van der Waals NbOCl₂ Nanodisks for Enhanced Second-Harmonic Generation

Niobium oxide dichloride (NbOCl₂), a van der Waals crystal, exhibits exceptional second-harmonic generation (SHG) with high conversion efficiency, making it a promising candidate for on-chip quantum light sources, photon modulators, and sensors. To increase its suitability for integrated photonic systems, it is crucial to explore strategies for further improving optical nonlinear conversion efficiency. In this article, dielectric metasurfaces are employed to enhance SHG from patterned NbOCl₂ nanodisks. By precisely tuning their geometric parameters to achieve optical resonance near the excitation wavelength, a remarkable 25-fold enhancement in second-harmonic emission at 400 nm is achieved in nanodisks compared to the unpatterned thin film. The strong field enhancement within the NbOCl₂ nanodisks at nanophotonic resonances contributes to the observed increase in SHG. This work offers an effective strategy for boosting SHG in van der Waals NbOCl₂ thin films, paving the way for the development of efficient nonlinear optical components in integrated nanophotonics.