Abstract
Singlemode-multimode-singlemode fiber structures (SMS) based on distinct sections of a pure silica multimode fiber (coreless-MMF) with diameters of 125 and 55 mu m, were reported for the measurement of curvature and temperature. The sensing concept relies on the multimode interference that occurs in the coreless-MMF section and, in accordance with the length of the MMF section used, two fiber devices were developed: one based on a bandpass filter (self-image effect) and the other on a band-rejection filter. Maximum sensitivities of 64.7 nm.m and 13.08 pm/degrees C could be attained, for curvature and temperature, respectively, using the band-rejection filter with 55 mu m-MMF diameter. A proof of concept was also explored for the simultaneous measurement of curvature and temperature by means of the matrix method.

Abstract
A fibre Bragg grating structure arranged in a twisted configuration is proposed for sensing applications. The characteristics of the sensing head for measuring temperature, longitudinal strain and transverse load are analysed. It is shown that this configuration is particularly applicable for transverse load measurement. In this case a resolution of 0.002 N mm(-1)Hz(-1/2) was achieved.

Abstract
This work describes a fiber optic sensing structure that is sensitive to curvature, and features a low temperature-and strain cross-sensitivity. It is based on multimode interference, and relies on a singlemode-step index multimode-singlemode fiber structure. It was observed that the transmitted optical power in such a layout is highly sensitive to the wavelength of operation, and to the length of the multimode fiber. The optical spectrum exhibits two dominant loss bands, at wavelengths that have similar responses both to temperature and strain, but different responses to curvature. Based on this result, an interrogation approach is proposed that permits substantial sensitivity to curvature (8.7 +/- 0.1 nm m) and residual sensitivities to temperature and strain (0.3 +/- 0.1 pm degrees C(-1) and (-0.06 +/- 0.01) x 10(-6) m m(-1), respectively). The beam-propagation method was employed for modeling the propagation of light along the optical fiber sensing device proposed.

Abstract
A robust all-fibre interferometric interrogation technique based on the wavelength modulation of a pi-shifted fibre Bragg grating is proposed. The concept is demonstrated for strain measurement using a Bragg-grating-based Fabry-Perot interferometer. The strain-phase relationship is shown to be linear with a sensitivity slope of (2.19 +/- 0.02)degrees/mu epsilon. A strain resolution of approximate to 2.4 mu e is demonstrated.

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.