ABSTRACT
The advance has been facilitated by the rapid progress made in the use of optical fibres by the telecommunications industry. The establishment of optical fibres for telecommunication links has encouraged their use for telemetry in some industrial fields. Telemetry based on metallic wire pairs, although by far the most common technique currently, is facing a growing challenge from optical fibres in all applications. The fibre material can absorb photons. The electrons in the molecules from which the fibre is made have discrete energy levels. Extrinsic optical fibre sensors have some external artefact connected to the fibre that is modified by the measurand. Optical fibre interferometers have been developed to measure refractive index, acceleration, electric and acoustic fields, electric current, temperature, strain and pressure. Optical fibre systems are classed as distributed when sensing takes place continuously along the fibre length. Signal processing techniques in the well-established field of radar have been adapted for use in distributed optical fibre sensing.
