Bending Vector Sensor Based on a Pair of Opposite Tilted Long-Period Fiber Gratings

A novel optical fiber grating vector bending sensor head is demonstrated. The sensor head is composed by two cascaded 6° tilted long period fiber gratings, which are separated by a distance $d$ . The asymmetric characteristics of the proposed sensor originate from two tilted long period gratings with angles placed oppositely and asymmetric exposure of the CO 2 laser pulses. Two selected dips shift toward each other when the sensor head is bent. The interval between the two dips is used for improving the sensitivity of curvature measurement and further decreasing the temperature crosstalk. For the curvature range from 0.5 to 2 $\text{m}^{-1}$ , the bending sensitivities reach −15.4935 and 15.2852 nm/ $\text{m}^{-1}$ for the opposite bending directions. The temperature sensitivity of the sensor is one third of the normal long period fiber grating.