Quasi-distributed temperature sensor combining Fibre Bragg Gratings and temporal reflectometry technique interrogation

• Published in: Optics and lasers in engineering 2009-03, Vol.47 (3), p.412-418
• Main Authors: Crunelle, C., Caucheteur, C., Wuilpart, M., Mégret, P.
• Format: Article
• Language: English
• Subjects: Devices; Diffraction gratings; Exact sciences and technology; Fiber optics; Fibre; Fibre Bragg Grating; Fundamental areas of phenomenology (including applications); General equipment and techniques; Gratings (spectra); Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Optics; OTDR; Other fiber-optical devices; Physics; Quasi-distributed sensor; Reflectometry; Sensors; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Sensors, gyros; Spectra; Temperature sensor; Wavelengths
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2008.06.020

Quasi-distributed sensors based on Fibre Bragg Gratings (FBG) usually deal with the concatenation of FBGs of different Bragg wavelengths analyzed through wavelength-sensitive devices. In these sensors, a given wavelengths range is dedicated to one particular FBG. The number of sensing points is directly limited by the source and detector spectral ranges, and by the wavelength spacing between two gratings. This spacing is linked to the maximum possible excursion of the physical parameter to be measured-before superimposition of the reflection spectra of the FBGs. In this paper, an original interrogating device is presented, that allows a very large number of concatenated gratings to be addressed. In this scheme, identical FBGs (same Bragg wavelength and same low reflectivity) are interrogated by the Optical Time Domain Reflectometry technique, for which a commercial device has been extended to a wavelength-tunable system, within an automated experimental set-up. Detection and localization of an important amount of sensing points along a unique optical fibre is demonstrated. Repeatability measurements did exhibit the very good accuracy of the presented sensor.