On-Chip Second-Harmonic Generation in a Singly Resonant Nanocavity with Integrated Cadmium Sulfide Nanowires

Efficient nonlinear frequency conversion at the nanometer scale is important for biosensing, integrated optical circuits, and quantum technologies. Semiconductor nanowires (NWs) offer large effective second-order nonlinear susceptibilities (χ(2)) and subwavelength optical confinement, making them attractive building blocks for integrated nonlinear photonics. However, the second-harmonic generation (SHG) efficiencies of NWs are typically low, owing to their small interaction volumes and limited optical mode coupling efficiency. Here, we report an approach to enhancing the SHG efficiency of NWs through a hybrid nanowire-cavity configuration in which a cadmium sulfide (CdS) NW is embedded into a waveguide-coupled one-dimensional photonic-crystal nanobeam cavity (PCNBC) on a polymer-loaded silicon nitride (SiN) platform to enhance light–nanowire interaction. The bare polymer-loaded SiN PCNBC exhibits an optimized loaded quality factor Q of up to 1.3 × 105, providing a high-Q cavity platform for resonant nanowire enhancement. After embedding the CdS NW at the cavity center, the hybrid device concentrates the pump field within the χ(2)-active NW and enables efficient SHG under low-power continuous-wave excitation. The hybrid CdS NW–PCNBC produces directional single-lobe second-harmonic emission at 776.95 nm and reaches an on-chip SHG conversion efficiency of 0.3% W–1. This performance exceeds previously reported plasmonic- or photonic-crystal-enhanced SHG in NWs by more than 2 orders of magnitude. These results show that high-Q cavity integration can strongly enhance nanowire-based nonlinear frequency conversion and provide a scalable route toward on-chip integrated nonlinear photonic devices.