Tuning the resonance of polarization-degenerate cladding mode LP1,j in excessively tilted long period fiber grating for highly sensitive refractive index sensing

The Ex-TLPFG is tuned to couple the guided core mode with only polarization-degenerate cladding mode LP1,l which consists of TE/TM0,l and HE2,l vector modes. It is found that the p-polarized LPp 1,l mode exhibits a higher sensitivity than that of s-polarized LPs 1,l mode.

An optimized sensitivity as high as 12182.9 nm/RIU is achieved for p-polarized LPp 1,2 mode at low refractive index region by tuning initial resonance condition. The sensing performance is also evaluated through the power measurement method for a single resonance band. It is demonstrated that the improved sensitivity in this work for diameter-reduced Ex-TLPFG is much higher than that for the conventional LPFG based devices, which makes this sensing platform very attractive for a variety of index sensing applications.