Abstract
We have investigated the sensitivity of arc-induced long-period gratings to changes of ambient refractive index. Two pure-silica-core fibres with different cladding diameters and a standard fibre were used in this study. For a 6 x 10(-3) change of the refractive index, a 240 pm shift of the resonant wavelength was achieved with long-period gratings written in the 125 mu m cladding diameter pure-silica-core fibre.

Abstract
A compact sensor able to discriminate between temperature and strain related effects was implemented. The proposed sensing head comprises a single long-period grating with two sections written consecutively in the SMF-28 fiber, by the electric arc discharge technique, using different fabrication parameters. The sensor performance is based on the distinct temperature and strain sensitivity values presented by two neighbor resonances belonging to each grating section. The temperature and strain resolutions are +/- 0.1 degrees C and +/- 40 mu epsilon, respectively.

Abstract
A new sensing configuration is proposed for simultaneous measurement of strain and temperature that relies on a single long period grating written by the electric arc technique. The underlying principle is the azimuthal asymmetry induced by the electric arc fabrication technique, which results in a device with polarization dependent insertion loss sensitive to both temperature and strain. With the proposed configuration, resolutions of +/- 2.8 degreesC/rootHz and +/- 13.9 muepsilon/rootHz are obtained for temperature and strain measurements, respectively.

Abstract
The radiation emitted by an optical fiber during heating due to an electric arc discharge was detected using a Cronin spectrometer. The fitting of the emission spectrum to the blackbody radiation, allowed the estimation of the temperature range attained by the fiber.

Abstract
In this paper we present and evaluate the spectral response of uniform gratings written in different tapered core sections of single mode fibre. This combination of uniform gratings and tapers leads to three, types of Chirped Fibre Bragg Gratings with different reflection spectra and different mechanical properties. These devices are characterized in function of the applied strain, showing interesting chirp tunability.

Abstract
Incipient fault diagnosis is closely related to insulation condition assessment. A great number of methods are available for condition monitoring and diagnosis of power transformer insulation systems, but only few of them can take direct measurements inside the transformer. Fiber optic sensors can be applied to incipient fault diagnosis. In particular, acoustic sensors have been developed for detection and location of partial discharges in oil-filled power transformers. We report the study of extrinsic and intrinsic fiber Fabry-Perot sensors that can be used to detect the acoustic waves that are generated by a partial discharge inside a power transformer. A comparative analysis is done to determine the best sensing head configuration and some methods to improve the parameter readout sensitivity are proposed. The sensing head behaviour when immersed in different fluids (air, water, and oil) is also investigated. (c) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3080752]