International audienceThe Dy3+ doped Ga5Ge20Sb10S65 bulk glass provides good emission efficiency in the middle IR with a better brightness than the blackbody sources. Sulfide single index fibers doped with Dy3+ (500-​3000 ppm) were drawn with optical attenuation of about 1-​3 dB​/m, suitable to develop fluorescence sources for chem. anal. by optical absorption in middle IR. They particularly present a broad emission around 4-​5 μm, making them attractive for CO2 detection. Considering the low cost and efficient Dy3+ pumping scheme by means of a com. laser diode, the Dy3+ sulfide fiber reveals potential for developing a CO2 optical sensor. Using the 4.35 μm broad emission of a Dy3+ doped Ga5Ge20Sb10S65 fiber combined with a differential measurement technique, the CO2 gas concn. measurement was carried out fruitfully. For this specific application, the CO2 detection threshold was fixed at about 400 ppm corresponding to atm. concn. and was successfully reached for a cell length of 1.5 cm with a resoln. of about 5​%. The sensitivity of the setup is mainly related to the size of the cell, deliberately reduced to develop a robust and compact system for natural geol. sites

This paper reports on the design and realization of a new optical fibre sensor for continuous measurement of concrete strain over very long distances.We propose a composite-made wave-like sensor body that enables continuous bonding between optical fibre and concrete. Finite element analysis shows that the stiffness of the optical fibre can be adapted to that of the concrete, reducing the strain concentrations and the need for a theoretical calibration factor. Moreover, unlike the body of traditional I-shaped sensors, a wave-like sensor body enables a symmetrical response in tensile and compressive loadings whatever the contact conditions may be.We have realized optical fibre extensometers based on this technique and on a low-coherence interferometry method for the measurements. Despite its wave-shape, the proposed sensor body does not introduce any losses or strain that would result from fibre microbending. The process of realization is adapted to distributed sensors and sensors with a very long gauge length. Furthermore, several sensors were multiplexed, demonstrating the ability to perform quasi-distributed measurements. Once embedded into concrete cylinders, the optical fibre sensors were tested under compressive and tensile loading, and compared with traditional sensors. The allocation of one of the multiplexed sensors as a dummy gauge provides self-compensation for thermal effects and ambient fluctuations. As a result, and without any calibration factor, optical sensor measurements perfectly agreed with external linear variable differential transducer measurements.

Chalcogenide glasses are a matchless material as far as mid-infrared (IR) applications are concerned. They transmit light typically from 2 to 12 μm and even as far as 20 μm depending on their composition, and numerous glass compositions can be designed for optical fibers. One of the most promising applications of these fibers consists in implementing fiber evanescent wave spectroscopy, which enables detection of the mid-IR signature of most biomolecules. The principles of fiber evanescent wave spectroscopy are recalled together with the benefit of using selenide glass to carry out this spectroscopy. Then, two large-scale studies in recent years in medicine and food safety are exposed. To conclude, the future strategy is presented. It focuses on the development of rare earth-doped fibers used as mid-IR sources on one hand and tellurium-based glasses to shift the limit of detection toward longer wavelength on the other hand.

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special issue « Fiber Optic Research in France » (Part II of III)International audienceIn this paper we present a review of different micro-lenses we have developed at the end of single-mode fibers for improving optical coupling efficiency in communication systems. These micro-lenses find their applications in laser-diodes or integrated waveguides to single mode fibers, fiber to detector coupling, or fiber-to-fiber interconnecting. More generally, the applications concern active or passive components to single mode fiber coupling. Three kinds of micro-lenses are considered whose fabrication process has been designed to be very simple and low cost. Some of them are produced by companies in Lannion such as IDIL Fibers Optiques