Abstract
An optical fibre sensor for determination of acetic acid is presented. The sensing probe is based on a fibre Bragg grating (FBG) Fabry-Perot cavity, coated with a thin film of sol-gel-PVP (polyvinylpyrrolidone) composite material. The polymeric thin film renders the interferometric output sensitive to the presence of carboxylic acid species. Results show that the wavelength of the interferometric peaks changes with acetic acid concentration, enabling its quantification. Coupling the fibre probe with a serrodyne modulated readout interferometer enables pseudo-heterodyne interrogation and the detection of acetic acid with a sensitivity of 92.6 deg/% L/L and a resolution of 0.2% L/L. The results demonstrate the potential of the proposed scheme to operate as a sensitive chemical sensor platform.

Abstract
Fiber Bragg grating (FBG) arrays in pure silica four-leaf-clover-shaped suspended core fibers were inscribed with two-beam interference and a deep UV femtosecond laser source. The target fibers are pure silica and do not contain any dopants, nor were they treated with hydrogen before grating inscription. The inscription method is appropriate to measure the effective mode field index of the fiber and allows confinement factors of the guided modes to be derived. Applications of such FBGs can be expected especially for fiber sensing.

Abstract
An interferometric setup for measuring Polarization Mode Dispersion (PMD) setup was tested. Using a low-coherence technique with a Michelson interferometer, it was possible to measure values of PMD from detected Differential Group Delay (DGD) values in two reels. The low-coherence source bounds the minimum value of DGD detected to 0.13 ps, leading to a minimum value detected around 0.14 ps. The mean value of PMD measured over a period of several days for one reel was 0.0405 +/- 0.0007 ps/km(1/2), and 0.0463 +/- 0.0044 ps/km(1/2) for the other. Stochastic and random behavior of PMD was observed.

Abstract
The aim of this work was the study and understanding of the behavior and linearity of an optical fiber Bragg grating (FBG) sensor embedded in bone cement. Test its ability to monitor strains inside bone cement during different mechanical tests, at real-time. Bone cement is a biomaterials based on polymethacrylate used as fixation method in artificial joints. Work as a bonding, load transfer and optimal Stress/strain distribution inside the complex human body environment, Bone cement is the weakest element in a joint implant, being considered the main reason of prosthesis loosening. Inside the bone cement, its temperature, longitudinal strain and load were measured using fiber Bragg gratings. All the measurements report a linear response showing a good adaptation and optimization of the load transfer between the biomaterial and the embedded optical sensor.

Abstract
Welding process monitoring using fibre Bragg grating (FBG) sensor technology is a promising technique to measure temperature and strain during the fabrication process. Examples of FBG sensor based temperature and strain measurements in butt-welding of plates are presented in this paper. In order to be able to measure strain and/or temperature it is however necessary to calibrate these instruments for accurate measurement results. In the present work calibration for strain measurements at constant temperature using a four point bending test is performed. This type of mechanical test allows enough space for instrumentation between the inner rollers. A finite element model is made using Abaqus for comparison and strain gauges are used for calibration purposes. Temperature calibration was carried out using an oven. The FBG sensors' measurements were calibrated with data obtained by thermocouples. Tests on welds are presented and the possible impact of this monitoring technology is briefly discussed in the light of process optimization and subsequent structural health monitoring. © AES-Advanced Engineering Solutions.

Abstract
In the present paper, the influence of the fiber Bragg grating (FBG) length and its coating on embedded FBGs in polymers is evaluated. Different FBG lengths and coatings, uncoated and acrylate-recoated, are used. The evolution of their spectra is also followed during laminate curing on a hot-plate press. The Bragg gratings are used as optical fiber sensors, and their sensitivity and reliability are analyzed. The resulting sensor signal characteristics and the strain answers to different loading modes, i.e. tensile, flexural and through-thickness compression, are also studied.