Capteurs distribués à fibres optiques : aspects physiques, développement et applications

This report dedicated to obtaining the HDR (Habilitation à Diriger des Recherches), is composed of two distinct parts: the first one summarizes my professional career highlighting my research activities in the different positions that I have held since obtaining my engineering degree, and the main research topics I am interested in. The scientific part describes precisely the content of my research related to the development of fiber-optic distributed sensors, the applications of distributed optical fiber sensors in civil engineering structures and other specific structures, and secondly, the impact of environmental parameters on the performances of optical fiber sensors.The summary of my professional career highlights a particular aspect of my profile since I had the chance to work in the field of applied research before my thesis, as a research engineer in optoelectronics. This experiment, in a laboratory carrying out activities of design, realization and characterization of solid laser sources, makes it possible to extend the wavelengths of the laser emission by using nonlinear optical crystals through the generation of the second harmonic or the optical parametric oscillation. This allowed me to conduct applied research and realize the importance of working in a team. The experience of the thesis in vertical external cavity semiconductor lasers for the generation of short pulses has allowed me to acquire new knowledge in fast non-linear optics, and the dynamics of semiconductor lasers. This step is followed by my postdoctoral experience, in which I worked on sorting techniques of carbon nanotubes, their photonic characteristics, and their uses as saturable absorbers in lasers.Following my recruitment at IFSTTAR in October 2010, as a researcher on the theme of fiber optic sensors, I have invested in different projects, to make the use of distributed optical fiber sensors an evident solution in the civil engineering structures monitoring, integration of optical fiber sensors in new specific applications. In parallel, I developed a research activity related to the "development of distributed optical fiber sensors". I worked on the study of impact of each component of the system and to focus first and foremost on the heart of a distributed fiber sensor system: the laser.In this thesis, I introduce the issues and challenges of my work, describe the main investigations conducted and their results, and prefigure medium and long-term research

Source d'impulsions brèves à 1,55µm en laser à cavité verticale externe pour application à l'échantillonnage optique linéaire

This thesis focuses on the development, fabrication and use of optically pumped vertical external cavity surface emitting lasers (VECSEL), to achieve short pulse sources at high repetition rate emitting at 1550nm. These sources are opening the door to interesting applications in optical communications to achieve very high repetition rate transmitters, or high speed linear optical sampling The objectives of this thesis were, in a first step, to develop and implement VECSEL structures containing an active zone formed by GaAlInAs/InP quantum wells located at the anti-nodes of the resonant electric field, positioned on a Bragg mirror, all this being bonded to a substrate of good thermal conductivity. For this, we have designed structures optimizing the evacuation of heat generated in the active zone. This has greatly improved the VECSEL performances, especially their output power. The VECSEL performances were evaluated in a simple cavity with two mirrors (plane-concave). The second point was to develop and implement SESAM structures which, owing to their nonlinear characteristics, would allow a passively mode-locked laser operation. The structures contained InGaAsN/GaAs quantum wells. The studied parameters were the number of quantum wells, and the resonant or anti-resonant behavior of the structure. The linear and nonlinear optical characterizations were used to optimize the SESAM structure and estimate their performances. Finally, the compatibility between the VECSEL and SESAM structures, in terms of modulation depth and resonance wavelength, made it possible to obtain the passive mode locking operation. The obtained pulses show two different behaviors depending on the dispersion properties of the structures. With low dispersion, we have made the first demonstration of a passively mode-locked VECSEL at 1550nm, operating at room temperature. An all-optical sampling device implementing the linear optical sampling technique using short laser pulses has been realized and tested. This device will allow displaying eye diagrams and constellation diagrams with an expected sensitivity around -20dBm of average power. Testing the device allowed to visualize the acquisition of very high repetition rate signals (40 Gb/s).Cette thèse porte sur l'élaboration et l'utilisation de structures semi-conductrices à émission laser par la surface en cavité externe (VECSEL) en pompage optique pour la réalisation de sources d'impulsions brèves à haut taux de répétition émettant à 1550nm. Ces sources ouvrent la voie à des applications intéressantes dans les télécommunications optiques pour réaliser des émetteurs à très haut débit ou pour l'échantillonnage optique linéaire ultra-rapide. Les objectifs de ce travail de thèse étaient, dans un premier temps, de développer et réaliser des structures VECSEL, qui contiennent une zone active formée par des puits quantiques GaAlInAs/InP localisés aux maxima du champ électrique résonant, positionnée sur un miroir de Bragg, le tout étant reporté par brasure sur un substrat de bonne conductivité thermique. Pour cela, nous avons conçu des structures permettant d'accélérer l'évacuation de la chaleur accumulée dans la zone active, ce qui a permis d'améliorer les performances du VECSEL, notamment la puissance de sortie. Les performances des VECSEL ont été évaluées dans une cavité simple à deux miroirs (plan-concave). Le second point était de développer et réaliser des structures SESAMs, qui permettent, par leur comportement non linéaire, d'obtenir un fonctionnement en verrouillage de modes passif. Les structures, contenant des puits quantiques InGaAsN/GaAs, ont pour paramètres : le nombre de puits quantique, la résonance de la structure. Les caractérisations optiques en régime linéaire et non linéaire ont permis d'optimiser les structures SESAM et d'estimer leurs performances. Enfin, la compatibilité entre les structures de VECSEL et de SESAM en terme de profondeur de modulation et de longueur d'onde de résonance, a permis d'obtenir un verrouillage de mode passif dans une cavité à quatre miroirs. Les impulsions obtenues présentent deux comportements différents suivant les propriétés de dispersion des structures. La réalisation d'une faible dispersion a permis d'obtenir la première démonstration d'un VECSEL en verrouillage de modes passif fonctionnant à 1550 nm et à température ambiante. Un dispositif d'échantillonnage tout optique mettant en oeuvre l'échantillonnage optique linéaire basé sur l'utilisation d'une source d'impulsions brèves, a été réalisé et testé. Ce dispositif permettra d'obtenir des diagrammes de l'oeil et diagrammes de constellation avec une sensibilité attendue de l'ordre de -20dBm de puissance moyenne, sur des signaux porteurs de données à 10Gbit/s, voire 40 Gb/s. Les tests effectués ont permis de visualiser l'acquisition à très haut débit (40Gb/s)

