Static DFOS: pushing towards the limits of chirped-pulse phase-sensitive OTDR

Phase-sensitive optical time domain reflectometry (Φ-OTDR) techniques allow for distributed measurements of various physical quantities involving local optical path variations along optical fibers, typically in response to either strain or temperature changes. Chirped-pulse (CP) Φ-OTDR being a relative measurement, errors on the integrated signal accumulate in time, thus degrading slowly varying temperature measurements. This can be solved by performing a mapping of the fiber's Rayleigh scattering as a function of wavelength, which provides an absolute frame of reference for strain and temperature changes. However, previously assumed limitations required using impractically high wavelength tuning resolutions. In this paper, relying on a theoretical description, supported by numerical simulations and experiments, we show that this apparent limit of CP-Φ-OTDR is only noise related and can be overcome thanks to the spectral content of the chirp. This paves the way for industrial applications.