Abstract
A sensing head based on two fiber Bragg gratings arranged in a twisted configuration is proposed to measure three parameters simultaneously, namely 1) temperature, 2) strain, and 3) transverse load. One of the gratings is impressed into a high-birefringence fiber that provides two distinct spectral signatures, which, together with the signature of the second grating and the geometric characteristics of the sensing head, enable the degrees of freedom required to achieve the simultaneous measurement functionality. The resolutions achieved with this configuration for the measurement of temperature, strain, and transverse load are +/- 3.1 degrees C, +/- 46 mu epsilon, and +/- 0.01 N/mm, respectively.

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.