Abstract
Hollow-core photonic crystal fibres have a high potential for gas sensing applications, since large light-gas interaction lengths can be effectively attained. Nevertheless, in order to enhance effective diffusion of gas into the fibre hollow-core multi-coupling gaps are needed, which raise coupling loss issues that must be evaluated prior to the development of practical systems. In this communication we present a study on the coupling losses dependence on lateral and axial gap misalignment for single-mode fibre and two different types of hollow-core photonic crystal fibres. In addition, experimental results on the splicing of these fibres are also presented.

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
This work addresses a humidity sensor using long-period fiber gratings (LPG) coated with silica nanospheres film. SiO2-nanospheres coating is deposited onto the LPG using the electrostatic self-assembly technique (ESA). The polymeric overlay changes its optical properties when exposed to different humidity levels, resulting in a shift of the resonance wavelength of the LPG. The obtained results are accordant with the theoretical simulations. Wavelength shifts up to 12nm in a humidity range from 20% to 80% are reported, maintaining the same dependence at different temperatures.

Abstract
In this work it is investigated the strain and temperature sensing characteristics of modal interferometers supported by two Bragg fibers with different cross-section cladding geometries. It is shown that the sensitivity to these measurands is different for the two fibers, which turns feasible the conception of several sensing configurations based on the combination of these two fiber types for simultaneous measurement of strain and temperature.

Abstract
This work describes a fibre 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 single mode - step index multimode - single mode fibre configuration. It was observed that the transmitted optical power in such layout becomes highly sensitive to the wavelength of operation and to the length of the multimode fibre. The optical spectrum entertains two dominant loss bands, at wavelengths that have similar responses both to temperature and strain, and 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 and -0.06 +/- 0.01 pm/mu epsilon, respectively).

Abstract
The study of a single short length Bragg grating for sensing applications is presented. The dependences of the central wavelength, reflected optical power and spectral width of a 250 mu m length grating on strain and temperature are analyzed. The obtained results indicate the feasibility of this novel sensing head for simultaneous measurement of strain and temperature.