Conventional analytical instruments for detecting biochemical and biological species are often expensive, complex and voluminous. Research efforts have to be made to develop simple and compact devices to provide complementary solutions to traditional analytical techniques. These biosensors must interface between the physical, chemical and biological environments by combining molecular recognition elements with a detection transducer.
This study relies on an innovative approach called Lab-Around-Fiber. This method consists in biofunctionalizing silica optical fibers by grafting antibodies onto their external surface, resulting in the specific capture of biological targets of interest. The optical fiber sensor, in our case a fiber Bragg grating, acts as a transducer converting the biochemical signal into an optical signal; the functional layer (gold nanoparticle and antibodies) grafted onto the fiber surface serves as a bioreceptor; collectively forming the integrated sensor. Its proper functioning and sensitivity enable the detection of target biomolecules binding, such as those associated with Antimicrobial resistance.
Fiber Bragg gratings are widely used for optical sensing applications, including their deployment in harsh environments. The use of Type III femtosecond gratings shows a prominent interest due to their ability to withstand very high temperatures (over 1000°C for 100’s of hours). These Type III fiber Bragg gratings correspond to a periodic structure of micro-voids generated by femtosecond-laser in silica-based optical fibers, fabricated by the point-by-point technique. The physicochemical characteristics of the micro-voids were investigated by quantitative phase microscopy technique and their thermal stability monitored through isochronal annealing experiments up to 1250°C.
A fiber Bragg grating has been inscribed in a 100-µm diameter sapphire optical fiber with the phase mask technique and a fs-laser emitting at 800 nm. The grating was placed inside a sealed alumina capillary to protect the fiber from the environment. Then the fiber was set inside an oven and cycled up 7 times to a maximum temperature of 1500°C during 2 h. We observed that after two cycles, the grating is stabilized and no more hysteresis on the Bragg wavelength is observed. However, the temperature uncertainty is as high as 15°C and is principally due to modal interference. Then the grating is submitted to a 3-day annealing and two annealing successive 4-day annealing – for a total of eleven days – at a temperature of 1500°C. During this treatment, the grating amplitude remained constant and the Bragg wavelength showed no significant drift. As a conclusion, the packaged grating did not exhibit any erasure during these annealing experiments and perform reliable temperature measurement up to 1500°C.
Pairs of arrays of point-by-point fiber Bragg Gratings written with a femtosecond laser were anchored with K-type thermocouple within an asymmetrical titanium substrate. Three anchoring methods were used, including silica based, graphite based glue commercially available as well as Yttria Stabilized Zirconia deposited by Atmospheric Plasma Spraying. The optical fibers were first recoated with an inorganic coating, specifically developed to resist to high temperatures above 800°C. The titanium plate was exposed to an intense heat flow delivered by tungsten halogen lamps to reach temperature of around 800°C. High temperature and strain measurements was performed in situ with a relative error of less than 10% at 800°C.
We investigate the behavior and stability of fiber Bragg gratings written by femtosecond laser pulses in Ge-doped fused silica optical fibers, using both the phase mask and point-by-point techniques, during their annealing at 1200°C for 30 min and subsequent aging at 1000°C during 43 hours. Bragg wavelength drifts and reflected peak amplitude variations were shown to drastically differ depending on the writing scheme and thermal history. Particularly, we show that amplitude decay of point-by-point gratings at 1200°C may be easily mitigated by tuning the writing pulse energy. Future work may be pursued in order to finely unravel the high temperature mechanisms regarding the stability of fs-written fiber Bragg gratings used as temperature sensors in order to improve measurement stability and accuracy.
Femtosecond laser point-by-point writing is a commonly used method for fabrication of Fiber Bragg Grating sensors dedicated to harsh environments, such as high temperature or irradiation. In addition, a femtosecond laser platform allows for inscription of compact fiber optic diffraction gratings that consist of micro-voids or filaments formed into the fiber core and cladding by focusing laser pulses using microscope objectives. Light propagating in the fiber is coupled to radiation modes due to Mie scattering, thus providing wavelength dispersion in free space. Chirping the grating period further allows focusing of the outcoupled light in a given plane. Such an all-fiber focusing grating forms a compact photonic device permitting its use for FBG sensor interrogation. In this paper, fabrication of such spectrometers operating at 850 and 1550 nanometers is described. A characterization setup allowing measurements of spectra of FBGs at those wavelength bands is presented, and results corresponding to various focusing distances, grating lengths and chosen microscope objectives are exposed. Azimuthal distribution of scattered light is discussed, as well as focusing distance versus grating period chirp and spectrometer resolution versus grating length. Finally, spectra reflected by pointby- point FBG sensors are presented, thus demonstrating the great potential interest of such gratings for FBG interrogation.
