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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 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 we show that a sizeable second-order nonlinearity at optical wavelengths is induced in a silicon waveguide by using a stressing silicon nitride overlayer. We carried out second-harmonic-generation experiments and first-principle calculations, which both yield large values of strain-induced bulk second-order nonlinear susceptibility, up to 40 pm V−1 at 2,300 nm. We envisage 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.

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Figure 1: First-principle calculations of strained Si second-order nonlinearity.
Figure 2: Strained Si waveguides used to measure SHG.
Figure 3: Summary of the results of micro-Raman measurements on the waveguide facet.
Figure 4: Strain profiles (ɛY Y) for the different waveguide types.
Figure 5: Summary of the SHG measurements.


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We acknowledge discussions and experimental help by P. Bettotti, A. Pitanti, B. Dierre, F. Enrichi, K. Fedus and A. Yeremian. This work was supported by the FU-PAT (Provincia Autonoma di Trento) project NAOMI, by a grant from Fondazione Cariplo no 2009-2730 and by Fondazione Cassa di Risparmio di Modena through the project ‘Progettazione di materiali nanostrutturati semiconduttori per la fotonica, l’energia rinnovabile e l’ambiente’. We also acknowledge the supercomputing facility CINECA for granted central processing unit time.

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M.C. and L.P. conceived the experiments. E.B., F.B. and M.C. made the nonlinear optical measurements. M.G. and G.P. fabricated the waveguides. E.D., E.L., V.V. and S.O. carried out the ab initio simulations. D.M. and S.W. did the nonlinear propagation modelling. R.P. and F.B. made the micro-Raman measurements. L.P. wrote the manuscript in collaboration with all the authors.

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Correspondence to L. Pavesi.

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The authors declare no competing financial interests.

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Cazzanelli, M., Bianco, F., Borga, E. et al. Second-harmonic generation in silicon waveguides strained by silicon nitride. Nature Mater 11, 148–154 (2012).

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