Effects of the bonding length on the reflected spectra and strain measurement of the surface bonded fiber Bragg grating sensor

Abstract

Surface bonded fiber Bragg grating (FBG) sensors have the limitation that signal characteristics are affected by the bonding layer. Previously conducted studies with regard to this limitation used different optical fiber sensors and load types during the experiments, and didn’t consider the effects on the reflected spectra. Therefore, in this study, the effects of the bonding length on the reflected spectra and strain measurement of the surface bonded FBG sensor were experimentally investigated. From the experimentation results, sufficiently bonded FBG sensor showed stable
reflected spectra and enough strain transfer rate. However, insufficiently bonded FBG sensor showed distorted reflected spectra with high multiple peak ratio due to internal strain gradients within the grating length of the FBG sensor. In addition, distorted reflected spectra made it difficult to calculate adequate peak and decreased the strain transfer rates. Therefore, it was found that effective bonding length need to be determined to get a stable reflected spectra and enough strain transfer rate from the surface bonded FBG sensors.