Bending vector sensing based on periodic core-offset ultra-long period fiber grating

Abstract

Bending vector sensing is demonstrated based on periodic core-offset ultra-long period fiber grating, which is mainly composed of splicing two fiber ends with a purposed lateral offset in a single mode fiber (SMF).Through the measured resonance wavelength and the peak attenuation of the core-offset ultra-long period fiber grating(CO-ULPFG), the curvature amplitude and orientation can be simultaneously determined in vertical directions, reaching up to -1.833 nm/m^-1 and -1.674 nm/m^-1 at the 0° and 180° orientations range and reaching up to -0.583 nm/m^-1 and -0.479 nm/m^-1 at the 90° and 270° orientations ranging from 0 m^-1 to 7.041 m^-1, respectively. The bending sensitivity in different directions is 6-10 times that of LPFG with similar structure. Because of the excellent linear response, the effect of temperature on bending sensing can be eliminated by using a measurement matrix. The advantages of bending direction recognition, high bending sensitivities and compact structure make the sensor attractive for structural deformation monitoring.