Two-axis bending vector sensor based on a long-period fiber grating cascading with a hump-shaped taper

A novel fiber-bending vector sensor based on a Mach-Zehnder interferometer (MZI) is proposed and fabricated. The device consists of a long-period fiber grating (LPFG) written by a high-frequency CO2 laser and a hump-shaped taper (HST) in a segment of single-mode fiber (SMF). The HST is an up-taper with the asymmetry perpendicular to the irradiated direction of the LPFG, which induces asymmetry into the fiber in two-axis directions. In the curvature range of 0.3-1.6 m(-1), the device can measure bending curvature as well as distinguish the bending direction with two dips at 1480.45 nm and 1493.20 nm, and the sensitivity can reach -6.592 nm m(-1). The response for temperature is also investigated and the temperature sensitivity is about 0.05 nm degrees C-1 in the range of 25 degrees C-80 degrees C. By measuring the separation of the two interference dips, the temperature cross-sensitivity can be almost eliminated.