Aghiad Khadour

Université Gustave Eiffel

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...

The present study investigates the environmental durability of a distributed optical fiber sensing (DOFS) cable on the market, commonly used for distributed strain measurements in reinforced concrete structures. An extensive experimental program was conducted on different types of specimens (including samples of bare DOFS cable and plain concrete s...

The present study investigated the strain response of a distributed optical fiber sensor (DOFS) sealed in a groove at the surface of a concrete structure using a polymer adhesive and aimed to identify optimal conditions for crack monitoring. A finite element model (FEM) was first proposed to describe the strain transfer process between the host str...

This study focuses on the modeling of the local bond behavior of Fiber Reinforced Polymer (FRP) reinforcing bars and the surrounding concrete. An analytical bond-slip model is first proposed to describe the interface behavior of the bars embedded in concrete. Then, the parameters of the bond-slip law are identified from experimental data of pull-ou...

In the present study, mechanical tests are performed on concrete specimens instrumented with bonded optical fiber sensors. Two test configurations are considered: the first involves a plain cylindrical concrete specimen loaded in compression, while the other is based on a notched prismatic fiber-reinforced concrete specimen subjected to three-point...

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 composite...

This paper deals with the experimental determination of ductility of ultra-high-performance fiber-reinforced concrete (UHPFRC) columns with longitudinal passive reinforcement, tested under combined axial and alternate flexural load. The influence of axial load has been studied, as well as the presence or not of a reduced shear reinforcement. One co...

This study focuses on the experimental characterization of the bond behavior between concrete and Fiber Reinforced Polymer (FRP) reinforcing bars (rebars). Pull-out tests were performed on glass, carbon, and aramid FRP rebars, as well as on deformed steel rebars. The influence of various parameters on the bond behavior was studied, such as the type...

This chapter addresses the use of distributed optical fibers for the monitoring of concrete structures. After overviewing optical fiber technologies, we propose a practical guide to select the appropriate optical fiber system for a given monitoring purpose, such as for crack detection or strain measurements. It is noted that optical fibers can be u...

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...

This chapter addresses the use of distributed optical fibers for the monitoring of concrete structures. After overviewing optical fiber technologies, we propose a practical guide to select the appropriate optical fiber system for a given monitoring purpose, such as for crack detection or strain measurements. It is noted that optical fibers can be u...

We have realized a dual-frequency VECSEL at 1.5 μm. Laser emission of two orthogonally-polarized cavity modes is obtained by inserting a birefringent crystal into the VECSEL cavity. We have examined the influence of the different intra-cavity elements on the laser emission. It is shown that optimizing the free spectral range and the bandwidth of th...

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 p...

The shear strength of concrete/rock interface must be clearly assessed to design the rock foundations. However, the concrete/rock interface has different failure modes which depend on the mechanical characteristics of the materials and the morphology of the rock surface. Consequently, to study thoroughly the shear behavior of concrete/rock interfac...

We aim at realizing an optically-pumped, dual-frequency VECSEL at telecom wavelength (1.5 µm) with a frequency difference in the radio-frequency (RF) range (around 11 GHz), to be used in a sensor unit based on Brillouin scattering in optical fibers. Laser emission of two orthogonally-polarized cavity modes with a controlled frequency difference is...

Distributed optical fiber systems (DOFSs) are an emerging and innovative technology that allows long-range and continuous strain/temperature monitoring with a high resolution. Sensing cables are either surface-mounted or embedded into civil engineering structures to ensure long-term structural monitoring and early crack detection. However, strain p...

This paper deals with the experimental determination of the bond behaviour between ultra-high performance fiber-reinforced concrete (UHPFRC) and reinforcing bars (rebars). An experimental campaign has been carried out to assess the bond behaviour considering different rebar diameters, different embedment lengths and different concrete covers. A rel...

Distributed Fiber Optic Systems (DOFS) are an emerging and innovative technology that allows long-range and continuous strain/temperature monitoring with a high resolution. However, strain profiles measured in the optical fiber may differ from actual strain in the structure, due to the shear transfer through the intermediate material layers between...

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 d...

L'interface acier-béton est un important sujet d'études depuis de nombreuses années. La connaissance expérimentale des mécanismes locaux de dégradation de l'interface et de sa résistance mécanique globale favorise le développement de modèles numériques fiables pour le dimensionnement de structures complexes, enceintes de confinement de centrale nuc...

UHPFRC 2013 - International Symposium on Ultra-High Performance Fibre-Reinforced Concrete, MARSEILLE, FRANCE, 01-/10/2013 - 03/10/2013

This paper is concerned with the implementation of Optical Fibers (OF) in reinforcement bars (rebars) for strain measurement in reinforced concrete (RC) structures. The measurement chain consists of an OBR interrogation unit (Optical Backscatter Reflectometer, based on relative Rayleigh measurements) paired with OF sensor. In the proposed technique...