Fiber Bragg Grating (FBG) sensors offer multiple benefits in comparison with electronic sensors due to their compactness, electromagnetic immunity as well as their resistance to harsh environments and their multiplexing capabilities. Structural Health Monitoring (SHM) is one of the various potential industrial applications that could take full advantage of those sensors. However, there is a need for a low size, weight, power and cost interrogation unit for certain application areas such as aerospace or aeronautics. That is the reason why recent efforts have been made to use integrated components and circuits for interrogation of FBGs. Among different techniques, interrogation with a swept laser source is of high interest since it has a high multiplexing capability and could reach a high level of integration using other integrated components such as photodetectors, grating couplers or directional couplers to form a compact interrogation unit. In this paper, we present characterization results of a fully-packaged hybrid III-V on silicon tunable laser diode operating in the C and L bands. Wavelength maps are produced and analyzed and modulation of emitted wavelength is discussed. Preliminary results corresponding to a moderate frequency (10-Hz sweep rate) were obtained and FBG reflection spectra acquired with a broadband source (BBS) and a swept laser diode are compared. Finally, we discuss potential design improvements in order to reach high scan rates (< 10 kHz) and a large tuning range
Fiber Bragg gratings can be used to monitor temperature or strain in harsh environments. We investigate the effect of Xrays on type III gratings – also called void gratings –which are known for their capacity to withstand high temperatures. The tested gratings are inscribed in a SMF28 germanosilicate optical fiber using the point-by-point method and a frequency-doubled Yb femtosecond laser emitting at 515 nm. The tested FBGs are separated in two groups depending on their reflectivity levels (Low/High). Half of each group is pre-annealed at a temperature of 750°C during 30 min. We have irradiated all the gratings up to 100 kGy(SiO2) at a dose-rate of 10 Gy/s at two different irradiation temperatures: 25°C and 150°C. For all the irradiations, the grating radiation response is identical independently of the chosen writing and preannealing conditions. When the irradiation is performed at 25°C, a Bragg wavelength shift of 10 pm is observed for all the gratings, which represents an error of less than 1°C at the total dose of 100 kGy while at 150°C the Bragg peak shift only of less than 4 pm corresponding to an error of 0.3°C.
We investigated the Bragg Wavelength Shift (BWS) induced by X-rays in a large set of conventional FBGs up to 100kGy dose. Obtained results give some insights on the influence of irradiation parameters such as dose, dose rate as well as the impact of some writing process parameters such as thermal treatment or acrylate recoating on the FBG radiation tolerance.
This paper presents the development of a CO2 laser-based heating system to simulate fast thermal phenomena on high temperature resistant FBGs dedicated to high temperature profiles monitoring within components exposed to hot plasma inside Tokamak.. We have demonstrated the reliability of two optical fiber based sensing techniques to control spatial and temporal annealing measurement during high and fast thermal process.
KEYWORDS: Temperature metrology, High temperature raman spectroscopy, Environmental sensing, Raman spectroscopy, Fiber optics sensors, Coating, Signal attenuation, Raman scattering, Temperature sensors, Fiber coatings, Temperature metrology, High temperature raman spectroscopy, Environmental monitoring, Optical fibers, Gold, Photodiodes, Fiber optics tests
Optical fiber temperature sensors using Raman effect are a promising technology for temperature mapping of nuclear power plant pipes. These pipes are exposed to high temperature (350 °C) and gamma radiations, which is a harsh environment for standard telecom fibers. Therefore metal coated fibers are to be used to perform measurement over 300 °C. Temperature variations can affect the attenuation of the metallic coated fiber before irradiation. The latter induces an extra attenuation, due to light absorption along the fiber by radiation-induced defects. The recombination of these defects can be strongly accelerated by the high temperature value. As backscattered Raman signal is weak it is important to test optical fibers under irradiation to observe how it gets attenuated. Different experiments are described in this conference paper: two in situ irradiation campaigns with different dose rates at, both ambient and high temperature. We observe that the tested off-the-shelf metallic coated fibers have a high attenuation under irradiation. We also noticed the fact that thermal annealing plays a massive role in the +300 °C temperature range.
For the first time, a gold coated single mode optical fiber has been used to detect a liquid sodium leakage on a pipe of secondary circuit pipe mock-up of nuclear fast reactor (Gen IV) by means of Optical Frequency Domain Reflectometry-based on Rayleigh backscattering. During 150 min of the experiment we were able to detect and monitor the evolution of a liquid sodium leakage on the surface of the pipe.
The regeneration of Tilted Fiber Bragg Gratings photowritten in a singlemode SMF-28e fiber is investigated. Three tilted FBGs, with respectively 0°, 4° and 8° external tilt angles are annealed according to a conventional high temperature regeneration protocol. We monitor the evolution of distinct spectral features during the thermal annealing process. We also propose a method in order to follow the regeneration process of tilted FBG, without focusing on individual spectral resonances. Regeneration of tilted FBGs presents numerous interests for the realization of high temperature sensors and devices, but also to improve their resistance to preliminary manufacturing processes requiring high temperature steps.
