Torsion Sensor Based on Helical Long-Period Grating Inscribed in the Etched Double Cladding Fiber

We proposed a high-sensitivity torsion sensor based on the helical long-period grating (HLPG) inscribed in the cladding-etched double cladding fiber (DCF). The torsion sensitivity has been greatly improved by reducing the cladding diameter of the DCF, from 0.342 to 1.162 nm/(rad/m), which is one order of magnitude higher than that of the conventional long-period fiber grating (LPFG). The cladding mode coupling characteristics during the etching process are also investigated experimentally. The DCF-HLPG has a low strain and temperature sensitivity, and the maximum strain sensitivity is only about 0.0022 nm/ <tex-math notation="LaTeX">μ ε </tex-math> . The proposed DCF-HLPG has a potential application as a high-sensitivity torsion sensor with low strain and temperature crosstalk.