The authors demonstrate distributed temperature sensing based on slope-assisted Brillouin optical correlation-domain reflectometry (BOCDR) with a long measurement range of >10 km. They find that to achieve such a long-range measurement, a delay line in a reference path needs to be at least four times longer than the sensing fibre. In addition, they show that the use of such a long delay line induces forward-propagating Brillouin-scattered light in the reference path, which deteriorates the signal-to-noise ratio (SNR) of the system and should be suppressed. Finally, by exploiting a beyond-nominal-resolution effect of the slope-assisted BOCDR, they detect a 3-m-long heated section in a 13-km-long silica fibre in a distributed manner; the reason for its low SNR is also discussed.
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