Cancellation of reference update-induced 1/f noise in a chirped-pulse DAS

Vidal-Moreno, Pedro J.; Rochat, Etienne; Fermoso, Pablo; Fernández-Ruiz, María R.; Martins, Hugo; Martin-Lopez, Sonia; Ocaña, Manuel; Gonzalez-Herraez, Miguel
Year: 2022
Type of Publication: Article
Keywords: Erbium-doped fiber amplifiers; Fiber optic sensors; Semiconductor optical amplifiers; Single mode fibers; Spatial resolution; Variable optical attenuators
Journal: Opt. Lett.
Volume: 47
Number: 14
Pages: 3588-3591
Month: July
DOI: 10.1364/OL.465367
Distributed acoustic sensors (DAS) perform distributed and dynamic strain or temperature change measurements by comparing a measured time-domain trace with a previous fiber reference state. Large strain or temperature fluctuations or laser frequency noise impose the need to update such a reference, making it necessary to integrate the short-term variation measurements if absolute strain or temperature variations are to be obtained. This has the drawback of introducing a 1/f noise component, as noise is integrated with each cumulative variation measurement, which is detrimental to the determination of very slow processes (i.e., in the mHz frequency range or below). This work analyzes the long-term stability of chirped-pulse phase-sensitive optical time-domain reflectometry (CP-$\Phi$OTDR) with multi-frequency database demodulation (MFDD) to carry out ``calibrated'' measurements in a DAS along an unmodified SMF. It is shown that, under the conditions studied in this work, a ``calibrated'' chirped-pulse DAS (CP-DAS) with a completely suppressed reference update-induced 1/f noise component is achieved capable of making measurements over periods of more than 2 months with the same set of references, even when switching off the interrogator during the measurement.
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