Experimental investigation of the grout-bolt interface behavior by optical fiber

14th International Congress of Rock Mechanics and Rock Engineering, FOZ DO IGUACU, BRESIL, 13-/09/2019 - 18/09/2019Fully grouted rockbolts are common anchorages used in the domain of rockfalls protection devices. Their intern behaviour being not established, current design methods are conservative. The issues are due to the complex behaviour at the intern interfaces. To investigate the behaviour of the bolt-grout interface, a series of pull-out tests was performed on fully grouted rockbolts within a limestone rock cliff. Optical fiber sensors were embedded in the steel bars so that the axial deformations along the bars were monitored. Considering the elastic behaviour for steel under loads applied, the tangential stress of the bolt-grout interface was determined along the bars. The study underlines the propagation of tangential load along the grout-bolt interface from the head of grout with increasing axial load. The interface is progressivelydamaged : firstly, cracks occur and then, the contact between steel and grout is completely debonded

Fiber Optic Sensor Embedment Study for Multi-Parameter Strain Sensing

The fiber optic sensors (FOSs) are commonly used for large-scale structure monitoring systems for their small size, noise free and low electrical risk characteristics. Embedded fiber optic sensors (FOSs) lead to micro-damage in composite structures. This damage generation threshold is based on the coating material of the FOSs and their diameter. In addition, embedded FOSs are aligned parallel to reinforcement fibers to avoid micro-damage creation. This linear positioning of distributed FOS fails to provide all strain parameters. We suggest novel sinusoidal sensor positioning to overcome this issue. This method tends to provide multi-parameter strains in a large surface area. The effectiveness of sinusoidal FOS positioning over linear FOS positioning is studied under both numerical and experimental methods. This study proves the advantages of the sinusoidal positioning method for FOS in composite material’s bonding

Numerical simulation analysis as a tool to identify areas of weakness in a turbine wind-blade and solutions for their reinforcement

Offshore wind energy is one of the main sources of renewable energy that can benefit from new generation materials that exhibit good oxidation resistance and mechanical reliability. Composite materials are the best consideration for harsh environment and deep sea wind turbine manufacturing. In this study, a numerical simulation was implemented to predict the stress distribution over a wind turbine-blade and to determine areas with high stress concentration. Finite Element Analysis (FEA) was used to find optimal material and bonding techniques to construct the blade. By using Abaqus commercial software, a finite element model of wind turbine blade was analyzed under bending-torsion coupled with a static-load condition in flap-wise direction. Structural damage in critical zones varies according to ply orientation and stack thickness as a result of composite orthotropic nature. This study leads existing scenarios and techniques which would provide a new and better solutions for wind turbine blade designers. The root section and trailing edge were found to be critical zones in the wind turbine blade. The root section failure can be reduced by (1) adjusting the thickness of the structure or increasing the number of plies in the composites laminate stacking and by (2) adjusting the bonding technique to prevent trailing-edge failure. Transverse-stitch method and the carbon cord tying methods are most effective for trailing edge reinforcement. Both solutions are proposed to reduce failures in wind turbine blades and proven by step-by-step numerical study. The goal of this study is to deliver a good reference for wind turbine blade designers and to improve the accuracy during design phase as well as to avoid failure

Analyse du comportement de poutres en béton précontraint: Instrumentation des torons de précontrainte par fibres optiques

