Vidal-Moreno Pedro J, Rochat Etienne, Fermoso Pablo, Fernández-Ruiz María R, Martins Hugo, Martin-Lopez Sonia, Ocaña Manuel, Gonzalez-Herraez Miguel
Opt Lett. 2022 Jul 15;47(14):3588-3591. 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-ΦOTDR) 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.
分布式声学传感器（DAS）通过将测量的时域迹线与先前的光纤参考状态进行比较，来执行分布式和动态应变或温度变化测量。大应变或温度波动以及激光频率噪声使得需要更新这样的参考，因此如果要获得绝对应变或温度变化，就有必要对短期变化测量进行积分。这具有引入1/f噪声分量的缺点，因为噪声会随着每次累积变化测量而积分，这对非常缓慢的过程（即mHz频率范围或更低）的测定不利。这项工作分析了具有多频数据库解调（MFDD）的啁啾脉冲相敏光时域反射仪（CP-ΦOTDR）的长期稳定性，以便在未修改的单模光纤（SMF）上沿分布式声学传感器（DAS）进行“校准”测量。结果表明，在本工作所研究的条件下，实现了一种“校准”的啁啾脉冲分布式声学传感器（CP-DAS），其参考更新引起的1/f噪声分量被完全抑制，即使在测量期间关闭询问器，也能够使用同一组参考进行超过2个月的测量。
