V-Shaped Long-Period Fiber Grating High-Sensitive Bending Vector Sensor

A novel V-shaped grating grid with a composite structure comprised of two oppositely tilted tracks is firstly proposed, which can provide both asymmetry and high refractive index modulation (RIM) to support the bending vector sensing. A long-period fiber grating formed by the V-shaped grids is fabricated with a high-frequency-CO
₂
laser on a single-mode fiber, and it provides different responses of wavelength shift in two-axis directions' bending. The V-shaped grid model is established to theoretically analyze the change of RIM caused by bending. The formula of bending sensitivity is deduced, and the values of sensitivity in two-axis directions are calculated. The experimental bending sensitivities are 16.315 and -23.085 nm/m
^-1
in the opposite directions within the plane perpendicular to the laser-irradiated direction, which can coincide with the theoretical expectation. Its temperature recycle characteristic is also provided.