Two-Axis Bending Sensor Based on Cascaded Eccentric Core Fiber Bragg Gratings

A two-axis bending sensor based on cascaded eccentric core fiber Bragg gratings (ECFBGs) is presented and demonstrated. The sensor is fabricated by independently writing two FBGs in two ECFs, which are spliced with orthogonal core-offset directions. Each ECFBG is most sensitive at the core-offset direction and insensitive at the perpendicular direction. When one ECFBG is in the state of most insensitive to bend, the other ECFBG must be in the most sensitive state. Therefore, the cascaded ECFBG structure can easily realize 2-D bending measurement. The sensor’s spectral responses to the curvature at different bending directions are experimentally investigated. The maximum curvature sensitivities of the two ECFBGs are 37 and 39 pm/ $\text{m}^{-1}$ , respectively, within the curvature range from 0 to 8.18 $\text{m}^{-1}$ .