Double-formant surface plasmon resonance for refractive index sensing by anti-resonance fibers with high sensitivity and wide detection range

•The biggest innovation of this paper is that SPR is excited in ARF by numerical analysis for the first time.•In this paper, the detailed optimization process of optical fiber performance is given, and the optimal structural parameters are obtained.•The proposed ARF-SPR refractive index sensor has two formants, both of which can detect analytes with refractive index ranging from 1.31 to 1.445, and the maximum wavelength sensitivity of the two formants can reach 20000 nm/RIU and 36400 nm/RIU, respectively.•The structure is filled with gold in the negative curvature tube to excite SPR, which reduces the manufacturing difficulty compared with the traditional coating method.