van der Waals\nNbOCl<sub>2</sub> Nanodisks for Enhanced\nSecond-Harmonic Generation

Niobium oxide dichloride (NbOCl<sub>2</sub>), a van der\nWaals crystal,\nexhibits exceptional second-harmonic generation (SHG) with high conversion\nefficiency, making it a promising candidate for on-chip quantum light\nsources, photon modulators, and sensors. To increase its suitability\nfor integrated photonic systems, it is crucial to explore strategies\nfor further improving optical nonlinear conversion efficiency. In\nthis article, dielectric metasurfaces are employed to enhance SHG\nfrom patterned NbOCl<sub>2</sub> nanodisks. By precisely tuning their\ngeometric parameters to achieve optical resonance near the excitation\nwavelength, a remarkable 25-fold enhancement in second-harmonic emission\nat 400 nm is achieved in nanodisks compared to the unpatterned thin\nfilm. The strong field enhancement within the NbOCl<sub>2</sub> nanodisks\nat nanophotonic resonances contributes to the observed increase in\nSHG. This work offers an effective strategy for boosting SHG in van\nder Waals NbOCl<sub>2</sub> thin films, paving the way for the development\nof efficient nonlinear optical components in integrated nanophotonics.