Passive Temperature-Compensating Technique for Microstructured Fiber Bragg Gratings

The thermal drift of the characteristic wavelength of fiber Bragg gratings (FBGs) photowritten in the core of microstructured fibers (MOFs) is significantly reduced by inserting a liquid of suitable refractive index into their holes. For instance, the spectral range of variations is divided by a factor of 4 over a temperature range larger than 20\degree C in a six-hole MOF, and the maximum sensitivity is reduced. Such passive FBG temperature compensation technique is of great interest for applications involving accurate sensing free of thermal effects

OFDR Distributed Temperature and Strain Measurements with Optical Fibre Sensing Cables: Application to Drain Pipeline Monitoring in a Nuclear Power Plant

International audienceThis study deals with the testing of innovative Optical Fibre Sensing (OFS) cables deployed on ducts, with the aim to perform distributed temperature and strain measurements. Such cables contain several optical fibres devoted to be interrogated by Optical Frequency Domain Reflectometry (OFDR). The methodology has first been developed and qualified in laboratory. Then, real tests have been performed on a Nuclear Power Plant (NPP) drain system to demonstrate the industrial feasibility of such technology. To do so, two small diameter sensing cables, compatible with distributed temperature and strain measurements, have been qualified and afterwards installed along a sodium drain line at Superphenix NPP (liquid sodium coolant fast breeder reactor in current dismantling). Measurements have been performed during the preheating operation. Recorded data were post-processed according to a semi-empirical model taking into account temperature dependence and thermo-mechanical sensing cable behaviour. Optical fibre distributed temperature measurements were then successfully compared to thermocouple reference measurements, whereas optical sensing cable data were processed to provide distributed strain, then distributed curvature radius, which will enable, after numerical integration, to compute distributed displacement data. The goal is to assess the use of OFS for monitoring both temperature and mechanical strain distribution along a pipe under heat stress

Taking the lead on climate change: Modelling and monitoring the fate of an Amazonian frog

Climate change is expected to have important impacts on biodiversity. However, cases showing explicit links between species decline and climate are scarce, mostly because of a lack of baseline data. Tropical ectotherms with narrow altitudinal ranges are particularly sensitive to climate change; for example the frog Pristimantis espedeus may be at risk, with only nine populations known to date in French Guiana, all on isolated massifs. Ecological niche modelling indicated that these populations could disappear by 2070. To facilitate testing of this prediction we conducted a study to design an efficient, cost-effective monitoring protocol, combining occupancy rate estimations using passive acoustic recorders, and abundance estimations using acoustic repeated counts and capture-mark-recapture. We found the passive recorders to be effective, with a detection probability of 0.8. Two recording sessions were sufficient to estimate occupancy rates reliably. A minimum of 57 surveyed sites were required to detect a decline of 15% in occupancy between two consecutive monitoring events. Acoustic repeated counts and capture-mark-recapture yielded similar density estimates (1.6 and 1.8 calling males per 100 m2, respectively). Based on these results we present a protocol based on passive acoustic recording and abundance monitoring to monitor P. espedeus populations

Tilted Fiber Bragg Grating photowritten in microstructured optical fiber for improved refractive index measurement

International audienceWe report what we believe to be the first Tilted short-period Fiber Bragg Grating photowritten in a microstructured optical fiber for refractive index measurement. We investigate the spectral sensitivity of Tilted Fiber Bragg Grating to refractive index liquid inserted into the holes of a multimode microstructured fiber. We measure the wavelength shift of the first four modes experimentally observed when calibrated oils are inserted into the fiber holes, and thus we determine the refractive index resolution for each of these modes. Moreover, a cross comparison between experimental and simulation results of a modal analysis is performed. Two simulation tools are used, respectively based on the localized functions method and on a finite element method. All results are in very good agreement

Three-hole microstructured optical fiber for efficient Fiber Bragg Grating refractometer

International audienceWe present a photosensitive three-hole microstructured optical fiber specifically designed to improve the refractive index sensitivity of a standard Fiber Bragg Grating (FBG) sensor photowritten in the suspended Ge-doped silica core. We describe the specific photowriting procedure used to realize gratings in such a fiber. We then determine their spectral sensitivity to the refractive index changes of material filling the holes surrounding the core. The sensitivity is compared to that of standard FBGs photowritten in a six-hole fiber with a larger core diameter. We demonstrate an improvement of the sensitivity by two orders of magnitude and reach a resolution of 3 x 10-5 and 6 x 10-6 around mean refractive index values of 1.33 and 1.40, respectively

Fibre Bragg grating photowriting in microstructured optical fibres for refractive index measurement

International audienceWe report results relating to fibre Bragg grating photowriting in two kinds of Ge-doped core microstructured optical fibre devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of the spectral sensitivity of a Bragg grating in relation to the refractive index of calibrated oils inserted into the holes