Abstract

Abstract

Abstract
In this paper we present a novel microbend optical fibre sensor embedded in composite material, which acts as a load cell for structural monitoring in civil engineering. The sensing system is based on a self-referenced fibre optic intensity sensor supported by a Michelson topology with optical feedback. The sensing system is tested in a sand testing bed for different values of load. Results are presented and discussed.

Abstract
Dither demodulation of fibre Bragg grating sensors illuminated with multimode light from cheap compact disc laser diodes is investigated. Quasi-static temperature and strain sensitivities of 0.09 degrees C/root Hz and 0.6 mu epsilon/root Hz are obtained. It is shown that small ac signals outside the loop bandwidth can be measured using synchronous detection at double the dither frequency.

Abstract
A passive all-fibre technique for fibre Bragg grating wavelength shift detection previously presented is used here for the demodulation of two Bragg sensors placed in a tree topology and addressed in time. The scheme involves a light source with particular spectral profile that allows the direct tracking of the Bragg wavelength shifts, providing satisfactory resolution over a large dynamic range and direct application in demultiplexing fibre sensing systems. Experimental results are presented relative to the measurement of static and dynamic strain, as well as temperature.

Abstract
An investigation is performed of the characteristics of the self-referencing intensity based Q-type fibre optic sensor using a recirculation loop structure. Both transmissive and reflective configurations are analysed. Via the definition of the measurement parameter (the R parameter) the linearity and sensitivity of the sensor are addressed. Theoretical and experimental results are compared, considering the problem of sensor design and optimization.