Distributed Twist Sensing With Uncoupled Multi-Core Fibers Using Polarization-Sensitive Reflectometry

We explore the use of uncoupled multi-core fibers employed for telecommunications as a technological platform for implementing polarization-based distributed twist sensors. Through polarimetric-optical frequency domain reflectometry we assess the twist-induced birefringence along the cores of an uncoupled four-core fiber. By applying controlled twist, we show that the elasto-optic coefficient in each core is consistent with the value reported for single-mode fibers, and that the cores experience the same birefringence variations in response to the applied twist. Moreover, we leverage the distinctive birefringence properties of unspun uncoupled multi-core fibers to achieve long-range twist sensing, showing that the measured twist is in excellent agreement with the applied one even when the perturbed fiber location is 500-m away from the source. We achieve a remarkable accuracy of 4 degrees in measuring the angle by which the fiber is twisted, with a spatial resolution of 8 cm. These results support the potential of uncoupled multi-core fibers to realize twist sensors that are relevant for applications such as umbilical cable monitoring.