Une analyse expérimentale et numérique de poutres en béton précontraint est proposée dans cette communication. Une instrumentation des torons de précontrainte par fibres optiques est validée et utilisée afin d’évaluer la contribution des câbles au cours d’un chargement mécanique de la structure. Les résultats expérimentaux obtenus sont comparés à des simulations numériques éléments finis, à des échelles locales et globales

Finer SHM-Coverage of Inter-Plies and Bondings in Smart Composite by Dual Sinusoidal Placed Distributed Optical Fiber Sensors

Designing of new generation offshore wind turbine blades is a great challenge as size of blades are getting larger (typically larger than 100 m). Structural Health Monitoring (SHM), which uses embedded Fiber Optics Sensors (FOSs), is incorporated in critical stressed zones such as trailing edges and spar webs. When FOS are embedded within composites, a ‘penny shape’ region of resin concentration is formed around the section of FOS. The size of so-formed defects are depending on diameter of the FOS. Penny shape defects depend of FOS diameter. Consequently, care must be given to embed in composites reliable sensors that are as small as possible. The way of FOS placement within composite plies is the second critical issue. Previous research work done in this field (1) investigated multiple linear FOS and sinusoidal FOS placement, as well. The authors pointed out that better structural coverage of the critical zones needs some new concepts. Therefore, further advancement is proposed in the current article with novel FOS placement (anti-phasic sinusoidal FOS placement), so as to cover more critical area and sense multi-directional strains, when the wind blade is in-use. The efficiency of the new positioning is proven by numerical and experimental study

Numerical simulation analysis as a tool to identify areas of weakness in a turbine wind-blade and solutions for their reinforcement

Offshore wind energy is one of the main sources of renewable energy that can benefit from new generation materials that exhibit good oxidation resistance and mechanical reliability. Composite materials are the best consideration for harsh environment and deep sea wind turbine manufacturing. In this study, a numerical simulation was implemented to predict the stress distribution over a wind turbine-blade and to determine areas with high stress concentration. Finite Element Analysis (FEA) was used to find optimal material and bonding techniques to construct the blade. By using Abaqus commercial software, a finite element model of wind turbine blade was analyzed under bending-torsion coupled with a static-load condition in flap-wise direction. Structural damage in critical zones varies according to ply orientation and stack thickness as a result of composite orthotropic nature. This study leads existing scenarios and techniques which would provide a new and better solutions for wind turbine blade designers. The root section and trailing edge were found to be critical zones in the wind turbine blade. The root section failure can be reduced by (1) adjusting the thickness of the structure or increasing the number of plies in the composites laminate stacking and by (2) adjusting the bonding technique to prevent trailing-edge failure. Transverse-stitch method and the carbon cord tying methods are most effective for trailing edge reinforcement. Both solutions are proposed to reduce failures in wind turbine blades and proven by step-by-step numerical study. The goal of this study is to deliver a good reference for wind turbine blade designers and to improve the accuracy during design phase as well as to avoid failure

Durability of distributed optical fiber sensors used for SHM of Reinforced Concrete Structures

Proceedings of the IWSHM 2019, 12th International Workshop on Structural Health Monitoring, Stanford, ETATS-UNIS, 10-/09/2019 - 12/09/2019This paper presents an experimental study on the durability of two commercially available optical fiber cables intended for distributed strain measurements and crack monitoring of reinforced concrete structures. The experimental program is based on accelerated aging tests performed on small concrete specimens instrumented with these two embedded optical fiber cables. Pull-out tests are carried out after three months of accelerated aging, in order to evaluate the effect of aging on the mechanical response of the cable/concrete interfaces, as this response is directly related to the strain transfer from the host material (concrete) to the optical fiber core. After three months, the cable/concrete interface of one of the two cables was found severely damaged

Application of Distributed Optical Fiber Sensing Technology to the Detection and Monitoring of Internal Swelling Pathologies in Massive Concrete Blocks

This paper presents an experimental application of Distributed Optical Fiber Sensors (DOFS) for the Structural Health Monitoring (SHM) of concrete structures affected by internal swelling pathologies. In the framework of a large research project aiming to assess the possible extension of the operating lifetime of nuclear power plants from 40 to 60 years, massive blocks were cast from reactive concrete mixtures intended to develop delayed ettringite formation and alkali-silica reaction. These blocks were subjected to specific ageing conditions to initiate and accelerate the concrete pathologies. Some of the blocks were instrumented with DOFS bonded to the surface and embedded in the concrete. Using an interrogator device based on Rayleigh backscattering and a suitable procedure to eliminate temperature effects, distributed strain measurements were then performed at different time intervals. The first results of this ongoing study made it possible to demonstrate the feasibility and effectiveness of this sensing technology for detecting and monitoring expansion induced by swelling pathologies in representative-scale concrete structures