Effect of strong local stretching of sensing fibre on the operation of a phase-sensitive optical time-domain reflectometer

It has been shown experimentally and confirmed by numerical simulation that strong local stretching of sensing fibre distorts the signal detected by a phase-sensitive optical time-domain reflectometer (OTDR) from the fibre section behind the local disturbance region. Comparison of experimental data with theoretical estimates and numerical simulation results leads us to conclude that the physical mechanism underlying the distortion of the OTDR trace is related to the external disturbance-induced variable shift of the optical carrier frequency of probe pulses.