Single-shot distributed temperature and strain tracking using direct detection phase-sensitive OTDR with chirped pulses

TLDR

Traditional ΦOTDR uses optical pulses with a constant phase along the pulse. This work shows that altering the phase profile of the pulses can fundamentally change ΦOTDR operation, opening new possibilities. Resolution and sensitivity are tuned by adjusting the pulse chirp profile. With linearly chirped pulses and direct detection, the technique achieves 1 mK/4 nε resolution, eliminates the need for a frequency sweep, reduces measurement time and complexity, supports metric spatial resolution over tens of kilometers, and allows kHz‑rate measurements with several‑hour reliability.

Abstract

So far, the optical pulses used in phase-sensitive OTDR (ΦOTDR) were typically engineered so as to have a constant phase along the pulse. In this work, it is demonstrated that by acting on the phase profile of the optical pulses, it is possible to introduce important conceptual and practical changes to the traditional ΦOTDR operation, thus opening a door for new possibilities which are yet to be explored. Using a ΦOTDR with linearly chirped pulses and direct detection, the distributed measurement of temperature/strain changes from trace to trace, with 1mK/4nε resolution, is theoreticaly and experimentaly demonstrated. The measurand resolution and sensitivity can be tuned by acting on the pulse chirp profile. The technique does not require a frequency sweep, thus greatly decreasing the measurement time and complexity of the system, while maintaining the potential for metric spatial resolutions over tens of kilometers as in conventional ΦOTDR. The technique allows for measurements at kHz rates, while maintaining reliability over several hours.