High-Sensitivity U-Shaped Optical Fiber Strain Sensor With Avoidance of Temperature Cross-Sensitivity

To achieve highly sensitive measurements of strain, a U-shaped optical fiber sensor (OFS) based on seven-core photonic crystal fiber (SCPCF) was designed. The proposed Mach-Zehnder-based sensor utilizes gourd-shaped regions constructed by the discharge technique to achieve beam extension and coupling. The construction of the U-shaped region increases the strain-sensing capability of the sensor, and the sensitivities of the two interference dips in the transmission spectra are −67 and −66 pm/ $\mu \varepsilon $ in the range of 0– $140~\mu \varepsilon $ , respectively. The proposed sensor is able to respond linearly to the strain and exhibits good repeatability. Additionally, the weak modes present in the transmission spectra were eliminated using a filtering method; the interference dips formed by the superposition of the dominant modes exhibit higher sensitivities of −82 and −85.5 pm/ $\mu \varepsilon $ , respectively. With proper selection, the detection range of the sensor is not sacrificed. Notably, the presence of a temperature-insensitive interference dip in the transmission spectrum allows the sensor to avoid temperature crosstalk. Meanwhile, the simultaneous measurement of strain and temperature can be realized by using the different characteristics of interference dips. The proposed sensor is capable of realizing highly sensitive measurements of strain, which is promising for a wide range of applications in the field of deformation monitoring.