Scalable, polarization-insensitive broadband nonlinear metasurfaces for weak-light applications

In this work, we develop an ITO-based metasurface integrated with disordered silver nanoparticles (DSNPs). The localized plasmon resonance of the DSNPs couples and confines incident light within the ITO layer, enabling strong nonlinear responses across a broad visible-to-near-infrared spectrum with minimal polarization dependence (with a fluctuation of <15%). At a low pump intensity of 0.2 GW/cm², the ultrathin (∼35 nm) metasurfaces exhibit a nonlinear refractive index exceeding 0.1 cm²/GW, with a maximum value reaching 1.24 cm²/GW. This research provides a solution for low-power, high-integration-density nonlinear nanophotonic devices and all-optical control.