Second-harmonic generation in silicon waveguides strained by silicon nitride

Silicon photonics meets the electronics requirement of increased speed and bandwidth with on-chip optical networks.All-optical data management requires nonlinear silicon photonics. In silicon only third-order optical nonlinearities are presentowing to its crystalline inversion symmetry. Introducing a second-order nonlinearity into silicon photonics by proper materialengineering would be highly desirable. It would enable devices for wideband wavelength conversion operating at relatively lowoptical powers. Here we show that a sizeable second-order nonlinearity at optical wavelengths is induced in a silicon waveguideby using a stressing silicon nitride overlayer. We carried out second-harmonic-generation experiments and first-principlecalculations, which both yield large values of strain-induced bulk second-order nonlinear susceptibility, up to 40pm/V at2,300 nm. We envisage that nonlinear strained silicon could provide a competing platform for a new class of integrated lightsources spanning the near- to mid-infrared spectrum from 1.2 to 10 micrometri