Vector bending sensor based on chirped long-period grating with off-axis micro-helix taper

Vector bending sensing has been consistently growing in many fields. A low-cost and high sensitivity vector bending sensor based on a chirped long-period fiber grating (LPFG) with an off-axis micro helix taper is proposed and experimentally demonstrated. The grating is composed of several sections of single-mode fiber with gradually larger lengths, and the off-axis micro helix tapers with fixed lengths when they are fabricated by using the arc discharge technology. The large refractive index modulation in the micro-helix taper greatly reduces the sensor size. The total length of the sensor is only 4.67 mm. The micro-helix taper-based LPFG can identify the bending direction due to the asymmetric structure introduced by the micro helix. The experimental results show that the transmission spectra of the sensor have distinct responses for different bending directions, and the maximum bending sensitivity is 14.08 nm/m − 1 in the range from 0.128 m − 1 to 1.28 m − 1 . The proposed bending sensor possesses pronounced advantages, such as high sensitivity, small size, low cost, and orientation identification, and offers a very promising method for bend measurement.