Research on pure bending characteristic of tilted fiber Bragg grating

In this letter, we propose a novel structure of the pure macro-bending sensor based on the tilted fiber Bragg grating (TFBG). The TFBG located in the half circle with the different diameters is bent at a constant angle with respect to the tilted grating planes. With the variations of the curvature, the core-mode resonance is unchanged and the transmission power of cladding modes detected by the photodiodes varies linearly with curvature, while the ghost mode changes by the form of two-order polynomial. So we can use the transmission power of ghost mode or other cladding modes to detect bending curvature as shape sensor. From a practical point of view, the sensor proposed here is simple, low cost and easy to implement. Moreover, it is possible to make a temperature-insensitive shape senor due to the same temperature characteristic between the core mode and the cladding modes.