Highly strain sensitivity sensor by long period fiber grating inscribed in multi-mode fiber using CO2 laser

We propose a novel long period fiber grating (LPFG) with enhanced strain sensitivity, which is inscribed in hydrofluoric acid-etched multi-mode fiber (MMF) by a CO₂ laser. Experimental results indicate that the strain sensitivity of the LPFG progressively increases as the MMF diameter decreases, while the temperature sensitivity remains consistently stable at - 575.58 pm/°C. Notably, when the fiber diameter is reduced to 61 μm, the strain sensitivity achieves a remarkable value of -177.93 pm/με. The proposed LPFG offers several advantages, including compact design, ease of fabrication, linear response characteristics, high sensitivity, and low cost. Thus, it holds significant promise for widespread application in industrial fields such as health monitoring of bridge structures, seismic physical detection, and fire alarm system.