Interest in silicon as a material for optoelectronics has increased year after year. We propose numerical analysis of an integrated waveguide-vanishing-based modulator realized by ion implantation in SOI wafer. The active region is 3×3 <i>μm<sup>2</sup></i> and the lateral confinement is guaranteed by two highly-doped <i>As (8×10<sup>19</sup>cm<sup>-3</sup>)</i> and <i>B</i> (2×10<sup>19</sup>cm<sup>-3</sup>) implanted regions 1-<i>μm</i>-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 <i>dB/mm</i>, which are acceptable for short structures.
The modulation is based on a lateral <i>p-i-n </i>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 <i>V</i>, with electrical power consumption below 1<i> mW</i>, 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 <i>ns</i>. A set of numerical simulations has been performed in order to evaluate the thermal response of the device and thus to estimate the thermo-optic effect related to the biasing of the device itself. The main advantages of this device are the low cost and full integrability with electronic devices; thus the device can be suitable in many application fields.