Abstract
A fiber optic sensor for liquid refractive index measurement based on a Fabry-Perot interferometer is described. The interferometer is achieved between the reflection of a short fiber Bragg grating and the Fresnel reflection from the cleaved fiber end. This fiber end is then in contact with the liquid sample to provide refractive index measurements. The sensor is characterized by immersing the fiber tip in distilled water with different concentrations of ethylene glycol. A linear relation of the interferometer fringe visibility with refractive index variation is observed, and a resolution of similar to 10(-3) is obtained. It is also shown that the sensor operation is independent of temperature effects, other than the one related to temperature-induced change of the liquid refractive index. (c) 2008 Society of Photo-Optical Instrumentation Engineers.

Abstract
We present results on the characterization of the response of a dual resonance observed in the spectrum of a single long-period grating arc-induced in a B/Ge co-doped fiber to different physical parameters. The dual resonance is formed by two overlapping resonances corresponding to coupling of the core mode to symmetric and antisymmetric cladding modes. The behavior of the resonances is studied when the grating is subject to strain, bending, torsion, temperature, or external refractive-index changes. The strain, bending, and torsion sensitivities of the two resonances differ, whereas the temperature sensitivities are almost the same. The sensitivities to variation in external refractive index are the same for the two resonances when the long-period grating is straight and differ when the fiber with the grating is curved. (c) 2010 Optical Society of America

Abstract
We present what we believe to be a novel miniaturized sensor configuration based on fiber Bragg gratings for simultaneous measurement of curvature and temperature in smart structures and composite materials. Because of the particular geometry of the sensing head, it is possible not only to measure the radius of curvature but also to determine the plane of curvature. We arrange three Bragg gratings in the vertices of the smallest equilateral triangle that can be defined by the cross sections of the fibers. The set is then inserted into a glue-filled capillary stainless-steel tube to provide both suitable protection for the Bragg sensors and rotational symmetry to the sensing head. This tube also ensures isolation from axial strain, allowing for the additional determination of temperature. The proposed sensing head is particularly well suited for applications in smart structures because it can be embedded along any layer of a composite material (including the neutral line) without special concern for the relative orientation of the Bragg gratings and the composite layers. We can also use this sensing configuration to implement more-sophisticated sensors dedicated, for example, to the measurement of multiaxial acceleration or flow and temperature. (C) 2002 Optical Society of America.

Abstract
In this work, a hybrid interferometer for simultaneous measurement of the partial pressures of O-2 and CO2 mixtures is reported. The sensing head consist in two different interferometers based on a Fabry-Perot cavity and a modal interference configuration. The intrinsic FP cavity was created by splicing a single mode fiber (SMF28) with a graded index fiber section that was then subjected to chemical etching creating a cavity. The second interferometer is based on a splice of a pure silica tube in series with the Fabry-Perot. Due to the design, different sensitivities are achieved for the pressure inducing refractive index changes of each gas. The rms deviations were found to be +/- 0.079 kPa and +/- 0.029 kPa for CO2 and O-2 partial pressure measurements, respectively.

Abstract
In this Work a new configuration of a refractometric sensor for aqueous solutions based on the combination of surface plasmon resonance (SPR) with fibre Bragg gratings (FBG) is presented. Two FBGs are selected having reflection maxima in each side of the plasmon resonance peak. These FBGs enable a different processing scheme for the information provided by the SPR transducer. This improved interrogation method increases the sensitivity and resolution of the sensor compared with those obtained with the usual method of tracking the spectral transmittance minimum and makes the system performance independent of optical Source power fluctuations. The experimental results obtained with a double-layer uniform-waist tapered fibre show the feasibility of this approach and its applicability in SPR-based biosensors that Must face very exigent measuring conditions.

Abstract
A scheme for the simultaneous determination of temperature and analyte concentration for application in luminescence-based chemical sensors is proposed. This scheme is applied to an optical oxygen sensor, which is based on the quenching of the fluorescence of a ruthenium complex. Temperature measurement is performed using the excitation radiation and an absorption long-pass filter. Preliminary results are presented that show the viability of an oxygen measurement that is independent of temperature and optical power level. The possibility of self-referenced temperature measurements with semiconductor nanoparticles is also investigated. In order to optimize the sensor design, several different optical fiber probe geometries for oxygen sensing are tested and compared, including different methods of coupling radiation into the optical fiber system. Polyvinyl alcohol (PVA) and polyacrylamide membranes are tested as supports for sensor immobilization in fiber-optical pH sensing devices in aqueous solution. Some results are presented that show the feasibility of using fiber-optical pH indicators for remote monitoring.