Alexandre Fellay

Distributed sensing using stimulated Brillouin scattering : towards ultimate resolution

In this paper, we discuss the fundamental limitations of the SBS analysis as a distributed sensing method when the spatial resolution is in the meter range. We also present a novel experimental configuration that reaches the best performances achievable for this kind of sensors.

Truly distributed strain and temperature sensing using embedded optical fibers

Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brillouin scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is +/- 1 degree C for temperature and +/- 20 (mu) e for deformation. The spatial resolution is 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element has been performed using an embedded standard cabled fiber. The temperature dynamics of lake waters have been also observed by simply laying a cable over the lake bed.

Applications of distributed Brillouin fiber sensing

Long-range distributed strain and temperature measurements along an optical fiber is presented, using a novel optical sensor based on stimulated Brillouin scattering. The optical effect only depends on the fiber material, so that the bare fiber itself acts as sensing element without any special fiber processing or preparation. The sensor accuracy is plus or minus 1 degree Celsius for temperature and plus or minus 20 (mu) (epsilon) for deformation. The spatial resolution is 1 meter and the sensor range is more than 20 km. Successful monitoring of a concrete dam element has been performed using an embedded standard cabled fiber. The temperature dynamics of lake waters have been also observed by simply laying a cable over the lake bed.

Monitoring of large structure using distributed Brillouin fibre sensing

On-site distributed measurements using a sensor based on stimulated Brillouin scattering are presented. Long fibre length can be used, so that a dense 2D or 3D measurement of strain or temperature can be obtained in large structure.

Brillouin optical fiber sensor for cryogenic thermometry

Supraconductive installations are now commonly used in large facilities, such as power plants and particle accelerators. This requires a permanent temperature control at very low temperature, but cryogenic temperature measurements in the 1-77K range requires expensive calibrated temperature probes. We report here the possibility to use stimulated Brillouin scattering in optical fibers for temperature sensing down to 1K. Such a technique offers the additional advantage to make possible distributed measurement, so that very large structures and systems can be controlled using a single fiber and a single analyzing instrument. In addition only one by-pass for the fiber is required as input to the cryogenic vessel, that is definitely a key advantage for the design and the energy loss. Brillouin scattering in optical fibers has never been investigated so far at temperature below 77K (nitrogen boiling point). This absence of interest probably results from the constant decrease of scattering efficiency that was observed while cooling the fiber down to 77K. Our measurements show the unexpected feature that scattering efficiency is significantly raised below 50K and is even much better than observed at room temperature. The relevance and the feasibility of the technique is demonstrated in real scale on the supraconductive magnets for the future world largest particle accelerator, namely the large hadron collider (LHC) at CERN Laboratory in Geneva.

Field tests of distributed temperature and strain measurement for smart structures

Brillouin time-domain analysis in optical fibres is a novel technique making possible a distributed measurement of temperature and strain over long distance and will deeply modify our view about monitoring large structures, such as dam, bridges, tunnels and pipelines.

Brillouin-based temperature sensing in optical fibres down to 1 K

In this paper we will present the Brillouin scattering properties of optical fibres as experimentally measured at ultra-low temperatures and discuss the possibilities for distributed cryogenic temperature sensing, accordingly. We then present a first example of real scale application.