Temperature- and strain-insensitive torsion sensor based on phase-shifted ultra-long-period grating

A temperature- and strain-insensitive torsion sensor is proposed and demonstrated by utilising a phase-shifted ultra-long-period grating. Experimental results demonstrate that the separation of phase shift resonant peaks changes with the twist rate, but remains invariant with the temperature or strain changes. In addition, it was found that the influence of twisting to the fibre grating is non-uniform along the fibre axis.