Design considerations for a fibre Bragg grating interrogation system utilizing an arrayed waveguide grating for dynamic strain measurement

Dynamic strain signals are important for many structural monitoring applications, but high speed interrogation of strain sensors based on fibre Bragg gratings (FBG) remains a challenge. Arrayed waveguide grating (AWG) interrogation schemes have been proposed and by using modelling and validation experiments several design considerations are investigated and their relationship to system performance indicators determined. The Bragg grating length has an impact on the ability of the grating to ‘observe’ the transient strain field, while the spectral widths of both the FBG and AWG influence the recovered strain resolution. The system performance was examined for both high frequency noise as well as the long-term drifts over an hour; with strain resolution of 1.4 µe observed and drift of less than 3.1µe h^-1. The noise dependance on the relative overlap of the AWG and FBG spectra was found to be significant and the inclusion of a semiconductor optical amplifer to boost light intensity at the detectors was found to significantly improve performance with an improvement in signal-to-noise ratio of upto 200%.