Formation of Bragg gratings in pristine SMF-28e fibre using cw 244-nm Ar+-laser

The formation of short Bragg gratings in SMF-28e non-hydrogen loaded pristine fibre using a cw Ar+ laser operating at 244 nm is reported. Mean refractive index changes >10-3 were obtained for a laser intensity of about 513 W/cm2 and a total dose of 5.9 MJ/cm2. Strong stress changes indicate a contribution of compaction to the refractive index change

An experimental-numerical investigation of hydrothermal response in adhesively bonded composite structures

Water absorption and thermal response of adhesive composite joints were investigated by measurements and numerical simulations. Water diffusivity, saturation, swelling, and thermal expansion of the constituent materials and the joint were obtained from gravimetric experiments and strain measurements using embedded fiber Bragg grating (FBG) sensors. The mechanical response of these materials at different temperatures and water content was characterized by dynamic mechanical analysis. Thermal loading and water absorption in joint specimens were detected by monitoring the FBG wavelength shift caused by thermal expansion or water swelling. The measured parameters were used in finite element models to simulate the response of the embedded sensor. The good correlation of experimental data and simulations confirmed that the change in FBG wavelength could be accurately related to the thermal load or water absorption process. The suitability of the embedded FBG sensors for monitoring of water uptake in adhesive composite joints was demonstrated. (C) 2015 Elsevier Ltd. All rights reserved

Monitoring strain gradients in adhesive composite joints by embedded fiber Bragg grating sensors

The adhesive bonding of composite materials can be applied to assemble light-weight structures for aeronautical applications. However, the application of adhesive bonds in primary load-bearing structures is limited by the lack of adequate techniques to monitor the quality of the joint during service. This work evaluates the feasibility of using Fiber Bragg Grating (FBG) arrays to monitor the distribution of strains developed along the bonded region in single lap shear specimens. Three different positions for the FBGs were both experimentally and numerically studied namely in the first ply, at the composite/adhesive interface, and in the adhesive. The mechanical performance of the joint was not modified due to the embedding of the optical fiber at the different positions. The simulations and the measurements showed good agreement for the three positions. The optical sensor placed at the composite/adhesive interface captured the strongest strain gradient. (C) 2014 Elsevier Ltd. All rights reserved

Fabrication of Bragg gratings in microstructured and step index Bi-SiO2 optical fibers using an ArF laser

An ArF excimer laser was used to fabricate Bragg gratings in fibers with Bi-SiO2 core and microstructured or F-doped claddings without fiber presensitization. Average and modulated refractive index changes of 2.7 x 10(-4) and 1.0 x 10(-4) were induced in pristine microstructured fiber while 1.0 x 10(-4) and 0.7 x 10(-4) were observed in the F-doped-cladding fiber. Fiber luminescence was also measured under 1064 nm pumping for both fibers. Photosensitivity and luminescence were compared to a Bi-Al2O3-SiO2 core optical fiber. (c) 2012 Optical Society of Americ