Strain-insensitive twist and temperature sensor based on seven-core fiber

We propose a fiber-optic sensor for simultaneous measurement of twist and temperature using a Mach-Zehnder interferometer by sandwiching a segment of seven-core fiber (SCF) between two sections of very short multimode fibers via fusion splicing technique. The cladding diameter and the pitch between adjacent cores of the SCF are measured to be 150 and 41.5 μm, respectively, larger than those of conventional SCFs, which lead to a higher twist sensitivity. Within twist range from 4.758 to 40.439 rad/m and temperature range from 30 to 100 °C, this sensor shows a twist sensitivity of −400 pm/(rad/m) and a temperature sensitivity of 123 pm/°C, respectively. The influence of strain is negligible since the strain sensitivity is much lower. The sensor configuration possesses other advantages such as ease of fabricate, high contrast, and low-cost, therefore it exhibits practical applications potentials in engineering machinery and building structural health monitoring.