Tuning the resonance of polarization-degenerate LP cladding mode in excessively tilted long period fiber grating for highly sensitive refractive index sensing.

This work presents a sensitive refractive index sensor based on the dual resonance of an excessively tilted long period fiber grating (Ex-TLPFG). The Ex-TLPFG is tuned to couple the guided core mode with only the polarization-degenerate cladding mode LP, which consists of TE/TM and HE vector modes. It is found that the p-polarized LP1,lp mode exhibits a higher sensitivity than that of the s-polarized LP1,ls mode.