Abstract
This work shows the changes of bending curvature sensitivity when the same long- period fibre grating has different phase shifts. From the knowledge that the coupling constant is reduced as curvature increases, we theoretically and experimentally assess the possibility that the bend sensitivity follows the grating spectrum evolution during the point- to-point fabrication technique. We also show that control of bend sensitivity can be applied to the simultaneous measurement of bend and temperature.

Abstract
We used a pair of Bragg gratings written in high birefringence fibre optics to measure, simultaneously, longitudinal and transverse strain and temperature. The Bragg gratings are superimposed in the same position of the fibre optic, so as to behave as a punctual sensor. The sensitivity of the spectral response of the device to longitudinal strain, transverse strain and temperature are all characterized, and the results of its application as a three-parameter sensor are also presented.

Abstract
Fiber structures based on the combination of abrupt tapers and fiber Bragg gratings are studied. Two situations are exploredin one, the taper is fabricated in the fiber region with a fiber Bragg grating; in the other, the taper is first fabricated followed by the fiber Bragg grating. It is shown that the first device presents the properties of a Fabry-Perot cavity and the other of a phase-shifted Bragg grating, where the phase shift is associated to the tapered fiber region. The sensing characteristics of these structures are studied, and it is shown that the temperature sensitivities are similar but with observable different responses to strain.

Abstract
A reflective multimode interference based-fiber optic sensor is described, aimed at measuring refractive index variations by means of intensity variation based on the fiber tip-interaction concept. The sensing head is a section of a multimode fiber, spliced to a single-mode fiber at the input end; its characteristics are studied when two multimode fibers, with distinct core diameters (viz. 50 and 105 mu m), are considered. The multimode fiber end face is placed in contact with the liquid sample, so as to provide a refractive index measurement via variation in amplitude of the interference spectral peaks - which is essentially insensitive to temperature changes. Therefore, the proposed configuration permits measurement of refractive index variations free from system temperature cross-sensitivity effects. Resolutions of 2.2 x 10(-4) RIU and 3.8 x 10(-4) RIU, for multimode fiber tips with core diameters of 50 mu m and 105 mu m, respectively, could be achieved.

Abstract
In this work, two all-fiber interferometric configurations based on suspended core fibers (SCF) are investigated. A Fabry-Perot cavity (FPC) made of SCF spliced in-between segments of single-mode and hollow-core fiber is proposed. The interferometric signals are generated by the refractive-index mismatches between the two fibers in the splice region and at the end of the suspended-core fiber. An alternative sensing head configuration formed by the insertion of a length of SCF as a birefringence element in a Sagnac loop interferometer is also demonstrated. In this structure, the interferometric signals are generated by interfering two counter propagating beams with different polarization states which propagate through a length of SCF as a birefringence element. The sensitivity to pressure and temperature was determined for both configurations. The results show that the pressure sensitivities are -4.68 x 10(-5) nm/psi and 0.032 nm/psi for FPC and Sagnac loop interferometers, respectively. The temperature sensitivity of both structures has been obtained and the results have been discussed.

Abstract
In this study an optical fibre sensor system was conceived for simultaneous detection of the strain and the acoustic emission due to damage. It consists of a fibre Bragg grating and a Fabry-Perot interferometer. For the interrogation of the Fabry-Perot cavity, an innovative low cost process based on the generation of two quadrature phase-shifted signals using two fibre Bragg gratings was implemented, allowing the recovery of the change in the cavity length. An automated processing system, based on Kohonen's self-organizing maps is also presented, for future classification of the acoustic emission waves detected by the optic fibre sensor.