Distributed dynamic strain sensing in coherent Φ-OTDR with a pulse conversion algorithm.

In this Letter, a chirped-pulse conversion algorithm (CPCA) is proposed to convert a normal probe pulse into an equivalent chirped probe pulse by convolving a chirp factor on the received signal in coherent phase-sensitive optical time-domain reflectometry ( Φ -OTDR). With this algorithm, the Rayleigh interference pattern (RIP) demodulation once applied to chirped-pulse Φ -OTDR can be adopted to quantify the dynamic strain in the traditional coherent Φ -OTDR. Since the equivalent chirped pulse is generated by digital processing, complex and costly chirp modulation is not required. The proposed scheme is capable of fully quantifying perturbations with spatial resolution of 4 m, a sensing range of 8 km, frequency response of 5 kHz, and strain resolution of 56 p ε/√ H z .