Temperature-strain discrimination in distributed optical fiber sensing using phase-sensitive optical time-domain reflectometry.

Xin Lu,Luc Thévenaz,Marcelo A Soto

doi:10.1364/oe.25.016059

Abstract

A method based on coherent Rayleigh scattering distinctly evaluating temperature and strain is proposed and experimentally demonstrated for distributed optical fiber sensing. Combining conventional phase-sensitive optical time-domain domain reflectometry (ϕOTDR) and ϕOTDR-based birefringence measurements, independent distributed temperature and strain profiles are obtained along a polarization-maintaining fiber. A theoretical analysis, supported by experimental data, indicates that the proposed system for temperature-strain discrimination is intrinsically better conditioned than an equivalent existing approach that combines classical Brillouin sensing with Brillouin dynamic gratings. This is due to the higher sensitivity of coherent Rayleigh scatting compared to Brillouin scattering, thus offering better performance and lower temperature-strain uncertainties in the discrimination. Compared to the Brillouin-based approach, the ϕOTDR-based system here proposed requires access to only one fiber-end, and a much simpler experimental layout. Experimental results validate the full discrimination of temperature and strain along a 100 m-long elliptical-core polarization-maintaining fiber with measurement uncertainties of ~40 mK and ~0.5 με, respectively. These values agree very well with the theoretically expected measurand resolutions.

Highlights

Distributed optical fiber sensors based on Rayleigh, Brillouin or Raman scattering have been the subject of research and development for several decades [1,2,3]
On the other hand, distributed fiber sensors based on coherent Rayleigh scattering [3] utilize the restorability features of the temporal trace shape to measure temperature and strain, which can be obtained by using techniques such as optical time-domain reflectometry (OTDR) [3] or optical frequency-domain reflectometry (OFDR) [7]
Using Eq (1) and the measured frequency shift profile, the local birefringence Δn can be calculated. 4.2 Distributed temperature and strain sensing based on birefringence Since birefringence is dependent on the environmental variations, the proposed technique based on coherent Rayleigh scattering is first validated for distributed temperature and strain sensing

Summary

Introduction

Distributed optical fiber sensors based on Rayleigh, Brillouin or Raman scattering have been the subject of research and development for several decades [1,2,3] They enable a monitoring of environmental variables, such as temperature, strain or vibrations, continuously along an optical fiber. Whilst Brillouin sensors can inherently provide more accurate measurements and achieve longer distances than Raman sensors, they are typically affected by the cross-sensitivity of the Brillouin frequency on the temperature and strain [6]. On the other hand, distributed fiber sensors based on coherent Rayleigh scattering [3] utilize the restorability features of the temporal trace shape to measure temperature and strain, which can be obtained by using techniques such as optical time-domain reflectometry (OTDR) [3] or optical frequency-domain reflectometry (OFDR) [7]. Being a highly sensitive sensor, the system typically requires a very broad spectral scanning range, increasing the complexity and cost of the sensor

Methods

Results

Conclusion