Simultaneous vector bending and temperature sensing based on eccentric multi-mode fiber Bragg gratings.

[Display omitted] • The eccentric multi-mode FBG can measure the vector bending and temperature simultaneously. • Rectangular structure was adopted to resolve bending direction. • The intensity difference of two opposite FBGs realized the sensitivity multiplication. • The curvature sensitivity reaches 4.42 dB/m-1 and the temperature sensitivity is greater than 13 pm/°C. • The fluctuation of intensity with temperature is weakened by multiple temperature cycles. Vector bending sensing is a key parameter in posture detection and structural health monitoring. Eccentric fiber Bragg gratings (FBGs), which can measure vector bending and temperature simultaneously, were fabricated by femtosecond laser direct writing in multi-mode fiber. The intensity of the FBG is only sensitive to curvature when the temperature is below 260 ℃. Rectangular structure was adopted to resolve bending direction. The intensity difference of the symmetrically inscribed FBG realizes the multiplication of the bending sensitivity, and the bending sensitivity is 4.42 dB/m−1. In addition, the difference between the two symmetrical peaks eliminates the power fluctuation noise caused by the fluctuation of the light source and the contamination of the fiber end. The wavelength of the FBG is only sensitive to temperature when the curvature is in the range of −2.353 m−1–2.353 m−1, and the temperature sensitivity is more than 13 pm/℃. [ABSTRACT FROM AUTHOR]