Abstract
Permanent long-period gratings were written using arc discharges in two aluminosilicate fibers, one of which was doped with erbium. Reversible gratings were also mechanically induced in both fibers. The thermal behavior of the arc-induced gratings was investigated at up to 1100 degrees C. It was found that the shift of the resonant wavelengths exhibited a well-defined linear dependence on temperature up to 700 degrees C. (c) 2005 Optical Society of America.

Abstract
We experimentally study the effect of ionizing radiation on the properties of long-period gratings fabricated in two pure-silica-core fibers with the arc-discharge technique. It is observed that the spectra of the gratings remain almost unchanged after being subjected to doses in excess of 0.5 MGy. The results also show that the gratings' temperature and strain sensitivities are not affected by gamma radiation. (c) 2005 Optical Society of America.

Abstract
Type S thermocouples were assembled in situ by applying high intensity electric are discharges to the contact junction of two platinum (Pt) and Pt-10% rhodium (Pt-10% Rh) wires, inserted on a silica capillary. The electrically insulated thermocouples built in this way were afterwards employed to estimate the temperature of an optical fiber subjected to arc discharges. For typical values of the arc discharge parameters used to arc-induce long-period fiber gratings (electric current I = 9 mA and arc duration t = 1 s), a capillary peak temperature value of 1420 degreesC +/- 400 degreesC was obtained by extrapolation of the experimental data for the limit situation of having a thermocouple with negligible diameter. The temperature profiles in the capillary and in an optical fiber were calculated based on a heat transfer model implemented by a finite element algorithm and fitted to the experimental temperature distribution in the Pt and Pt-10% Rh wires. The correspondent peak temperatures computed for the capillary and for the fiber were 1450 degreesC and 1320 degreesC, respectively. A good agreement between the capillary temperature values determined graphically and numerically was obtained.

Abstract
A fiber-sensing scheme with controlled sensitivity comprising a fiber Bragg grating (FBG) and a mechanically induced long-period fiber grating (MLPFG) is presented. The FBG was written by exposing the fiber to 248-nm UV laser radiation such that the Bragg wavelength is localized on the slope of a resonant band of a mechanical grating, which was produced by winding a nylon string around a fiber/grooved tube set. The strength of that resonant band was altered by applying loads to the MLPFG. For different loads, the FBG was submitted to strain values of up to 2200 mu epsilon, in steps of 200 mu epsilon, during which the Bragg wavelength and the respective transmitted peak power through the MLPFG were recorded. It was demonstrated that by applying a weight with a value of 0.78 kg to the MLPFG, the sensitivity of the FBG interrogation technique to strain variations increased from 2.23 (without load) to 3.20 pW/mu epsilon.

Abstract
A fibre Bragg grating interrogation technique with tunable sensitivity is reported. It relies on the utilization of the edge filtering concept applied to a chirped fibre Bragg grating (CFBG) written in an erbium-doped fibre as the processing element. Through the combination of the optical gain properties of the erbium-doped fibre and of the distributed wavelength reflection characteristics of the CFBG, it is possible to achieve different reading sensitivities and amplification of the remote sensing signal.

Abstract
A full characterization of reversible long-period fibre gratings produced through the wind of a string around a fibre/grooved tube set is presented. This technique enables a good control over the gratings isolation loss-peaks and has high repeatability. The tunability of the resonant wavelengths through the etching of the fibres cladding, prior to perform the gratings, have been investigated. These mechanically induced long-period fibre gratings have shown high sensitivity to loads.