A new sensor for simultaneous measurement of strain and temperature

A new cascaded structure based on two long-period fiber gratings (LPFGs) for simultaneous measurement of strain and temperature is proposed and studied. The proposed structure is cascaded by a LPFG and a S-type long-period fiber grating (S-LPFG). The LPFG is fabricated using the CO2 laser by etched method. The S-LPFG is fabricated using the CO2 laser by polished method. The grooves of the S-LPFG are staggered in opposite directions, and this special geometry results in high strain sensitivity. The experimental results show that the strain sensitivities of the two resonant dips of the cascaded structure are 16.31 pm/ $\mu \varepsilon $ and −2.42 pm/ $\mu \varepsilon $ with the range of 0- $500~\mu \varepsilon $ , respectively. Strain sensitivity varies greatly between two dips and the resonant wavelength shifts in the opposite direction. The temperature sensitivities of the two resonant dips of the cascaded structure are 59.73 pm/°C and 60.38 pm/°C, respectively. Since the difference between temperature and strain sensitivity, matrix method can be used for simultaneous measurement of two parameters. The feasibility of the cascaded structure has been experimentally demonstrated for the simultaneous measurement. Therefore, the cascaded structure has the potential to measure strain and temperature simultaneously.