All-fiber curvature sensor based on offset splicing structure cascaded with long-period fiber grating

A highly sensitive curvature sensor based on a single mode-few mode-single mode fiber offset splicing structure cascaded with long-period fiber grating is proposed and demonstrated. High-order mode is inspired by the offset splicing structure and coupled into the LPFG, resulting in a splitting into two dips of LPFG attenuation band, which are more sensitive to the external environment change. The experimental results show that in the range of 0.124m^-1 to 0.304m^-1, the transmitted optical intensity of the two dips is linear and the curvature sensitivity is about 93.01dB/m^-1, which has increased by one order of magnitude than before. High sensitivity and easy fabrication make it a preferable candidate for curvature sensing in the field of structural health monitoring.