical modulation depth close to 100% can be reached with a switching time of about 30 ns.