Bidirectional Torsion Sensor Based on a Pair of Helical Long-Period Fiber Gratings

A novel torsion sensor is proposed by cascading two identical helical long-period fiber gratings. On the basis of interference theory, the separation between the dips in the transmission spectrum will be affected by the applied torsion. In addition, a linear response of the split dependent on the torsion rate in different directions can be deduced. Moreover, the ambient temperature has a limited influence on the sensor result. Confirmation experiments were carried out, and good agreement of derivations and experimental results is obtained.