Abstract
A highly-birefringent photonic bandgap Bragg fiber loop mirror sensor is proposed. Thanks to the Bragg fiber geometry, one can observe the group birefringence and the bandgap fiber in the transfer function. The sensing head presented different sensitivities for strain and temperature measurements. Using the matrix method, both the physical parameters can be discriminated. It is important to highlight that this Bragg fiber presents sensitivity to temperature of similar to 5.75 nm/degrees C, for the group birefringence measurand.

Abstract
We experimentally studied several sensing characteristics of a birefringent microstructured polymer optical fiber. The fiber exhibits a birefringence of the order 2x10(-5) at 1.3 mu m because of two small holes adjacent to the core. In this fiber, we measured spectral dependence of phase and group modal birefringence, bending losses, polarimetric sensitivity to strain and temperature. The sensitivity to strain was also examined for intermodal interference observed in the spectral range below 0.8 mu m. Finally, we showed that the material transmission windows shift as function of the applied strain. This shift has an exponential character and saturates for greater strain.

Abstract
A fiber optic FBG cladding modes based sensor, for simultaneous measurement of strain and temperature is presented. The FBG cladding modes are efficiently excited by the large core misalignment. This technique enables the possibility to readout simultaneously in reflection the cladding mode (lambda(cl)) and the core mode (lambda(co)). lambda(cl), lambda(co) depend on strain and temperature and show different sensibilities for each parameter, enabling their discrimination. The experimental result shows a good performance in terms of linearity and sensitivity.

Abstract
An optical fibre sensor for determination of acetic acid is presented. The sensing probe is based on a fiber Bragg grating (FBG) Fabry-Perot cavity, coated with a thin film of sol-gel-PVP (polyVynil Pirrolidone) composite material. The polymeric thin film renders interferometric output sensitive to the presence of carboxylic acid species. Results show that the wavelength of the interferometric peaks change with acetic acid concentration, enabling its quantification. Coupling the fibre probe with a serrodyne modulated readout interferometer enables pseudo-heterodyne interrogation and the detection of acetic acid with a sensitivity of 1 deg/0.01% and a resolution of 0.2% v/v. The results demonstrate the potential of the proposed scheme to operate as a sensitive chemical sensor platform. © 2009 SPIE.

Abstract
An optical fibre sensor for simultaneous measurement of refractive index and temperature is presented. The refractive index measurement is based on the visibility variations of a Fabry- Perot interferometer with interfering waves generated in a low reflectivity Bragg grating inscribed on a Panda fibre and in the fibre tip (Fresnel reflection) in contact with the liquid. The temperature measurement is based on the wavelength shift of the FBG peaks. Results obtained show the feasibility of simultaneous measurement of refractive index and temperature and also the possibility of adjusting fringe visibility via polarization control.

Abstract
A novel fiber optic curvature sensor based on a core-offset single-mode fiber (SMF) and on a fiber Bragg grating (FBG) is presented. The FBG cladding modes are efficiently excited by the large core misalignment. The curvature of the beam can be obtained by the reflected power of the core mode and the recoupled cladding mode.