Simultaneous measurement of torsion and strain using a parallel structured fiber wave-guide sensor

A wave-guide sensor with two single-mode fibers in a parallel configuration (SMFP) is demonstrated for simultaneous measurement applications. The sensing structure is formed by joining the two ends of the SMFP using pigtail connectors. The torsion and axial strain characteristics of the sensor are investigated theoretically and experimentally. The results show that the transmission spectra exhibit a shift with the changing of the loading strain and torsion. The sensitivity of the axial strain of the sensor is 18.06 pm/mu epsilon. The torsion sensitivities are obtained to be -283.2 pm/(rad/m) and -157.3 pm/(rad/m) for the clockwise and counterclockwise twisting, respectively. The sensor can realize the simultaneous measurement of strain and torsion and can distinguish the direction of torsion. Due to its high sensitivity, ease of fabrication, and simultaneous measurement capabilities, the sensor has potential applications in fields such as machinery, railways, side slopes, etc. where the strain and torsion need to be measured simultaneously.