A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized ( 0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of 10 over the test period with a precision of 5 and a resolution of 1 . The readings from the FBG sensors were comparable to those from the foil gauge sensors to within 4 .

Several important digital processing techniques for optical-fiber sensor systems that use electronically scanned white-light interferometry are presented. These include fringe restoration, fringe-order identification, and resolution enhancement techniques. A pure low-coherence interference fringe pattern is restored by dividing, pixel by pixel, the beam intensity profile from the signal. The central (zero-order) fringe of the pattern is identified by using a centroid algorithm. A linear interpolation or a localized centroid algorithm is used to enhance further the phase resolution. Theoretical analyses, computer simulations, and experimental verifications have shown that these techniques are able to increase greatly the dynamic range of the measurement under a low signal-to-noise ratio environment.

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