Abstract
The potential applications of luminescent semiconductor nanocrystals to optical oxygen sensing are explored. The suitability of quantum dots to provide a reference signal in luminescence-based chemical sensors is addressed. A CdSe-ZnS nanocrystal, with an emission peak at 520 nm, is used to provide a reference signal. Measurements of oxygen concentration, which are based on the dynamic quenching of the luminescence of a ruthenium complex, are performed. Both the dye and the nanocrystal are immobilized in a solgel matrix and are excited by a blue LED. Experimental results show that the ratio between the reference and the sensor signals is highly insensitive to fluctuations of the excitation optical power. The use of CdTe, near-infrared quantum dots with an emission wavelength of 680 run, in combination with a ruthenium complex to provide a new mechanism for oxygen sensing, is investigated. The possibility of creating oxygen sensitivity in different spectral regions is demonstrated. The results obtained clearly show that this technique can be applied to develop a wavelength division multiplexed system of oxygen sensors. (c) 2006 Optical Society of America.

Abstract
A sensing head based on two fiber Bragg gratings arranged in a twisted configuration is proposed to measure three parameters simultaneously, namely 1) temperature, 2) strain, and 3) transverse load. One of the gratings is impressed into a high-birefringence fiber that provides two distinct spectral signatures, which, together with the signature of the second grating and the geometric characteristics of the sensing head, enable the degrees of freedom required to achieve the simultaneous measurement functionality. The resolutions achieved with this configuration for the measurement of temperature, strain, and transverse load are +/- 3.1 degrees C, +/- 46 mu epsilon, and +/- 0.01 N/mm, respectively.

Abstract
The use of semiconductor nano-particles as temperature probes in luminescence chemical sensing applications is addressed. Temperature changes the intensity, the peak wavelength and the spectral width of the quantum dots luminescent emission in a linear and reversible way. Results are presented that show the feasibility of implementing a self-referenced intensity-based sensor to perform temperature measurements independent of the optical power level in the sensing system. A resolution of 0.3 degrees C was achieved. In addition, it is demonstrated that self-referenced temperature measurements at multiple points could be performed using reflection or transmission based optical fibre configurations.

Abstract
In this study an optic fibre system for health monitoring of fibre reinforced plastics was developed. It is based on the detection of acoustic emission (AE) waves in a loaded material. A low-finesse Fabry-Perot interferometer sensor is used as alternative to the conventional piezoelectric transducers for AE waves sensing. An original procedure for optical fibre sensor interrogation is proposed.

Abstract
A fiber-sensing scheme with controlled sensitivity comprising a fiber Bragg grating (FBG) and a mechanically induced long-period fiber grating (MLPFG) is presented. The FBG was written by exposing the fiber to 248-nm UV laser radiation such that the Bragg wavelength is localized on the slope of a resonant band of a mechanical grating, which was produced by winding a nylon string around a fiber/grooved tube set. The strength of that resonant band was altered by applying loads to the MLPFG. For different loads, the FBG was submitted to strain values of up to 2200 mu epsilon, in steps of 200 mu epsilon, during which the Bragg wavelength and the respective transmitted peak power through the MLPFG were recorded. It was demonstrated that by applying a weight with a value of 0.78 kg to the MLPFG, the sensitivity of the FBG interrogation technique to strain variations increased from 2.23 (without load) to 3.20 pW/mu epsilon.

Abstract
We have investigated the polarization properties of long-period fibre gratings fabricated using the electric arc technique. It was found that the choice of the fabrication parameters (electric current, arc duration and pulling tension) affects the polarization dependent loss of the produced gratings. In particular, a non-monotonic dependence on the external pulling tension was obtained.