Abstract
A fiber optic sensing system for simultaneous measurement of displacement and temperature is presented. It is based on the use of a low finesse extrinsic Fabry-Perot cavity and a fiber Bragg grating for temperature compensation. A white light tandem interferometric technique is used to recover the signal from the low finesse cavity, providing both fringe visibility and phase measurements. These, together with the fiber grating signal, give two equations that can be used to simultaneously determine temperature and displacement. Theoretical analysis of the sensing scheme is performed. Experimental results are presented which validate theoretical predictions and also demonstrate the feasibility of this sensing system in practical applications.

Abstract
A passive all-fibre technique for fibre Bragg grating wavelength shift detection which has been discussed previously is used here for the demodulation of two Bragg sensors placed in a tree topology and addressed in time. The scheme involves a light source with a particular spectral profile that allows the direct tracking of the Bragg wavelength shifts, providing satisfactory resolution over a large dynamic range and a direct application in demultiplexing fibre sensing systems. Experimental results are presented relative to the measurement of static and dynamic strain, as well as temperature.

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
In this work a modal interferometer based on arc-induced long-period gratings (LPGs) in a Mach-Zehnder configuration is evaluated as a sensing structure for environmental refractive index measurement. To interrogate this sensing device, coherence addressing and pseudo-heterodyne processing were used. The influence of geometric effects such as stretching, bending and twisting the interferometer on the sensitivity to refractive index changes 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 to external refractive index by simple mechanical action. The experimental results show that it is possible to tune the sensitivity to external refractive index by more than 50% by control of the curvature in the Mach-Zehnder interferometer.

Abstract
A novel sensing configuration for measuring humidity based on a long-period fibre grating coated with a thin film of silica nanospheres is proposed. The polymeric overlay is deposited on the grating using the electrostatic self-assembly technique. This thin film changes its optical properties when exposed to different humidity levels that translate into a shift of the resonance wavelength of the fibre grating. Wavelength shifts up to 12 nm in a relative humidity range from 20% to 80% are reported, and it is further demonstrated that such humidity sensitivity has negligible thermal dependence.

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.