All-dielectric metasurface enhanced second-harmonic generation in NbOCl2 nanoflakes

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NbOCl 2 layered nonlinear optical materials hold great promise for on-chip photonic devices due to their strong light-matter interactions and integrability. Here, we propose a metasurface-based enhancement strategy by integrating few-layer NbOCl 2 crystals with a periodic array of SiO 2 nanopillars, leading to a significant boost in second-harmonic generation (SHG). Experimental results show that the fabricated SiO 2 /NbOCl 2 /SiO 2 metasurface structure yields a stable × 300% enhancement in SHG signal under 1064 nm pumping compared to a flat, encapsulated reference, with the enhancement factor remaining constant over a broad power range. Polarization-resolved SHG measurements reveal the in-plane anisotropic nonlinear response of NbOCl 2 , with the metasurface providing an enhancement for signals generated along the material’s polar axis. Electromagnetic simulations attribute this enhancement primarily to the Mie-type scattering supported by the SiO 2 nanopillars, which improve the incident field and boost the local intensity within the NbOCl 2 layer. This work establishes a viable platform for enhancing the efficiency of low-dimensional NbOCl 2 nonlinear optical materials and paves the way for developing high-performance nonlinear nanophotonic devices.