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To date, there is clear experimental evidence that gold-coated tilted fiber Bragg gratings (TFBGs) are highly sensitive plasmonicbiosensors that provide temperature-compensated detection of analytes at concentrations in the picomolar range. Asmost optical biosensors, they bring an evanescent wave in the surrounding medium, which makes them sensitive to both surface refractive index variations (= the useful biosensing signal) and to bulk refractive index changes (= the non-useful signal forbiosensing). This dual sensitivity makes them prone to drift. In this work, we study partially gold-coated TFBGs around theircross-section. These gratings present the ability to discriminate both volume and surface refractive index changes, which isinteresting in biosensing to enhance the signal-to-noise ratio. The effects induced in the TFBGs transmitted amplitude spectrawere analyzed for surrounding refractive index (SRI) changes in the range 1.3360–1.3370. Then, the gold film wasbiofunctionalized with human epidermal growth factor receptor (HER2) aptamers using thiol chemistry. The detection of HER2proteins (a relevant cancer biomarker) at 10−9g/mL, 10−8g/mL and 10−6g/mL demonstrated the advantage toidentifyenvironmental perturbations through the bare area of the TFBGs, which is left not functionalized. The non-specific driftsthatcould exist in samples are eliminated and a wavelength shift only related to the surface modification is obtained.&nbsp

We investigated post-irradiation variations of the radiation induced attenuation (RIA) of polymer perfluorinated (CYTOP) optical fiber exposed to gamma radiation. The RIA measured five months after the irradiation was qualitatively similar to that measured several hours after irradiation. However, quantitatively the RIA post-irradiation evolution significantly depends on the spectral range: in the visible range, the transmission partly recovers, while in the infrared, at wavelengths above 1300 nm the RIA grows and then saturates becoming permanent. The latter feature is prospective for gamma radiation dosimetry as a permanent long-term indicator of received radiation dose.

Tilted fiber Bragg gratings (TFBGs) coupled to the surface plasmon resonance (SPR) phenomenon represent a powerful sensing solution especially for biodetection purposes. Indeed, the excitation of plasmonic waves at the metal-coated surface of the sensor brings a significant improvement in terms of surface sensitivity. Until now, most of experimental results involving SPR have been obtained by using TFBGs inscribed in standard single-mode optical fibers (SMF), which requires the use of a polarizer to select the right state of polarization for plasmonic excitation. Investigations for the development of even more sensitive or robust sensing tools remain a topic of current interest. In this study, the bulk and surface refractometric sensitivities of plasmonic TFBGs photo-inscribed in multimode fiber (MMF) are compared to the one of standard SMF. Gold-coated TFBG in SMF exhibits a sensitivity value of ~102 nm/RIU. Plasmonic MMF TFBGs are more sensitive with a value of ~124 nm/RIU (enhancement of ~22 %) and open the way to multiplexing thanks to the narrowness of their spectral response. Surface refractometry was also assessed through HER2 bioassays (Human Epidermal Growth Factor Receptor-2), a breast cancer biomarker. For that purpose, aptasensors based on antiHER2 aptamers were developed and tested by using these two fiber types. Similar surface sensitivities were obtained for both fiber types.

PubMed: 32168970, Instrumentation techniques, implementation and installation methods are major concerns in today's distributed and quasi-distributed monitoring applications using fiber optic sensors. Although many successful traffic monitoring experiments have been reported using Fiber Bragg Gratings (FBGs), there has been no standardized solution proposed so far to have FBG seamlessly implemented in roads. In this work, we investigate a mobile platform including FBG sensors that can be positioned on roads for the purpose of vehicle speed measurements. The experimental results prove the efficiency of the proposed platform, providing a perspective toward weigh-in-motion systems.

Saccharide sensors represent a broad research area in the scope of sensing devices and their involvement in the medical diagnosis field is particularly relevant for cancer detection at early stage. In that context, we present a non-enzymatic optical fiber-based sensor that makes use of plasmon-assisted tilted fiber Bragg gratings (TFBGs) functionalized for D-glucose biosensing through polydopamine (PDA)-immobilized concanavalin A (Con A). Our probe allows a live and accurate monitoring of the PDA layer deposition leading improved surface biochemistry. The SPR shift observed was assessed to 3.83 ± 0.05 nm within 20 min for a 2 mg/mL dopamine solution. Tests performed in different D-Glucose solutions have revealed a limit of detection close to 10−7 M with the highest sensitivity in the 10−6 to 10−4 M range. This configuration has the capability to overcome the limitations of current enzyme-based solutions.

7th European Workshop on Optical Fibre Sensors (EWOFS); OCT 01-04, 2019; Limassol, Cyprus, This paper shows that fiber Bragg gratings written in standard single mode optical fiber with IR femtosecond pulses and point-by-point technique are high temperature resistant (< 1000 degrees C). Moreover, after calibration process, these gratings can be used as a reference to study and discriminate between different high temperature annealing mechanisms involved in other types of gratings and/or fibers. Here we have considered the regeneration process of gratings written by UV laser in boron/germanium co-doped single mode optical fiber. Hence, the monitoring of grating strength and differential wavelength shift between femtosecond and type-I gratings during annealing cycle yields the wavelength shift due to the annealing of doping (mainly boron) and UV-related defects and their relative contributions to the regeneration mechanism.

