Abstract
A system to interrogate optical fiber interferometric sensors with digital control is presented. The system is based on a receiving white light Mach-Zehnder interferometer and is capable of operating with four distinct synthetic and pseudo-heterodyne signal detection schemes. A differential phase detection scheme was implemented and system performance with the different processing schemes was compared using fiber Bragg grating based Fabry-Perot cavity strain sensors. With a lock-in time constant of 1 s, most digital techniques were able to nearly match the performance of a standard hardware system, demonstrating the feasibility of low-cost high-resolution interferometric systems operated with virtual instrumentation.

Abstract
A fiber-optic sensor for simultaneous measurement of refractive index and temperature is described. The refractive index measurement is based on the visibility variations of a Fabry-Perot interferometer. It is formed with the interfering waves generated from a low reflectivity Bragg grating inscribed on a Panda fiber and from the fiber end tip (Fresnel reflection) in contact with the liquid. 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. The temperature is determined by the wavelength shift of the FBG peaks. Results show the feasibility of simultaneous measurement of refractive index and temperature and also the possibility of adjusting fringe visibility via polarization control.

Abstract
In this paper, we present a novel smart composite based on single mode optical fibres embedded in a hybrid composite laminated. This smart composite comprehended three optical fibres: an optical fibre positioned between two layers of carbon fibres; other optical fibre embedded in two layers of glass fibres; and another optical fibre inserted between the two different composite laminates. Due to cure process using hot plate press, different optical attenuations were obtained for the three optical fibres. The optical fibre positioned between the two different layers (carbon/glass) presented higher losses when compared with the two other optical fibres embedded between equal types of layers. The losses result from the different diameter of carbon/glass and the different coefficient of thermal expansion of the composite material. The smart composite was characterised in terms of its sensitivity to temperature and pressure, independently. Using a matrix method, it was possible to discriminate the pressure and the temperature with only one measurement. Maximum errors of 2.45 degrees C and 0.6 kN/m(2) were found to 60 degrees C and 2500 kN/m(2) measurement ranges.

Abstract
The index-guiding PCF basic structure is a solid core surrounded by a microstructured cladding. Owing to the presence of air holes, the effective refractive index of the cladding is below that of the core and the light is guided along the core by the principle of total internal reflection. Several authors have presented different geometries for this type of fibre and one of them is the suspended-core structure, where relatively large holes surround the fibre core that looks suspended along the fibre axis by small width silica walls. The chapter is divided in two parts. The first is about the fabrication of suspended core fibre and the second part is about the main applications of this type of fibres as interferometers.

Abstract
The intrinsic advantages of optical sensor technology are very appealing for high voltage applications and can become a valuable asset in a new generation of smart grids. In this paper the authors present a review of optical sensors technologies for electrical current metering in high voltage applications. A brief historical overview is given together with a more detailed focus on recent developments. Technologies addressed include all fiber sensors, bulk magneto-optical sensors, piezoelectric transducers, magnetic force sensors and hybrid sensors. The physical principles and main advantages and disadvantages are discussed. Configurations and strategies to overcome common problems, such as interference from external currents and magnetic fields induced linear birefringence and others are discussed. The state-of-the-art is presented including commercial available systems.

Abstract