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>A record long external-disturbance detection distance of 140 km without employing optical amplifiers in the fibre line is demonstrated by a phase-sensitive optical time-domain reflectometer (Φ-OTDR) using a fibre section with inscribed chirped fibre Bragg gratings (CFBGs). This solution provides simultaneous operation of Φ-OTDR with a standard single-mode fibre at a distance of up to 100 km and with a CFBG fibre section located from the fibre line input point by at least 140 km.

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Using a point-by-point fs inscription technology, a Rayleigh reflector with unique characteristics has been designed and fabricated. The reflection coefficient of the structure with a length of 5 cm amounts to 0,03%, which corresponds to the reflection of 6-km SMF-28e+ fiber spool. The designed artificial Rayleigh scattering fiber in combination with distributed feedback (DFB) erbium-doped fiber laser allows to narrow the linewidth. A similar effect was observed in configuration with 25-km SMF-28e+ fiber spool, where it was used as an additional spectral filter. In both cases, an identical narrowing of the linewidth by an order of magnitude was observed at times less than 0,1 msec.