Abstract
A time division multiplexing technique is described in which the frequency of a laser source is modulated with a sampled ramp. The concept is demonstrated with two Mach-Zehnder interferometers in a parallel configuration, separated by a fibre delay line whose length is determined by the characteristics of the sampling waveform. Pseudo-heterodyne processing was used to recover the phase information from each interferometer. The expansion of the technique to a combined frequency and time division multiplexed fibre-optic sensing system is considered. © 1990.

Abstract

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.