Fabrication of Phase-Shifted Long-Period Fiber Grating and Its Application to Strain Measurement

Several kinds of phase-shifted long-period gratings (LPGs) have been fabricated using a high-repetitionrate CO₂ laser, where both the grating and the inserted phase shift are simultaneously produced in a commonly used single-mode fiber. Furthermore, using one of the fabricated phase-shifted LPGs, a temperature-insensitive sensor that allows for large axial strain measurement with a value up to 7600 με, is proposed and first demonstrated. Measurement accuracy for the strain ranging from 340 to 7600 με is estimated to be ±30 με, while the temperature is changed in a range of 20°C-140°C.