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.

Abstract

Abstract
This paper analyzes experimentally the limitations observed in lightwave systems using distributed Raman amplifiers operating under large pump power input conditions. The Brillouin effect is observed as the pump power becomes equal to watt centered in a specific pump wavelength. The presence of Brillouin peaks degrades the system performance. The Raman amplifier is set with singlemode and dispersion compensating fibers and evaluated in a high capacity WDM link at transmission rates up to 40 Gb/s per channel. The dispersion compensation was accomplished by adjusting the length of the dispersion compensating fiber. The system and amplifier characterization were developed in terms of the on-off gain, ripple, optical signal-to-noise ratio, eye diagram and extinction ratio.

Abstract
Long period gratings arc-induced in different types of fibre were annealed at 1000 degrees C for 24 h. During the annealing, the spectrum of the gratings written in Ge-doped fibres shifted towards longer wavelengths whereas an opposite shift was observed for gratings written in Ge-free fibres. A discussion on the mechanisms responsible for that behaviour is presented.

Abstract
Hybrid sol-gel planar optics devices for astronomy are produced for the first time. This material system can operate from the visible (0.5 mu m) up to the edge of astronomical J-band (1.4 mu m). The design, fabrication and characterization results of a coaxial three beam combiner are given as an example. Fringe contrasts above 94% are obtained with a source with spectral bandwidth of 50 nm. These results demonstrate that hybrid sol-gel technology can produce devices with high quality, opening the possibility of rapid prototyping of new designs and concepts for astronomical applications. (C) 2009 Optical Society of America