Surface plasmon resonance refractive index sensor based on photonic crystal fiber covering nano-ring gold film

•The higher order surface plasmon modes for the 7th, 6th, and 5th SPP are obtained in the simulation.•The 1st and 3rd peaks exhibited better sensitivity to the refractive index analyte.•The sensitivity is studied in the wide range from 1.33 to 1.43. The highest average linear sensitivity is 2150 nm/RIU in the refractive index from 1.40 to 1.43.