Low-cost temperature- and strain-insensitive twist sensor based on a hybrid fiber grating structure

We proposed and experimentally demonstrated a temperature- and strain-insensitive twist sensor based on a hybrid fiber grating structure, in which the hybrid grating structure is constructed with a 45°-tilted fiber grating and a chirped fiber Bragg grating UV-inscribed in a single-mode fiber in series. The sensing performance has been evaluated by experimental and numerical analyses, which are in good consistency. The experimental results show that the hybrid-grating-structure-based twist sensor has a maximum twist sensitivity up to 15.037 dB/rad. Moreover, due to the invariability of the fiber birefringence and the state of polarization of the input light, such sensor has intrinsically low temperature and strain sensitivities of 7.86×10^-3  dB/°C and 6.7×10^-5  dB/με, corresponding to the maximum twist measurement error resulting from temperature and strain of 5.2×10^-4  rad/°C and 4.5×10^-6  rad/με, respectively.