A novel long period fiber grating sensor measuring curvature and determining bend-direction simultaneously

A novel long period fiber-grating (LPFG) sensor that can not only measure curvature directly, but also determine every bend-direction within the circular range of 0 degrees-360 degrees, is proposed and demonstrated in this paper. Such a bend-sensor consists of one LPFG induced by a UV laser and two LPFGs induced by high-frequency CO2 laser pulses. The curvature is measured by the UV laser-induced LPFG whose bend-sensitivity is independent of the bend-directions, and the bend-direction is determined by the CO2 laser-induced LPFGs whose bend-sensitivities depend strongly on the curved directions. In addition, the unique bend-characteristics of LPFGs induced by high-frequency CO2 laser pulses are demonstrated.