An Inline Fiber Curvature Sensor Based on Eccentric Core Fiber and Off-Axis Air Cavity Fabry-Pérot Interferometer

Abstract

In this paper, we present a highly sensitive inline fiber curvature sensor based on an eccentric core fiber (ECF) and off-axis air cavity Fabry-Perot interferometer (OACFPI). This ECF-based bending sensor is fabricated by fusion-splicing a section of ECF between a single-mode fiber and an off-axis air cavity fiber. Due to the location of the core in the ECF, a bend applied to the ECF-based OACFPI leads to elongation or shortening of the optical path length in the air cavity, which makes the system suitable for bending measurement. To analyze bending characteristics, three ECFs with different eccentric core locations are investigated separately. In addition, a swept source is employed for measurement. The experimental results demonstrate that, the bending sensitivities of the sensors at the two opposite most-sensitive directions are 0.241 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 1), 0.131 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 2), and 0.0807 nm/ $\text{m}^{\mathrm {\mathbf {-1 }}}$ (sensor 3), and −0.245 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 1), −0.156 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 2), and −0.077 nm/ $\text{m}^{\mathbf {-1}}$ (sensor 3). The temperature sensitivities of the sensors are 0.84 pm/°C, 0.92 pm/°C, and 0.94 pm/°C, respectively. The proposed sensors are compact and versatile, and are expected to have potential applications in biomedical sensing.