High-sensitivity two-axis vector bending sensor based on side-grooved long period grating in eccentric core fiber

• Side grooved long period gratings (SG-LPG) are fabricated on eccentric core fiber (ECF) for the first time. Compared with single mode fiber, the side core of the ECF is close to the surface of the cladding, and the damage of the SG-LPG is limited. • Due to the direction of the SG-LPG is deviated with the direction of the side core, this sensor can identify bending directions on two orthogonal axes. • Since the RI modulation introduced by the SG-LPG is strong enough, the sensitivity in four bending directions can reach 27.23, −25.76, 14.74 and −16.83 nm/m −1 , respectively, the highest among all two-axis vector bending LPG structures. A novel vector bend sensor based on side-grooved Long period grating (SG-LPG) inscribed on eccentric core fiber (ECF) was proposed and investigated. The core of the ECF is close to the surface of the fiber, which makes it very convenient to fabricate different SG-LPGs in ECF by CO 2 laser with little damage. Since the direction of the SG-LPG deviates from the direction of the side core of the ECF, the sensor can identify bending directions on two orthogonal axes. At the same time, the strong refractive index modulation caused by grooves makes SG-LPG very sensitive to bending. In the curvature range of 0–2.52 m −1 , the bend sensitivity in four directions reaches 27.23 nm/m −1 , −25.76 nm/m −1 , 14.74 nm/m −1 and −16.83 nm/m −1 , respectively. Due to the simple structure, convenient fabrication, high sensitivity, and multi vectors bending detection characters, the sensor has potential in bending measurement.