Tilted long-period fiber grating strain sensor based on dual-peak resonance near PMTP

This paper puts forward a new kind of tilted long-period fiber grating (TLPFG) strain sensor's structure and its design methods based on high sensitivity of TLPFG sensors near the phase-matching turning point (PMTP). First, with the TLPFG phase-matching condition, the appropriate (2 m) cladding mode is selected and the grating period corresponding to PMTP under this mode is found. Further, the TLPFG transmission spectrum with strong attenuation peak is obtained by selecting the tilted angle and grating length. Finally, the dual-peak resonance characteristics and strain sensing characteristics of the TLPFG near PMTP is analyzed, it is found that dual peak wavelength spacing has a very high sensitivity and linearity to micro-strain. By selecting the appropriate grating structural parameters, the sensitivity could be effectively improved. The sensitivity of tilted long-period fiber grating strain sensor operating near PMTP is available to 525 pm/mu epsilon, and the corresponding resolution can be available to 0.019 mu epsilon. Compared with the resolution (19.8 mu epsilon) of the reported tilted phase-shifted long-period fiber grating strain sensor, the resolving power is enhanced by three orders of magnitude. This new TLPFG strain sensor is expected to be applied in micro-strain monitoring and structural health monitoring.