Sensitivity characteristics of LPFGs inscribed in FMF

Few mode fiber (FMF) has been studied a lot in recent years. It is told that the co-propagating coupling between different modes in few mode long-period fiber gratings (FM-LPFGs) can get a large sensitivity in sensing measurement. In this paper, we present a comprehensive simulation about the sensing sensitivity of long-period fiber gratings (LPFGs) inscribed in few mode fiber (FMF). We recognize a sensitivity factor which contributes a lot to the sensing sensitivity, and calculate the value in FMF. Our analysis reveals a high sensitivity factor at the resonance wavelength of 1550nm when the resonant cladding mode order equals to 20. Our simulation proves that LPFGs inscribed in FMF, comparing with sing mode fiber (SMF), have a much better sensing performance in the temperature, strain and surrounding refractive index (RI) when the cladding mode order is closed to 20. Particularly, the maximum value of RI sensitivity can reach 1512 nm/10⁻³ in FMF when the surrounding RI equals to 1.43, five times as much as the value in SMF.