Characteristics of dual-peak resonance in a tilted long-period fiber grating sensing film sensor

Abstract

Based on the coupled-mode theory of tilted long-period fiber gratings (TLPFGs) and the dual-peak resonance theory, we build the structure of a TLPFG with the phenomenon of dual-peak resonance. The influences of grating tilt angle, grating structure parameters, surrounding refractive index (SRI), and film optical parameters on the dual-peak resonance are analyzed in the transmission spectra of this structure. As the results show, the characteristics of the dual-peak resonance in the (1m) cladding modes and the (2m) cladding modes are similar, and the sensitivity of the (2m) cladding modes to refractive index, as well as the grating tilt angle, grating structure parameters, and film optical parameters, is higher than that of the (1m) cladding modes in this structure. The research provides the theoretical foundation for design of a dual-peak resonance coated TLPFG sensor for SRI, gas, humidity, pH, bending curvature, and strain.