Improvement of measurement accuracy of fibre Bragg grating sensor systems by use of gas absorption lines as multi-wavelength references

A broadband source and a Fabry-Perot tunable filter were used to analyze the wavelength measurement accuracy of fibre Bragg grating (FBG) sensor systems. The smoothed-out versions of measured absorption signals and reflected Bragg signals were fitted to Lorentzian and Gaussian line shapes to determine the centre wavelengths of the absorption lines. The analysis of acetylene absorption lines suggested for a three-FBG sensor system using an external cavity tunable laser demonstrated a wavelength measurement accuracy of 2pm.