NDE, SEATTLE, ETATS-UNIS, 22-/05/2012 - 24/05/2012

Mode-locked vertical-extended-cavity-surface emitting lasers (ML-VECSEL) are promising candidates for the generation of stable short pulses at multi-GHz rate. However, the poor thermal behavior of quaternary InP-based semiconductor compounds often limits the performance of ML-VECSELs operating at 1.55 μm. In this work, we report on a specific appro...

An Er 3 + fiber laser passively mode locked by a resonant saturable absorber mirror achieves more than 130 mW average power at 1560 nm from a Fabry–Perot cavity. The pulsed regime is self-starting from the CW regime without any Q-switch transition. The output pulse has a duration of 10.2 ps and can be extracavity dechirped with 42% efficiency down...

A technique for actively stabilizing the repetition rate of a mode-locked vertical external-cavity surface-emitting laser is presented using an optically triggered semiconductor saturable absorber mirror. This method enables a significant reduction of the timing jitter measured in the frequency range [100 Hz, 10 MHz] and makes this kind of external...

A 1.55 mu m VECSEL with a hybrid metal-GaAs/AlAs metamorphic mirror optimized for high power room temperature operation has been assembled with a fast InGaAsN/GaAsN saturable absorber mirror (SESAM) to generate mode-locked pulses at a frequency of 2 GHz. Nearly Fourier transform-limited pulses are obtained at 25 C avoiding the need for water coolin...

We report on a picosecond pulse source delivering near transform-limited pulses in the 1.55 µm wavelength region, based on an optically pumped InP-based mode locked Vertical External Cavity Surface Emitting Laser (VECSEL). The cavity combines two semiconductor elements, a gain structure which includes six strained InGaAlAs quantum wells and a hybri...

A 1.55μm VECSEL with a metal-GaAs/AlAs hybrid metamorphic mirror optimized for high power room temperature operation has been assembled with a fast saturable absorber mirror (SESAM) in a four-mirror cavity to generate mode-locked pulses at a frequency of 2 GHz. Stable pulses are obtained at room temperature avoiding the need for water cooling, with...

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 transmitte...

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 structure...

A 1.55 mum VECSEL with a metal-GaAs/AlAs hybrid metamorphic mirror optimized for high power operation has been assembled with a fast saturable absorber mirror (SESAM) in a four mirror cavity to generate mode-locked pulses with an RF linewidth < 20 kHz at a frequency of 2 GHz.

We report a 2 GHz mode locked vertical external cavity surface emitting laser using a hybrid metal-metamorphic Bragg mirror on the gain structure with a resonant two quantum wells GaInNAs semiconductor saturable absorber mirror (SESAM).

We have used a two quantum-well GaInNAs semiconductor saturable absorber mirror (SESAM) with a high power InP-based semiconductor disk laser to obtain a 2 GHz mode locked OP-VECSEL laser with a pulse width

We report on the thermal design and the characterization of InP-based 1.55μm wavelength large diameter (∼100μm) optically pumped vertical external cavity surface emitting lasers (OP-VECSELs). The device is thermally optimized for high power (>70mW) room-temperature (RT) continuous-wave (CW) single-mode operation. Efficient bottom heat dissipation i...

Optically-pumped vertical-external-cavity surface-emitting laser at 1.55 mum emits 77 mW CW single-mode output power with a SMSR above 60 dB at 20degC. Linewidth measurements showed the importance of low frequency fluctuation stabilization.

In this paper, we demonstrate for the first time high output power, low pump power threshold density, room-temperature (RT), continuous-wave (CW) operation of an optically-pumped vertical-external-cavity surface-emitting lasers (OP-VECSEL) operating at 1.56 μm with an hybrid metal-metamorphic GaAs/AlAs mirror. We believe the maximum monomode TEM<su...

A report is presented on an optically-pumped vertical-external-cavity surface-emitting laser at 1.55 mum with an hybrid metal-metamorphic Bragg mirror on a SiC substrate. Output power up to 80 mW at room temperature is achieved and 77 mW in single-longitudinal-mode operation.

RÉSUMÉ Dans cette communication nous rapportons une étude systématique des caractéristiques de plusieurs cavités lasers à fibres optiques dopées erbium (du régime soliton à dispersion nette négative au régime d'oscillateur à impulsion étirée à dispersion nette fortement positive). Le régime d'impulsions brèves est obtenu par la technique du verroui...