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Electric field-induced second-order nonlinear optical effects in silicon waveguides


The symmetry of crystalline silicon inhibits a second-order optical nonlinear susceptibility, χ(2), in complementary metal–oxide–semiconductor-compatible silicon photonic platforms. However, χ(2) is required for important processes such as phase-only modulation, second-harmonic generation (SHG) and sum/difference frequency generation. Here, we break the crystalline symmetry by applying direct-current fields across p–i–n junctions in silicon ridge waveguides and induce a χ(2) proportional to the large χ(3) of silicon. The obtained χ(2) is first used to perturb the permittivity (the direct-current Kerr effect) and achieve phase-only modulation. Second, the spatial distribution of χ(2) is altered by periodically patterning p–i–n junctions to quasi-phase-match pump and second-harmonic modes and realize SHG. We measure a maximum SHG efficiency of P2ω/Pω2 = 13 ± 0.5% W−1 at λω = 2.29 µm and with field-induced χ(2) = 41 ± 1.5 pm V–1. We expect such field-induced χ(2) in silicon to lead to a new class of complex integrated devices such as carrier-envelope offset frequency stabilizers, terahertz generators, optical parametric oscillators and chirp-free modulators.

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Figure 1: The d.c. Kerr effect in silicon.
Figure 2: Design of a field-induced second-harmonic generator.
Figure 3: Analytical and experimental SHG.
Figure 4: Voltage and power dependence of the SHG.
Figure 5: SHG at multiple wavelengths.


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This work was supported by the Defense Advanced Research Projects Agency (DARPA) Microsystems Technology Office (MTO) E-PHI (HR0011-12-2-0007) and DODOS (HR0011-15-C-0056) projects. The authors thank programme managers J. Conway and R. Lutwak for support.

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Authors and Affiliations



E.T. and M.R.W. conceived the idea for the project. E.T. simulated and designed nonlinear silicon waveguides, laid out the mask, conducted experiments on second-harmonic generators and analysed the results. E.T. and C.V.P. designed the d.c. Kerr MZIs, laid out the mask and analysed the results. C.V.P., M.J.B. and E.T. conducted experiments on d.c. Kerr MZIs. All authors wrote and edited the manuscript. M.R.W. supervised the project.

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Correspondence to E. Timurdogan.

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Timurdogan, E., Poulton, C., Byrd, M. et al. Electric field-induced second-order nonlinear optical effects in silicon waveguides. Nature Photon 11, 200–206 (2017).

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