Self-referenced refractive index sensor based on hybrid mode resonances in 2D metal-dielectric grating

In this paper, we propose a refractive index sensor with self-reference performance based on a two-dimensional grating structure, mainly consisting of periodic arrays of triple layer dielectric nanodisks and a continuous substrate separated by a thin gold film. Three reflection dips are observed and manipulated to realize self-reference and high sensing performance due to the excitation of magnetic dipole mode resonance, substrate mode resonance and metal layer assisted guide mode resonance. These hybrid modes have been explained by the distributions of the electric and magnetic fields in the nanostructure. A detailed analysis of the influences of material thickness on the optical properties of the proposed refractive index sensor is also investigated. Moreover, the proposed refractive index sensor demonstrates a high sensing performance, an important application for future biomedical applications, with a bulk refractive index sensitivity of 672 nm RIU⁻¹ (RIU: refractive index unit) and figure of merit of 1050 RIU⁻¹. Importantly, the function of self-reference is realized simultaneously. Finally, it also shows excellent sensing performance, with the maximum value exceeding 168 000 by measuring the light intensity change in the reflected light at a certain wavelength. This makes it much more suitable for applications in the field of portable detection. (paper)