Safety must always prevail in Nuclear Power Plants (NPPs), as shown at Fukushima-Daiichi. So, innovations are clearly needed to strengthen instrumentations, which went inoperative during this nuclear accident as a consequence of power supply losses. Possible improvements concern materials and structures, which may be remotely monitored thanks to Optical Fiber Sensors (OFS). We detail topics involving OFS helpful for monitoring, in nominal conditions as well as during a severe accident. They include distributed sensing (Rayleigh, Raman, Brillouin) for both temperature sensing and structure monitoring as well as H2 concentration and ionizing radiation monitoring. For future plants, Fiber Bragg Grating (FBG) sensors are considered up to high temperature for sodium-cooled fast reactor monitoring. These applications can benefit from fiber advantages: sensor multiplexing, multi-km range, no risk-to-people, no common failure mode with other technologies, remote sensing, and the ability to operate in case of power supply lost in the NPP.
Regenerated Fiber Bragg Gratings have been annealed at high temperatures up to 890°C during 9000 hours in continuous. This test has been conducted in order to experimentally assess the long-term stability of regenerated FBGs dedicated to measurements in high temperature environments. The evolution of both reflectivities and Bragg wavelengths of four wavelength-multiplexed regenerated FBGs simultaneously annealed at respectively 760°C, 810°C, 850°C and 890°C is reported.
Following the pioneering work of the Lawrence Livermore National Laboratory, Chirped Fiber Bragg Gratings are investigated as in situ, real-time, wavelength-position discriminators for measuring detonation speeds inside explosives.
High temperature gradient of a conventional tubular furnace is characterized using a single fiber sensing line with
wavelength-multiplexed short-length regenerated Fiber Bragg Gratings. The multiplexed gratings are simultaneously
regenerated using a high temperature annealing process. Temperature calibration from ambient temperature up to 850°C
is conducted leading to a standard deviation of 0.33°C after polynomial fitting of the wavelength shift with temperature.
Current collection is a key issue in modern electrical railway, and its performances are mainly determined by the
pantograph/catenary interactions. Whilst being the less investigated topic, the pantograph/catenary mechanical interface
is the most crucial one. Many incidents and traffic interruptions are due to degraded, or even damaged, electrical contacts
between current collectors and contact wires. During the 6th European Framework Program (FP6) CATIEMON project
(CATenary InterfacE MONitoring), both FBG-based sensors and systems dedicated to the pantograph/catenary
interaction monitoring - directly from the high voltage contact wire - have been developed and tested. This paper
describes their design and installation but also results coming from field-tests. It highlights their advantages for the
railway stakeholders and end-users in term of train operation enhancement.
We present a study aimed at developing fibre-optic-based biosensors for the specific detection of biological species.
These sensors rely on the combined use of a Tilted short period Fibre Bragg Grating that detects changes in the refractive
index of the surrounding solution and of an electrostatic self-assembly technique: self-assembled polyelectrolyte layers
and immobilization of the sensor protein on the fibre surface were used for sensor fabrication. We observed changes in
the sensor's spectrum induced by specific binding and we imaged fibre surface with atomic force microscopy (AFM).
The results show the feasibility of the sensor for various biological or chemical applications.
The thermal drift of the characteristic wavelength of a Fiber Bragg Grating photowritten in the core of an 18-hole-microstructured
fiber is significantly reduced by inserting a liquid of suitable refractive index into its holes. The
maximum sensitivity is reduced, and the spectral range of variations is divided by a factor of 8, over a temperature range
larger than 20°C. Such passive FBG temperature compensation technique is of great interest for applications involving
accurate sensing free of thermal effects.
A wavelength tunable erbium-doped fiber ring laser dedicated to high-speed interrogation of Fiber Bragg Grating (FBG) sensors has been realised and characterized. A standard FBG is used as the output mirror whereas an intra cavity spectral filter formed by a π-phase-shifted FBG is implemented to narrow the output laser spectrum down to 0.5 pm. The emitting wavelength is tuned at 500 Hz over 3.6 nm by simultaneously straining both the standard and π-phase-shifted FBG with a piezoelectric actuator. An all-fiber Michelson interferometer is used to accurately determine the spectral scanning range. Bragg wavelength increments equal to 1.3 pm are resolved combining both wavelength referencing with an absorption gas cell and amplitude normalisation versus the laser output power. This instrumentation is designed to be embedded in a train cabin for making on-board strain and temperature measurements on pantographs with FBG sensors.
In this paper we present results relative to Fiber Bragg Grating (FBG) photowritten in two kinds of Ge-doped microstructured optical fiber cores devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of spectral sensitivity of Bragg grating in relation to the refractive index of the substance inserted into the holes.
The propagation properties of microstructured optical fibers useful for sensing applications are reviewed. The interaction between light and sample can reach 95 % in singlemode hollow core fibers and examples of structures exhibiting such large overlap ratios are described. The generation of 300 nm and 700 nm flat continua of visible and IR light in a single highly nonlinear holey fiber, well suited for the detection of biological species by spectroscopy, is reported. The low temperature sensitivity of long period gratings and of the birefringence in holey fibers is attractive for sensors operating in varying environmental conditions.
We investigate the changes in transmission spectra of Long Period Gratings and Slanted FBGs versus the refractive index of the surrounding medium. The metrological characteristics of Slanted FBGs and an analytical method enabling their potential use in accurate refractometry are discussed.
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