Ultra-high-Q and sensitive refractive index sensing in low refractive index dielectric gratings based on bound states in the continuum

The realization of a high quality factor ( Q -factor) and strong local optical fields has long been of great interest in the field of nanophotonics. Unfortunately, it is still challenging to achieve high- Q and strong localized fields in nanostructures made of low refractive index materials. In this study, drawing upon the concept of bound states in the continuum (BICs), an asymmetric dielectric grating composed of low refractive index materials is demonstrated to generate an ultra-high- Q symmetry-protected quasi-BIC in the visible wavelength. Importantly, the design of BIC (quasi-BIC) mode enables the strong localized confinement of light in air. By leveraging this property, we realize ultra-sensitive refractive index sensing with a remarkable sensitivity of 669 nm/RIU and a high figure of merit (FOM) of 45,314RIU −1 . This study offers an approach to achieve highly sensitive and high precision refractive index sensing with potential applications in the practical realization of strong light–matter interactions using low index materials.