Fiber Bragg gratings (FBGs) are well-known to be essential elements in optical communications, optical fiber based sensors and fiber lasers [1]. One of the most recent methods for fabricating FBGs is referred to as point-by-point inscription and uses femtosecond duration pulses of an infrared laser tightly focused to the fiber core region, such that every pulse forms a single grating period [2]. The periodicity of the grating is controlled by moving the fiber along its axis using translation stages at a pre-defined speed for a known repetition rate of the laser. A multi-photon absorption process is responsible for the local refractive index modification induced by a single pulse. Gratings obtained using point-by-point inscription can for example be used at much higher temperatures than those fabricated using conventional UV laser based inscription.

International audience; In this article, we study the possibility to use a pair of specifically designed microstructured optical fiber Bragg gratings (MOFBGs) as a multi-component strain sensor when embedded within composite materials. The dependence on the orientation of the transverse sensitivity of the MOFBGs is exploited to build a sensing device able to measure the strain field along the three principal mechanical directions of a laminate composite. We developed an analytical and numerical model of such a sensor and benchmarked it with experiments performed on laminated composite coupons equipped with this sensor. We report on a theoretical strain resolution of about 5 μ in the transverse directions of the composite material, which is a six-fold improvement over results reported in literature. © 2015 IOP Publishing Ltd.

We present dedicated shear stress optical fiber sensors for in situ disbond monitoring of adhesive bonds. The shear stress sensitivity of these sensors is about 60 pm MPa−1, which corresponds to a shear strain sensing resolution of 50 μϵ. By integrating a combination of three such sensors in the adhesive bond line of a single lap joint, we can assess the internal shear stress distribution when the joint is tensile loaded. Disbonding of this joint was initiated by cyclic tensile loading, and the sensor responses were monitored during this process. Our results show that this sensing system can detect disbonds as small as 100 μm.

The possibility of embedding optical fiber sensors inside carbon fiber reinforced polymer (CFRP) for structural health monitoring purposes has already been demonstrated previously. So far however, these sensors only allowed axial strain measurements because of their low sensitivity for strain in the direction perpendicular to the optical fiber's axis. The design flexibility provided by novel photonic crystal fiber (PCF) technology now allows developing dedicated fibers with substantially enhanced sensitivity to such transverse loads. We exploited that flexibility and we developed a PCF that, when equipped with a fiber Bragg grating (FBG), leads to a sensor that allows measuring transverse strains in reinforced composite materials, with an order of magnitude increase of the sensitivity over the state-of-the-art. In addition it allows shear strain sensing in adhesive bonds, which are used in composite repair patches. This is confirmed both with experiments and finite element simulations on such fibers embedded in CFRP coupons and adhesive bonds. Our sensor brings the achievable transverse strain measurement resolution close to a target value of 1 mu strain and could therefore play an important role for multi-dimensional strain sensing, not only in the domain of structural health monitoring, but also in the field of composite material production monitoring. Our results thereby illustrate the added value that PCFs have to offer for internal strain measurements inside composite materials and structures.

The application of shear stress sensors in structural health monitoring remains limited because current sensors are either difficult to implement, they feature a low measurement resolution or the interrogation of the output signal is complex. We propose to use fiber Bragg grating-based sensors fabricated in dedicated highly birefringent microstructured optical fibers. When embedded in a host material, the orientation angle of the fiber should be chosen such that their polarization axes are aligned parallel with the direction of maximum shear stress when the host is mechanically loaded. We present experimental results of sensors embedded in the adhesive layer of single lap and double lap structural joints. These tests demonstrate that when the joints are tension loaded, the embedded sensors have a shear stress sensitivity of around 60 pm/MPa. We study the influence of the adhesive material on the sensor response, as well as the influence of sensor orientation and location in the bond line Finally, we demonstrate the minimal thermal cross-sensitivity of the shear stress sensitivity of this sensor.

Fiber optic sensors outperform traditional sensor technologies in fields such as structural health monitoring, vibration and seismic activity monitoring, intrusion detection, and many other applications. Their key advantages include electromagnetic interference immunity, lightweight, small size, multiplexing capabilities, low power consumption, corrosion and high temperature resistance. To meet the demand of more and more challenging optical sensors a new generation of optical fibers, the so-called microstructured optical fibers (MOFs), has appeared. These fibers are composed of a structure of holes surrounding a solid core, which offers a unique design flexibility to optimize their waveguide properties for specific applications. In particular, the design can be optimized to strongly reduce the crosssensitivity of a sensor to parasitic physical parameters like temperature variations, as is the case for the sensor presented here. Our sensor is based on a Bragg grating inside a temperature independent highly birefringent MOF with a high transverse strain sensitivity, to evaluate vibrations by a polarimetric measurement of the reflection spectrum. This technique takes advantage of the stress-induced phase shift between the two orthogonally polarized fiber eigenmodes. It consists in coupling linearly polarized light through one arm of an optical coupler (50:50) in the sensing optical fiber in which a highly reflective fiber Bragg grating is inscribed. The reflected signal is analysed through a linear polarizer. The optical fiber is crushed by a mechanical transducer designed to transform the vibration into a mechanical stress transversal to the fiber's axis. The vibration therefore induces a change of the phase modal birefringence that varies in time at the vibration frequency. In this study we show that using standard single-mode fibers to realize the sensor do not provide stable measurements and that using conventional polarization-maintaining fibers lead to a significant crosssensitivity to temperature. We then show that the use of a specific type of highly birefringent microstructured optical fiber allows temperature independent (up to 120 degrees C) and repeatable vibration measurements.

