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.

Abstract
In this work, an LPG-based Mach-Zehnder modal interferometer with a tapered fiber section between the two LPGs is studied as a sensing structure for measuring environmental refractive index. To interrogate this sensing device, coherence addressing and pseudo-heterodyne processing were used. A fiber taper was made between the two LPGs to improve and tailor the sensitivity of the sensor. Experimental results show that the sensitivity to external refractive index increases with the length of the taper and that the sensitivity enhancement is stronger for lower order cladding modes. © 2009 SPIE.

Abstract
In this work, interferometric sensors based on antiresonance reflecting waveguide (ARROW) fibers were developed and their performances were characterized for measurement of physical parameters, particularly strain and temperature. Two types of ARROW fibers were considered and signal demodulation was achieved using the white light interferometric technique. Application issues of sensing heads based on these fibers are also addressed. © 2009 SPIE.