Nanoporous-structured metasurface refractive index sensor employing quasi-bound states in the continuum

Bound states in the continuum represent a unique optical phenomenon characterized by extremely high-quality factors and low energy losses, offering great potential for high-sensitivity sensing applications. In this study, we investigated the optical properties of nanoporous silica substrates (NSS) and nanoporous silicon dimer (NSD) structures with varying porosity percentages in different refractive index environments. The results demonstrate that the combined architecture achieves high refractive index sensitivity ([Formula: see text]) and an exceptionally high figure of merit ([Formula: see text]). The lower refractive index of the NSS accelerates the decay of localized quasi-bound states in the continuum evanescent modes into the substrate, channeling the field into the surrounding medium, while the NSD further boosts local field intensity. The nanoporous medium structure design presented in this work offers a new strategy for developing high-performance refractive index sensors, deepening our understanding of nanoporous materials for optical sensing, and updating valuable theoretical and technical support for the practical sensor design.