Abstract
An optical fiber sensing system, for monitoring oxygen aiming in vivo nuclear magnetic resonance (NMR) applications is presented. Oxygen detection is based on the dynamic quenching of the fluorescence of a ruthenium complex trapped in the porous structure of a sol-gel silica film. Oxygen concentration is determined by phase-modulation fluorometry. Preliminary results concerning the characterization of doped sol-gel thin films deposited by dip coating in glass slides and in optical fiber probes are presented. Four different probe configurations are tested and compared. Best results are obtained with a fiber taper configuration which shows reproducibility and best excitation efficiency. This structure is fully characterized and some considerations regarding optimal fiber optical sensing probes for 02 detection are addressed.

Abstract
A novel Mach-Zehnder interferometer based on a fibre multimode interference structure combined with a long period fibre grating is proposed. The multimode interference is achieved through the use of a multimode fibre section splices between two sin-le-mode fibres, with a length adjusted to couple a fraction of light into the cladding modes. A LP placed after the multimode fibre couples light back into the fibre core completing the Mach-Zehnder interferometer. The novel configuration was demonstrated as a bending sensor.

Abstract
In this work, an LPG-based Mach-Zehnder interferometer was evaluated as a sensing structure for environmental refractive index measurement. To interrogate this sensing device, coherence addressing and pseudo-heterodyne processing were used. The impact of stretching, bending and twisting the interferometer on the sensitivity to refractive index changes r was studied. It is shown that, due to the antisymmetric nature of cladding modes in arc-induced LPGs, it is possible to tune the system sensitivity by simple mechanical action.

Abstract
It is described a fibre optic sensor for liquid refractive index measurement based on the visibility variations of a Fabry-Perot interferometer with interfering waves generated in a short Bragg grating and in the fibre tip (Fresnel reflection) in contact with the liquid. The sensor was characterized emerging the fibre tip in distilled water with different concentrations of ethylene glycol. A linear relation was obtained, with a readout resolution of similar to 10(-3). It was also observed that the temperature direct cross sensitivity is residual.

Abstract
In this work it is presented a novel in-fibre modal interferometer based on a non-adiabatic biconical fused taper that couples light between the cladding and the core, combined with the Fresnel reflection at the fibre end. It is observed that the returned liaht from this fibre structure shows a channelled spectrum similar to that of a two-wave Michelson interferometer. The application of this device as a fibre optic flowmeter sensor is demonstrated.

Abstract
A long-period grating written in the SMF-28 fiber was heat treated at 1000 degrees C for 15 days. The spectrum of the grating shifted to longer wavelengths and the amplitude of the cladding mode resonances decreased as a result of structural relaxation. The background loss increased considerably for time longer than 200 h, and this loss is caused by devitrification of the fiber.