Second-Harmonic and Sum-Frequency Generation in Silicon Nitride Photonics Integrated with Cadmium Sulfide Nanowire

We demonstrate second-order (χ⁽²⁾) nonlinear responses including second-harmonic generation (SHG) and sum-frequency generation (SFG) from the silicon nitride (SiN) waveguides by deterministically incorporating χ⁽²⁾-active subwavelength CdS nanowires (NWs) inside them, addressing the χ⁽²⁾ deficiency of the SiN for being centrosymmetric. By engineering the dimensions of the hybrid CdS NW-SiN waveguide, we achieved modal phase-matching for SHG, yielding conversion efficiencies of 0.76% W^-1 from a stripe waveguide. By implanting a microring resonator configuration, ∼ 100 times higher conversion efficiencies of them were obtained. Finally, using the χ⁽²⁾-based optical wave-mixing of the hybrid waveguide, we explored its use as an autocorrelator for the on-chip measurement of the ultrafast laser pulse duration and achieved a result only 4% deviated from that of a commercial product. This hybrid CdS NW-SiN waveguide strategy solved the lack of the χ⁽²⁾-related functionalities of the SiN waveguide platform and paves the way for its applications in integrated nonlinear photonics.