Spatially scanned interferometric interrogation of fiber Bragg grating sensors based on Hilbert transform processing

We have demonstrated a spatially-scanned interferometric technique for demodulation of Bragg grating sensors, overcoming the ´moving parts´ and measurement bandwidth limitations associated with temporally scanned interferometric schemes. The wavelength measurement is derived from the phase of the complex analytic signal of spatial interferograms, in contrast to spectral measurement by FTS. The technique incorporates precise delay mapping based on the analytic signal of a laser interferogram, thus overcoming limitations of conventional spatial interferometers caused by nonuniformities in optical surfaces and in the imaging array. We achieved a resolution of 25 pm for a limited OPD scan of 200 mm. This result compares favourably to reported temporally-scanned schemes and indicates potential for far higher resolutions and measurement bandwidth in larger spatial interferometer designs using long high-speed imaging arrays. We have further reported our investigation of the fundamental limits of the accuracy of the approach when using sampling densities close to the Nyquist limit.