Fourier-transform-based spectral measurements on multiplexed fibre Bragg grating arrays

We demonstrate a Fourier Transform Spectroscopic approach to achieve high-resolution measurement of the structural detail of the reflected spectra from an infrared FBG grating array, with the inherent measurement capability over a wavelength range of 900 nm. Measurements on all gratings in the array are achieved in a single scan of the OPD, from an interferogram captured on a single InGaAs photodiode. We demonstrate the approach for measurements on standard gratings and in the case of a grating subjected to a nonuniform measurand. The OPD is referenced from a visible HeNe beam propagated on the array downlead, and we demonstrate the robustness of the measurement in the presence of the complex transverse modal structure of that reference beam.