Second-harmonic generation in germanium-on-insulator from visible to telecom wavelengths

The second-order $\chi^{2}$ process underpins many important nonlinear optical applications in the field of classical and quantum optics. Generally, the $\chi^{2}$ process manifests itself only in a non-centrosymmetric dielectric medium via an anharmonic electron oscillation when driven by an intense optical field. Due to inversion symmetry, group-IV semiconductors like silicon (Si) and germanium (Ge) are traditionally not considered as ideal candidates for second-order nonlinear optics applications. Here, we report the experimental observation of the second-harmonic generation (SHG) in a Ge-on-insulator (GOI) sample under femtosecond optical pumping. Specially, we report the first-time measurement of the SHG signal from a GOI sample in the telecom S-band by pumping at $\sim$$3000$ nm.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)National Research Foundation (NRF)Published versionThe research of the project was in part supported by Ministry of Education, Singapore, under Grant No. AcRF TIER 1 (RG 115/21). The research of the project was also supported by Ministry of Education, Singapore, under grant AcRF TIER 2 [No. MOE2018-T2- 2-011 (S)]. This work was also supported by the National Research Foundation of Singapore through the Competitive Research Program (No. NRF-CRP19-2017-01). This work was also supported by the National Research Foundation of Singapore through the NRF-ANR Joint Grant (No. NRF2018-NRF-ANR009 TIGER). This work was also supported by the iGrant of Singapore A STAR AME IRG (No. A2083c0053). The authors would like to acknowledge and thank the Nanyang NanoFabrication Centre (N2FC)