Plasmonic tilted fiber Bragg gratings (TFBGs) are well-suited for accurate, rapid and minimally-invasive biosensing. They present a very dense transmitted amplitude spectrum of narrowband cladding mode resonances (full width at half maximum < 1 nm). This response is commonly demodulated using highly-resolved interrogators (wavelength resolution < 10 pm). This work investigates the possibility of reading-out the amplitude spectrum of a gold-coated TFBG by using a coarsely resolved spectrometer (166 pm). A refractometric sensitivity of 2656 nm/RIU has been observed thanks to a refined analysis of the spectral content which has led to the development a more efficient signal processing. This value represents a fivefold enhancement compared to previously reported read-out methods. Biosensing has been successfully achieved with gold-coated TFBGs used in reflection mode for the detection of insulin, with specific antibodies grafted on the gold surface. Our experimental study is an advance towards an industrialization of the FBG technology, as it opens the way to rapid parallel biodetection, benefiting from the multiple sensing channels (up to 64) of the interrogator as well as its high processing speed (repetition rate up to 3 kHz).
This paper reports on the development of a smart elastic textile band containing pre-strained fiber Bragg gratings (FBG) that was specifically designed with the ambition to dynamically measure the position of the backbone. To this aim, the textile band is 700 mm long and 60 mm wide. A piece of standard single-mode optical fiber, in which four fiber Bragg gratings were inscribed, is sewn on the band. Each FBG is glued on a 3D-printed pad in a pre-strained way, allowing the detection of FBG compression in addition to elongation. Measurements were performed on this sensing elastic band and the resulting sensitivity is a Bragg wavelength shift of 12 pm per mm of textile elongation. Validation tests were also carried out to highlight the sensitivity to compression and to show that the sensing system is capable of repeatability in a dynamic environment.
Fiber Bragg gratings (FBGs) have already proven their efficiency in axle counting when distributed along a railway track and bring advantages with respect to competing sensors. In this work, two relevant originalities are proposed to broaden the state-of-the-art solutions. First, the strain distribution in the rail cross-section is studied to identify the sensitivity, depending on the charge and the position. Secondly, the sensor head, composed of four wavelength-division-multiplexed FBGs in a single optical fiber, is deployed along the railway and interrogated by a small smart read-out device. Two FBGs are used for the train direction determination and the remaining two bring redundancy to reach safety integrity level (SIL) 4. The smart interrogator has been especially developed for this work and is composed of a vertical-cavity surface-emitting laser (VCSEL) and a photodiode driven by a high-speed microprocessor. The useful information (i.e. the number of counted axles) can be wireless communicated. On-field experiments confirm that this approach offers an easier installation process and a democratization of the technology.
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