Directional torsion sensor based on long period fiber gratings inscribed by periodically micro taper

A micro tapered long-period fiber grating (MTLPFG) fabricated by periodically tapering a standard single-mode fiber (SMF) with arc discharge technology, is proposed and experimentally demonstrated. The effective refractive index difference between the core and the cladding modes is periodically modulated by micro taper. During torsion experiment, the MTLPFG shows the ability of direction discrimination. Experimental results show that the torsion sensitivity reaches −0.2087 nm/(rad/m) in the twist range from 0° to 360°, and −0.1378 nm/(rad/m) in the range from 0° to −360°. Moreover, temperature sensitivity was measured to be about 40.88 pm/℃. Since the resonant wavelength responds differently to torsion and temperature simultaneously, the cross-influence of torsion and temperature can be eliminated effectively, which implies such a sensor based on MTLPFG could be an excellent candidate for torsion sensors.