Two-Axis Bending Sensor Based on Asymmetric Grid Long-Period Fiber Grating

A novel bidirectional high-sensitivity bending sensor based on the $\upsilon $ -shaped long-period fiber grating (LPFG) is designed and demonstrated. The $\upsilon $ -shaped LPFG is composed of an array of asymmetrical $\upsilon $ -shaped grating planes, which can provide stronger refractive index modulation than conventional planar grids. Therefore, the proposed sensor provides a more sensitive result. The experimental results show that the maximum bending sensitivity of $\upsilon $ -shaped LPFG reaches −24.08 nm/ $\text{m}^{-{1}}$ within the bending range of 0.22 $\text{m}^{-{1}}\,\,\sim \,\,2.21\,\,\text{m}^{-{1}}$ , enhancing the bending sensitivity while improving sensitivity to the micro-bending area. The sensitivity of $\upsilon $ -shaped LPFG can be potentially improved by optimizing the structural parameters of the grid.