A quasi-distributed temperature monitoring system based on the concatenation of identical low reflective Fibre Bragg
Gratings and interrogated by means of an Optical Time Domain Reflectometer is presented. A wavelength sensitive
system placed before the OTDR detector is used to analyse the reflected signal. This system allows the height of the
FBG reflection peaks in the OTDR trace to depend on their resonance wavelength, and therefore to temperature.
Simulations and experimental results are exposed.
The explosion risk linked to the use of hydrogen (H2) as combustible requires low-cost and efficient sensors. We present
a multipoint in-fiber sensor capable of H2 leak detection as low as 1% concentration in air with a response time smaller
than a few seconds. Our solution utilizes uniform fiber Bragg gratings (FBGs) surrounded by a catalytic sensitive layer
made of a ceramic doped with a noble metal. In the presence of H2 in air, the sensitive layer undergoes an exothermic
reaction and elevates the temperature around the FBGs. The sensor interrogation technique is based on the monitoring of
the resonant wavelength shift. In this paper, the performances of the sensor are also discussed.
A new fast demodulation technique for a quasi-distributed temperature sensor based on the interrogation of identical
concatenated fibre Bragg gratings is presented. The interrogation scheme is based on the optical time domain
reflectometry technique, for which a commercial device has been extended to a wavelength-tuneable system, within an
automated experimental set-up. Detection and localization of an important amount of sensing points along a unique
optical fibre is demonstrated. The demodulation method is based on the optimization of the least square differences
between reference and measured data. Repeatability measurements and associated accuracy of the sensor are presented.
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