Refractive index sensing using quasi-bound states in the continuum in silicon metasurfaces

By systematically detuning the size and position of silicon nanoparticles in periodic arrays, we have shown multiple optical resonances in the arrays with a very narrow linewidth. These resonances, known as quasi-bound states in the continuum are interesting for optical sensing. Changes in the refractive index of the surrounding medium lead to shifts in the resonances that define the sensitivity. We demonstrate different sensitivities for the various resonances and explained them by the concentration of the electromagnetic fields surrounding the nanoparticles.