Understanding the mechanical interactions between the coolant and the core structure in nuclear reactors helps to determine the lifetime, health or optimal design of the reactor core. The flow of the coolant produces vibrations in the reactor core containing the fuel assemblies that consists of a matrix of fuel pins. We report on an evaluation of the performance of different vibration measurement techniques considered for measuring the flow induced vibrations on a fuel pin mock-up. These techniques include a laser Doppler vibrometer (LDV), a grid method (GRID), fiber Bragg grating sensors (FBGs), electrical strain gages and two types of accelerometers. In this paper we first show the practical aspects of the validation experiments before proceeding with the influence of the techniques on the pin dynamics. Finally we compare the signal-to-noise ratio (SNR) and the level of determination of the response signal of the sensors for low amplitudes and low frequencies. We conclude that for our setup the optical techniques and MEMS-type accelerometer prove to offer superior performance. Considering the space constraints, we believe that the fiber Bragg gratings are the best candidate for vibration monitoring in nuclear reactor core mock-ups. (C) 2013 Elsevier Ltd. All rights reserved.

We demonstrate shear stress sensing with a Bragg grating-based microstructured optical fiber sensor embedded in a single lap adhesive joint. We achieved an unprecedented shear stress sensitivity of 59.8 pm/MPa when the joint is loaded in tension. This corresponds to a shear strain sensitivity of 0.01 pm/mu epsilon. We verified these results with 2D and 3D finite element modeling. A comparative FEM study with conventional highly birefringent side-hole and bow-tie fibers shows that our dedicated fiber design yields a fourfold sensitivity improvement. (C) 2013 Optical Society of America

International audience; We report on the use of a fiber Bragg grating (FBG) based sensor written in a photonic crystal fiber (PCF) to monitor the cure cycle of composite materials. The PCF under study has been specifically designed to feature a high phase modal birefringence sensitivity to transverse strain and a very low sensitivity to temperature. We exploit these particular properties to measure strain inside a composite material in the out-of-plane direction. The embedded FBG sensor has been calibrated for transverse and axial strain as well as for temperature changes. These FBGs have then been used as embedded sensors during the manufacturing of a composite material in order to monitor how strain develops inside the composite during the cure cycle. We show that our sensors allow gaining insight in the composite cure cycle in a way that would be very difficult to achieve with any other sensor technology. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Fiber Bragg gratings written in Bow-tie fiber and in highly birefringent micro-structured optical fiber are embedded in a carbon fiber reinforced epoxy. The Bragg peak wavelength shifts are measured under controlled bending, transversal load and thermal cycling of the composite sample. The results evidence the feasibility of using micro-structured fibers in structural integrity monitoring. We obtain similar axial as well as transversal strain sensitivities for the two embedded fiber types. We also highlight an important advantage of the micro-structured fibers for this application which is the low temperature dependence of the birefringence.

We present a dedicated fiber Bragg grating (FBG) inscription experiment to investigate the compatibility of a microstructured optical fiber (MOF) with conventional FBG inscription setups. For the studied MOF, the angular orientation of the fiber in the interferometric excimer laser setup was found to have no significant influence on the final reflection of the inscribed FBGs. We also show that an array of multiplexed FBGs can be inscribed in a single MOF with a repeatability and quality that match fiber sensing requirements.

The Belgian Agency for Radioactive Waste and Enriched Fissile Materials (ONDRAF/NIRAS) is developing a conceptual design for a supercontainer made of concrete and carbon steel for the post-conditioning of high-level nuclear waste prior to disposal in a geological repository site. This supercontainer should be instrumented to follow the temperature and strain evolution over time during and after the fabrication process. This paper shows that it is possible to embed bare fiber Bragg gratings in the supercontainer concrete to monitor in situ temperature and strain. The reason for choosing bare fibers, despite their known fragile nature, was to optimize the contact between the fibers and the concrete. Due to the simultaneous temperature and strain sensitivity of the fiber Bragg gratings, some sensors were also installed in a protective shielding consisting of plastic or aluminum to isolate them from effects of stress. This makes it also possible to extract both temperature and strain from the measured Bragg wavelength shifts. Moreover, the protective shielding also provides mechanical protection to avoid fiber breakage during concrete casting. The preliminary results of temperature closely agree with measurements obtained from thermocouples located near the fibers for validation purposes. Finally, the use of shielding in some of the fibers allowed to estimate strain levels in the concrete.