Damien Kinet

Fiber Bragg grating sensors toward structural health monitoring in composite materials: challenges and solutions.

Nowadays, smart composite materials embed miniaturized sensors for structural health monitoring (SHM) in order to mitigate the risk of failure due to an overload or to unwanted inhomogeneity resulting from the fabrication process. Optical fiber sensors, and more particularly fiber Bragg grating (FBG) sensors, outperform traditional sensor technologies, as they are lightweight, small in size and offer convenient multiplexing capabilities with remote operation. They have thus been extensively associated to composite materials to study their behavior for further SHM purposes. This paper reviews the main challenges arising from the use of FBGs in composite materials. The focus will be made on issues related to temperature-strain discrimination, demodulation of the amplitude spectrum during and after the curing process as well as connection between the embedded optical fibers and the surroundings. The main strategies developed in each of these three topics will be summarized and compared, demonstrating the large progress that has been made in this field in the past few years.

Optical Fiber Sensors Embedded Into Medical Textiles for Healthcare Monitoring

The potential impact of optical fiber sensors embedded into medical textiles for the monitoring of respiratory movements in a magnetic resonance imaging environment is presented. We report on three different designs, all textile based: a macrobending sensor, a Bragg grating sensor, and a time reflectometry sensor. In all three cases, the sensing principle is based on the measure of the elongation of the abdominal circumference during breathing movements. We demonstrate that the three sensors can successfully sense textile elongations between 0% and 3%, while maintaining the stretching properties of the textile substrates for a good comfort of the patients.

Medical Textiles With Embedded Fiber Optic Sensors for Monitoring of Respiratory Movement

For patients under Magnetic Resonance Imaging (MRI) spontaneous respiration is constantly at risk of being impaired by anesthetic drugs or by upper airway obstruction. Therefore, continuous monitoring of the breathing activity is needed to assess adequate ventilation or to detect specific obstruction patterns. The paper describes three MRI compatible respiration sensors based on pure optical technologies developed within the EU FP6 project OFSETH. The sensors are based on fiber Bragg gratings, optical time-domain reflectometry and macrobending effects. The developed smart medical textiles can sense elongation up to 3% while maintaining the stretching properties of the textile substrates for patients comfort. The OFSETH harness allows a continuous measurement of abdominal and thoracic respiration movement while all vitals organs are free for medical staff actions. The sensors were tested in MRI environment and on healthy adults.

Femtosecond-laser-induced highly birefringent Bragg gratings in standard optical fiber

We report highly birefringent fiber Bragg gratings in standard single-mode optical fiber realized with UV femtosecond pulses and line-by-line inscription. By controlling the three-dimensional positioning of the focused laser beam with respect to the fiber core, we achieve very high birefringence at the grating location in a single exposure. A maximum birefringence value of 7.93×10(-4) has been reached for 10th-order gratings when using 2 μJ pulses, which is to our knowledge the highest birefringence value reported so far. This birefringence results from UV-induced high-densification lines shifted from the center of the core, increasing the asymmetry of the induced-stress lines. With a Bragg wavelength spacing reaching more than 800 pm between polarization modes, such gratings are particularly well suited for selective filtering or, as demonstrated here, for temperature-insensitive transverse-strain measurements.

All-normal dispersion, all-fibered PM laser mode-locked by SESAM

We report a PM all-normal, all-in-fiber passively mode-locked laser operating at 1030 nm. The main pulse shaping mechanism is provided by a tilted chirped-FBG. The laser delivers nanojoule range highly chirped pulses at a repetition rate of about 40 MHz. The FWHM of the optical spectrum is up to 7.8 nm leading to sub-500 fs compressed optical pulses. The influence of the filtering bandwidth and the output coupling ratio has been investigated.

Review of Trackside Monitoring Solutions: From Strain Gages to Optical Fibre Sensors

A review of recent research on structural monitoring in railway industry is proposed in this paper, with a special focus on stress-based solutions. After a brief analysis of the mechanical behaviour of ballasted railway tracks, an overview of the most common monitoring techniques is presented. A special attention is paid on strain gages and accelerometers for which the accurate mounting position on the track is requisite. These types of solution are then compared to another modern approach based on the use of optical fibres. Besides, an in-depth discussion is made on the evolution of numerical models that investigate the interaction between railway vehicles and tracks. These models are used to validate experimental devices and to predict the best location(s) of the sensors. It is hoped that this review article will stimulate further research activities in this continuously expanding field.

OFSETH: Smart medical textile for continuous monitoring of respiratory motions under magnetic resonance imaging

The potential impact of optical fiber sensors embedded into medical textiles for the continuous monitoring of the patient during Magnetic Resonance Imaging is presented. We report on two pure optical sensing technologies for respiratory movements monitoring – a macro bending sensor and a Bragg grating sensor, designed to measure the elongation due to abdominal and thoracic motions during breathing. We demonstrate that the two sensors can successfully sense textile elongation between, 0% and 3%, while maintaining the stretching properties of the textile substrates for a good comfort of the patient.

Optical fibre sensors embedded into technical textile for a continuous monitoring of patients under Magnetic Resonance Imaging

The potential impact of optical fiber sensors embedded into medical textiles for the continuous monitoring of the patient during Magnetic Resonance Imaging (MRI) is presented. In that way, we report on several pure optical sensing technologies for pulse oximetry and respiratory movements monitoring. The technique for pulse oximetry measurement is known as NIRS (Near Infra-Red Spectroscopy) in a reflectance mode. On the other hand, we tested two different optical based designs for the respiratory motions measurements - a macro bending sensor and a Bragg grating sensor, designed to measure the elongation of thoracic and abdominal circumferences during breathing.

Surface plasmon resonance in eccentric femtosecond-laser-induced fiber Bragg gratings

Highly localized refractive index modulations are photo-written in the core of pure silica fiber using point-by-point focused UV femtosecond pulses. These specific gratings exhibit a comb-like transmitted amplitude spectrum, with polarization-dependent narrowband cladding mode resonances. In this work, eccentric gratings are surrounded by a gold sheath, allowing the excitation of surface plasmon polaritons (SPP) for radially-polarized light modes. The spectral response is studied as a function of the surrounding refractive index and a maximum sensitivity of 50  nm/RIU (refractive index unit) is reported for a well-defined cladding-mode resonance among the spectral comb. This novel kind of plasmonic fiber grating sensor offers rapidity of production, design flexibility, and high temperature stability.

Smart Textile Embedding Optical Fibre Sensors for Healthcare Monitoring during MRI

The potential impact of optical fibre sensors embedded into medical textiles for the continuous monitoring of the patient during Magnetic Resonance Imaging (MRI) is presented. In that way, we report on several pure optical sensing technologies for pulse oximetry and respiratory movements monitoring. The technique for pulse oximetry measurement is known as NIRS (Near Infra-Red Spectroscopy) in a reflectance mode. In parallel, we tested two different optical sensor based fabric designs breathing activity detection – a macro bending sensor and a fibre Bragg grating sensor consisting in respiratory frequency measurement by intensity variation detection and optical spectral analysis.