Long period fiber grating based on periodically screw-Type distortions for torsion sensing

A novel long-period fiber grating (LPFG), fabricated by periodically cascading a series of screw-Type distortions, is proposed and experimentally demonstrated. These screwtype distortions are induced by twisting the fiber during CO2 laser beam exposure. The resulting LPFG will either be left-or right-hand helical, depending on the twist rate and direction used during fabrication, with a certain frozen shear strain. Due to the independence between grating pitch and twist rate, this type of LPFG could be more flexible than the helical-or chiral-fiber gratings reported previously. During LPFG twisting, the device displays good directional dependence and an enhanced torsion sensitivity of 0.1604 nm/(rad/m), which implies the structure could be an excellent candidate for torsion sensors.