Second order nonlinearities in silicon photonics

In this thesis, second order optical nonlinearities in silicon waveguides are studied. At the beginning, the strained silicon platform is investigated in detail. In recent years, second order nonlinearities have been demonstrated on this platform. However, the origin of these nonlinearities was not clear. This thesis offers a clear answer to this question, demonstrating that this nonlinearity does not originate on the applied strain, but on the presence of trapped charges that induce a static electric field inside the waveguide. Based on this outcome, a way to induce larger electric fields in silicon waveguide is studied. Using lateral p-n junctions, strong electric fields are introduced in the waveguides, demonstrating both electro-optic effects and second-harmonic generation. These results, together with a detailed modeling of the system, pave the way through the demonstration of spontaneous parametric down-conversion in silicon.