Abstract
A new interrogation method based on Fibre Bragg Gratings (FBG) for Surface Plamon Resonance (SPR) sensors in the region of refractive indices of aqueous solutions is described. Two FBGs are selected with their Bragg wavelengths at opposite sides of the plasmon resonance peak. The response of the system can be made independent of the fluctuations of the optical power source, and the linearity and the sensitivity of the sensor are improved. The use of the spectral selectivity of gratings for the interrogation of SPR sensors in different configurations is also promising in terms of multiplexing, temperature referencing or multiparameter detection. © 2009 SPIE.

Abstract
Incipient fault diagnosis is closely related to insulation condition assessment. A great number of methods are available for condition monitoring and diagnosis of power transformer insulation systems, but only few of them can take direct measurements inside the transformer. Fiber optic sensors can be applied to incipient fault diagnosis. In particular, acoustic sensors have been developed for detection and location of partial discharges in oil-filled power transformers. We report the study of extrinsic and intrinsic fiber Fabry-Perot sensors that can be used to detect the acoustic waves that are generated by a partial discharge inside a power transformer. A comparative analysis is done to determine the best sensing head configuration and some methods to improve the parameter readout sensitivity are proposed. The sensing head behaviour when immersed in different fluids (air, water, and oil) is also investigated. (c) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3080752]

Abstract
Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in high voltage apparatus. A great number of methods are available for condition monitoring and diagnosis of power transformer insulation, but only a few can take direct measurements inside a transformer. Partial discharges are a major source of insulation failure in power transformers and their detection can be achieved through the associated acoustic emissions. This paper reports the development of two sensing head configurations based on extrinsic and intrinsic fiber Fabry-Perot interferometers for the detection of incipient faults in oil-filled power transformers. These sensors can be placed inside the transformer tank without affecting the insulation integrity, improving fault detection and location. The performances of the sensing heads are characterized and compared with the situations where it operates in air, water and oil and promising results are obtained, which will allow the industrial development of practical solutions.

Abstract
A smart laminated composite with a simple geometry was produced with embedded fiber Bragg grating sensors. The smart structure is composed of two Bragg gratings located in regions of different thicknesses of the laminated composite. Although one of the Bragg gratings is embedded between two layers, the other is embedded in jour layers. When the strain is applied to the smart composite, different response is obtained. Because of this characteristic it is possible to discriminate strain and temperature using a traditional matrix method. To reduce the inherent error, an artificial neural network approach is proposed that will improve the strain and temperature measurement discrimination when using this new configuration. These instrumented carbon fiber laminates can be used for monitoring of reinforcement and protection of structures. (C) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 235-239, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23990

Abstract
Semiconductor nanocrystals have unique optical properties that make them promising alternatives to traditional dyes in many luminescence based analytical techniques. An overview of the more relevant progresses in the application of quantum dots (QDs) as analytical probes in optical fibre sensing and imaging application will be addressed. Experimental results regarding the use of QDs as self-referenced multiplexed probes for chemical sensing and analytical imaging will be presented.

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.