Nanogap enhancement of the refractometric sensitivity at quasi-bound states in the continuum in all-dielectric metasurfaces

Abstract All-dielectric metasurfaces have great potential as highly sensitive refractometric sensors relying on their spectral shifts because of an extensive range design flexibilities and smaller absorption losses than plasmonic platforms. However, simultaneously realizing both high quality ( Q ) factors the large interplay light with external medium in such photonic remains one key challenges for better performance. This study proposes silicon block nanogaps to overcome this challenge based quasi-bound states continuum (BICs). We show that metasurface has two quasi-BIC modes—magnetic dipole (MD) electric quadrupole (EQ)—and fields experience enhancement at ∼30 nm nanogap regions. Consequently, introducing into increases environmental refractive index sensitivity by up 2.7 times MD mode while keeping achieves figure-of-merit (FOM) 239. In addition, we appropriate selection amount asymmetry is needed under trade-off between FOM signal-to-noise ratio, which provides guidelines biosensors quasi-BICs.