10 November 2005 Pickup suppression in Sagnac-based fiber-optic acoustic sensor array
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Proceedings Volume 6004, Fiber Optic Sensor Technology and Applications IV; 600407 (2005) https://doi.org/10.1117/12.633773
Event: Optics East 2005, 2005, Boston, MA, United States
Abstract
Large-scale acoustic fiber sensor arrays consisting of hundreds of hydrophones distributed along kilometers-long fiber buses are required for applications such as undersea oil exploration. Sagnac-based Sensor Arrays (SSAs) exhibit attractive performance; however the acoustic wave incident on the buses generates a pickup signal that can swamp the signals from the hydrophones. We propose, model, and demonstrate a simple technique for reducing this unwanted pickup by periodically inserting null sensors in the buses instead of hydrophones, so the pickup signal is measured at different locations along the buses. The signal from the null sensor (pickup only) is then subtracted from the signal seen by the adjacent hydrophone (true signal and pickup) to recover the true hydrophone signal. This paper describes in detail the signal processing steps used to perform this recovery. Applied to an experimental two-rung SSA, this technique produced a -18.6 dB pickup suppression for a pickup amplitude as large as 0.44 rad and signal amplitudes up to 0.44 rad, and -15 dB for a signal as large as 0.88 rad. These values are limited by the accuracy of the 8-bit data acquisition and/or electronic noise. With a low-noise 12-bit data acquisition, the pickup suppression for small signal amplitudes is predicted to be -35 dB. This work makes headway towards practical SSAs.
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Stéphane Blin, Stéphane Blin, Michael Bishop, Michael Bishop, Krishnan Parameswaran, Krishnan Parameswaran, Michel J.F. Digonnet, Michel J.F. Digonnet, Gordon S. Kino, Gordon S. Kino, } "Pickup suppression in Sagnac-based fiber-optic acoustic sensor array", Proc. SPIE 6004, Fiber Optic Sensor Technology and Applications IV, 600407 (10 November 2005); doi: 10.1117/12.633773; https://doi.org/10.1117/12.633773
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