OPTICAL FIBERS FOR SENSORS

Silica-based optical fibres are eminently suitable for use as long-distance information transmission lines. They have a very low transmission loss, enormously large band-width and are relatively immune to environmental conditions. The features which make them potentially attractive for sensing applications are their small size and weight, chemically passive nature, freedom from electromagnetic interference and the absence of sparking hazard. Optical fibres can thus be used in situations where metal systems would be prohibited for reasons of safety. On the other hand, optical sources are not cheap. Optical fibre sensors clearly will not be introduced unless they can be justified on economic grounds and there is always a reluctance to introduce a radically new technology into existing industrial processes. Applications must therefore be sought where fibres provide a more economic solution or perform a function not easily undertaken by conventional methods. Examples are the distributed temperature sensor, where a single fibre can replace several hundred point sensors, and the current monitor, which is physically separated from the high-voltage conductor. These and other specific devices will be discussed and reviewed.