A Torsion Sensor Based on a Core-Deformed Long Period Fiber Grating

In this letter, a novel core-deformed long period fiber grating (CD-LPFG) for torsion measurement is proposed and experimentally demonstrated. This sensor is prepared by the CO
₂
laser polishing method and filament heating method. The deformed core of the structure is achieved by tapering on a dual-side polished single mode fiber (SMF), which enhances the torsion sensitivity. Experimental results show that the torsion sensitivity of the CD-LPFG reaches 0.314 nm/rad
$\cdot \text{m}$
⁻¹
in the dynamic range of
$-12.32 {\mathrm {rad}}\cdot \text{m}$
⁻¹
to 12.32 rad
$\cdot \text{m}$
⁻¹
. In addition, comparative torsion measuring experiments of CD-LPFGs with the different polishing thickness were carried out, showing that the tapered LPFG fabricated on a thinner polished fiber has a higher torsion sensitivity. Furthermore, the temperature response of the structure is 66 pm/°C, which indicates a relatively low temperature-torsion crosstalk of 0.208 rad
$\cdot \text{m}$
⁻¹
/°C.