Abstract
This work describes a large-core air-clad photonic crystal fibre-based sensing structure that is sensitive to refractive index, temperature and strain. The sensing head is based on multimodal interference, and relies on a single mode - large-core air-clad photonic crystal fibre - single mode fibre configuration. Using two distinct large-core air-clad PCF geometries it is possible to obtain an optical spectrum with two dominant loss bands, at wavelengths that have different sensitivities to physical parameters. This characteristic is explored to demonstrate a sensing head that permits the strain-temperature discrimination functionality. It is also shown the large-core air-clad photonic crystal fibre can be applied to implement a sensing head sensitive to the water refractive index changes induced by temperature variations.

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
Optical fibre sensors for Hydrogen detection at low concentrations has become a growing research area using Palladium as an active medium. Palladium is widely used in hydrogen sensing as it show a high and selective affinity for hydrogen. This metal is capable to absorb hydrogen up to 900 times its own volume which permits that during the expansion mechanical forces are applied in the fibre modifying the optical response. Several optical fibre hydrogen sensor heads coated with Palladium are presented and compared using different working principles: interferometric, intensity and fiber grating-based sensors. These principles were applied in Fabry-Perot cavities, fibre Bragg gratings written in fibre SMF28 with etching in the cladding, multimode interferometers and fibre end micro-mirrors. Palladium thin film coatings over the fibre surface and with thicknesses from 10nm to 350nm were produced by using the sputtering RF technique. These studies were performed in a Hydrogen/Nitrogen atmosphere with Hydrogen concentrations from 0% to 4% (lower limit explosion). The Bragg grating inscribed in a fibre with reduced cladding diameter appears to be one of the best approaches for a fibre optic sensing head for Hydrogen detection. Future work will continue the investigation of other fibre optic structures with Hydrogen sensing capabilities and their application in specific field situations will be assessed.

Abstract
A miniature fiber Bragg grating strain rosette is presented. The proposed design is made possible through the development of low curvature radius lossless tapers, thus offering advantages in miniaturization of the rosette configuration. We report on the experimental validation of the miniature rosette design, demonstrating its effective operation.

Abstract
The interrogation of a suspended-core Fabry-Perot interferometric cavity through the illumination of a dual wavelength Raman fiber laser is reported. The proposed scheme is based on the use of a dual wavelength source for the generation of two quadrature phase-shifted signals that allows the recovery of the temperature change. The dual wavelength Raman fiber laser is based on fiber Bragg gratings combined with a virtual mirror. The use of this source allows a passive and accurate interrogation of the temperature variation, while taking advantage of the Rayleigh scattering growth as a virtual mirror in the laser.

Abstract
It is shown how the design possibilities offered by double-layer uniform-waist tapered optical fibers (DLUWTs) permit to move the wavelength detection range to adapt the response of the sensors to varied conditions. In particular, we have obtained very good experimental curves showing that we can achieve plasmon resonances in the C-band of the optical communications, around 1.5 mu m, for the range of refractive indices of aqueous media, highly interesting in the biosensors field. Also, we show results for other interesting wavelength region, around 500 nm, where we can take advantage of the absorption peaks of the analytes. Finally, we explore the possibilities of using InN as a dielectric material for the second layer of the deposition. These results contribute to considerably expand the applicability and performance of SPR fiber sensors.