Highly Efficient Refractive Index Sensor Of Multiple Fano-Resonances Simulated By Polarization-Insensitive Meta-Surface With Silver Nanorings

An optical refractive index(RI)sensor is a sensing equipment that can alter variations in the RI into measurable optical data. The grouping of surface plasmon resonance (SPR) and Fano resonance can enhance some key parameters, which are all linked to the complete performance for highly-precise and multi-band sensor. This study purposes and analyze Fabry–Perot (F-P) cavity for optical RI sensing based on the critical coupling condition, effective in a near-infrared (NIR) wavelength range. The simulation shows that the proposed meta-surface exhibits double Fano-resonance by the coupling of the confined surface plasmon resonances (LSPR) of the NR array and the cavity mode of the F-P resonant cavity, at the wavelength of 785 and 1064 nm for an aqueous background medium surrounding the metasurface. Some important optical indexes, polarization sensitivity, figure of merit (FOM) and sensing sensitivity can be improved by the grouping of surface plasmon resonance (SPR) and Fano resonance which are entirely associated to the wide-ranging performance for excellent accuracy and multi-band detecting. Proposed simulation results shows that the excellent sensing sensitivities can attain 650 nm/RIU and 1001.5 nm/RIU, and the corresponding FOMs can significantly attain 226.48 and 247.89. Then we considered the effect of the structural limitations on the sensitivity and FOM of the sensor by simulations and confirmed the structure is in-sensitive to the polarization angle of incident light. Our sensor has excellent performance in polarization insensitivity, good sensing sensitivity and FOM in both resonance bands, which is further appropriate for applied applications.