Abstract
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.
Highlights
Brillouin optical time-domain analysis (BOTDA) sensors are bound to become a fundamental tool for monitoring in a number of industries ranging from civil engineering to oil and gas pipelines or electric power
One of the main trends is the development of long-range BOTDA sensors, where the ultimate distance is constrained by several effects including the so-called non-local effects
These are caused by the continuous transfer of energy between the probe and pump waves along the fiber, which modifies the pump power by introducing a wavelength dependence that leads to errors in the Brillouin frequency shift (BFS) measurements [1]
Summary
Brillouin optical time-domain analysis (BOTDA) sensors are bound to become a fundamental tool for monitoring in a number of industries ranging from civil engineering to oil and gas pipelines or electric power. One of the main trends is the development of long-range BOTDA sensors, where the ultimate distance is constrained by several effects including the so-called non-local effects These are caused by the continuous transfer of energy between the probe and pump waves along the fiber, which modifies the pump power by introducing a wavelength dependence that leads to errors in the Brillouin frequency shift (BFS) measurements [1]. We introduce a novel phasorial differential pulse-width pair (PDPP) technique that provides tolerance to non-local effects in addition to enhancement of the spatial resolution It is derived from a BOTDA scheme that we have recently proposed, which uses a phase-modulated probe wave and RF demodulation to give measurements largely immune to changes of the pump pulse power [8,9]. The method takes advantage of the complex signals (magnitude and phase-shift) supplied by this system to perform a full phasorial subtraction of the responses to two sequential pump pulses with differential duration
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