Nature Materials publication demonstrates second-order nonlinearity at optical wavelengths

ETSF scientists Elena Degoli, Valerie Véniard and Stefano Ossicini, in collaboration with other theoreticians and experimentalists, demonstrated second-order nonlinearities in strained silicon, a step towards enabling devices for wideband wavelength conversion operating at relatively low optical powers. The combination of strained silicon with suitable photonics design could produce materials with superior characteristics compared with conventional non-linear materials.

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 present owing to its crystalline inversion symmetry. Introducing a second-order nonlinearity into silicon photonics by proper material engineering would be highly desirable. It would enable devices for wideband wavelength conversion operating at relatively low optical powers. Here it was shown that a sizeable second-order nonlinearity at optical wavelengths is induced in a silicon waveguide by using a stressing silicon nitride overlayer. Second-harmonic-generation experiments and first-principle calculations were carried out, which both yield large values of strain-induced bulk second-order nonlinear susceptibility, up to 40 pm V−1 at 2,300 nm. It is envisaged that nonlinear strained silicon could provide a competing platform for a new class of integrated light sources spanning the near- to mid-infrared spectrum from 1.2 to 10 μm.

The results were published in Nature Materials in a paper entitled "Second-harmonic generation in silicon waveguides strained by silicon nitride".