Abstract
The performance of unipolar unicolor coded Brillouin optical time-domain analysis (BOTDA) is evaluated based on both Simplex and Golay codes. Four major detrimental factors that limit the system performance, including decoded-gain trace distortion, coding pulse power non-uniformity, polarization pulling and higher-order non-local effects, are thoroughly investigated. Through theoretical analysis and an experimental validations, solutions and optimal design conditions for unipolar unicolor coded BOTDA are clearly established. First, a logarithmic normalization approach is proposed to resolve the linear accumulated Brillouin amplification without distortion. Then it is found out that Simplex codes are more robust to pulse power non-uniformity compared to Golay codes; whilst the use of a polarization scrambler must be preferred in comparison to a polarization switch to mitigate uncompensated fading induced by polarization pulling in the decoded traces. These optimal conditions enables the sensing performance only limited by higher-order non-local effects. To secure systematic errors below 1.3 MHz on the Brillouin frequency estimation, while simultaneously reaching the maximum signal-to-noise ratio (SNR), a mathematical model is established to trade-off the key parameters in the design, i.e., the single-pulse Brillouin amplification, code length and probe power. It turns out that the optimal SNR performance depends in inverse proportion on the value of maximum single-pulse Brillouin amplification, which is ultimately determined by the spatial resolution. The analysis here presented is expected to serve as a quantitative guideline to design a distortion-free coded BOTDA system operating at maximum SNR.
Highlights
During the last decades distributed optical fiber sensing based on Brillouin optical timedomain analysis (BOTDA) [1] has become a mature technology to measure distributed temperature and strain profiles over long optical fibers
The maximum tolerable pump power imposed by modulation instability (MI) is ~100 mW in fibers longer than 20 km [3,4], while the probe power is limited to −6 dBm per sideband in a conventional dual-sideband configuration to mitigate the impact of higher-order nonlocal effects [5,6,7]
The presented study suggests solutions and quantitatively defines the optimal working conditions, providing the following design rules to enable distortion-free unipolar-coded BOTDA sensing operating at the highest signal-to-noise ratio (SNR): 1) Before performing the linear decoding process, the linear accumulated Brillouin amplification must be retrieved using the proposed logarithmic normalization
Summary
During the last decades distributed optical fiber sensing based on Brillouin optical timedomain analysis (BOTDA) [1] has become a mature technology to measure distributed temperature and strain profiles over long optical fibers. Results indicate that a cascaded depletion effect occurs over the different pulses of the coded sequence, imposing limitations to the maximum probe power that can be launched into the sensing fiber The impact of this probe power limitation on the overall SNR improvement provided by coding, when compared to a fully optimized single-pulse BOTDA scheme, is modelled and experimentally verified
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
