Description
Phase-sensitive optical time-domain reflectometry (ϕ-OTDR) enables distributed acoustic sensing (DAS) by tracking the phase of Rayleigh backscattered light from an optical fibre [1]. DAS systems resolve both vibration over time, and signal location along the sensing fibre by tracking pulse return times, and phase respectively [1].
One challenge for DAS systems is the pulse return time, which increases with the length of the sensing fibre. This limits the sampling rate for long range measurements, decreasing the measurement efficiency [1]. While optical pulse coding has previously been used to increase the probe energy [2], here, we propose a solution to interrogate an optical fibre with multiple concurrent pulses, enabling higher detection efficiency, improved duty cycle and potential for pulse averaging to increase recovered signal strength. The architecture is a digitally enhanced ϕ-OTDR using a frequency shift keyed (FSK) pulse sequence based on a pseudo-random code. The scheme produces a temporally periodic pulse sequence where each pulse frequency is mapped to the code. Using the code autocorrelation, we can recover and isolate sub-ranges within the optical fibre using the code time-of-flight[3]. The use of an independent ranging measurement here enables multiple pulses to probe the fibre simultaneously. This increases the effective probe efficiency by replacing the isolated pulses with a quasi-continuous emitted coded-probe, while retaining the spatial-resolution benefit of short pulses.
In this talk we will discuss the proposed architecture, present initial experimental results. We will highlight some of the advantages of the system for data volume reduction, signal-to-noise enhancement and as a platform towards lower cost DAS deployments.
References
[1] Z. Wang, et al, Sensors, vol.20, p.6594, 2020. doi: 10.3390/s20226594.
[2] Y. Liang et al, Science China Information Sciences, vol.65, p.192303, 2022. doi:10.1007/s11432-021-3329-6.
[3] D. A. Shaddock, Optics Letters, vol.32, no.22, pp.3355–3357, 2007. doi: 10.1364/OL.32.003355.
| I am the presenting author | Yes |
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