A Highly Sensitive Curvature Sensor Based on Omega-Shaped Long-Period Fiber Grating

A compact omega-shaped long-period fiber grating (OS-LPFG) for vector bending measurement is proposed and investigated in this article. This sensor is fabricated by periodically splicing single-mode fiber (SMF) and multimode fiber (MMF) into omega shape to get the purpose of sensitivity enhancement. The proposed OS-LPFG can distinguish the bending direction and achieves the curvature sensitivities in X-, Y-, and
$- {X}$
-directions are 12.03, −69.95, and −19.84 nm/
$\text{m}^{-{1}}$
at the range of 0–1.5
$\text{m}^{-{1}}$
, respectively. Meanwhile, the sensor has a small temperature crosstalk of 0.0011
$\text{m}^{-{1}}/^{\circ }\text{C}$
at the temperature range of 20 °C–110 °C. In addition, the sensor features a compact structure with the length of 1.5 mm due to the strong refractive index (RI) modulation induced by fabricating method, which proposes a feasible idea for compact fiber curvature sensor design.