Phasorial differential pulse-width pair technique for long-range Brillouin optical time-domain analysis sensors.

We introduce a novel phasorial differential pulse-width pair (PDPP) method for Brillouin optical time-domain analysis (BOTDA) sensors that combines spatial resolution enhancement with increased tolerance to non-local effects. It is based on the subtraction of the complex time-domain traces supplied by a sensor configuration that uses a phase-modulated probe wave and RF demodulation. The fundamentals of the technique are first described theoretically and using numerical simulation of the propagating waves. Then, proof-of-concept experiments demonstrate the measurement of the Brillouin frequency shift distribution over 50-km. The system is shown to withstand large variations of the pump power generated by its interaction with a powerful probe wave along the fiber; hence, highlighting the potential of the PDPP technique to increase the detected signal-to-noise ratio in long-range BOTDA. Moreover, the PDPP is also shown to increase the measurement contrast by allowing the use of relatively long duration pulses while retaining 1-m spatial resolution.