Abstract
In this work a novel optical-fiber sensor for carbon dioxide measurement is presented. A polymeric sensitive layer based on the acid-base equilibrium of phenol and of its derivative 4-nitro-phenol is used for carbon dioxide determination. The sensitive material presents changes in color and in its refractive index. Colorimetric and refractometric measurements were performed. The results show the sensor is more sensitive for lower concentrations and a saturation effect occurs for higher levels. For the colorimetric response, a resolution of +/- 0.15% was estimated and a response time of 30s was measured. For the refractometric measurements, a resolution of +/- 0.50% could be estimated and a response time of 12s was measured. Reversibility and reproducibility were also demonstrated.

Abstract
An indicator free optical fiber sensor for determination of carbon dioxide is presented. The sensing layer is based on the acid-basic equilibrium of phenol and of its derivative p-nitro-phenol that, in the presence of CO2, are prone to protonation introducing refractive index changes. The new sensitive layer is characterized and tested in different refractometric fiber optic sensor configurations. Using a fiber based interferometric setup, a CO 2 dependent refractive index change of ~0.05 RIU is observed, in the 10%-90% CO2 concentration range, demonstrating the membrane viability. Preliminary results are presented for an all-fiber LPG-based carbon dioxide sensor.

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.

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