Vibrations in the lead cables is known to cause noise in interferometric sensor systems, through modulation
of the polarization state of the transmitted light, and through Doppler stretching of the interrogating signals.
We demonstrate effective methods for suppression of both these noise sources. The polarization modulation
sensitivity is suppressed by 36 dB by using a polarization resolved interrogation technique. The sensitivity to
Doppler shift is suppressed by 22 dB by using a reference interferometer that is interrogated through the same
Suppression of crosstalk in an FBG-based serially multiplexed interferometric sensor array is demonstrated by employing the layer peeling inverse scattering algorithm. A polarization resolved impulse response (array reflection Jones matrix versus time) is measured using dual pulse heterodyne interrogation with varying combinations of polarization states in the interrogating pulse pair, and used as input to the layer peeling algorithm. < -40 dB crosstalk is achieved with > 97% confidence in a sensor array with 5 % FBG reflectivity. This is a 15-20 dB improvement compared to interrogation without inverse scattering.
Characterization of the complex relection spectrum and the spatial profile of fiber Bragg gratings using optical frequency domain reflectometry and the layer peeling algorithm is presented. The importance of correct scaling and polarization effects are discussed. The method gives accurate measurement of the spatial profile for grating with reflectivity < 98-99 %. Immunity to spurious reflections and high dynamic range in spectral measurements are achieved.
Both piezoelectric and fiber-optic hydrophones are sensitive to acceleration. The acceleration can be a major noise source in rough environment. The pressure to acceleration responsivity ratio is therefore a figure of merit for a hydrophone.