All-dielectric refractive index sensor based on Fano resonance with high sensitivity in the mid-infrared region.

• We design a polarization-insensitive and incident angle-independent Fano resonance device based on all-dielectric "lucky knot" shaped nanostructure in the mid-infrared region. • We proposed a mid-infrared refractive index sensor with a sensitivity of 986 nm/RIU and a figure of merit of 32.7 simultaneously. • The proposed device can be applied in biosensing, environmental monitoring and other fields. We design and numerically analyze a Fano resonance device based on periodical all-dielectric "lucky knot" shaped nanostructure in the mid-infrared region with high sensitivity, which is insensitive to polarization and incident angle. The proposed nanostructure is sensitive to the change of the refractive index of the substance to be tested. We established the correspondence between the change of the refractive index and the peak position of the reflection spectrum. And then we propose an optical refractive index sensor with a sensitivity of 986 nm/RIU, and a maximum figure of merit of 32.7, which is much higher compared to the sensor based on metallic materials. The maximum Q-factor can reach 520. This study may provide a further step in optical sensing, biosensing and environmental monitoring. [ABSTRACT FROM AUTHOR]